Merging upstream version 1.66.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

285 files changed, 7944 insertions, 4580 deletions

diff --git a/library/alloc/benches/lib.rs b/library/alloc/benches/lib.rs
index 72ac897d4..d418965cd 100644
--- a/library/alloc/benches/lib.rs
+++ b/library/alloc/benches/lib.rs
@@ -3,7 +3,6 @@
 #![cfg(not(target_os = "android"))]
 #![feature(btree_drain_filter)]
 #![feature(iter_next_chunk)]
-#![feature(map_first_last)]
 #![feature(repr_simd)]
 #![feature(slice_partition_dedup)]
 #![feature(test)]
diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index 80b067812..8187517cc 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -28,16 +28,20 @@ extern "Rust" {
     // The rustc fork of LLVM 14 and earlier also special-cases these function names to be able to optimize them
     // like `malloc`, `realloc`, and `free`, respectively.
     #[rustc_allocator]
-    #[rustc_allocator_nounwind]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
     #[rustc_deallocator]
-    #[rustc_allocator_nounwind]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
     #[rustc_reallocator]
-    #[rustc_allocator_nounwind]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
     #[rustc_allocator_zeroed]
-    #[rustc_allocator_nounwind]
+    #[cfg_attr(not(bootstrap), rustc_nounwind)]
+    #[cfg_attr(bootstrap, rustc_allocator_nounwind)]
     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
 }
 
diff --git a/library/alloc/src/borrow.rs b/library/alloc/src/borrow.rs
index 904a53bb4..83a138559 100644
--- a/library/alloc/src/borrow.rs
+++ b/library/alloc/src/borrow.rs
@@ -21,7 +21,6 @@ use Cow::*;
 impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
 where
     B: ToOwned,
-    <B as ToOwned>::Owned: 'a,
 {
     fn borrow(&self) -> &B {
         &**self
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 65e323c9e..d6681a317 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -151,7 +151,6 @@ use core::async_iter::AsyncIterator;
 use core::borrow;
 use core::cmp::Ordering;
 use core::convert::{From, TryFrom};
-#[cfg(not(bootstrap))]
 use core::error::Error;
 use core::fmt;
 use core::future::Future;
@@ -176,7 +175,6 @@ use crate::borrow::Cow;
 use crate::raw_vec::RawVec;
 #[cfg(not(no_global_oom_handling))]
 use crate::str::from_boxed_utf8_unchecked;
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 use crate::string::String;
 #[cfg(not(no_global_oom_handling))]
@@ -1622,6 +1620,22 @@ impl<T, const N: usize> From<[T; N]> for Box<[T]> {
     }
 }
 
+/// Casts a boxed slice to a boxed array.
+///
+/// # Safety
+///
+/// `boxed_slice.len()` must be exactly `N`.
+unsafe fn boxed_slice_as_array_unchecked<T, A: Allocator, const N: usize>(
+    boxed_slice: Box<[T], A>,
+) -> Box<[T; N], A> {
+    debug_assert_eq!(boxed_slice.len(), N);
+
+    let (ptr, alloc) = Box::into_raw_with_allocator(boxed_slice);
+    // SAFETY: Pointer and allocator came from an existing box,
+    // and our safety condition requires that the length is exactly `N`
+    unsafe { Box::from_raw_in(ptr as *mut [T; N], alloc) }
+}
+
 #[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
 impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> {
     type Error = Box<[T]>;
@@ -1637,13 +1651,46 @@ impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]> {
     /// `boxed_slice.len()` does not equal `N`.
     fn try_from(boxed_slice: Box<[T]>) -> Result<Self, Self::Error> {
         if boxed_slice.len() == N {
-            Ok(unsafe { Box::from_raw(Box::into_raw(boxed_slice) as *mut [T; N]) })
+            Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) })
         } else {
             Err(boxed_slice)
         }
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "boxed_array_try_from_vec", since = "1.66.0")]
+impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]> {
+    type Error = Vec<T>;
+
+    /// Attempts to convert a `Vec<T>` into a `Box<[T; N]>`.
+    ///
+    /// Like [`Vec::into_boxed_slice`], this is in-place if `vec.capacity() == N`,
+    /// but will require a reallocation otherwise.
+    ///
+    /// # Errors
+    ///
+    /// Returns the original `Vec<T>` in the `Err` variant if
+    /// `boxed_slice.len()` does not equal `N`.
+    ///
+    /// # Examples
+    ///
+    /// This can be used with [`vec!`] to create an array on the heap:
+    ///
+    /// ```
+    /// let state: Box<[f32; 100]> = vec![1.0; 100].try_into().unwrap();
+    /// assert_eq!(state.len(), 100);
+    /// ```
+    fn try_from(vec: Vec<T>) -> Result<Self, Self::Error> {
+        if vec.len() == N {
+            let boxed_slice = vec.into_boxed_slice();
+            Ok(unsafe { boxed_slice_as_array_unchecked(boxed_slice) })
+        } else {
+            Err(vec)
+        }
+    }
+}
+
 impl<A: Allocator> Box<dyn Any, A> {
     /// Attempt to downcast the box to a concrete type.
     ///
@@ -2037,8 +2084,7 @@ impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> {
  *  could have a method to project a Pin<T> from it.
  */
 #[stable(feature = "pin", since = "1.33.0")]
-#[rustc_const_unstable(feature = "const_box", issue = "92521")]
-impl<T: ?Sized, A: Allocator> const Unpin for Box<T, A> where A: 'static {}
+impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {}
 
 #[unstable(feature = "generator_trait", issue = "43122")]
 impl<G: ?Sized + Generator<R> + Unpin, R, A: Allocator> Generator<R> for Box<G, A>
@@ -2091,7 +2137,6 @@ impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S> {
     }
 }
 
-#[cfg(not(bootstrap))]
 impl dyn Error {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
@@ -2109,7 +2154,6 @@ impl dyn Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 impl dyn Error + Send {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
@@ -2124,7 +2168,6 @@ impl dyn Error + Send {
     }
 }
 
-#[cfg(not(bootstrap))]
 impl dyn Error + Send + Sync {
     #[inline]
     #[stable(feature = "error_downcast", since = "1.3.0")]
@@ -2139,7 +2182,6 @@ impl dyn Error + Send + Sync {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
@@ -2173,7 +2215,6 @@ impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
@@ -2213,7 +2254,6 @@ impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync +
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<String> for Box<dyn Error + Send + Sync> {
@@ -2258,7 +2298,6 @@ impl From<String> for Box<dyn Error + Send + Sync> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "string_box_error", since = "1.6.0")]
 impl From<String> for Box<dyn Error> {
@@ -2281,7 +2320,6 @@ impl From<String> for Box<dyn Error> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
@@ -2306,7 +2344,6 @@ impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "string_box_error", since = "1.6.0")]
 impl From<&str> for Box<dyn Error> {
@@ -2329,7 +2366,6 @@ impl From<&str> for Box<dyn Error> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "cow_box_error", since = "1.22.0")]
 impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
@@ -2352,7 +2388,6 @@ impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "cow_box_error", since = "1.22.0")]
 impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
@@ -2374,7 +2409,6 @@ impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "box_error", since = "1.8.0")]
 impl<T: core::error::Error> core::error::Error for Box<T> {
     #[allow(deprecated, deprecated_in_future)]
diff --git a/library/alloc/src/boxed/thin.rs b/library/alloc/src/boxed/thin.rs
index 0a20c74b0..c477c4490 100644
--- a/library/alloc/src/boxed/thin.rs
+++ b/library/alloc/src/boxed/thin.rs
@@ -2,7 +2,6 @@
 // https://github.com/matthieu-m/rfc2580/blob/b58d1d3cba0d4b5e859d3617ea2d0943aaa31329/examples/thin.rs
 // by matthieu-m
 use crate::alloc::{self, Layout, LayoutError};
-#[cfg(not(bootstrap))]
 use core::error::Error;
 use core::fmt::{self, Debug, Display, Formatter};
 use core::marker::PhantomData;
@@ -274,7 +273,6 @@ impl<H> WithHeader<H> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[unstable(feature = "thin_box", issue = "92791")]
 impl<T: ?Sized + Error> Error for ThinBox<T> {
     fn source(&self) -> Option<&(dyn Error + 'static)> {
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index cacbd54b6..8a7719347 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -580,7 +580,7 @@ impl<K, V> BTreeMap<K, V> {
     /// map.insert(1, "a");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_stable(feature = "const_btree_new", since = "1.66.0")]
     #[must_use]
     pub const fn new() -> BTreeMap<K, V> {
         BTreeMap { root: None, length: 0, alloc: ManuallyDrop::new(Global), _marker: PhantomData }
@@ -703,7 +703,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -712,7 +711,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// map.insert(2, "a");
     /// assert_eq!(map.first_key_value(), Some((&1, &"b")));
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn first_key_value(&self) -> Option<(&K, &V)>
     where
         K: Ord,
@@ -727,7 +726,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -741,7 +739,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// assert_eq!(*map.get(&1).unwrap(), "first");
     /// assert_eq!(*map.get(&2).unwrap(), "b");
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V, A>>
     where
         K: Ord,
@@ -765,7 +763,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// Draining elements in ascending order, while keeping a usable map each iteration.
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -776,7 +773,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// }
     /// assert!(map.is_empty());
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn pop_first(&mut self) -> Option<(K, V)>
     where
         K: Ord,
@@ -792,7 +789,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -800,7 +796,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// map.insert(2, "a");
     /// assert_eq!(map.last_key_value(), Some((&2, &"a")));
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn last_key_value(&self) -> Option<(&K, &V)>
     where
         K: Ord,
@@ -815,7 +811,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -829,7 +824,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// assert_eq!(*map.get(&1).unwrap(), "a");
     /// assert_eq!(*map.get(&2).unwrap(), "last");
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V, A>>
     where
         K: Ord,
@@ -853,7 +848,6 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// Draining elements in descending order, while keeping a usable map each iteration.
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
@@ -864,7 +858,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// }
     /// assert!(map.is_empty());
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn pop_last(&mut self) -> Option<(K, V)>
     where
         K: Ord,
@@ -1099,6 +1093,9 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
 
     /// Moves all elements from `other` into `self`, leaving `other` empty.
     ///
+    /// If a key from `other` is already present in `self`, the respective
+    /// value from `self` will be overwritten with the respective value from `other`.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1107,10 +1104,10 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// let mut a = BTreeMap::new();
     /// a.insert(1, "a");
     /// a.insert(2, "b");
-    /// a.insert(3, "c");
+    /// a.insert(3, "c"); // Note: Key (3) also present in b.
     ///
     /// let mut b = BTreeMap::new();
-    /// b.insert(3, "d");
+    /// b.insert(3, "d"); // Note: Key (3) also present in a.
     /// b.insert(4, "e");
     /// b.insert(5, "f");
     ///
@@ -1121,7 +1118,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     ///
     /// assert_eq!(a[&1], "a");
     /// assert_eq!(a[&2], "b");
-    /// assert_eq!(a[&3], "d");
+    /// assert_eq!(a[&3], "d"); // Note: "c" has been overwritten.
     /// assert_eq!(a[&4], "e");
     /// assert_eq!(a[&5], "f");
     /// ```
@@ -2392,7 +2389,11 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn len(&self) -> usize {
         self.length
     }
@@ -2413,7 +2414,11 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
diff --git a/library/alloc/src/collections/btree/map/entry.rs b/library/alloc/src/collections/btree/map/entry.rs
index cd7cdc192..370b58864 100644
--- a/library/alloc/src/collections/btree/map/entry.rs
+++ b/library/alloc/src/collections/btree/map/entry.rs
@@ -133,7 +133,6 @@ impl<'a, K: Debug + Ord, V: Debug, A: Allocator + Clone> fmt::Display
     }
 }
 
-#[cfg(not(bootstrap))]
 #[unstable(feature = "map_try_insert", issue = "82766")]
 impl<'a, K: core::fmt::Debug + Ord, V: core::fmt::Debug> core::error::Error
     for crate::collections::btree_map::OccupiedError<'a, K, V>
diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs
index f1d2d3b30..da766b67a 100644
--- a/library/alloc/src/collections/btree/node.rs
+++ b/library/alloc/src/collections/btree/node.rs
@@ -206,9 +206,9 @@ impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
 
 unsafe impl<BorrowType, K: Sync, V: Sync, Type> Sync for NodeRef<BorrowType, K, V, Type> {}
 
-unsafe impl<'a, K: Sync + 'a, V: Sync + 'a, Type> Send for NodeRef<marker::Immut<'a>, K, V, Type> {}
-unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::Mut<'a>, K, V, Type> {}
-unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::ValMut<'a>, K, V, Type> {}
+unsafe impl<K: Sync, V: Sync, Type> Send for NodeRef<marker::Immut<'_>, K, V, Type> {}
+unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Mut<'_>, K, V, Type> {}
+unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::ValMut<'_>, K, V, Type> {}
 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}
 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Dying, K, V, Type> {}
 
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 2cfc08074..4ddb21192 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -343,7 +343,7 @@ impl<T> BTreeSet<T> {
     /// let mut set: BTreeSet<i32> = BTreeSet::new();
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_stable(feature = "const_btree_new", since = "1.66.0")]
     #[must_use]
     pub const fn new() -> BTreeSet<T> {
         BTreeSet { map: BTreeMap::new() }
@@ -786,7 +786,6 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set = BTreeSet::new();
@@ -797,7 +796,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// assert_eq!(set.first(), Some(&1));
     /// ```
     #[must_use]
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn first(&self) -> Option<&T>
     where
         T: Ord,
@@ -813,7 +812,6 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set = BTreeSet::new();
@@ -824,7 +822,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// assert_eq!(set.last(), Some(&2));
     /// ```
     #[must_use]
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn last(&self) -> Option<&T>
     where
         T: Ord,
@@ -838,7 +836,6 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set = BTreeSet::new();
@@ -849,7 +846,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// }
     /// assert!(set.is_empty());
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn pop_first(&mut self) -> Option<T>
     where
         T: Ord,
@@ -863,7 +860,6 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(map_first_last)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set = BTreeSet::new();
@@ -874,7 +870,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// }
     /// assert!(set.is_empty());
     /// ```
-    #[unstable(feature = "map_first_last", issue = "62924")]
+    #[stable(feature = "map_first_last", since = "1.66.0")]
     pub fn pop_last(&mut self) -> Option<T>
     where
         T: Ord,
@@ -1174,7 +1170,11 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn len(&self) -> usize {
         self.map.len()
     }
@@ -1193,7 +1193,11 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_btree_new", issue = "71835")]
+    #[rustc_const_unstable(
+        feature = "const_btree_len",
+        issue = "71835",
+        implied_by = "const_btree_new"
+    )]
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index 6480fcaf9..f2f5dffc2 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -1613,7 +1613,7 @@ impl<'a, T> CursorMut<'a, T> {
             None
         } else {
             // We can't point to the node that we pop. Copying the behavior of
-            // `remove_current`, we move on the the next node in the sequence.
+            // `remove_current`, we move on to the next node in the sequence.
             // If the list is of length 1 then we end pointing to the "ghost"
             // node at index 0, which is expected.
             if self.list.head == self.current {
diff --git a/library/alloc/src/collections/mod.rs b/library/alloc/src/collections/mod.rs
index 21d0def08..161a37573 100644
--- a/library/alloc/src/collections/mod.rs
+++ b/library/alloc/src/collections/mod.rs
@@ -153,6 +153,5 @@ trait SpecExtend<I: IntoIterator> {
     fn spec_extend(&mut self, iter: I);
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "try_reserve", since = "1.57.0")]
 impl core::error::Error for TryReserveError {}
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index e3f4deb08..2a57dad89 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -12,11 +12,17 @@ use core::fmt;
 use core::hash::{Hash, Hasher};
 use core::iter::{repeat_with, FromIterator};
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice;
 
+// This is used in a bunch of intra-doc links.
+// FIXME: For some reason, `#[cfg(doc)]` wasn't sufficient, resulting in
+// failures in linkchecker even though rustdoc built the docs just fine.
+#[allow(unused_imports)]
+use core::mem;
+
 use crate::alloc::{Allocator, Global};
 use crate::collections::TryReserveError;
 use crate::collections::TryReserveErrorKind;
@@ -177,7 +183,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// Marginally more convenient
     #[inline]
     fn cap(&self) -> usize {
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // For zero sized types, we are always at maximum capacity
             MAXIMUM_ZST_CAPACITY
         } else {
@@ -3038,7 +3044,7 @@ impl<T, A: Allocator> From<Vec<T, A>> for VecDeque<T, A> {
     /// `Vec<T>` came from `From<VecDeque<T>>` and hasn't been reallocated.
     fn from(mut other: Vec<T, A>) -> Self {
         let len = other.len();
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // There's no actual allocation for ZSTs to worry about capacity,
             // but `VecDeque` can't handle as much length as `Vec`.
             assert!(len < MAXIMUM_ZST_CAPACITY, "capacity overflow");
@@ -3124,7 +3130,7 @@ impl<T, const N: usize> From<[T; N]> for VecDeque<T> {
     fn from(arr: [T; N]) -> Self {
         let mut deq = VecDeque::with_capacity(N);
         let arr = ManuallyDrop::new(arr);
-        if mem::size_of::<T>() != 0 {
+        if !<T>::IS_ZST {
             // SAFETY: VecDeque::with_capacity ensures that there is enough capacity.
             unsafe {
                 ptr::copy_nonoverlapping(arr.as_ptr(), deq.ptr(), N);
diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index aede6d54c..11bd4c4dc 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -1122,7 +1122,6 @@ impl CStr {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl core::error::Error for NulError {
     #[allow(deprecated)]
@@ -1131,11 +1130,9 @@ impl core::error::Error for NulError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
 impl core::error::Error for FromVecWithNulError {}
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "cstring_into", since = "1.7.0")]
 impl core::error::Error for IntoStringError {
     #[allow(deprecated)]
diff --git a/library/alloc/src/fmt.rs b/library/alloc/src/fmt.rs
index ed398b566..799ce9d5d 100644
--- a/library/alloc/src/fmt.rs
+++ b/library/alloc/src/fmt.rs
@@ -327,7 +327,7 @@
 //! - `text` must not contain any `'{'` or `'}'` characters,
 //! - `ws` is any character for which [`char::is_whitespace`] returns `true`, has no semantic
 //!   meaning and is completely optional,
-//! - `integer` is a decimal integer that may contain leading zeroes and
+//! - `integer` is a decimal integer that may contain leading zeroes and must fit into an `usize` and
 //! - `identifier` is an `IDENTIFIER_OR_KEYWORD` (not an `IDENTIFIER`) as defined by the [Rust language reference](https://doc.rust-lang.org/reference/identifiers.html).
 //!
 //! # Formatting traits
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 8619467c2..ce36b116f 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -69,6 +69,8 @@
     any(not(feature = "miri-test-libstd"), test, doctest),
     no_global_oom_handling,
     not(no_global_oom_handling),
+    not(no_rc),
+    not(no_sync),
     target_has_atomic = "ptr"
 ))]
 #![no_std]
@@ -97,7 +99,7 @@
 #![feature(coerce_unsized)]
 #![cfg_attr(not(no_global_oom_handling), feature(const_alloc_error))]
 #![feature(const_box)]
-#![cfg_attr(not(no_global_oom_handling), feature(const_btree_new))]
+#![cfg_attr(not(no_global_oom_handling), feature(const_btree_len))]
 #![feature(const_cow_is_borrowed)]
 #![feature(const_convert)]
 #![feature(const_size_of_val)]
@@ -109,10 +111,11 @@
 #![feature(core_intrinsics)]
 #![feature(const_eval_select)]
 #![feature(const_pin)]
+#![feature(const_waker)]
 #![feature(cstr_from_bytes_until_nul)]
 #![feature(dispatch_from_dyn)]
-#![cfg_attr(not(bootstrap), feature(error_generic_member_access))]
-#![cfg_attr(not(bootstrap), feature(error_in_core))]
+#![feature(error_generic_member_access)]
+#![feature(error_in_core)]
 #![feature(exact_size_is_empty)]
 #![feature(extend_one)]
 #![feature(fmt_internals)]
@@ -122,20 +125,21 @@
 #![feature(iter_advance_by)]
 #![feature(iter_next_chunk)]
 #![feature(layout_for_ptr)]
-#![feature(maybe_uninit_array_assume_init)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]
+#![feature(maybe_uninit_uninit_array_transpose)]
 #![cfg_attr(test, feature(new_uninit))]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(pattern)]
 #![feature(pointer_byte_offsets)]
-#![cfg_attr(not(bootstrap), feature(provide_any))]
+#![feature(provide_any)]
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
 #![feature(receiver_trait)]
 #![feature(saturating_int_impl)]
 #![feature(set_ptr_value)]
+#![feature(sized_type_properties)]
 #![feature(slice_from_ptr_range)]
 #![feature(slice_group_by)]
 #![feature(slice_ptr_get)]
@@ -169,7 +173,6 @@
 #![cfg_attr(not(test), feature(generator_trait))]
 #![feature(hashmap_internals)]
 #![feature(lang_items)]
-#![cfg_attr(bootstrap, feature(let_else))]
 #![feature(min_specialization)]
 #![feature(negative_impls)]
 #![feature(never_type)]
@@ -224,16 +227,17 @@ mod boxed {
 }
 pub mod borrow;
 pub mod collections;
-#[cfg(not(no_global_oom_handling))]
+#[cfg(all(not(no_rc), not(no_sync), not(no_global_oom_handling)))]
 pub mod ffi;
 pub mod fmt;
+#[cfg(not(no_rc))]
 pub mod rc;
 pub mod slice;
 pub mod str;
 pub mod string;
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 pub mod sync;
-#[cfg(all(not(no_global_oom_handling), target_has_atomic = "ptr"))]
+#[cfg(all(not(no_global_oom_handling), not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 pub mod task;
 #[cfg(test)]
 mod tests;
diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index b0f4529ab..5a10121bb 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/library/alloc/src/raw_vec.rs
@@ -3,7 +3,7 @@
 use core::alloc::LayoutError;
 use core::cmp;
 use core::intrinsics;
-use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::Drop;
 use core::ptr::{self, NonNull, Unique};
 use core::slice;
@@ -168,7 +168,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
         // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
-        if mem::size_of::<T>() == 0 || capacity == 0 {
+        if T::IS_ZST || capacity == 0 {
             Self::new_in(alloc)
         } else {
             // We avoid `unwrap_or_else` here because it bloats the amount of
@@ -229,7 +229,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// This will always be `usize::MAX` if `T` is zero-sized.
     #[inline(always)]
     pub fn capacity(&self) -> usize {
-        if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
+        if T::IS_ZST { usize::MAX } else { self.cap }
     }
 
     /// Returns a shared reference to the allocator backing this `RawVec`.
@@ -238,7 +238,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     }
 
     fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
-        if mem::size_of::<T>() == 0 || self.cap == 0 {
+        if T::IS_ZST || self.cap == 0 {
             None
         } else {
             // We have an allocated chunk of memory, so we can bypass runtime
@@ -380,7 +380,7 @@ impl<T, A: Allocator> RawVec<T, A> {
         // This is ensured by the calling contexts.
         debug_assert!(additional > 0);
 
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // Since we return a capacity of `usize::MAX` when `elem_size` is
             // 0, getting to here necessarily means the `RawVec` is overfull.
             return Err(CapacityOverflow.into());
@@ -406,7 +406,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     // `grow_amortized`, but this method is usually instantiated less often so
     // it's less critical.
     fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // Since we return a capacity of `usize::MAX` when the type size is
             // 0, getting to here necessarily means the `RawVec` is overfull.
             return Err(CapacityOverflow.into());
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 6d247681c..006d813e5 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -1110,8 +1110,8 @@ impl<T: ?Sized> Rc<T> {
 
     #[inline]
     #[stable(feature = "ptr_eq", since = "1.17.0")]
-    /// Returns `true` if the two `Rc`s point to the same allocation
-    /// (in a vein similar to [`ptr::eq`]).
+    /// Returns `true` if the two `Rc`s point to the same allocation in a vein similar to
+    /// [`ptr::eq`]. See [that function][`ptr::eq`] for caveats when comparing `dyn Trait` pointers.
     ///
     /// # Examples
     ///
@@ -1386,7 +1386,7 @@ impl<T: ?Sized> Rc<T> {
             Self::allocate_for_layout(
                 Layout::for_value(&*ptr),
                 |layout| Global.allocate(layout),
-                |mem| mem.with_metadata_of(ptr as *mut RcBox<T>),
+                |mem| mem.with_metadata_of(ptr as *const RcBox<T>),
             )
         }
     }
@@ -2419,9 +2419,9 @@ impl<T: ?Sized> Weak<T> {
         }
     }
 
-    /// Returns `true` if the two `Weak`s point to the same allocation (similar to
-    /// [`ptr::eq`]), or if both don't point to any allocation
-    /// (because they were created with `Weak::new()`).
+    /// Returns `true` if the two `Weak`s point to the same allocation similar to [`ptr::eq`], or if
+    /// both don't point to any allocation (because they were created with `Weak::new()`). See [that
+    /// function][`ptr::eq`] for caveats when comparing `dyn Trait` pointers.
     ///
     /// # Notes
     ///
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index bcd3f49e2..a5e7bf2a1 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -16,9 +16,7 @@ use core::borrow::{Borrow, BorrowMut};
 #[cfg(not(no_global_oom_handling))]
 use core::cmp::Ordering::{self, Less};
 #[cfg(not(no_global_oom_handling))]
-use core::mem;
-#[cfg(not(no_global_oom_handling))]
-use core::mem::size_of;
+use core::mem::{self, SizedTypeProperties};
 #[cfg(not(no_global_oom_handling))]
 use core::ptr;
 
@@ -205,7 +203,7 @@ impl<T> [T] {
     where
         T: Ord,
     {
-        merge_sort(self, |a, b| a.lt(b));
+        merge_sort(self, T::lt);
     }
 
     /// Sorts the slice with a comparator function.
@@ -1018,7 +1016,7 @@ where
     const MIN_RUN: usize = 10;
 
     // Sorting has no meaningful behavior on zero-sized types.
-    if size_of::<T>() == 0 {
+    if T::IS_ZST {
         return;
     }
 
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index f2448396c..c436adf70 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -44,7 +44,6 @@
 
 #[cfg(not(no_global_oom_handling))]
 use core::char::{decode_utf16, REPLACEMENT_CHARACTER};
-#[cfg(not(bootstrap))]
 use core::error::Error;
 use core::fmt;
 use core::hash;
@@ -68,7 +67,7 @@ use core::str::Utf8Chunks;
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 use crate::collections::TryReserveError;
-use crate::str::{self, Chars, Utf8Error};
+use crate::str::{self, from_utf8_unchecked_mut, Chars, Utf8Error};
 #[cfg(not(no_global_oom_handling))]
 use crate::str::{from_boxed_utf8_unchecked, FromStr};
 use crate::vec::Vec;
@@ -1850,6 +1849,35 @@ impl String {
         let slice = self.vec.into_boxed_slice();
         unsafe { from_boxed_utf8_unchecked(slice) }
     }
+
+    /// Consumes and leaks the `String`, returning a mutable reference to the contents,
+    /// `&'static mut str`.
+    ///
+    /// This is mainly useful for data that lives for the remainder of
+    /// the program's life. Dropping the returned reference will cause a memory
+    /// leak.
+    ///
+    /// It does not reallocate or shrink the `String`,
+    /// so the leaked allocation may include unused capacity that is not part
+    /// of the returned slice.
+    ///
+    /// # Examples
+    ///
+    /// Simple usage:
+    ///
+    /// ```
+    /// #![feature(string_leak)]
+    ///
+    /// let x = String::from("bucket");
+    /// let static_ref: &'static mut str = x.leak();
+    /// assert_eq!(static_ref, "bucket");
+    /// ```
+    #[unstable(feature = "string_leak", issue = "102929")]
+    #[inline]
+    pub fn leak(self) -> &'static mut str {
+        let slice = self.vec.leak();
+        unsafe { from_utf8_unchecked_mut(slice) }
+    }
 }
 
 impl FromUtf8Error {
@@ -1941,7 +1969,6 @@ impl fmt::Display for FromUtf16Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for FromUtf8Error {
     #[allow(deprecated)]
@@ -1950,7 +1977,6 @@ impl Error for FromUtf8Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for FromUtf16Error {
     #[allow(deprecated)]
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 4377edeee..81cd77074 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -3,6 +3,10 @@
 //! Thread-safe reference-counting pointers.
 //!
 //! See the [`Arc<T>`][Arc] documentation for more details.
+//!
+//! **Note**: This module is only available on platforms that support atomic
+//! loads and stores of pointers. This may be detected at compile time using
+//! `#[cfg(target_has_atomic = "ptr")]`.
 
 use core::any::Any;
 use core::borrow;
@@ -82,6 +86,11 @@ macro_rules! acquire {
 /// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
 /// types.
 ///
+/// **Note**: This type is only available on platforms that support atomic
+/// loads and stores of pointers, which includes all platforms that support
+/// the `std` crate but not all those which only support [`alloc`](crate).
+/// This may be detected at compile time using `#[cfg(target_has_atomic = "ptr")]`.
+///
 /// ## Thread Safety
 ///
 /// Unlike [`Rc<T>`], `Arc<T>` uses atomic operations for its reference
@@ -1108,8 +1117,8 @@ impl<T: ?Sized> Arc<T> {
         drop(Weak { ptr: self.ptr });
     }
 
-    /// Returns `true` if the two `Arc`s point to the same allocation
-    /// (in a vein similar to [`ptr::eq`]).
+    /// Returns `true` if the two `Arc`s point to the same allocation in a vein similar to
+    /// [`ptr::eq`]. See [that function][`ptr::eq`] for caveats when comparing `dyn Trait` pointers.
     ///
     /// # Examples
     ///
@@ -1195,7 +1204,7 @@ impl<T: ?Sized> Arc<T> {
             Self::allocate_for_layout(
                 Layout::for_value(&*ptr),
                 |layout| Global.allocate(layout),
-                |mem| mem.with_metadata_of(ptr as *mut ArcInner<T>),
+                |mem| mem.with_metadata_of(ptr as *const ArcInner<T>),
             )
         }
     }
@@ -1980,33 +1989,26 @@ impl<T: ?Sized> Weak<T> {
         // We use a CAS loop to increment the strong count instead of a
         // fetch_add as this function should never take the reference count
         // from zero to one.
-        let inner = self.inner()?;
-
-        // Relaxed load because any write of 0 that we can observe
-        // leaves the field in a permanently zero state (so a
-        // "stale" read of 0 is fine), and any other value is
-        // confirmed via the CAS below.
-        let mut n = inner.strong.load(Relaxed);
-
-        loop {
-            if n == 0 {
-                return None;
-            }
-
-            // See comments in `Arc::clone` for why we do this (for `mem::forget`).
-            if n > MAX_REFCOUNT {
-                abort();
-            }
-
+        self.inner()?
+            .strong
             // Relaxed is fine for the failure case because we don't have any expectations about the new state.
             // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner
             // value can be initialized after `Weak` references have already been created. In that case, we
             // expect to observe the fully initialized value.
-            match inner.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) {
-                Ok(_) => return Some(unsafe { Arc::from_inner(self.ptr) }), // null checked above
-                Err(old) => n = old,
-            }
-        }
+            .fetch_update(Acquire, Relaxed, |n| {
+                // Any write of 0 we can observe leaves the field in permanently zero state.
+                if n == 0 {
+                    return None;
+                }
+                // See comments in `Arc::clone` for why we do this (for `mem::forget`).
+                if n > MAX_REFCOUNT {
+                    abort();
+                }
+                Some(n + 1)
+            })
+            .ok()
+            // null checked above
+            .map(|_| unsafe { Arc::from_inner(self.ptr) })
     }
 
     /// Gets the number of strong (`Arc`) pointers pointing to this allocation.
@@ -2067,9 +2069,9 @@ impl<T: ?Sized> Weak<T> {
         }
     }
 
-    /// Returns `true` if the two `Weak`s point to the same allocation (similar to
-    /// [`ptr::eq`]), or if both don't point to any allocation
-    /// (because they were created with `Weak::new()`).
+    /// Returns `true` if the two `Weak`s point to the same allocation similar to [`ptr::eq`], or if
+    /// both don't point to any allocation (because they were created with `Weak::new()`). See [that
+    /// function][`ptr::eq`] for caveats when comparing `dyn Trait` pointers.
     ///
     /// # Notes
     ///
@@ -2764,7 +2766,6 @@ fn data_offset_align(align: usize) -> usize {
     layout.size() + layout.padding_needed_for(align)
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "arc_error", since = "1.52.0")]
 impl<T: core::error::Error + ?Sized> core::error::Error for Arc<T> {
     #[allow(deprecated, deprecated_in_future)]
diff --git a/library/alloc/src/task.rs b/library/alloc/src/task.rs
index 528ee4ff1..9d8e309a9 100644
--- a/library/alloc/src/task.rs
+++ b/library/alloc/src/task.rs
@@ -1,5 +1,11 @@
 #![stable(feature = "wake_trait", since = "1.51.0")]
+
 //! Types and Traits for working with asynchronous tasks.
+//!
+//! **Note**: This module is only available on platforms that support atomic
+//! loads and stores of pointers. This may be detected at compile time using
+//! `#[cfg(target_has_atomic = "ptr")]`.
+
 use core::mem::ManuallyDrop;
 use core::task::{RawWaker, RawWakerVTable, Waker};
 
diff --git a/library/alloc/src/vec/drain.rs b/library/alloc/src/vec/drain.rs
index 5b73906a1..541f99bcf 100644
--- a/library/alloc/src/vec/drain.rs
+++ b/library/alloc/src/vec/drain.rs
@@ -1,7 +1,7 @@
 use crate::alloc::{Allocator, Global};
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen};
-use core::mem::{self, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, SizedTypeProperties};
 use core::ptr::{self, NonNull};
 use core::slice::{self};
 
@@ -202,7 +202,7 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
 
         let mut vec = self.vec;
 
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // ZSTs have no identity, so we don't need to move them around, we only need to drop the correct amount.
             // this can be achieved by manipulating the Vec length instead of moving values out from `iter`.
             unsafe {
diff --git a/library/alloc/src/vec/in_place_collect.rs b/library/alloc/src/vec/in_place_collect.rs
index b211421b2..87d61deb1 100644
--- a/library/alloc/src/vec/in_place_collect.rs
+++ b/library/alloc/src/vec/in_place_collect.rs
@@ -55,6 +55,9 @@
 //! This is handled by the [`InPlaceDrop`] guard for sink items (`U`) and by
 //! [`vec::IntoIter::forget_allocation_drop_remaining()`] for remaining source items (`T`).
 //!
+//! If dropping any remaining source item (`T`) panics then [`InPlaceDstBufDrop`] will handle dropping
+//! the already collected sink items (`U`) and freeing the allocation.
+//!
 //! [`vec::IntoIter::forget_allocation_drop_remaining()`]: super::IntoIter::forget_allocation_drop_remaining()
 //!
 //! # O(1) collect
@@ -135,10 +138,10 @@
 //! vec.truncate(write_idx);
 //! ```
 use core::iter::{InPlaceIterable, SourceIter, TrustedRandomAccessNoCoerce};
-use core::mem::{self, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, SizedTypeProperties};
 use core::ptr::{self};
 
-use super::{InPlaceDrop, SpecFromIter, SpecFromIterNested, Vec};
+use super::{InPlaceDrop, InPlaceDstBufDrop, SpecFromIter, SpecFromIterNested, Vec};
 
 /// Specialization marker for collecting an iterator pipeline into a Vec while reusing the
 /// source allocation, i.e. executing the pipeline in place.
@@ -154,7 +157,7 @@ where
     default fn from_iter(mut iterator: I) -> Self {
         // See "Layout constraints" section in the module documentation. We rely on const
         // optimization here since these conditions currently cannot be expressed as trait bounds
-        if mem::size_of::<T>() == 0
+        if T::IS_ZST
             || mem::size_of::<T>()
                 != mem::size_of::<<<I as SourceIter>::Source as AsVecIntoIter>::Item>()
             || mem::align_of::<T>()
@@ -191,14 +194,17 @@ where
             );
         }
 
-        // Drop any remaining values at the tail of the source but prevent drop of the allocation
-        // itself once IntoIter goes out of scope.
-        // If the drop panics then we also leak any elements collected into dst_buf.
+        // The ownership of the allocation and the new `T` values is temporarily moved into `dst_guard`.
+        // This is safe because `forget_allocation_drop_remaining` immediately forgets the allocation
+        // before any panic can occur in order to avoid any double free, and then proceeds to drop
+        // any remaining values at the tail of the source.
         //
         // Note: This access to the source wouldn't be allowed by the TrustedRandomIteratorNoCoerce
         // contract (used by SpecInPlaceCollect below). But see the "O(1) collect" section in the
         // module documenttation why this is ok anyway.
+        let dst_guard = InPlaceDstBufDrop { ptr: dst_buf, len, cap };
         src.forget_allocation_drop_remaining();
+        mem::forget(dst_guard);
 
         let vec = unsafe { Vec::from_raw_parts(dst_buf, len, cap) };
 
diff --git a/library/alloc/src/vec/in_place_drop.rs b/library/alloc/src/vec/in_place_drop.rs
index 1b1ef9130..25ca33c6a 100644
--- a/library/alloc/src/vec/in_place_drop.rs
+++ b/library/alloc/src/vec/in_place_drop.rs
@@ -22,3 +22,18 @@ impl<T> Drop for InPlaceDrop<T> {
         }
     }
 }
+
+// A helper struct for in-place collection that drops the destination allocation and elements,
+// to avoid leaking them if some other destructor panics.
+pub(super) struct InPlaceDstBufDrop<T> {
+    pub(super) ptr: *mut T,
+    pub(super) len: usize,
+    pub(super) cap: usize,
+}
+
+impl<T> Drop for InPlaceDstBufDrop<T> {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe { super::Vec::from_raw_parts(self.ptr, self.len, self.cap) };
+    }
+}
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index b4157fd58..02cc7691a 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -8,7 +8,7 @@ use core::iter::{
     FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
 };
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
 use core::ptr::{self, NonNull};
@@ -95,13 +95,16 @@ impl<T, A: Allocator> IntoIter<T, A> {
     }
 
     /// Drops remaining elements and relinquishes the backing allocation.
+    /// This method guarantees it won't panic before relinquishing
+    /// the backing allocation.
     ///
     /// This is roughly equivalent to the following, but more efficient
     ///
     /// ```
     /// # let mut into_iter = Vec::<u8>::with_capacity(10).into_iter();
+    /// let mut into_iter = std::mem::replace(&mut into_iter, Vec::new().into_iter());
     /// (&mut into_iter).for_each(core::mem::drop);
-    /// unsafe { core::ptr::write(&mut into_iter, Vec::new().into_iter()); }
+    /// std::mem::forget(into_iter);
     /// ```
     ///
     /// This method is used by in-place iteration, refer to the vec::in_place_collect
@@ -118,6 +121,8 @@ impl<T, A: Allocator> IntoIter<T, A> {
         self.ptr = self.buf.as_ptr();
         self.end = self.buf.as_ptr();
 
+        // Dropping the remaining elements can panic, so this needs to be
+        // done only after updating the other fields.
         unsafe {
             ptr::drop_in_place(remaining);
         }
@@ -149,7 +154,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
     fn next(&mut self) -> Option<T> {
         if self.ptr == self.end {
             None
-        } else if mem::size_of::<T>() == 0 {
+        } else if T::IS_ZST {
             // purposefully don't use 'ptr.offset' because for
             // vectors with 0-size elements this would return the
             // same pointer.
@@ -167,7 +172,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let exact = if mem::size_of::<T>() == 0 {
+        let exact = if T::IS_ZST {
             self.end.addr().wrapping_sub(self.ptr.addr())
         } else {
             unsafe { self.end.sub_ptr(self.ptr) }
@@ -179,7 +184,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
         let step_size = self.len().min(n);
         let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // SAFETY: due to unchecked casts of unsigned amounts to signed offsets the wraparound
             // effectively results in unsigned pointers representing positions 0..usize::MAX,
             // which is valid for ZSTs.
@@ -209,7 +214,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
         let len = self.len();
 
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             if len < N {
                 self.forget_remaining_elements();
                 // Safety: ZSTs can be conjured ex nihilo, only the amount has to be correct
@@ -218,7 +223,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
             self.ptr = self.ptr.wrapping_byte_add(N);
             // Safety: ditto
-            return Ok(unsafe { MaybeUninit::array_assume_init(raw_ary) });
+            return Ok(unsafe { raw_ary.transpose().assume_init() });
         }
 
         if len < N {
@@ -236,7 +241,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         return unsafe {
             ptr::copy_nonoverlapping(self.ptr, raw_ary.as_mut_ptr() as *mut T, N);
             self.ptr = self.ptr.add(N);
-            Ok(MaybeUninit::array_assume_init(raw_ary))
+            Ok(raw_ary.transpose().assume_init())
         };
     }
 
@@ -253,7 +258,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         // that `T: Copy` so reading elements from the buffer doesn't invalidate
         // them for `Drop`.
         unsafe {
-            if mem::size_of::<T>() == 0 { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
+            if T::IS_ZST { mem::zeroed() } else { ptr::read(self.ptr.add(i)) }
         }
     }
 }
@@ -264,7 +269,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     fn next_back(&mut self) -> Option<T> {
         if self.end == self.ptr {
             None
-        } else if mem::size_of::<T>() == 0 {
+        } else if T::IS_ZST {
             // See above for why 'ptr.offset' isn't used
             self.end = self.end.wrapping_byte_sub(1);
 
@@ -280,7 +285,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     #[inline]
     fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
         let step_size = self.len().min(n);
-        if mem::size_of::<T>() == 0 {
+        if T::IS_ZST {
             // SAFETY: same as for advance_by()
             self.end = self.end.wrapping_byte_sub(step_size);
         } else {
diff --git a/library/alloc/src/vec/is_zero.rs b/library/alloc/src/vec/is_zero.rs
index 2e025c8a4..8e652d676 100644
--- a/library/alloc/src/vec/is_zero.rs
+++ b/library/alloc/src/vec/is_zero.rs
@@ -160,3 +160,25 @@ unsafe impl<T: IsZero> IsZero for Saturating<T> {
         self.0.is_zero()
     }
 }
+
+macro_rules! impl_for_optional_bool {
+    ($($t:ty,)+) => {$(
+        unsafe impl IsZero for $t {
+            #[inline]
+            fn is_zero(&self) -> bool {
+                // SAFETY: This is *not* a stable layout guarantee, but
+                // inside `core` we're allowed to rely on the current rustc
+                // behaviour that options of bools will be one byte with
+                // no padding, so long as they're nested less than 254 deep.
+                let raw: u8 = unsafe { core::mem::transmute(*self) };
+                raw == 0
+            }
+        }
+    )+};
+}
+impl_for_optional_bool! {
+    Option<bool>,
+    Option<Option<bool>>,
+    Option<Option<Option<bool>>>,
+    // Could go further, but not worth the metadata overhead
+}
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 60b36af5e..bbbdc3aa2 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -64,7 +64,7 @@ use core::iter;
 #[cfg(not(no_global_oom_handling))]
 use core::iter::FromIterator;
 use core::marker::PhantomData;
-use core::mem::{self, ManuallyDrop, MaybeUninit};
+use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
@@ -125,7 +125,7 @@ use self::set_len_on_drop::SetLenOnDrop;
 mod set_len_on_drop;
 
 #[cfg(not(no_global_oom_handling))]
-use self::in_place_drop::InPlaceDrop;
+use self::in_place_drop::{InPlaceDrop, InPlaceDstBufDrop};
 
 #[cfg(not(no_global_oom_handling))]
 mod in_place_drop;
@@ -483,15 +483,13 @@ impl<T> Vec<T> {
         Self::with_capacity_in(capacity, Global)
     }
 
-    /// Creates a `Vec<T>` directly from the raw components of another vector.
+    /// Creates a `Vec<T>` directly from a pointer, a capacity, and a length.
     ///
     /// # Safety
     ///
     /// This is highly unsafe, due to the number of invariants that aren't
     /// checked:
     ///
-    /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
-    ///   (at least, it's highly likely to be incorrect if it wasn't).
     /// * `T` needs to have the same alignment as what `ptr` was allocated with.
     ///   (`T` having a less strict alignment is not sufficient, the alignment really
     ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
@@ -500,6 +498,14 @@ impl<T> Vec<T> {
     ///   to be the same size as the pointer was allocated with. (Because similar to
     ///   alignment, [`dealloc`] must be called with the same layout `size`.)
     /// * `length` needs to be less than or equal to `capacity`.
+    /// * The first `length` values must be properly initialized values of type `T`.
+    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    /// * The allocated size in bytes must be no larger than `isize::MAX`.
+    ///   See the safety documentation of [`pointer::offset`].
+    ///
+    /// These requirements are always upheld by any `ptr` that has been allocated
+    /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
+    /// upheld.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures. For example it is normally **not** safe
@@ -551,6 +557,32 @@ impl<T> Vec<T> {
     ///     assert_eq!(rebuilt, [4, 5, 6]);
     /// }
     /// ```
+    ///
+    /// Using memory that was allocated elsewhere:
+    ///
+    /// ```rust
+    /// #![feature(allocator_api)]
+    ///
+    /// use std::alloc::{AllocError, Allocator, Global, Layout};
+    ///
+    /// fn main() {
+    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
+    ///     let vec = unsafe {
+    ///         let mem = match Global.allocate(layout) {
+    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
+    ///             Err(AllocError) => return,
+    ///         };
+    ///
+    ///         mem.write(1_000_000);
+    ///
+    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
+    ///     };
+    ///
+    ///     assert_eq!(vec, &[1_000_000]);
+    ///     assert_eq!(vec.capacity(), 16);
+    /// }
+    /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
@@ -641,21 +673,30 @@ impl<T, A: Allocator> Vec<T, A> {
         Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
     }
 
-    /// Creates a `Vec<T, A>` directly from the raw components of another vector.
+    /// Creates a `Vec<T, A>` directly from a pointer, a capacity, a length,
+    /// and an allocator.
     ///
     /// # Safety
     ///
     /// This is highly unsafe, due to the number of invariants that aren't
     /// checked:
     ///
-    /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
-    ///   (at least, it's highly likely to be incorrect if it wasn't).
-    /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
+    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
     ///   (`T` having a less strict alignment is not sufficient, the alignment really
     ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
     ///   allocated and deallocated with the same layout.)
+    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+    ///   to be the same size as the pointer was allocated with. (Because similar to
+    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
     /// * `length` needs to be less than or equal to `capacity`.
-    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    /// * The first `length` values must be properly initialized values of type `T`.
+    /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
+    /// * The allocated size in bytes must be no larger than `isize::MAX`.
+    ///   See the safety documentation of [`pointer::offset`].
+    ///
+    /// These requirements are always upheld by any `ptr` that has been allocated
+    /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
+    /// upheld.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures. For example it is **not** safe
@@ -673,6 +714,7 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// [`String`]: crate::string::String
     /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
+    /// [*fit*]: crate::alloc::Allocator#memory-fitting
     ///
     /// # Examples
     ///
@@ -711,6 +753,29 @@ impl<T, A: Allocator> Vec<T, A> {
     ///     assert_eq!(rebuilt, [4, 5, 6]);
     /// }
     /// ```
+    ///
+    /// Using memory that was allocated elsewhere:
+    ///
+    /// ```rust
+    /// use std::alloc::{alloc, Layout};
+    ///
+    /// fn main() {
+    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///     let vec = unsafe {
+    ///         let mem = alloc(layout).cast::<u32>();
+    ///         if mem.is_null() {
+    ///             return;
+    ///         }
+    ///
+    ///         mem.write(1_000_000);
+    ///
+    ///         Vec::from_raw_parts(mem, 1, 16)
+    ///     };
+    ///
+    ///     assert_eq!(vec, &[1_000_000]);
+    ///     assert_eq!(vec.capacity(), 16);
+    /// }
+    /// ```
     #[inline]
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub unsafe fn from_raw_parts_in(ptr: *mut T, length: usize, capacity: usize, alloc: A) -> Self {
@@ -803,13 +868,14 @@ impl<T, A: Allocator> Vec<T, A> {
         (ptr, len, capacity, alloc)
     }
 
-    /// Returns the number of elements the vector can hold without
+    /// Returns the total number of elements the vector can hold without
     /// reallocating.
     ///
     /// # Examples
     ///
     /// ```
-    /// let vec: Vec<i32> = Vec::with_capacity(10);
+    /// let mut vec: Vec<i32> = Vec::with_capacity(10);
+    /// vec.push(42);
     /// assert_eq!(vec.capacity(), 10);
     /// ```
     #[inline]
@@ -1774,6 +1840,51 @@ impl<T, A: Allocator> Vec<T, A> {
         }
     }
 
+    /// Appends an element if there is sufficient spare capacity, otherwise an error is returned
+    /// with the element.
+    ///
+    /// Unlike [`push`] this method will not reallocate when there's insufficient capacity.
+    /// The caller should use [`reserve`] or [`try_reserve`] to ensure that there is enough capacity.
+    ///
+    /// [`push`]: Vec::push
+    /// [`reserve`]: Vec::reserve
+    /// [`try_reserve`]: Vec::try_reserve
+    ///
+    /// # Examples
+    ///
+    /// A manual, panic-free alternative to [`FromIterator`]:
+    ///
+    /// ```
+    /// #![feature(vec_push_within_capacity)]
+    ///
+    /// use std::collections::TryReserveError;
+    /// fn from_iter_fallible<T>(iter: impl Iterator<Item=T>) -> Result<Vec<T>, TryReserveError> {
+    ///     let mut vec = Vec::new();
+    ///     for value in iter {
+    ///         if let Err(value) = vec.push_within_capacity(value) {
+    ///             vec.try_reserve(1)?;
+    ///             // this cannot fail, the previous line either returned or added at least 1 free slot
+    ///             let _ = vec.push_within_capacity(value);
+    ///         }
+    ///     }
+    ///     Ok(vec)
+    /// }
+    /// assert_eq!(from_iter_fallible(0..100), Ok(Vec::from_iter(0..100)));
+    /// ```
+    #[inline]
+    #[unstable(feature = "vec_push_within_capacity", issue = "100486")]
+    pub fn push_within_capacity(&mut self, value: T) -> Result<(), T> {
+        if self.len == self.buf.capacity() {
+            return Err(value);
+        }
+        unsafe {
+            let end = self.as_mut_ptr().add(self.len);
+            ptr::write(end, value);
+            self.len += 1;
+        }
+        Ok(())
+    }
+
     /// Removes the last element from a vector and returns it, or [`None`] if it
     /// is empty.
     ///
@@ -1889,9 +2000,7 @@ impl<T, A: Allocator> Vec<T, A> {
         unsafe {
             // set self.vec length's to start, to be safe in case Drain is leaked
             self.set_len(start);
-            // Use the borrow in the IterMut to indicate borrowing behavior of the
-            // whole Drain iterator (like &mut T).
-            let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
+            let range_slice = slice::from_raw_parts(self.as_ptr().add(start), end - start);
             Drain {
                 tail_start: end,
                 tail_len: len - end,
@@ -2083,7 +2192,6 @@ impl<T, A: Allocator> Vec<T, A> {
     /// static_ref[0] += 1;
     /// assert_eq!(static_ref, &[2, 2, 3]);
     /// ```
-    #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "vec_leak", since = "1.47.0")]
     #[inline]
     pub fn leak<'a>(self) -> &'a mut [T]
@@ -2347,7 +2455,7 @@ impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
     #[unstable(feature = "slice_flatten", issue = "95629")]
     pub fn into_flattened(self) -> Vec<T, A> {
         let (ptr, len, cap, alloc) = self.into_raw_parts_with_alloc();
-        let (new_len, new_cap) = if mem::size_of::<T>() == 0 {
+        let (new_len, new_cap) = if T::IS_ZST {
             (len.checked_mul(N).expect("vec len overflow"), usize::MAX)
         } else {
             // SAFETY:
@@ -2677,7 +2785,7 @@ impl<T, A: Allocator> IntoIterator for Vec<T, A> {
             let mut me = ManuallyDrop::new(self);
             let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
             let begin = me.as_mut_ptr();
-            let end = if mem::size_of::<T>() == 0 {
+            let end = if T::IS_ZST {
                 begin.wrapping_byte_add(me.len())
             } else {
                 begin.add(me.len()) as *const T
diff --git a/library/alloc/tests/autotraits.rs b/library/alloc/tests/autotraits.rs
new file mode 100644
index 000000000..8ff5f0abe
--- /dev/null
+++ b/library/alloc/tests/autotraits.rs
@@ -0,0 +1,293 @@
+fn require_sync<T: Sync>(_: T) {}
+fn require_send_sync<T: Send + Sync>(_: T) {}
+
+struct NotSend(*const ());
+unsafe impl Sync for NotSend {}
+
+#[test]
+fn test_btree_map() {
+    // Tests of this form are prone to https://github.com/rust-lang/rust/issues/64552.
+    //
+    // In theory the async block's future would be Send if the value we hold
+    // across the await point is Send, and Sync if the value we hold across the
+    // await point is Sync.
+    //
+    // We test autotraits in this convoluted way, instead of a straightforward
+    // `require_send_sync::<TypeIWantToTest>()`, because the interaction with
+    // generators exposes some current limitations in rustc's ability to prove a
+    // lifetime bound on the erased generator witness types. See the above link.
+    //
+    // A typical way this would surface in real code is:
+    //
+    //     fn spawn<T: Future + Send>(_: T) {}
+    //
+    //     async fn f() {
+    //         let map = BTreeMap::<u32, Box<dyn Send + Sync>>::new();
+    //         for _ in &map {
+    //             async {}.await;
+    //         }
+    //     }
+    //
+    //     fn main() {
+    //         spawn(f());
+    //     }
+    //
+    // where with some unintentionally overconstrained Send impls in liballoc's
+    // internals, the future might incorrectly not be Send even though every
+    // single type involved in the program is Send and Sync.
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Iter<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    // Testing like this would not catch all issues that the above form catches.
+    require_send_sync(None::<alloc::collections::btree_map::Iter<'_, &u32, &u32>>);
+
+    require_sync(async {
+        let _v = None::<alloc::collections::btree_map::Iter<'_, u32, NotSend>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::BTreeMap<&u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<
+            alloc::collections::btree_map::DrainFilter<
+                '_,
+                &u32,
+                &u32,
+                fn(&&u32, &mut &u32) -> bool,
+            >,
+        >;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Entry<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::IntoIter<&u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::IntoKeys<&u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::IntoValues<&u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Iter<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::IterMut<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Keys<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::OccupiedEntry<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::OccupiedError<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Range<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::RangeMut<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::VacantEntry<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::Values<'_, &u32, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_map::ValuesMut<'_, &u32, &u32>>;
+        async {}.await;
+    });
+}
+
+#[test]
+fn test_btree_set() {
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::BTreeSet<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::Difference<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::DrainFilter<'_, &u32, fn(&&u32) -> bool>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::Intersection<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::IntoIter<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::Iter<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::Range<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::SymmetricDifference<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::btree_set::Union<'_, &u32>>;
+        async {}.await;
+    });
+}
+
+#[test]
+fn test_binary_heap() {
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::BinaryHeap<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::Drain<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::DrainSorted<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::IntoIter<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::IntoIterSorted<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::Iter<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::binary_heap::PeekMut<'_, &u32>>;
+        async {}.await;
+    });
+}
+
+#[test]
+fn test_linked_list() {
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::Cursor<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::CursorMut<'_, &u32>>;
+        async {}.await;
+    });
+
+    // FIXME
+    /*
+    require_send_sync(async {
+        let _v =
+            None::<alloc::collections::linked_list::DrainFilter<'_, &u32, fn(&mut &u32) -> bool>>;
+        async {}.await;
+    });
+    */
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::IntoIter<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::Iter<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::IterMut<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::linked_list::LinkedList<&u32>>;
+        async {}.await;
+    });
+}
+
+#[test]
+fn test_vec_deque() {
+    require_send_sync(async {
+        let _v = None::<alloc::collections::vec_deque::Drain<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::vec_deque::IntoIter<&u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::vec_deque::Iter<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::vec_deque::IterMut<'_, &u32>>;
+        async {}.await;
+    });
+
+    require_send_sync(async {
+        let _v = None::<alloc::collections::vec_deque::VecDeque<&u32>>;
+        async {}.await;
+    });
+}
diff --git a/library/alloc/tests/lib.rs b/library/alloc/tests/lib.rs
index 490c0d8f7..ffc5ca7a5 100644
--- a/library/alloc/tests/lib.rs
+++ b/library/alloc/tests/lib.rs
@@ -2,6 +2,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(assert_matches)]
 #![feature(box_syntax)]
+#![feature(btree_drain_filter)]
 #![feature(cow_is_borrowed)]
 #![feature(const_box)]
 #![feature(const_convert)]
@@ -14,6 +15,8 @@
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
+#![feature(linked_list_cursors)]
+#![feature(map_try_insert)]
 #![feature(new_uninit)]
 #![feature(pattern)]
 #![feature(trusted_len)]
@@ -32,7 +35,7 @@
 #![feature(slice_group_by)]
 #![feature(slice_partition_dedup)]
 #![feature(string_remove_matches)]
-#![feature(const_btree_new)]
+#![feature(const_btree_len)]
 #![feature(const_default_impls)]
 #![feature(const_trait_impl)]
 #![feature(const_str_from_utf8)]
@@ -41,7 +44,6 @@
 #![feature(pointer_is_aligned)]
 #![feature(slice_flatten)]
 #![feature(thin_box)]
-#![feature(bench_black_box)]
 #![feature(strict_provenance)]
 #![feature(once_cell)]
 #![feature(drain_keep_rest)]
@@ -50,6 +52,7 @@ use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 
 mod arc;
+mod autotraits;
 mod borrow;
 mod boxed;
 mod btree_set_hash;
diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index f140fc414..e02711870 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1191,48 +1191,53 @@ fn test_from_iter_specialization_panic_during_iteration_drops() {
 }
 
 #[test]
-fn test_from_iter_specialization_panic_during_drop_leaks() {
-    static mut DROP_COUNTER: usize = 0;
+fn test_from_iter_specialization_panic_during_drop_doesnt_leak() {
+    static mut DROP_COUNTER_OLD: [usize; 5] = [0; 5];
+    static mut DROP_COUNTER_NEW: [usize; 2] = [0; 2];
 
     #[derive(Debug)]
-    enum Droppable {
-        DroppedTwice(Box<i32>),
-        PanicOnDrop,
-    }
+    struct Old(usize);
 
-    impl Drop for Droppable {
+    impl Drop for Old {
         fn drop(&mut self) {
-            match self {
-                Droppable::DroppedTwice(_) => {
-                    unsafe {
-                        DROP_COUNTER += 1;
-                    }
-                    println!("Dropping!")
-                }
-                Droppable::PanicOnDrop => {
-                    if !std::thread::panicking() {
-                        panic!();
-                    }
-                }
+            unsafe {
+                DROP_COUNTER_OLD[self.0] += 1;
+            }
+
+            if self.0 == 3 {
+                panic!();
             }
+
+            println!("Dropped Old: {}", self.0);
         }
     }
 
-    let mut to_free: *mut Droppable = core::ptr::null_mut();
-    let mut cap = 0;
+    #[derive(Debug)]
+    struct New(usize);
+
+    impl Drop for New {
+        fn drop(&mut self) {
+            unsafe {
+                DROP_COUNTER_NEW[self.0] += 1;
+            }
+
+            println!("Dropped New: {}", self.0);
+        }
+    }
 
     let _ = std::panic::catch_unwind(AssertUnwindSafe(|| {
-        let mut v = vec![Droppable::DroppedTwice(Box::new(123)), Droppable::PanicOnDrop];
-        to_free = v.as_mut_ptr();
-        cap = v.capacity();
-        let _ = v.into_iter().take(0).collect::<Vec<_>>();
+        let v = vec![Old(0), Old(1), Old(2), Old(3), Old(4)];
+        let _ = v.into_iter().map(|x| New(x.0)).take(2).collect::<Vec<_>>();
     }));
 
-    assert_eq!(unsafe { DROP_COUNTER }, 1);
-    // clean up the leak to keep miri happy
-    unsafe {
-        drop(Vec::from_raw_parts(to_free, 0, cap));
-    }
+    assert_eq!(unsafe { DROP_COUNTER_OLD[0] }, 1);
+    assert_eq!(unsafe { DROP_COUNTER_OLD[1] }, 1);
+    assert_eq!(unsafe { DROP_COUNTER_OLD[2] }, 1);
+    assert_eq!(unsafe { DROP_COUNTER_OLD[3] }, 1);
+    assert_eq!(unsafe { DROP_COUNTER_OLD[4] }, 1);
+
+    assert_eq!(unsafe { DROP_COUNTER_NEW[0] }, 1);
+    assert_eq!(unsafe { DROP_COUNTER_NEW[1] }, 1);
 }
 
 // regression test for issue #85322. Peekable previously implemented InPlaceIterable,
diff --git a/library/core/benches/iter.rs b/library/core/benches/iter.rs
index 0abe20e4c..38887f29a 100644
--- a/library/core/benches/iter.rs
+++ b/library/core/benches/iter.rs
@@ -1,4 +1,6 @@
 use core::iter::*;
+use core::mem;
+use core::num::Wrapping;
 use test::{black_box, Bencher};
 
 #[bench]
@@ -364,6 +366,13 @@ fn bench_partial_cmp(b: &mut Bencher) {
 }
 
 #[bench]
+fn bench_chain_partial_cmp(b: &mut Bencher) {
+    b.iter(|| {
+        (0..50000).chain(50000..100000).map(black_box).partial_cmp((0..100000).map(black_box))
+    })
+}
+
+#[bench]
 fn bench_lt(b: &mut Bencher) {
     b.iter(|| (0..100000).map(black_box).lt((0..100000).map(black_box)))
 }
@@ -391,3 +400,21 @@ fn bench_trusted_random_access_adapters(b: &mut Bencher) {
         acc
     })
 }
+
+/// Exercises the iter::Copied specialization for slice::Iter
+#[bench]
+fn bench_copied_array_chunks(b: &mut Bencher) {
+    let v = vec![1u8; 1024];
+
+    b.iter(|| {
+        black_box(&v)
+            .iter()
+            .copied()
+            .array_chunks::<{ mem::size_of::<u64>() }>()
+            .map(|ary| {
+                let d = u64::from_ne_bytes(ary);
+                Wrapping(d.rotate_left(7).wrapping_add(1))
+            })
+            .sum::<Wrapping<u64>>()
+    })
+}
diff --git a/library/core/benches/lib.rs b/library/core/benches/lib.rs
index a6c174d2f..1e462e3fc 100644
--- a/library/core/benches/lib.rs
+++ b/library/core/benches/lib.rs
@@ -4,6 +4,7 @@
 #![feature(int_log)]
 #![feature(test)]
 #![feature(trusted_random_access)]
+#![feature(iter_array_chunks)]
 
 extern crate test;
 
diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index f03502429..920e559cc 100644
--- a/library/core/src/alloc/layout.rs
+++ b/library/core/src/alloc/layout.rs
@@ -5,7 +5,6 @@
 // Your performance intuition is useless. Run perf.
 
 use crate::cmp;
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 use crate::mem::{self, ValidAlign};
@@ -65,6 +64,7 @@ impl Layout {
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[rustc_const_stable(feature = "const_alloc_layout_size_align", since = "1.50.0")]
     #[inline]
+    #[rustc_allow_const_fn_unstable(ptr_alignment_type)]
     pub const fn from_size_align(size: usize, align: usize) -> Result<Self, LayoutError> {
         if !align.is_power_of_two() {
             return Err(LayoutError);
@@ -114,6 +114,7 @@ impl Layout {
     #[rustc_const_stable(feature = "const_alloc_layout_unchecked", since = "1.36.0")]
     #[must_use]
     #[inline]
+    #[rustc_allow_const_fn_unstable(ptr_alignment_type)]
     pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
         // SAFETY: the caller is required to uphold the preconditions.
         unsafe { Layout { size, align: ValidAlign::new_unchecked(align) } }
@@ -134,6 +135,7 @@ impl Layout {
     #[must_use = "this returns the minimum alignment, \
                   without modifying the layout"]
     #[inline]
+    #[rustc_allow_const_fn_unstable(ptr_alignment_type)]
     pub const fn align(&self) -> usize {
         self.align.as_usize()
     }
@@ -463,7 +465,6 @@ pub type LayoutErr = LayoutError;
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct LayoutError;
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "alloc_layout", since = "1.28.0")]
 impl Error for LayoutError {}
 
diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs
index 94efa7666..a4bf6a853 100644
--- a/library/core/src/alloc/mod.rs
+++ b/library/core/src/alloc/mod.rs
@@ -21,7 +21,6 @@ pub use self::layout::LayoutErr;
 #[stable(feature = "alloc_layout_error", since = "1.50.0")]
 pub use self::layout::LayoutError;
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 use crate::ptr::{self, NonNull};
@@ -34,7 +33,6 @@ use crate::ptr::{self, NonNull};
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct AllocError;
 
-#[cfg(not(bootstrap))]
 #[unstable(
     feature = "allocator_api",
     reason = "the precise API and guarantees it provides may be tweaked.",
@@ -107,6 +105,7 @@ impl fmt::Display for AllocError {
 ///
 /// [*currently allocated*]: #currently-allocated-memory
 #[unstable(feature = "allocator_api", issue = "32838")]
+#[const_trait]
 pub unsafe trait Allocator {
     /// Attempts to allocate a block of memory.
     ///
diff --git a/library/core/src/array/iter.rs b/library/core/src/array/iter.rs
index f4885ed9f..b91c63018 100644
--- a/library/core/src/array/iter.rs
+++ b/library/core/src/array/iter.rs
@@ -1,10 +1,10 @@
 //! Defines the `IntoIter` owned iterator for arrays.
 
 use crate::{
-    cmp, fmt,
+    fmt,
     iter::{self, ExactSizeIterator, FusedIterator, TrustedLen},
     mem::{self, MaybeUninit},
-    ops::Range,
+    ops::{IndexRange, Range},
     ptr,
 };
 
@@ -29,9 +29,10 @@ pub struct IntoIter<T, const N: usize> {
     /// The elements in `data` that have not been yielded yet.
     ///
     /// Invariants:
-    /// - `alive.start <= alive.end`
     /// - `alive.end <= N`
-    alive: Range<usize>,
+    ///
+    /// (And the `IndexRange` type requires `alive.start <= alive.end`.)
+    alive: IndexRange,
 }
 
 // Note: the `#[rustc_skip_array_during_method_dispatch]` on `trait IntoIterator`
@@ -69,7 +70,7 @@ impl<T, const N: usize> IntoIterator for [T; N] {
         // Until then, we can use `mem::transmute_copy` to create a bitwise copy
         // as a different type, then forget `array` so that it is not dropped.
         unsafe {
-            let iter = IntoIter { data: mem::transmute_copy(&self), alive: 0..N };
+            let iter = IntoIter { data: mem::transmute_copy(&self), alive: IndexRange::zero_to(N) };
             mem::forget(self);
             iter
         }
@@ -103,8 +104,7 @@ impl<T, const N: usize> IntoIter<T, N> {
     ///
     /// ```
     /// #![feature(array_into_iter_constructors)]
-    ///
-    /// #![feature(maybe_uninit_array_assume_init)]
+    /// #![feature(maybe_uninit_uninit_array_transpose)]
     /// #![feature(maybe_uninit_uninit_array)]
     /// use std::array::IntoIter;
     /// use std::mem::MaybeUninit;
@@ -133,7 +133,7 @@ impl<T, const N: usize> IntoIter<T, N> {
     ///     }
     ///
     ///     // SAFETY: We've initialized all N items
-    ///     unsafe { Ok(MaybeUninit::array_assume_init(buffer)) }
+    ///     unsafe { Ok(buffer.transpose().assume_init()) }
     /// }
     ///
     /// let r: [_; 4] = next_chunk(&mut (10..16)).unwrap();
@@ -147,7 +147,9 @@ impl<T, const N: usize> IntoIter<T, N> {
         buffer: [MaybeUninit<T>; N],
         initialized: Range<usize>,
     ) -> Self {
-        Self { data: buffer, alive: initialized }
+        // SAFETY: one of our safety conditions is that the range is canonical.
+        let alive = unsafe { IndexRange::new_unchecked(initialized.start, initialized.end) };
+        Self { data: buffer, alive }
     }
 
     /// Creates an iterator over `T` which returns no elements.
@@ -283,16 +285,11 @@ impl<T, const N: usize> Iterator for IntoIter<T, N> {
     }
 
     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
-        let len = self.len();
-
-        // The number of elements to drop.  Always in-bounds by construction.
-        let delta = cmp::min(n, len);
+        let original_len = self.len();
 
-        let range_to_drop = self.alive.start..(self.alive.start + delta);
-
-        // Moving the start marks them as conceptually "dropped", so if anything
-        // goes bad then our drop impl won't double-free them.
-        self.alive.start += delta;
+        // This also moves the start, which marks them as conceptually "dropped",
+        // so if anything goes bad then our drop impl won't double-free them.
+        let range_to_drop = self.alive.take_prefix(n);
 
         // SAFETY: These elements are currently initialized, so it's fine to drop them.
         unsafe {
@@ -300,7 +297,7 @@ impl<T, const N: usize> Iterator for IntoIter<T, N> {
             ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(slice));
         }
 
-        if n > len { Err(len) } else { Ok(()) }
+        if n > original_len { Err(original_len) } else { Ok(()) }
     }
 }
 
@@ -338,16 +335,11 @@ impl<T, const N: usize> DoubleEndedIterator for IntoIter<T, N> {
     }
 
     fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
-        let len = self.len();
-
-        // The number of elements to drop.  Always in-bounds by construction.
-        let delta = cmp::min(n, len);
-
-        let range_to_drop = (self.alive.end - delta)..self.alive.end;
+        let original_len = self.len();
 
-        // Moving the end marks them as conceptually "dropped", so if anything
-        // goes bad then our drop impl won't double-free them.
-        self.alive.end -= delta;
+        // This also moves the end, which marks them as conceptually "dropped",
+        // so if anything goes bad then our drop impl won't double-free them.
+        let range_to_drop = self.alive.take_suffix(n);
 
         // SAFETY: These elements are currently initialized, so it's fine to drop them.
         unsafe {
@@ -355,7 +347,7 @@ impl<T, const N: usize> DoubleEndedIterator for IntoIter<T, N> {
             ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(slice));
         }
 
-        if n > len { Err(len) } else { Ok(()) }
+        if n > original_len { Err(original_len) } else { Ok(()) }
     }
 }
 
@@ -372,9 +364,7 @@ impl<T, const N: usize> Drop for IntoIter<T, N> {
 #[stable(feature = "array_value_iter_impls", since = "1.40.0")]
 impl<T, const N: usize> ExactSizeIterator for IntoIter<T, N> {
     fn len(&self) -> usize {
-        // Will never underflow due to the invariant `alive.start <=
-        // alive.end`.
-        self.alive.end - self.alive.start
+        self.alive.len()
     }
     fn is_empty(&self) -> bool {
         self.alive.is_empty()
@@ -396,14 +386,15 @@ impl<T: Clone, const N: usize> Clone for IntoIter<T, N> {
     fn clone(&self) -> Self {
         // Note, we don't really need to match the exact same alive range, so
         // we can just clone into offset 0 regardless of where `self` is.
-        let mut new = Self { data: MaybeUninit::uninit_array(), alive: 0..0 };
+        let mut new = Self { data: MaybeUninit::uninit_array(), alive: IndexRange::zero_to(0) };
 
         // Clone all alive elements.
         for (src, dst) in iter::zip(self.as_slice(), &mut new.data) {
             // Write a clone into the new array, then update its alive range.
             // If cloning panics, we'll correctly drop the previous items.
             dst.write(src.clone());
-            new.alive.end += 1;
+            // This addition cannot overflow as we're iterating a slice
+            new.alive = IndexRange::zero_to(new.alive.end() + 1);
         }
 
         new
diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs
index 9effb3790..eae0e1c76 100644
--- a/library/core/src/array/mod.rs
+++ b/library/core/src/array/mod.rs
@@ -7,7 +7,6 @@
 use crate::borrow::{Borrow, BorrowMut};
 use crate::cmp::Ordering;
 use crate::convert::{Infallible, TryFrom};
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 use crate::hash::{self, Hash};
@@ -33,6 +32,10 @@ pub use iter::IntoIter;
 /// # Example
 ///
 /// ```rust
+/// // type inference is helping us here, the way `from_fn` knows how many
+/// // elements to produce is the length of array down there: only arrays of
+/// // equal lengths can be compared, so the const generic parameter `N` is
+/// // inferred to be 5, thus creating array of 5 elements.
 /// let array = core::array::from_fn(|i| i);
 /// assert_eq!(array, [0, 1, 2, 3, 4]);
 /// ```
@@ -121,7 +124,6 @@ impl fmt::Display for TryFromSliceError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "try_from", since = "1.34.0")]
 impl Error for TryFromSliceError {
     #[allow(deprecated)]
@@ -184,6 +186,18 @@ impl<T, const N: usize> const BorrowMut<[T]> for [T; N] {
     }
 }
 
+/// Tries to create an array `[T; N]` by copying from a slice `&[T]`. Succeeds if
+/// `slice.len() == N`.
+///
+/// ```
+/// let bytes: [u8; 3] = [1, 0, 2];
+///
+/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
+/// assert_eq!(1, u16::from_le_bytes(bytes_head));
+///
+/// let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
+/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
+/// ```
 #[stable(feature = "try_from", since = "1.34.0")]
 impl<T, const N: usize> TryFrom<&[T]> for [T; N]
 where
@@ -196,6 +210,18 @@ where
     }
 }
 
+/// Tries to create an array `[T; N]` by copying from a mutable slice `&mut [T]`.
+/// Succeeds if `slice.len() == N`.
+///
+/// ```
+/// let mut bytes: [u8; 3] = [1, 0, 2];
+///
+/// let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
+/// assert_eq!(1, u16::from_le_bytes(bytes_head));
+///
+/// let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
+/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
+/// ```
 #[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
 impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]
 where
@@ -208,6 +234,18 @@ where
     }
 }
 
+/// Tries to create an array ref `&[T; N]` from a slice ref `&[T]`. Succeeds if
+/// `slice.len() == N`.
+///
+/// ```
+/// let bytes: [u8; 3] = [1, 0, 2];
+///
+/// let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
+/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
+///
+/// let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
+/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
+/// ```
 #[stable(feature = "try_from", since = "1.34.0")]
 impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
     type Error = TryFromSliceError;
@@ -223,6 +261,18 @@ impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
     }
 }
 
+/// Tries to create a mutable array ref `&mut [T; N]` from a mutable slice ref
+/// `&mut [T]`. Succeeds if `slice.len() == N`.
+///
+/// ```
+/// let mut bytes: [u8; 3] = [1, 0, 2];
+///
+/// let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
+/// assert_eq!(1, u16::from_le_bytes(*bytes_head));
+///
+/// let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
+/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
+/// ```
 #[stable(feature = "try_from", since = "1.34.0")]
 impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] {
     type Error = TryFromSliceError;
@@ -386,7 +436,8 @@ impl<T: Copy> SpecArrayClone for T {
 macro_rules! array_impl_default {
     {$n:expr, $t:ident $($ts:ident)*} => {
         #[stable(since = "1.4.0", feature = "array_default")]
-        impl<T> Default for [T; $n] where T: Default {
+        #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+        impl<T> const Default for [T; $n] where T: ~const Default {
             fn default() -> [T; $n] {
                 [$t::default(), $($ts::default()),*]
             }
@@ -865,7 +916,7 @@ where
 
     mem::forget(guard);
     // SAFETY: All elements of the array were populated in the loop above.
-    let output = unsafe { MaybeUninit::array_assume_init(array) };
+    let output = unsafe { array.transpose().assume_init() };
     Ok(Try::from_output(output))
 }
 
diff --git a/library/core/src/bool.rs b/library/core/src/bool.rs
index 7667a6508..db1c505ba 100644
--- a/library/core/src/bool.rs
+++ b/library/core/src/bool.rs
@@ -18,6 +18,18 @@ impl bool {
     /// assert_eq!(false.then_some(0), None);
     /// assert_eq!(true.then_some(0), Some(0));
     /// ```
+    ///
+    /// ```
+    /// let mut a = 0;
+    /// let mut function_with_side_effects = || { a += 1; };
+    ///
+    /// true.then_some(function_with_side_effects());
+    /// false.then_some(function_with_side_effects());
+    ///
+    /// // `a` is incremented twice because the value passed to `then_some` is
+    /// // evaluated eagerly.
+    /// assert_eq!(a, 2);
+    /// ```
     #[stable(feature = "bool_to_option", since = "1.62.0")]
     #[rustc_const_unstable(feature = "const_bool_to_option", issue = "91917")]
     #[inline]
@@ -37,6 +49,17 @@ impl bool {
     /// assert_eq!(false.then(|| 0), None);
     /// assert_eq!(true.then(|| 0), Some(0));
     /// ```
+    ///
+    /// ```
+    /// let mut a = 0;
+    ///
+    /// true.then(|| { a += 1; });
+    /// false.then(|| { a += 1; });
+    ///
+    /// // `a` is incremented once because the closure is evaluated lazily by
+    /// // `then`.
+    /// assert_eq!(a, 1);
+    /// ```
     #[stable(feature = "lazy_bool_to_option", since = "1.50.0")]
     #[rustc_const_unstable(feature = "const_bool_to_option", issue = "91917")]
     #[inline]
diff --git a/library/core/src/borrow.rs b/library/core/src/borrow.rs
index 8378611eb..fdd56cb4e 100644
--- a/library/core/src/borrow.rs
+++ b/library/core/src/borrow.rs
@@ -154,6 +154,7 @@
 /// [`String`]: ../../std/string/struct.String.html
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Borrow"]
+#[const_trait]
 pub trait Borrow<Borrowed: ?Sized> {
     /// Immutably borrows from an owned value.
     ///
@@ -184,6 +185,7 @@ pub trait Borrow<Borrowed: ?Sized> {
 /// an underlying type by providing a mutable reference. See [`Borrow<T>`]
 /// for more information on borrowing as another type.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait BorrowMut<Borrowed: ?Sized>: Borrow<Borrowed> {
     /// Mutably borrows from an owned value.
     ///
diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index fb4454c94..7bf32cb0d 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -405,6 +405,7 @@ impl<T> Cell<T> {
     /// assert_eq!(cell.replace(10), 5);
     /// assert_eq!(cell.get(), 10);
     /// ```
+    #[inline]
     #[stable(feature = "move_cell", since = "1.17.0")]
     pub fn replace(&self, val: T) -> T {
         // SAFETY: This can cause data races if called from a separate thread,
@@ -614,6 +615,7 @@ impl<T, const N: usize> Cell<[T; N]> {
 /// A mutable memory location with dynamically checked borrow rules
 ///
 /// See the [module-level documentation](self) for more.
+#[cfg_attr(not(test), rustc_diagnostic_item = "RefCell")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RefCell<T: ?Sized> {
     borrow: Cell<BorrowFlag>,
@@ -1021,15 +1023,18 @@ impl<T: ?Sized> RefCell<T> {
 
     /// Returns a mutable reference to the underlying data.
     ///
-    /// This call borrows `RefCell` mutably (at compile-time) so there is no
-    /// need for dynamic checks.
+    /// Since this method borrows `RefCell` mutably, it is statically guaranteed
+    /// that no borrows to the underlying data exist. The dynamic checks inherent
+    /// in [`borrow_mut`] and most other methods of `RefCell` are therefor
+    /// unnecessary.
     ///
-    /// However be cautious: this method expects `self` to be mutable, which is
-    /// generally not the case when using a `RefCell`. Take a look at the
-    /// [`borrow_mut`] method instead if `self` isn't mutable.
+    /// This method can only be called if `RefCell` can be mutably borrowed,
+    /// which in general is only the case directly after the `RefCell` has
+    /// been created. In these situations, skipping the aforementioned dynamic
+    /// borrowing checks may yield better ergonomics and runtime-performance.
     ///
-    /// Also, please be aware that this method is only for special circumstances and is usually
-    /// not what you want. In case of doubt, use [`borrow_mut`] instead.
+    /// In most situations where `RefCell` is used, it can't be borrowed mutably.
+    /// Use [`borrow_mut`] to get mutable access to the underlying data then.
     ///
     /// [`borrow_mut`]: RefCell::borrow_mut()
     ///
@@ -1811,6 +1816,61 @@ impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
 ///
 /// [`.get_mut()`]: `UnsafeCell::get_mut`
 ///
+/// # Memory layout
+///
+/// `UnsafeCell<T>` has the same in-memory representation as its inner type `T`. A consequence
+/// of this guarantee is that it is possible to convert between `T` and `UnsafeCell<T>`.
+/// Special care has to be taken when converting a nested `T` inside of an `Outer<T>` type
+/// to an `Outer<UnsafeCell<T>>` type: this is not sound when the `Outer<T>` type enables [niche]
+/// optimizations. For example, the type `Option<NonNull<u8>>` is typically 8 bytes large on
+/// 64-bit platforms, but the type `Option<UnsafeCell<NonNull<u8>>>` takes up 16 bytes of space.
+/// Therefore this is not a valid conversion, despite `NonNull<u8>` and `UnsafeCell<NonNull<u8>>>`
+/// having the same memory layout. This is because `UnsafeCell` disables niche optimizations in
+/// order to avoid its interior mutability property from spreading from `T` into the `Outer` type,
+/// thus this can cause distortions in the type size in these cases.
+///
+/// Note that the only valid way to obtain a `*mut T` pointer to the contents of a
+/// _shared_ `UnsafeCell<T>` is through [`.get()`]  or [`.raw_get()`]. A `&mut T` reference
+/// can be obtained by either dereferencing this pointer or by calling [`.get_mut()`]
+/// on an _exclusive_ `UnsafeCell<T>`. Even though `T` and `UnsafeCell<T>` have the
+/// same memory layout, the following is not allowed and undefined behavior:
+///
+/// ```rust,no_run
+/// # use std::cell::UnsafeCell;
+/// unsafe fn not_allowed<T>(ptr: &UnsafeCell<T>) -> &mut T {
+///   let t = ptr as *const UnsafeCell<T> as *mut T;
+///   // This is undefined behavior, because the `*mut T` pointer
+///   // was not obtained through `.get()` nor `.raw_get()`:
+///   unsafe { &mut *t }
+/// }
+/// ```
+///
+/// Instead, do this:
+///
+/// ```rust
+/// # use std::cell::UnsafeCell;
+/// // Safety: the caller must ensure that there are no references that
+/// // point to the *contents* of the `UnsafeCell`.
+/// unsafe fn get_mut<T>(ptr: &UnsafeCell<T>) -> &mut T {
+///   unsafe { &mut *ptr.get() }
+/// }
+/// ```
+///
+/// Coverting in the other direction from a `&mut T`
+/// to an `&UnsafeCell<T>` is allowed:
+///
+/// ```rust
+/// # use std::cell::UnsafeCell;
+/// fn get_shared<T>(ptr: &mut T) -> &UnsafeCell<T> {
+///   let t = ptr as *mut T as *const UnsafeCell<T>;
+///   // SAFETY: `T` and `UnsafeCell<T>` have the same memory layout
+///   unsafe { &*t }
+/// }
+/// ```
+///
+/// [niche]: https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#niche
+/// [`.raw_get()`]: `UnsafeCell::raw_get`
+///
 /// # Examples
 ///
 /// Here is an example showcasing how to soundly mutate the contents of an `UnsafeCell<_>` despite
diff --git a/library/core/src/char/decode.rs b/library/core/src/char/decode.rs
index dc8ea66cc..11f1c30f6 100644
--- a/library/core/src/char/decode.rs
+++ b/library/core/src/char/decode.rs
@@ -1,6 +1,5 @@
 //! UTF-8 and UTF-16 decoding iterators
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 
@@ -124,7 +123,6 @@ impl fmt::Display for DecodeUtf16Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "decode_utf16", since = "1.9.0")]
 impl Error for DecodeUtf16Error {
     #[allow(deprecated)]
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index b7a63b7c6..bb8359936 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -597,9 +597,14 @@ impl char {
     /// Returns the number of 16-bit code units this `char` would need if
     /// encoded in UTF-16.
     ///
+    /// That number of code units is always either 1 or 2, for unicode scalar values in
+    /// the [basic multilingual plane] or [supplementary planes] respectively.
+    ///
     /// See the documentation for [`len_utf8()`] for more explanation of this
     /// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
     ///
+    /// [basic multilingual plane]: http://www.unicode.org/glossary/#basic_multilingual_plane
+    /// [supplementary planes]: http://www.unicode.org/glossary/#supplementary_planes
     /// [`len_utf8()`]: #method.len_utf8
     ///
     /// # Examples
@@ -1444,6 +1449,38 @@ impl char {
         matches!(*self, '0'..='9')
     }
 
+    /// Checks if the value is an ASCII octal digit:
+    /// U+0030 '0' ..= U+0037 '7'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_ascii_octdigit)]
+    ///
+    /// let uppercase_a = 'A';
+    /// let a = 'a';
+    /// let zero = '0';
+    /// let seven = '7';
+    /// let nine = '9';
+    /// let percent = '%';
+    /// let lf = '\n';
+    ///
+    /// assert!(!uppercase_a.is_ascii_octdigit());
+    /// assert!(!a.is_ascii_octdigit());
+    /// assert!(zero.is_ascii_octdigit());
+    /// assert!(seven.is_ascii_octdigit());
+    /// assert!(!nine.is_ascii_octdigit());
+    /// assert!(!percent.is_ascii_octdigit());
+    /// assert!(!lf.is_ascii_octdigit());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[rustc_const_unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[inline]
+    pub const fn is_ascii_octdigit(&self) -> bool {
+        matches!(*self, '0'..='7')
+    }
+
     /// Checks if the value is an ASCII hexadecimal digit:
     ///
     /// - U+0030 '0' ..= U+0039 '9', or
diff --git a/library/core/src/char/mod.rs b/library/core/src/char/mod.rs
index 72d63ac4b..b34a71216 100644
--- a/library/core/src/char/mod.rs
+++ b/library/core/src/char/mod.rs
@@ -38,7 +38,6 @@ pub use self::methods::encode_utf16_raw;
 #[unstable(feature = "char_internals", reason = "exposed only for libstd", issue = "none")]
 pub use self::methods::encode_utf8_raw;
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt::{self, Write};
 use crate::iter::FusedIterator;
@@ -587,6 +586,5 @@ impl fmt::Display for TryFromCharError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "u8_from_char", since = "1.59.0")]
 impl Error for TryFromCharError {}
diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
index d9f2d3d64..f0fa2e1d2 100644
--- a/library/core/src/cmp.rs
+++ b/library/core/src/cmp.rs
@@ -22,6 +22,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use crate::const_closure::ConstFnMutClosure;
 use crate::marker::Destruct;
 use crate::marker::StructuralPartialEq;
 
@@ -204,20 +205,10 @@ use self::Ordering::*;
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(alias = "==")]
 #[doc(alias = "!=")]
-#[cfg_attr(
-    bootstrap,
-    rustc_on_unimplemented(
-        message = "can't compare `{Self}` with `{Rhs}`",
-        label = "no implementation for `{Self} == {Rhs}`"
-    )
-)]
-#[cfg_attr(
-    not(bootstrap),
-    rustc_on_unimplemented(
-        message = "can't compare `{Self}` with `{Rhs}`",
-        label = "no implementation for `{Self} == {Rhs}`",
-        append_const_msg,
-    )
+#[rustc_on_unimplemented(
+    message = "can't compare `{Self}` with `{Rhs}`",
+    label = "no implementation for `{Self} == {Rhs}`",
+    append_const_msg
 )]
 #[const_trait]
 #[rustc_diagnostic_item = "PartialEq"]
@@ -1076,20 +1067,10 @@ impl const PartialOrd for Ordering {
 #[doc(alias = "<")]
 #[doc(alias = "<=")]
 #[doc(alias = ">=")]
-#[cfg_attr(
-    bootstrap,
-    rustc_on_unimplemented(
-        message = "can't compare `{Self}` with `{Rhs}`",
-        label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`",
-    )
-)]
-#[cfg_attr(
-    not(bootstrap),
-    rustc_on_unimplemented(
-        message = "can't compare `{Self}` with `{Rhs}`",
-        label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`",
-        append_const_msg,
-    )
+#[rustc_on_unimplemented(
+    message = "can't compare `{Self}` with `{Rhs}`",
+    label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`",
+    append_const_msg
 )]
 #[const_trait]
 #[rustc_diagnostic_item = "PartialOrd"]
@@ -1242,7 +1223,12 @@ pub const fn min<T: ~const Ord + ~const Destruct>(v1: T, v2: T) -> T {
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
+#[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+pub const fn min_by<T, F: ~const FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T
+where
+    T: ~const Destruct,
+    F: ~const Destruct,
+{
     match compare(&v1, &v2) {
         Ordering::Less | Ordering::Equal => v1,
         Ordering::Greater => v2,
@@ -1264,8 +1250,24 @@ pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
-    min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
+#[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+pub const fn min_by_key<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(v1: T, v2: T, mut f: F) -> T
+where
+    T: ~const Destruct,
+    F: ~const Destruct,
+    K: ~const Destruct,
+{
+    const fn imp<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(
+        f: &mut F,
+        (v1, v2): (&T, &T),
+    ) -> Ordering
+    where
+        T: ~const Destruct,
+        K: ~const Destruct,
+    {
+        f(v1).cmp(&f(v2))
+    }
+    min_by(v1, v2, ConstFnMutClosure::new(&mut f, imp))
 }
 
 /// Compares and returns the maximum of two values.
@@ -1306,7 +1308,12 @@ pub const fn max<T: ~const Ord + ~const Destruct>(v1: T, v2: T) -> T {
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
+#[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+pub const fn max_by<T, F: ~const FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T
+where
+    T: ~const Destruct,
+    F: ~const Destruct,
+{
     match compare(&v1, &v2) {
         Ordering::Less | Ordering::Equal => v2,
         Ordering::Greater => v1,
@@ -1328,8 +1335,24 @@ pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
-    max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
+#[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+pub const fn max_by_key<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(v1: T, v2: T, mut f: F) -> T
+where
+    T: ~const Destruct,
+    F: ~const Destruct,
+    K: ~const Destruct,
+{
+    const fn imp<T, F: ~const FnMut(&T) -> K, K: ~const Ord>(
+        f: &mut F,
+        (v1, v2): (&T, &T),
+    ) -> Ordering
+    where
+        T: ~const Destruct,
+        K: ~const Destruct,
+    {
+        f(v1).cmp(&f(v2))
+    }
+    max_by(v1, v2, ConstFnMutClosure::new(&mut f, imp))
 }
 
 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
diff --git a/library/core/src/const_closure.rs b/library/core/src/const_closure.rs
new file mode 100644
index 000000000..9e9c02093
--- /dev/null
+++ b/library/core/src/const_closure.rs
@@ -0,0 +1,77 @@
+use crate::marker::Destruct;
+
+/// Struct representing a closure with mutably borrowed data.
+///
+/// Example:
+/// ```no_build
+/// #![feature(const_mut_refs)]
+/// use crate::const_closure::ConstFnMutClosure;
+/// const fn imp(state: &mut i32, (arg,): (i32,)) -> i32 {
+///   *state += arg;
+///   *state
+/// }
+/// let mut i = 5;
+/// let mut cl = ConstFnMutClosure::new(&mut i, imp);
+///
+/// assert!(7 == cl(2));
+/// assert!(8 == cl(1));
+/// ```
+pub(crate) struct ConstFnMutClosure<CapturedData, Function> {
+    /// The Data captured by the Closure.
+    /// Must be either a (mutable) reference or a tuple of (mutable) references.
+    pub data: CapturedData,
+    /// The Function of the Closure, must be: Fn(CapturedData, ClosureArgs) -> ClosureReturn
+    pub func: Function,
+}
+impl<'a, CapturedData: ?Sized, Function> ConstFnMutClosure<&'a mut CapturedData, Function> {
+    /// Function for creating a new closure.
+    ///
+    /// `data` is the a mutable borrow of data that is captured from the environment.
+    /// If you want Data to be a tuple of mutable Borrows, the struct must be constructed manually.
+    ///
+    /// `func` is the function of the closure, it gets the data and a tuple of the arguments closure
+    ///   and return the return value of the closure.
+    pub(crate) const fn new<ClosureArguments, ClosureReturnValue>(
+        data: &'a mut CapturedData,
+        func: Function,
+    ) -> Self
+    where
+        Function: ~const Fn(&mut CapturedData, ClosureArguments) -> ClosureReturnValue,
+    {
+        Self { data, func }
+    }
+}
+
+macro_rules! impl_fn_mut_tuple {
+    ($($var:ident)*) => {
+        #[allow(unused_parens)]
+        impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
+            FnOnce<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
+        where
+            Function: ~const Fn(($(&mut $var),*), ClosureArguments) -> ClosureReturnValue+ ~const Destruct,
+        {
+            type Output = ClosureReturnValue;
+
+            extern "rust-call" fn call_once(mut self, args: ClosureArguments) -> Self::Output {
+            self.call_mut(args)
+            }
+        }
+        #[allow(unused_parens)]
+        impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
+            FnMut<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
+        where
+            Function: ~const Fn(($(&mut $var),*), ClosureArguments)-> ClosureReturnValue,
+        {
+            extern "rust-call" fn call_mut(&mut self, args: ClosureArguments) -> Self::Output {
+                #[allow(non_snake_case)]
+                let ($($var),*) = &mut self.data;
+                (self.func)(($($var),*), args)
+            }
+        }
+    };
+}
+impl_fn_mut_tuple!(A);
+impl_fn_mut_tuple!(A B);
+impl_fn_mut_tuple!(A B C);
+impl_fn_mut_tuple!(A B C D);
+impl_fn_mut_tuple!(A B C D E);
diff --git a/library/core/src/convert/mod.rs b/library/core/src/convert/mod.rs
index 05637c166..33493964b 100644
--- a/library/core/src/convert/mod.rs
+++ b/library/core/src/convert/mod.rs
@@ -25,6 +25,7 @@
 //! # Generic Implementations
 //!
 //! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference
+//!   (but not generally for all [dereferenceable types][core::ops::Deref])
 //! - [`From`]`<U> for T` implies [`Into`]`<T> for U`
 //! - [`TryFrom`]`<U> for T` implies [`TryInto`]`<T> for U`
 //! - [`From`] and [`Into`] are reflexive, which means that all types can
@@ -34,7 +35,6 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
@@ -110,10 +110,12 @@ pub const fn identity<T>(x: T) -> T {
 /// If you need to do a costly conversion it is better to implement [`From`] with type
 /// `&T` or write a custom function.
 ///
+/// # Relation to `Borrow`
+///
 /// `AsRef` has the same signature as [`Borrow`], but [`Borrow`] is different in a few aspects:
 ///
 /// - Unlike `AsRef`, [`Borrow`] has a blanket impl for any `T`, and can be used to accept either
-///   a reference or a value.
+///   a reference or a value. (See also note on `AsRef`'s reflexibility below.)
 /// - [`Borrow`] also requires that [`Hash`], [`Eq`] and [`Ord`] for a borrowed value are
 ///   equivalent to those of the owned value. For this reason, if you want to
 ///   borrow only a single field of a struct you can implement `AsRef`, but not [`Borrow`].
@@ -123,9 +125,66 @@ pub const fn identity<T>(x: T) -> T {
 ///
 /// # Generic Implementations
 ///
-/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
-///   reference (e.g.: `foo.as_ref()` will work the same if `foo` has type
-///   `&mut Foo` or `&&mut Foo`)
+/// `AsRef` auto-dereferences if the inner type is a reference or a mutable reference
+/// (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`).
+///
+/// Note that due to historic reasons, the above currently does not hold generally for all
+/// [dereferenceable types], e.g. `foo.as_ref()` will *not* work the same as
+/// `Box::new(foo).as_ref()`. Instead, many smart pointers provide an `as_ref` implementation which
+/// simply returns a reference to the [pointed-to value] (but do not perform a cheap
+/// reference-to-reference conversion for that value). However, [`AsRef::as_ref`] should not be
+/// used for the sole purpose of dereferencing; instead ['`Deref` coercion'] can be used:
+///
+/// [dereferenceable types]: core::ops::Deref
+/// [pointed-to value]: core::ops::Deref::Target
+/// ['`Deref` coercion']: core::ops::Deref#more-on-deref-coercion
+///
+/// ```
+/// let x = Box::new(5i32);
+/// // Avoid this:
+/// // let y: &i32 = x.as_ref();
+/// // Better just write:
+/// let y: &i32 = &x;
+/// ```
+///
+/// Types which implement [`Deref`] should consider implementing `AsRef<T>` as follows:
+///
+/// [`Deref`]: core::ops::Deref
+///
+/// ```
+/// # use core::ops::Deref;
+/// # struct SomeType;
+/// # impl Deref for SomeType {
+/// #     type Target = [u8];
+/// #     fn deref(&self) -> &[u8] {
+/// #         &[]
+/// #     }
+/// # }
+/// impl<T> AsRef<T> for SomeType
+/// where
+///     T: ?Sized,
+///     <SomeType as Deref>::Target: AsRef<T>,
+/// {
+///     fn as_ref(&self) -> &T {
+///         self.deref().as_ref()
+///     }
+/// }
+/// ```
+///
+/// # Reflexivity
+///
+/// Ideally, `AsRef` would be reflexive, i.e. there would be an `impl<T: ?Sized> AsRef<T> for T`
+/// with [`as_ref`] simply returning its argument unchanged.
+/// Such a blanket implementation is currently *not* provided due to technical restrictions of
+/// Rust's type system (it would be overlapping with another existing blanket implementation for
+/// `&T where T: AsRef<U>` which allows `AsRef` to auto-dereference, see "Generic Implementations"
+/// above).
+///
+/// [`as_ref`]: AsRef::as_ref
+///
+/// A trivial implementation of `AsRef<T> for T` must be added explicitly for a particular type `T`
+/// where needed or desired. Note, however, that not all types from `std` contain such an
+/// implementation, and those cannot be added by external code due to orphan rules.
 ///
 /// # Examples
 ///
@@ -155,6 +214,7 @@ pub const fn identity<T>(x: T) -> T {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "AsRef")]
+#[const_trait]
 pub trait AsRef<T: ?Sized> {
     /// Converts this type into a shared reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -172,31 +232,141 @@ pub trait AsRef<T: ?Sized> {
 ///
 /// # Generic Implementations
 ///
-/// - `AsMut` auto-dereferences if the inner type is a mutable reference
-///   (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo`
-///   or `&mut &mut Foo`)
+/// `AsMut` auto-dereferences if the inner type is a mutable reference
+/// (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo` or `&mut &mut Foo`).
+///
+/// Note that due to historic reasons, the above currently does not hold generally for all
+/// [mutably dereferenceable types], e.g. `foo.as_mut()` will *not* work the same as
+/// `Box::new(foo).as_mut()`. Instead, many smart pointers provide an `as_mut` implementation which
+/// simply returns a reference to the [pointed-to value] (but do not perform a cheap
+/// reference-to-reference conversion for that value). However, [`AsMut::as_mut`] should not be
+/// used for the sole purpose of mutable dereferencing; instead ['`Deref` coercion'] can be used:
+///
+/// [mutably dereferenceable types]: core::ops::DerefMut
+/// [pointed-to value]: core::ops::Deref::Target
+/// ['`Deref` coercion']: core::ops::DerefMut#more-on-deref-coercion
+///
+/// ```
+/// let mut x = Box::new(5i32);
+/// // Avoid this:
+/// // let y: &mut i32 = x.as_mut();
+/// // Better just write:
+/// let y: &mut i32 = &mut x;
+/// ```
+///
+/// Types which implement [`DerefMut`] should consider to add an implementation of `AsMut<T>` as
+/// follows:
+///
+/// [`DerefMut`]: core::ops::DerefMut
+///
+/// ```
+/// # use core::ops::{Deref, DerefMut};
+/// # struct SomeType;
+/// # impl Deref for SomeType {
+/// #     type Target = [u8];
+/// #     fn deref(&self) -> &[u8] {
+/// #         &[]
+/// #     }
+/// # }
+/// # impl DerefMut for SomeType {
+/// #     fn deref_mut(&mut self) -> &mut [u8] {
+/// #         &mut []
+/// #     }
+/// # }
+/// impl<T> AsMut<T> for SomeType
+/// where
+///     <SomeType as Deref>::Target: AsMut<T>,
+/// {
+///     fn as_mut(&mut self) -> &mut T {
+///         self.deref_mut().as_mut()
+///     }
+/// }
+/// ```
+///
+/// # Reflexivity
+///
+/// Ideally, `AsMut` would be reflexive, i.e. there would be an `impl<T: ?Sized> AsMut<T> for T`
+/// with [`as_mut`] simply returning its argument unchanged.
+/// Such a blanket implementation is currently *not* provided due to technical restrictions of
+/// Rust's type system (it would be overlapping with another existing blanket implementation for
+/// `&mut T where T: AsMut<U>` which allows `AsMut` to auto-dereference, see "Generic
+/// Implementations" above).
+///
+/// [`as_mut`]: AsMut::as_mut
+///
+/// A trivial implementation of `AsMut<T> for T` must be added explicitly for a particular type `T`
+/// where needed or desired. Note, however, that not all types from `std` contain such an
+/// implementation, and those cannot be added by external code due to orphan rules.
 ///
 /// # Examples
 ///
-/// Using `AsMut` as trait bound for a generic function we can accept all mutable references
-/// that can be converted to type `&mut T`. Because [`Box<T>`] implements `AsMut<T>` we can
-/// write a function `add_one` that takes all arguments that can be converted to `&mut u64`.
-/// Because [`Box<T>`] implements `AsMut<T>`, `add_one` accepts arguments of type
-/// `&mut Box<u64>` as well:
+/// Using `AsMut` as trait bound for a generic function, we can accept all mutable references that
+/// can be converted to type `&mut T`. Unlike [dereference], which has a single [target type],
+/// there can be multiple implementations of `AsMut` for a type. In particular, `Vec<T>` implements
+/// both `AsMut<Vec<T>>` and `AsMut<[T]>`.
+///
+/// In the following, the example functions `caesar` and `null_terminate` provide a generic
+/// interface which work with any type that can be converted by cheap mutable-to-mutable conversion
+/// into a byte slice (`[u8]`) or byte vector (`Vec<u8>`), respectively.
+///
+/// [dereference]: core::ops::DerefMut
+/// [target type]: core::ops::Deref::Target
 ///
 /// ```
-/// fn add_one<T: AsMut<u64>>(num: &mut T) {
-///     *num.as_mut() += 1;
+/// struct Document {
+///     info: String,
+///     content: Vec<u8>,
 /// }
 ///
-/// let mut boxed_num = Box::new(0);
-/// add_one(&mut boxed_num);
-/// assert_eq!(*boxed_num, 1);
+/// impl<T: ?Sized> AsMut<T> for Document
+/// where
+///     Vec<u8>: AsMut<T>,
+/// {
+///     fn as_mut(&mut self) -> &mut T {
+///         self.content.as_mut()
+///     }
+/// }
+///
+/// fn caesar<T: AsMut<[u8]>>(data: &mut T, key: u8) {
+///     for byte in data.as_mut() {
+///         *byte = byte.wrapping_add(key);
+///     }
+/// }
+///
+/// fn null_terminate<T: AsMut<Vec<u8>>>(data: &mut T) {
+///     // Using a non-generic inner function, which contains most of the
+///     // functionality, helps to minimize monomorphization overhead.
+///     fn doit(data: &mut Vec<u8>) {
+///         let len = data.len();
+///         if len == 0 || data[len-1] != 0 {
+///             data.push(0);
+///         }
+///     }
+///     doit(data.as_mut());
+/// }
+///
+/// fn main() {
+///     let mut v: Vec<u8> = vec![1, 2, 3];
+///     caesar(&mut v, 5);
+///     assert_eq!(v, [6, 7, 8]);
+///     null_terminate(&mut v);
+///     assert_eq!(v, [6, 7, 8, 0]);
+///     let mut doc = Document {
+///         info: String::from("Example"),
+///         content: vec![17, 19, 8],
+///     };
+///     caesar(&mut doc, 1);
+///     assert_eq!(doc.content, [18, 20, 9]);
+///     null_terminate(&mut doc);
+///     assert_eq!(doc.content, [18, 20, 9, 0]);
+/// }
 /// ```
 ///
-/// [`Box<T>`]: ../../std/boxed/struct.Box.html
+/// Note, however, that APIs don't need to be generic. In many cases taking a `&mut [u8]` or
+/// `&mut Vec<u8>`, for example, is the better choice (callers need to pass the correct type then).
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "AsMut")]
+#[const_trait]
 pub trait AsMut<T: ?Sized> {
     /// Converts this type into a mutable reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -273,6 +443,7 @@ pub trait AsMut<T: ?Sized> {
 /// [`Vec`]: ../../std/vec/struct.Vec.html
 #[rustc_diagnostic_item = "Into"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait Into<T>: Sized {
     /// Converts this type into the (usually inferred) input type.
     #[must_use]
@@ -368,12 +539,13 @@ pub trait Into<T>: Sized {
     all(_Self = "&str", T = "std::string::String"),
     note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
 ))]
+#[const_trait]
 pub trait From<T>: Sized {
     /// Converts to this type from the input type.
     #[lang = "from"]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    fn from(_: T) -> Self;
+    fn from(value: T) -> Self;
 }
 
 /// An attempted conversion that consumes `self`, which may or may not be
@@ -392,6 +564,7 @@ pub trait From<T>: Sized {
 /// [`Into`], see there for details.
 #[rustc_diagnostic_item = "TryInto"]
 #[stable(feature = "try_from", since = "1.34.0")]
+#[const_trait]
 pub trait TryInto<T>: Sized {
     /// The type returned in the event of a conversion error.
     #[stable(feature = "try_from", since = "1.34.0")]
@@ -436,7 +609,7 @@ pub trait TryInto<T>: Sized {
 ///
 ///     fn try_from(value: i32) -> Result<Self, Self::Error> {
 ///         if value <= 0 {
-///             Err("GreaterThanZero only accepts value superior than zero!")
+///             Err("GreaterThanZero only accepts values greater than zero!")
 ///         } else {
 ///             Ok(GreaterThanZero(value))
 ///         }
@@ -468,6 +641,7 @@ pub trait TryInto<T>: Sized {
 /// [`try_from`]: TryFrom::try_from
 #[rustc_diagnostic_item = "TryFrom"]
 #[stable(feature = "try_from", since = "1.34.0")]
+#[const_trait]
 pub trait TryFrom<T>: Sized {
     /// The type returned in the event of a conversion error.
     #[stable(feature = "try_from", since = "1.34.0")]
@@ -718,7 +892,6 @@ impl fmt::Display for Infallible {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "str_parse_error2", since = "1.8.0")]
 impl Error for Infallible {
     fn description(&self) -> &str {
diff --git a/library/core/src/default.rs b/library/core/src/default.rs
index b53cd6074..a5b4e9655 100644
--- a/library/core/src/default.rs
+++ b/library/core/src/default.rs
@@ -99,6 +99,7 @@
 /// ```
 #[cfg_attr(not(test), rustc_diagnostic_item = "Default")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///
diff --git a/library/core/src/error.rs b/library/core/src/error.rs
index 4a8efe15e..2738b4994 100644
--- a/library/core/src/error.rs
+++ b/library/core/src/error.rs
@@ -493,8 +493,8 @@ impl Error for crate::char::ParseCharError {
     }
 }
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-impl Error for crate::time::FromFloatSecsError {}
+#[stable(feature = "duration_checked_float", since = "1.66.0")]
+impl Error for crate::time::TryFromFloatSecsError {}
 
 #[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
 impl Error for crate::ffi::FromBytesWithNulError {
diff --git a/library/core/src/ffi/c_str.rs b/library/core/src/ffi/c_str.rs
index 21f80ec02..8923f548a 100644
--- a/library/core/src/ffi/c_str.rs
+++ b/library/core/src/ffi/c_str.rs
@@ -221,9 +221,7 @@ impl CStr {
     /// # Examples
     ///
     /// ```ignore (extern-declaration)
-    /// # fn main() {
-    /// use std::ffi::CStr;
-    /// use std::os::raw::c_char;
+    /// use std::ffi::{c_char, CStr};
     ///
     /// extern "C" {
     ///     fn my_string() -> *const c_char;
@@ -233,14 +231,26 @@ impl CStr {
     ///     let slice = CStr::from_ptr(my_string());
     ///     println!("string returned: {}", slice.to_str().unwrap());
     /// }
-    /// # }
+    /// ```
+    ///
+    /// ```
+    /// #![feature(const_cstr_methods)]
+    ///
+    /// use std::ffi::{c_char, CStr};
+    ///
+    /// const HELLO_PTR: *const c_char = {
+    ///     const BYTES: &[u8] = b"Hello, world!\0";
+    ///     BYTES.as_ptr().cast()
+    /// };
+    /// const HELLO: &CStr = unsafe { CStr::from_ptr(HELLO_PTR) };
     /// ```
     ///
     /// [valid]: core::ptr#safety
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
+    #[rustc_const_unstable(feature = "const_cstr_methods", issue = "101719")]
+    pub const unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
         // SAFETY: The caller has provided a pointer that points to a valid C
         // string with a NUL terminator of size less than `isize::MAX`, whose
         // content remain valid and doesn't change for the lifetime of the
@@ -252,13 +262,29 @@ impl CStr {
         //
         // The cast from c_char to u8 is ok because a c_char is always one byte.
         unsafe {
-            extern "C" {
-                /// Provided by libc or compiler_builtins.
-                fn strlen(s: *const c_char) -> usize;
+            const fn strlen_ct(s: *const c_char) -> usize {
+                let mut len = 0;
+
+                // SAFETY: Outer caller has provided a pointer to a valid C string.
+                while unsafe { *s.add(len) } != 0 {
+                    len += 1;
+                }
+
+                len
             }
-            let len = strlen(ptr);
-            let ptr = ptr as *const u8;
-            CStr::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr, len as usize + 1))
+
+            fn strlen_rt(s: *const c_char) -> usize {
+                extern "C" {
+                    /// Provided by libc or compiler_builtins.
+                    fn strlen(s: *const c_char) -> usize;
+                }
+
+                // SAFETY: Outer caller has provided a pointer to a valid C string.
+                unsafe { strlen(s) }
+            }
+
+            let len = intrinsics::const_eval_select((ptr,), strlen_ct, strlen_rt);
+            Self::from_bytes_with_nul_unchecked(slice::from_raw_parts(ptr.cast(), len + 1))
         }
     }
 
@@ -474,6 +500,34 @@ impl CStr {
         self.inner.as_ptr()
     }
 
+    /// Returns `true` if `self.to_bytes()` has a length of 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cstr_is_empty)]
+    ///
+    /// use std::ffi::CStr;
+    /// # use std::ffi::FromBytesWithNulError;
+    ///
+    /// # fn main() { test().unwrap(); }
+    /// # fn test() -> Result<(), FromBytesWithNulError> {
+    /// let cstr = CStr::from_bytes_with_nul(b"foo\0")?;
+    /// assert!(!cstr.is_empty());
+    ///
+    /// let empty_cstr = CStr::from_bytes_with_nul(b"\0")?;
+    /// assert!(empty_cstr.is_empty());
+    /// # Ok(())
+    /// # }
+    /// ```
+    #[inline]
+    #[unstable(feature = "cstr_is_empty", issue = "102444")]
+    pub const fn is_empty(&self) -> bool {
+        // SAFETY: We know there is at least one byte; for empty strings it
+        // is the NUL terminator.
+        (unsafe { self.inner.get_unchecked(0) }) == &0
+    }
+
     /// Converts this C string to a byte slice.
     ///
     /// The returned slice will **not** contain the trailing nul terminator that this C
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index 905212eb3..c8d285505 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -709,12 +709,19 @@ pub use macros::Debug;
 
 /// Format trait for an empty format, `{}`.
 ///
+/// Implementing this trait for a type will automatically implement the
+/// [`ToString`][tostring] trait for the type, allowing the usage
+/// of the [`.to_string()`][tostring_function] method. Prefer implementing
+/// the `Display` trait for a type, rather than [`ToString`][tostring].
+///
 /// `Display` is similar to [`Debug`], but `Display` is for user-facing
 /// output, and so cannot be derived.
 ///
 /// For more information on formatters, see [the module-level documentation][module].
 ///
 /// [module]: ../../std/fmt/index.html
+/// [tostring]: ../../std/string/trait.ToString.html
+/// [tostring_function]: ../../std/string/trait.ToString.html#tymethod.to_string
 ///
 /// # Examples
 ///
@@ -2603,7 +2610,7 @@ impl Debug for () {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Debug for PhantomData<T> {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
-        f.debug_struct("PhantomData").finish()
+        write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
     }
 }
 
diff --git a/library/core/src/fmt/num.rs b/library/core/src/fmt/num.rs
index 25789d37c..d8365ae9b 100644
--- a/library/core/src/fmt/num.rs
+++ b/library/core/src/fmt/num.rs
@@ -211,7 +211,7 @@ macro_rules! impl_Display {
         fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             // 2^128 is about 3*10^38, so 39 gives an extra byte of space
             let mut buf = [MaybeUninit::<u8>::uninit(); 39];
-            let mut curr = buf.len() as isize;
+            let mut curr = buf.len();
             let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();
 
@@ -228,7 +228,7 @@ macro_rules! impl_Display {
 
                 // eagerly decode 4 characters at a time
                 while n >= 10000 {
-                    let rem = (n % 10000) as isize;
+                    let rem = (n % 10000) as usize;
                     n /= 10000;
 
                     let d1 = (rem / 100) << 1;
@@ -238,29 +238,29 @@ macro_rules! impl_Display {
                     // We are allowed to copy to `buf_ptr[curr..curr + 3]` here since
                     // otherwise `curr < 0`. But then `n` was originally at least `10000^10`
                     // which is `10^40 > 2^128 > n`.
-                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
-                    ptr::copy_nonoverlapping(lut_ptr.offset(d2), buf_ptr.offset(curr + 2), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(d2), buf_ptr.add(curr + 2), 2);
                 }
 
                 // if we reach here numbers are <= 9999, so at most 4 chars long
-                let mut n = n as isize; // possibly reduce 64bit math
+                let mut n = n as usize; // possibly reduce 64bit math
 
                 // decode 2 more chars, if > 2 chars
                 if n >= 100 {
                     let d1 = (n % 100) << 1;
                     n /= 100;
                     curr -= 2;
-                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
                 }
 
                 // decode last 1 or 2 chars
                 if n < 10 {
                     curr -= 1;
-                    *buf_ptr.offset(curr) = (n as u8) + b'0';
+                    *buf_ptr.add(curr) = (n as u8) + b'0';
                 } else {
                     let d1 = n << 1;
                     curr -= 2;
-                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
                 }
             }
 
@@ -268,7 +268,7 @@ macro_rules! impl_Display {
             // UTF-8 since `DEC_DIGITS_LUT` is
             let buf_slice = unsafe {
                 str::from_utf8_unchecked(
-                    slice::from_raw_parts(buf_ptr.offset(curr), buf.len() - curr as usize))
+                    slice::from_raw_parts(buf_ptr.add(curr), buf.len() - curr))
             };
             f.pad_integral(is_nonnegative, "", buf_slice)
         }
@@ -339,18 +339,18 @@ macro_rules! impl_Exp {
             // Since `curr` always decreases by the number of digits copied, this means
             // that `curr >= 0`.
             let mut buf = [MaybeUninit::<u8>::uninit(); 40];
-            let mut curr = buf.len() as isize; //index for buf
+            let mut curr = buf.len(); //index for buf
             let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();
 
             // decode 2 chars at a time
             while n >= 100 {
-                let d1 = ((n % 100) as isize) << 1;
+                let d1 = ((n % 100) as usize) << 1;
                 curr -= 2;
                 // SAFETY: `d1 <= 198`, so we can copy from `lut_ptr[d1..d1 + 2]` since
                 // `DEC_DIGITS_LUT` has a length of 200.
                 unsafe {
-                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
                 }
                 n /= 100;
                 exponent += 2;
@@ -362,7 +362,7 @@ macro_rules! impl_Exp {
                 curr -= 1;
                 // SAFETY: Safe since `40 > curr >= 0` (see comment)
                 unsafe {
-                    *buf_ptr.offset(curr) = (n as u8 % 10_u8) + b'0';
+                    *buf_ptr.add(curr) = (n as u8 % 10_u8) + b'0';
                 }
                 n /= 10;
                 exponent += 1;
@@ -372,7 +372,7 @@ macro_rules! impl_Exp {
                 curr -= 1;
                 // SAFETY: Safe since `40 > curr >= 0`
                 unsafe {
-                    *buf_ptr.offset(curr) = b'.';
+                    *buf_ptr.add(curr) = b'.';
                 }
             }
 
@@ -380,10 +380,10 @@ macro_rules! impl_Exp {
             let buf_slice = unsafe {
                 // decode last character
                 curr -= 1;
-                *buf_ptr.offset(curr) = (n as u8) + b'0';
+                *buf_ptr.add(curr) = (n as u8) + b'0';
 
                 let len = buf.len() - curr as usize;
-                slice::from_raw_parts(buf_ptr.offset(curr), len)
+                slice::from_raw_parts(buf_ptr.add(curr), len)
             };
 
             // stores 'e' (or 'E') and the up to 2-digit exponent
@@ -392,13 +392,13 @@ macro_rules! impl_Exp {
             // SAFETY: In either case, `exp_buf` is written within bounds and `exp_ptr[..len]`
             // is contained within `exp_buf` since `len <= 3`.
             let exp_slice = unsafe {
-                *exp_ptr.offset(0) = if upper { b'E' } else { b'e' };
+                *exp_ptr.add(0) = if upper { b'E' } else { b'e' };
                 let len = if exponent < 10 {
-                    *exp_ptr.offset(1) = (exponent as u8) + b'0';
+                    *exp_ptr.add(1) = (exponent as u8) + b'0';
                     2
                 } else {
                     let off = exponent << 1;
-                    ptr::copy_nonoverlapping(lut_ptr.offset(off), exp_ptr.offset(1), 2);
+                    ptr::copy_nonoverlapping(lut_ptr.add(off), exp_ptr.add(1), 2);
                     3
                 };
                 slice::from_raw_parts(exp_ptr, len)
@@ -479,7 +479,7 @@ mod imp {
 impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);
 
 /// Helper function for writing a u64 into `buf` going from last to first, with `curr`.
-fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], curr: &mut isize) {
+fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], curr: &mut usize) {
     let buf_ptr = MaybeUninit::slice_as_mut_ptr(buf);
     let lut_ptr = DEC_DIGITS_LUT.as_ptr();
     assert!(*curr > 19);
@@ -505,14 +505,14 @@ fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], cu
 
             *curr -= 16;
 
-            ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d3 as isize), buf_ptr.offset(*curr + 4), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d4 as isize), buf_ptr.offset(*curr + 6), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d5 as isize), buf_ptr.offset(*curr + 8), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d6 as isize), buf_ptr.offset(*curr + 10), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d7 as isize), buf_ptr.offset(*curr + 12), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d8 as isize), buf_ptr.offset(*curr + 14), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d3 as usize), buf_ptr.add(*curr + 4), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d4 as usize), buf_ptr.add(*curr + 6), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d5 as usize), buf_ptr.add(*curr + 8), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d6 as usize), buf_ptr.add(*curr + 10), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d7 as usize), buf_ptr.add(*curr + 12), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d8 as usize), buf_ptr.add(*curr + 14), 2);
         }
         if n >= 1e8 as u64 {
             let to_parse = n % 1e8 as u64;
@@ -525,10 +525,10 @@ fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], cu
             let d4 = ((to_parse / 1e0 as u64) % 100) << 1;
             *curr -= 8;
 
-            ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d3 as isize), buf_ptr.offset(*curr + 4), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d4 as isize), buf_ptr.offset(*curr + 6), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d3 as usize), buf_ptr.add(*curr + 4), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d4 as usize), buf_ptr.add(*curr + 6), 2);
         }
         // `n` < 1e8 < (1 << 32)
         let mut n = n as u32;
@@ -540,8 +540,8 @@ fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], cu
             let d2 = (to_parse % 100) << 1;
             *curr -= 4;
 
-            ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
-            ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
         }
 
         // `n` < 1e4 < (1 << 16)
@@ -550,17 +550,17 @@ fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], cu
             let d1 = (n % 100) << 1;
             n /= 100;
             *curr -= 2;
-            ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr), 2);
         }
 
         // decode last 1 or 2 chars
         if n < 10 {
             *curr -= 1;
-            *buf_ptr.offset(*curr) = (n as u8) + b'0';
+            *buf_ptr.add(*curr) = (n as u8) + b'0';
         } else {
             let d1 = n << 1;
             *curr -= 2;
-            ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr), 2);
+            ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr), 2);
         }
     }
 }
@@ -593,21 +593,21 @@ impl fmt::Display for i128 {
 fn fmt_u128(n: u128, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     // 2^128 is about 3*10^38, so 39 gives an extra byte of space
     let mut buf = [MaybeUninit::<u8>::uninit(); 39];
-    let mut curr = buf.len() as isize;
+    let mut curr = buf.len();
 
     let (n, rem) = udiv_1e19(n);
     parse_u64_into(rem, &mut buf, &mut curr);
 
     if n != 0 {
         // 0 pad up to point
-        let target = (buf.len() - 19) as isize;
+        let target = buf.len() - 19;
         // SAFETY: Guaranteed that we wrote at most 19 bytes, and there must be space
         // remaining since it has length 39
         unsafe {
             ptr::write_bytes(
-                MaybeUninit::slice_as_mut_ptr(&mut buf).offset(target),
+                MaybeUninit::slice_as_mut_ptr(&mut buf).add(target),
                 b'0',
-                (curr - target) as usize,
+                curr - target,
             );
         }
         curr = target;
@@ -616,16 +616,16 @@ fn fmt_u128(n: u128, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::R
         parse_u64_into(rem, &mut buf, &mut curr);
         // Should this following branch be annotated with unlikely?
         if n != 0 {
-            let target = (buf.len() - 38) as isize;
+            let target = buf.len() - 38;
             // The raw `buf_ptr` pointer is only valid until `buf` is used the next time,
             // buf `buf` is not used in this scope so we are good.
             let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
             // SAFETY: At this point we wrote at most 38 bytes, pad up to that point,
             // There can only be at most 1 digit remaining.
             unsafe {
-                ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
+                ptr::write_bytes(buf_ptr.add(target), b'0', curr - target);
                 curr = target - 1;
-                *buf_ptr.offset(curr) = (n as u8) + b'0';
+                *buf_ptr.add(curr) = (n as u8) + b'0';
             }
         }
     }
@@ -634,8 +634,8 @@ fn fmt_u128(n: u128, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::R
     // UTF-8 since `DEC_DIGITS_LUT` is
     let buf_slice = unsafe {
         str::from_utf8_unchecked(slice::from_raw_parts(
-            MaybeUninit::slice_as_mut_ptr(&mut buf).offset(curr),
-            buf.len() - curr as usize,
+            MaybeUninit::slice_as_mut_ptr(&mut buf).add(curr),
+            buf.len() - curr,
         ))
     };
     f.pad_integral(is_nonnegative, "", buf_slice)
diff --git a/library/core/src/future/ready.rs b/library/core/src/future/ready.rs
index 48f20f90a..a07b63fb6 100644
--- a/library/core/src/future/ready.rs
+++ b/library/core/src/future/ready.rs
@@ -24,6 +24,30 @@ impl<T> Future for Ready<T> {
     }
 }
 
+impl<T> Ready<T> {
+    /// Consumes the `Ready`, returning the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this [`Ready`] was already polled to completion.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ready_into_inner)]
+    /// use std::future;
+    ///
+    /// let a = future::ready(1);
+    /// assert_eq!(a.into_inner(), 1);
+    /// ```
+    #[unstable(feature = "ready_into_inner", issue = "101196")]
+    #[must_use]
+    #[inline]
+    pub fn into_inner(self) -> T {
+        self.0.expect("Called `into_inner()` on `Ready` after completion")
+    }
+}
+
 /// Creates a future that is immediately ready with a value.
 ///
 /// Futures created through this function are functionally similar to those
diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index 764e27962..c53175ba4 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -100,7 +100,10 @@ use crate::intrinsics;
 pub const unsafe fn unreachable_unchecked() -> ! {
     // SAFETY: the safety contract for `intrinsics::unreachable` must
     // be upheld by the caller.
-    unsafe { intrinsics::unreachable() }
+    unsafe {
+        intrinsics::assert_unsafe_precondition!("hint::unreachable_unchecked must never be reached", () => false);
+        intrinsics::unreachable()
+    }
 }
 
 /// Emits a machine instruction to signal the processor that it is running in
@@ -217,7 +220,7 @@ pub fn spin_loop() {
 ///
 /// [`std::convert::identity`]: crate::convert::identity
 #[inline]
-#[unstable(feature = "bench_black_box", issue = "64102")]
+#[stable(feature = "bench_black_box", since = "1.66.0")]
 #[rustc_const_unstable(feature = "const_black_box", issue = "none")]
 pub const fn black_box<T>(dummy: T) -> T {
     crate::intrinsics::black_box(dummy)
diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index 11c75e2c9..1dc79afe8 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -54,8 +54,6 @@
 )]
 #![allow(missing_docs)]
 
-#[cfg(bootstrap)]
-use crate::marker::Destruct;
 use crate::marker::DiscriminantKind;
 use crate::mem;
 
@@ -790,6 +788,7 @@ extern "rust-intrinsic" {
     /// uninitialized at that point in the control flow.
     ///
     /// This intrinsic should not be used outside of the compiler.
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn rustc_peek<T>(_: T) -> T;
 
     /// Aborts the execution of the process.
@@ -807,6 +806,7 @@ extern "rust-intrinsic" {
     /// On Unix, the
     /// process will probably terminate with a signal like `SIGABRT`, `SIGILL`, `SIGTRAP`, `SIGSEGV` or
     /// `SIGBUS`.  The precise behaviour is not guaranteed and not stable.
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn abort() -> !;
 
     /// Informs the optimizer that this point in the code is not reachable,
@@ -845,6 +845,7 @@ extern "rust-intrinsic" {
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_likely", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn likely(b: bool) -> bool;
 
     /// Hints to the compiler that branch condition is likely to be false.
@@ -859,6 +860,7 @@ extern "rust-intrinsic" {
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_likely", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn unlikely(b: bool) -> bool;
 
     /// Executes a breakpoint trap, for inspection by a debugger.
@@ -878,6 +880,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`core::mem::size_of`].
     #[rustc_const_stable(feature = "const_size_of", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn size_of<T>() -> usize;
 
     /// The minimum alignment of a type.
@@ -889,6 +892,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`core::mem::align_of`].
     #[rustc_const_stable(feature = "const_min_align_of", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn min_align_of<T>() -> usize;
     /// The preferred alignment of a type.
     ///
@@ -917,6 +921,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`core::any::type_name`].
     #[rustc_const_unstable(feature = "const_type_name", issue = "63084")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn type_name<T: ?Sized>() -> &'static str;
 
     /// Gets an identifier which is globally unique to the specified type. This
@@ -930,6 +935,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`core::any::TypeId::of`].
     #[rustc_const_unstable(feature = "const_type_id", issue = "77125")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn type_id<T: ?Sized + 'static>() -> u64;
 
     /// A guard for unsafe functions that cannot ever be executed if `T` is uninhabited:
@@ -937,6 +943,7 @@ extern "rust-intrinsic" {
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_stable(feature = "const_assert_type", since = "1.59.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn assert_inhabited<T>();
 
     /// A guard for unsafe functions that cannot ever be executed if `T` does not permit
@@ -944,6 +951,7 @@ extern "rust-intrinsic" {
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn assert_zero_valid<T>();
 
     /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
@@ -951,6 +959,7 @@ extern "rust-intrinsic" {
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn assert_uninit_valid<T>();
 
     /// Gets a reference to a static `Location` indicating where it was called.
@@ -962,6 +971,7 @@ extern "rust-intrinsic" {
     ///
     /// Consider using [`core::panic::Location::caller`] instead.
     #[rustc_const_unstable(feature = "const_caller_location", issue = "76156")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn caller_location() -> &'static crate::panic::Location<'static>;
 
     /// Moves a value out of scope without running drop glue.
@@ -974,6 +984,7 @@ extern "rust-intrinsic" {
     /// Therefore, implementations must not require the user to uphold
     /// any safety invariants.
     #[rustc_const_unstable(feature = "const_intrinsic_forget", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn forget<T: ?Sized>(_: T);
 
     /// Reinterprets the bits of a value of one type as another type.
@@ -983,14 +994,14 @@ extern "rust-intrinsic" {
     /// `transmute` is semantically equivalent to a bitwise move of one type
     /// into another. It copies the bits from the source value into the
     /// destination value, then forgets the original. Note that source and destination
-    /// are passed by-value, which means if `T` or `U` contain padding, that padding
+    /// are passed by-value, which means if `Src` or `Dst` contain padding, that padding
     /// is *not* guaranteed to be preserved by `transmute`.
     ///
     /// Both the argument and the result must be [valid](../../nomicon/what-unsafe-does.html) at
     /// their given type. Violating this condition leads to [undefined behavior][ub]. The compiler
     /// will generate code *assuming that you, the programmer, ensure that there will never be
     /// undefined behavior*. It is therefore your responsibility to guarantee that every value
-    /// passed to `transmute` is valid at both types `T` and `U`. Failing to uphold this condition
+    /// passed to `transmute` is valid at both types `Src` and `Dst`. Failing to uphold this condition
     /// may lead to unexpected and unstable compilation results. This makes `transmute` **incredibly
     /// unsafe**. `transmute` should be the absolute last resort.
     ///
@@ -1001,7 +1012,7 @@ extern "rust-intrinsic" {
     ///
     /// Because `transmute` is a by-value operation, alignment of the *transmuted values
     /// themselves* is not a concern. As with any other function, the compiler already ensures
-    /// both `T` and `U` are properly aligned. However, when transmuting values that *point
+    /// both `Src` and `Dst` are properly aligned. However, when transmuting values that *point
     /// elsewhere* (such as pointers, references, boxes…), the caller has to ensure proper
     /// alignment of the pointed-to values.
     ///
@@ -1237,7 +1248,7 @@ extern "rust-intrinsic" {
     #[rustc_allowed_through_unstable_modules]
     #[rustc_const_stable(feature = "const_transmute", since = "1.56.0")]
     #[rustc_diagnostic_item = "transmute"]
-    pub fn transmute<T, U>(e: T) -> U;
+    pub fn transmute<Src, Dst>(src: Src) -> Dst;
 
     /// Returns `true` if the actual type given as `T` requires drop
     /// glue; returns `false` if the actual type provided for `T`
@@ -1253,6 +1264,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`mem::needs_drop`](crate::mem::needs_drop).
     #[rustc_const_stable(feature = "const_needs_drop", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn needs_drop<T: ?Sized>() -> bool;
 
     /// Calculates the offset from a pointer.
@@ -1297,7 +1309,7 @@ extern "rust-intrinsic" {
     /// any safety invariants.
     ///
     /// Consider using [`pointer::mask`] instead.
-    #[cfg(not(bootstrap))]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn ptr_mask<T>(ptr: *const T, mask: usize) -> *const T;
 
     /// Equivalent to the appropriate `llvm.memcpy.p0i8.0i8.*` intrinsic, with
@@ -1489,6 +1501,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`f32::min`]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn minnumf32(x: f32, y: f32) -> f32;
     /// Returns the minimum of two `f64` values.
     ///
@@ -1499,6 +1512,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`f64::min`]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn minnumf64(x: f64, y: f64) -> f64;
     /// Returns the maximum of two `f32` values.
     ///
@@ -1509,6 +1523,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`f32::max`]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn maxnumf32(x: f32, y: f32) -> f32;
     /// Returns the maximum of two `f64` values.
     ///
@@ -1519,6 +1534,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is
     /// [`f64::max`]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn maxnumf64(x: f64, y: f64) -> f64;
 
     /// Copies the sign from `y` to `x` for `f32` values.
@@ -1639,6 +1655,7 @@ extern "rust-intrinsic" {
     /// primitives via the `count_ones` method. For example,
     /// [`u32::count_ones`]
     #[rustc_const_stable(feature = "const_ctpop", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn ctpop<T: Copy>(x: T) -> T;
 
     /// Returns the number of leading unset bits (zeroes) in an integer type `T`.
@@ -1676,6 +1693,7 @@ extern "rust-intrinsic" {
     /// assert_eq!(num_leading, 16);
     /// ```
     #[rustc_const_stable(feature = "const_ctlz", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn ctlz<T: Copy>(x: T) -> T;
 
     /// Like `ctlz`, but extra-unsafe as it returns `undef` when
@@ -1732,6 +1750,7 @@ extern "rust-intrinsic" {
     /// assert_eq!(num_trailing, 16);
     /// ```
     #[rustc_const_stable(feature = "const_cttz", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn cttz<T: Copy>(x: T) -> T;
 
     /// Like `cttz`, but extra-unsafe as it returns `undef` when
@@ -1764,6 +1783,7 @@ extern "rust-intrinsic" {
     /// primitives via the `swap_bytes` method. For example,
     /// [`u32::swap_bytes`]
     #[rustc_const_stable(feature = "const_bswap", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn bswap<T: Copy>(x: T) -> T;
 
     /// Reverses the bits in an integer type `T`.
@@ -1777,6 +1797,7 @@ extern "rust-intrinsic" {
     /// primitives via the `reverse_bits` method. For example,
     /// [`u32::reverse_bits`]
     #[rustc_const_stable(feature = "const_bitreverse", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn bitreverse<T: Copy>(x: T) -> T;
 
     /// Performs checked integer addition.
@@ -1790,6 +1811,7 @@ extern "rust-intrinsic" {
     /// primitives via the `overflowing_add` method. For example,
     /// [`u32::overflowing_add`]
     #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn add_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
 
     /// Performs checked integer subtraction
@@ -1803,6 +1825,7 @@ extern "rust-intrinsic" {
     /// primitives via the `overflowing_sub` method. For example,
     /// [`u32::overflowing_sub`]
     #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn sub_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
 
     /// Performs checked integer multiplication
@@ -1816,6 +1839,7 @@ extern "rust-intrinsic" {
     /// primitives via the `overflowing_mul` method. For example,
     /// [`u32::overflowing_mul`]
     #[rustc_const_stable(feature = "const_int_overflow", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn mul_with_overflow<T: Copy>(x: T, y: T) -> (T, bool);
 
     /// Performs an exact division, resulting in undefined behavior where
@@ -1890,6 +1914,7 @@ extern "rust-intrinsic" {
     /// primitives via the `rotate_left` method. For example,
     /// [`u32::rotate_left`]
     #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn rotate_left<T: Copy>(x: T, y: T) -> T;
 
     /// Performs rotate right.
@@ -1903,6 +1928,7 @@ extern "rust-intrinsic" {
     /// primitives via the `rotate_right` method. For example,
     /// [`u32::rotate_right`]
     #[rustc_const_stable(feature = "const_int_rotate", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn rotate_right<T: Copy>(x: T, y: T) -> T;
 
     /// Returns (a + b) mod 2<sup>N</sup>, where N is the width of T in bits.
@@ -1916,6 +1942,7 @@ extern "rust-intrinsic" {
     /// primitives via the `wrapping_add` method. For example,
     /// [`u32::wrapping_add`]
     #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn wrapping_add<T: Copy>(a: T, b: T) -> T;
     /// Returns (a - b) mod 2<sup>N</sup>, where N is the width of T in bits.
     ///
@@ -1928,6 +1955,7 @@ extern "rust-intrinsic" {
     /// primitives via the `wrapping_sub` method. For example,
     /// [`u32::wrapping_sub`]
     #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn wrapping_sub<T: Copy>(a: T, b: T) -> T;
     /// Returns (a * b) mod 2<sup>N</sup>, where N is the width of T in bits.
     ///
@@ -1940,6 +1968,7 @@ extern "rust-intrinsic" {
     /// primitives via the `wrapping_mul` method. For example,
     /// [`u32::wrapping_mul`]
     #[rustc_const_stable(feature = "const_int_wrapping", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn wrapping_mul<T: Copy>(a: T, b: T) -> T;
 
     /// Computes `a + b`, saturating at numeric bounds.
@@ -1953,6 +1982,7 @@ extern "rust-intrinsic" {
     /// primitives via the `saturating_add` method. For example,
     /// [`u32::saturating_add`]
     #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn saturating_add<T: Copy>(a: T, b: T) -> T;
     /// Computes `a - b`, saturating at numeric bounds.
     ///
@@ -1965,6 +1995,7 @@ extern "rust-intrinsic" {
     /// primitives via the `saturating_sub` method. For example,
     /// [`u32::saturating_sub`]
     #[rustc_const_stable(feature = "const_int_saturating", since = "1.40.0")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn saturating_sub<T: Copy>(a: T, b: T) -> T;
 
     /// Returns the value of the discriminant for the variant in 'v';
@@ -1977,6 +2008,7 @@ extern "rust-intrinsic" {
     ///
     /// The stabilized version of this intrinsic is [`core::mem::discriminant`].
     #[rustc_const_unstable(feature = "const_discriminant", issue = "69821")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn discriminant_value<T>(v: &T) -> <T as DiscriminantKind>::Discriminant;
 
     /// Returns the number of variants of the type `T` cast to a `usize`;
@@ -1989,6 +2021,7 @@ extern "rust-intrinsic" {
     ///
     /// The to-be-stabilized version of this intrinsic is [`mem::variant_count`].
     #[rustc_const_unstable(feature = "variant_count", issue = "73662")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn variant_count<T>() -> usize;
 
     /// Rust's "try catch" construct which invokes the function pointer `try_fn`
@@ -2022,17 +2055,9 @@ extern "rust-intrinsic" {
     /// Therefore, implementations must not require the user to uphold
     /// any safety invariants.
     #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
-    #[cfg(not(bootstrap))]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8;
 
-    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
-    #[cfg(bootstrap)]
-    pub fn ptr_guaranteed_eq<T>(ptr: *const T, other: *const T) -> bool;
-
-    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
-    #[cfg(bootstrap)]
-    pub fn ptr_guaranteed_ne<T>(ptr: *const T, other: *const T) -> bool;
-
     /// Allocates a block of memory at compile time.
     /// At runtime, just returns a null pointer.
     ///
@@ -2081,6 +2106,7 @@ extern "rust-intrinsic" {
     ///
     /// [`std::hint::black_box`]: crate::hint::black_box
     #[rustc_const_unstable(feature = "const_black_box", issue = "none")]
+    #[cfg_attr(not(bootstrap), rustc_safe_intrinsic)]
     pub fn black_box<T>(dummy: T) -> T;
 
     /// `ptr` must point to a vtable.
@@ -2143,7 +2169,6 @@ extern "rust-intrinsic" {
     /// `unreachable_unchecked` is actually being reached. The bug is in *crate A*,
     /// which violates the principle that a `const fn` must behave the same at
     /// compile-time and at run-time. The unsafe code in crate B is fine.
-    #[cfg(not(bootstrap))]
     #[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
     pub fn const_eval_select<ARG, F, G, RET>(arg: ARG, called_in_const: F, called_at_rt: G) -> RET
     where
@@ -2178,15 +2203,17 @@ extern "rust-intrinsic" {
 /// the occasional mistake, and this check should help them figure things out.
 #[allow_internal_unstable(const_eval_select)] // permit this to be called in stably-const fn
 macro_rules! assert_unsafe_precondition {
-    ($([$($tt:tt)*])?($($i:ident:$ty:ty),*$(,)?) => $e:expr) => {
+    ($name:expr, $([$($tt:tt)*])?($($i:ident:$ty:ty),*$(,)?) => $e:expr) => {
         if cfg!(debug_assertions) {
             // allow non_snake_case to allow capturing const generics
             #[allow(non_snake_case)]
             #[inline(always)]
             fn runtime$(<$($tt)*>)?($($i:$ty),*) {
                 if !$e {
-                    // abort instead of panicking to reduce impact on code size
-                    ::core::intrinsics::abort();
+                    // don't unwind to reduce impact on code size
+                    ::core::panicking::panic_str_nounwind(
+                        concat!("unsafe precondition(s) violated: ", $name)
+                    );
                 }
             }
             #[allow(non_snake_case)]
@@ -2204,6 +2231,16 @@ pub(crate) fn is_aligned_and_not_null<T>(ptr: *const T) -> bool {
     !ptr.is_null() && ptr.is_aligned()
 }
 
+/// Checks whether an allocation of `len` instances of `T` exceeds
+/// the maximum allowed allocation size.
+pub(crate) fn is_valid_allocation_size<T>(len: usize) -> bool {
+    let max_len = const {
+        let size = crate::mem::size_of::<T>();
+        if size == 0 { usize::MAX } else { isize::MAX as usize / size }
+    };
+    len <= max_len
+}
+
 /// Checks whether the regions of memory starting at `src` and `dst` of size
 /// `count * size_of::<T>()` do *not* overlap.
 pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -> bool {
@@ -2216,16 +2253,6 @@ pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -
     diff >= size
 }
 
-#[cfg(bootstrap)]
-pub const fn ptr_guaranteed_cmp(a: *const (), b: *const ()) -> u8 {
-    match (ptr_guaranteed_eq(a, b), ptr_guaranteed_ne(a, b)) {
-        (false, false) => 2,
-        (true, false) => 1,
-        (false, true) => 0,
-        (true, true) => unreachable!(),
-    }
-}
-
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
 /// and destination must *not* overlap.
 ///
@@ -2325,7 +2352,10 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
     // SAFETY: the safety contract for `copy_nonoverlapping` must be
     // upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!([T](src: *const T, dst: *mut T, count: usize) =>
+        assert_unsafe_precondition!(
+            "ptr::copy_nonoverlapping requires that both pointer arguments are aligned and non-null \
+            and the specified memory ranges do not overlap",
+            [T](src: *const T, dst: *mut T, count: usize) =>
             is_aligned_and_not_null(src)
                 && is_aligned_and_not_null(dst)
                 && is_nonoverlapping(src, dst, count)
@@ -2411,8 +2441,11 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 
     // SAFETY: the safety contract for `copy` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!([T](src: *const T, dst: *mut T) =>
-            is_aligned_and_not_null(src) && is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!(
+            "ptr::copy requires that both pointer arguments are aligned aligned and non-null",
+            [T](src: *const T, dst: *mut T) =>
+            is_aligned_and_not_null(src) && is_aligned_and_not_null(dst)
+        );
         copy(src, dst, count)
     }
 }
@@ -2480,49 +2513,10 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
 
     // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!(
+            "ptr::write_bytes requires that the destination pointer is aligned and non-null",
+            [T](dst: *mut T) => is_aligned_and_not_null(dst)
+        );
         write_bytes(dst, val, count)
     }
 }
-
-#[cfg(bootstrap)]
-#[unstable(
-    feature = "const_eval_select",
-    issue = "none",
-    reason = "const_eval_select will never be stable"
-)]
-#[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
-#[lang = "const_eval_select"]
-#[rustc_do_not_const_check]
-#[inline]
-pub const unsafe fn const_eval_select<ARG, F, G, RET>(
-    arg: ARG,
-    _called_in_const: F,
-    called_at_rt: G,
-) -> RET
-where
-    F: ~const FnOnce<ARG, Output = RET>,
-    G: FnOnce<ARG, Output = RET> + ~const Destruct,
-{
-    called_at_rt.call_once(arg)
-}
-
-#[cfg(bootstrap)]
-#[unstable(
-    feature = "const_eval_select",
-    issue = "none",
-    reason = "const_eval_select will never be stable"
-)]
-#[rustc_const_unstable(feature = "const_eval_select", issue = "none")]
-#[lang = "const_eval_select_ct"]
-pub const unsafe fn const_eval_select_ct<ARG, F, G, RET>(
-    arg: ARG,
-    called_in_const: F,
-    _called_at_rt: G,
-) -> RET
-where
-    F: ~const FnOnce<ARG, Output = RET>,
-    G: FnOnce<ARG, Output = RET> + ~const Destruct,
-{
-    called_in_const.call_once(arg)
-}
diff --git a/library/core/src/iter/adapters/array_chunks.rs b/library/core/src/iter/adapters/array_chunks.rs
index 9b479a9f8..d4fb88610 100644
--- a/library/core/src/iter/adapters/array_chunks.rs
+++ b/library/core/src/iter/adapters/array_chunks.rs
@@ -1,6 +1,6 @@
 use crate::array;
 use crate::iter::{ByRefSized, FusedIterator, Iterator};
-use crate::ops::{ControlFlow, NeverShortCircuit, Try};
+use crate::ops::{ControlFlow, Try};
 
 /// An iterator over `N` elements of the iterator at a time.
 ///
@@ -82,13 +82,7 @@ where
         }
     }
 
-    fn fold<B, F>(mut self, init: B, f: F) -> B
-    where
-        Self: Sized,
-        F: FnMut(B, Self::Item) -> B,
-    {
-        self.try_fold(init, NeverShortCircuit::wrap_mut_2(f)).0
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 }
 
 #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "100450")]
@@ -126,13 +120,7 @@ where
         try { acc }
     }
 
-    fn rfold<B, F>(mut self, init: B, f: F) -> B
-    where
-        Self: Sized,
-        F: FnMut(B, Self::Item) -> B,
-    {
-        self.try_rfold(init, NeverShortCircuit::wrap_mut_2(f)).0
-    }
+    impl_fold_via_try_fold! { rfold -> try_rfold }
 }
 
 impl<I, const N: usize> ArrayChunks<I, N>
diff --git a/library/core/src/iter/adapters/by_ref_sized.rs b/library/core/src/iter/adapters/by_ref_sized.rs
index 477e7117c..1945e402f 100644
--- a/library/core/src/iter/adapters/by_ref_sized.rs
+++ b/library/core/src/iter/adapters/by_ref_sized.rs
@@ -1,4 +1,7 @@
-use crate::ops::{NeverShortCircuit, Try};
+use crate::{
+    const_closure::ConstFnMutClosure,
+    ops::{NeverShortCircuit, Try},
+};
 
 /// Like `Iterator::by_ref`, but requiring `Sized` so it can forward generics.
 ///
@@ -36,12 +39,13 @@ impl<I: Iterator> Iterator for ByRefSized<'_, I> {
     }
 
     #[inline]
-    fn fold<B, F>(self, init: B, f: F) -> B
+    fn fold<B, F>(self, init: B, mut f: F) -> B
     where
         F: FnMut(B, Self::Item) -> B,
     {
         // `fold` needs ownership, so this can't forward directly.
-        I::try_fold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
+        I::try_fold(self.0, init, ConstFnMutClosure::new(&mut f, NeverShortCircuit::wrap_mut_2_imp))
+            .0
     }
 
     #[inline]
@@ -72,12 +76,17 @@ impl<I: DoubleEndedIterator> DoubleEndedIterator for ByRefSized<'_, I> {
     }
 
     #[inline]
-    fn rfold<B, F>(self, init: B, f: F) -> B
+    fn rfold<B, F>(self, init: B, mut f: F) -> B
     where
         F: FnMut(B, Self::Item) -> B,
     {
         // `rfold` needs ownership, so this can't forward directly.
-        I::try_rfold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
+        I::try_rfold(
+            self.0,
+            init,
+            ConstFnMutClosure::new(&mut f, NeverShortCircuit::wrap_mut_2_imp),
+        )
+        .0
     }
 
     #[inline]
diff --git a/library/core/src/iter/adapters/copied.rs b/library/core/src/iter/adapters/copied.rs
index f9bfd77d7..62d3afb81 100644
--- a/library/core/src/iter/adapters/copied.rs
+++ b/library/core/src/iter/adapters/copied.rs
@@ -2,7 +2,10 @@ use crate::iter::adapters::{
     zip::try_get_unchecked, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
 };
 use crate::iter::{FusedIterator, TrustedLen};
+use crate::mem::MaybeUninit;
+use crate::mem::SizedTypeProperties;
 use crate::ops::Try;
+use crate::{array, ptr};
 
 /// An iterator that copies the elements of an underlying iterator.
 ///
@@ -44,6 +47,15 @@ where
         self.it.next().copied()
     }
 
+    fn next_chunk<const N: usize>(
+        &mut self,
+    ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>>
+    where
+        Self: Sized,
+    {
+        <I as SpecNextChunk<'_, N, T>>::spec_next_chunk(&mut self.it)
+    }
+
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.it.size_hint()
     }
@@ -166,3 +178,65 @@ where
     T: Copy,
 {
 }
+
+trait SpecNextChunk<'a, const N: usize, T: 'a>: Iterator<Item = &'a T>
+where
+    T: Copy,
+{
+    fn spec_next_chunk(&mut self) -> Result<[T; N], array::IntoIter<T, N>>;
+}
+
+impl<'a, const N: usize, I, T: 'a> SpecNextChunk<'a, N, T> for I
+where
+    I: Iterator<Item = &'a T>,
+    T: Copy,
+{
+    default fn spec_next_chunk(&mut self) -> Result<[T; N], array::IntoIter<T, N>> {
+        array::iter_next_chunk(&mut self.map(|e| *e))
+    }
+}
+
+impl<'a, const N: usize, T: 'a> SpecNextChunk<'a, N, T> for crate::slice::Iter<'a, T>
+where
+    T: Copy,
+{
+    fn spec_next_chunk(&mut self) -> Result<[T; N], array::IntoIter<T, N>> {
+        let mut raw_array = MaybeUninit::uninit_array();
+
+        let len = self.len();
+
+        if T::IS_ZST {
+            if len < N {
+                let _ = self.advance_by(len);
+                // SAFETY: ZSTs can be conjured ex nihilo; only the amount has to be correct
+                return Err(unsafe { array::IntoIter::new_unchecked(raw_array, 0..len) });
+            }
+
+            let _ = self.advance_by(N);
+            // SAFETY: ditto
+            return Ok(unsafe { MaybeUninit::array_assume_init(raw_array) });
+        }
+
+        if len < N {
+            // SAFETY: `len` indicates that this many elements are available and we just checked that
+            // it fits into the array.
+            unsafe {
+                ptr::copy_nonoverlapping(
+                    self.as_ref().as_ptr(),
+                    raw_array.as_mut_ptr() as *mut T,
+                    len,
+                );
+                let _ = self.advance_by(len);
+                return Err(array::IntoIter::new_unchecked(raw_array, 0..len));
+            }
+        }
+
+        // SAFETY: `len` is larger than the array size. Copy a fixed amount here to fully initialize
+        // the array.
+        unsafe {
+            ptr::copy_nonoverlapping(self.as_ref().as_ptr(), raw_array.as_mut_ptr() as *mut T, N);
+            let _ = self.advance_by(N);
+            Ok(MaybeUninit::array_assume_init(raw_array))
+        }
+    }
+}
diff --git a/library/core/src/iter/adapters/map_while.rs b/library/core/src/iter/adapters/map_while.rs
index 1e8d6bf3e..fbdeca4d4 100644
--- a/library/core/src/iter/adapters/map_while.rs
+++ b/library/core/src/iter/adapters/map_while.rs
@@ -64,19 +64,7 @@ where
         .into_try()
     }
 
-    #[inline]
-    fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
-    where
-        Self: Sized,
-        Fold: FnMut(Acc, Self::Item) -> Acc,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_fold(init, ok(fold)).unwrap()
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
diff --git a/library/core/src/iter/adapters/mod.rs b/library/core/src/iter/adapters/mod.rs
index bf4fabad3..8cc2b7cec 100644
--- a/library/core/src/iter/adapters/mod.rs
+++ b/library/core/src/iter/adapters/mod.rs
@@ -1,5 +1,5 @@
 use crate::iter::{InPlaceIterable, Iterator};
-use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, NeverShortCircuit, Residual, Try};
+use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try};
 
 mod array_chunks;
 mod by_ref_sized;
@@ -203,13 +203,7 @@ where
             .into_try()
     }
 
-    fn fold<B, F>(mut self, init: B, fold: F) -> B
-    where
-        Self: Sized,
-        F: FnMut(B, Self::Item) -> B,
-    {
-        self.try_fold(init, NeverShortCircuit::wrap_mut_2(fold)).0
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
diff --git a/library/core/src/iter/adapters/scan.rs b/library/core/src/iter/adapters/scan.rs
index 80bfd2231..62470512c 100644
--- a/library/core/src/iter/adapters/scan.rs
+++ b/library/core/src/iter/adapters/scan.rs
@@ -74,19 +74,7 @@ where
         self.iter.try_fold(init, scan(state, f, fold)).into_try()
     }
 
-    #[inline]
-    fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
-    where
-        Self: Sized,
-        Fold: FnMut(Acc, Self::Item) -> Acc,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_fold(init, ok(fold)).unwrap()
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 }
 
 #[unstable(issue = "none", feature = "inplace_iteration")]
diff --git a/library/core/src/iter/adapters/skip.rs b/library/core/src/iter/adapters/skip.rs
index dbf0ae9ec..c6334880d 100644
--- a/library/core/src/iter/adapters/skip.rs
+++ b/library/core/src/iter/adapters/skip.rs
@@ -206,17 +206,7 @@ where
         if n == 0 { try { init } } else { self.iter.try_rfold(init, check(n, fold)).into_try() }
     }
 
-    fn rfold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
-    where
-        Fold: FnMut(Acc, Self::Item) -> Acc,
-    {
-        #[inline]
-        fn ok<Acc, T>(mut f: impl FnMut(Acc, T) -> Acc) -> impl FnMut(Acc, T) -> Result<Acc, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_rfold(init, ok(fold)).unwrap()
-    }
+    impl_fold_via_try_fold! { rfold -> try_rfold }
 
     #[inline]
     fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
diff --git a/library/core/src/iter/adapters/take.rs b/library/core/src/iter/adapters/take.rs
index 2962e0104..58a0b9d7b 100644
--- a/library/core/src/iter/adapters/take.rs
+++ b/library/core/src/iter/adapters/take.rs
@@ -98,19 +98,7 @@ where
         }
     }
 
-    #[inline]
-    fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
-    where
-        Self: Sized,
-        Fold: FnMut(Acc, Self::Item) -> Acc,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_fold(init, ok(fold)).unwrap()
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 
     #[inline]
     #[rustc_inherit_overflow_checks]
diff --git a/library/core/src/iter/adapters/take_while.rs b/library/core/src/iter/adapters/take_while.rs
index ded216da9..ec66dc3ae 100644
--- a/library/core/src/iter/adapters/take_while.rs
+++ b/library/core/src/iter/adapters/take_while.rs
@@ -94,19 +94,7 @@ where
         }
     }
 
-    #[inline]
-    fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
-    where
-        Self: Sized,
-        Fold: FnMut(Acc, Self::Item) -> Acc,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_fold(init, ok(fold)).unwrap()
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 }
 
 #[stable(feature = "fused", since = "1.26.0")]
diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs
index 9514466bd..ef0f39782 100644
--- a/library/core/src/iter/mod.rs
+++ b/library/core/src/iter/mod.rs
@@ -352,6 +352,29 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+// This needs to be up here in order to be usable in the child modules
+macro_rules! impl_fold_via_try_fold {
+    (fold -> try_fold) => {
+        impl_fold_via_try_fold! { @internal fold -> try_fold }
+    };
+    (rfold -> try_rfold) => {
+        impl_fold_via_try_fold! { @internal rfold -> try_rfold }
+    };
+    (@internal $fold:ident -> $try_fold:ident) => {
+        #[inline]
+        fn $fold<AAA, FFF>(mut self, init: AAA, mut fold: FFF) -> AAA
+        where
+            FFF: FnMut(AAA, Self::Item) -> AAA,
+        {
+            use crate::const_closure::ConstFnMutClosure;
+            use crate::ops::NeverShortCircuit;
+
+            let fold = ConstFnMutClosure::new(&mut fold, NeverShortCircuit::wrap_mut_2_imp);
+            self.$try_fold(init, fold).0
+        }
+    };
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::traits::Iterator;
 
diff --git a/library/core/src/iter/range.rs b/library/core/src/iter/range.rs
index f7aeee8c9..ac7b389b1 100644
--- a/library/core/src/iter/range.rs
+++ b/library/core/src/iter/range.rs
@@ -1150,19 +1150,7 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
         self.spec_try_fold(init, f)
     }
 
-    #[inline]
-    fn fold<B, F>(mut self, init: B, f: F) -> B
-    where
-        Self: Sized,
-        F: FnMut(B, Self::Item) -> B,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_fold(init, ok(f)).unwrap()
-    }
+    impl_fold_via_try_fold! { fold -> try_fold }
 
     #[inline]
     fn last(mut self) -> Option<A> {
@@ -1230,19 +1218,7 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
         self.spec_try_rfold(init, f)
     }
 
-    #[inline]
-    fn rfold<B, F>(mut self, init: B, f: F) -> B
-    where
-        Self: Sized,
-        F: FnMut(B, Self::Item) -> B,
-    {
-        #[inline]
-        fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
-            move |acc, x| Ok(f(acc, x))
-        }
-
-        self.try_rfold(init, ok(f)).unwrap()
-    }
+    impl_fold_via_try_fold! { rfold -> try_rfold }
 }
 
 // Safety: See above implementation for `ops::Range<A>`
diff --git a/library/core/src/iter/traits/collect.rs b/library/core/src/iter/traits/collect.rs
index 12ca508be..e099700e3 100644
--- a/library/core/src/iter/traits/collect.rs
+++ b/library/core/src/iter/traits/collect.rs
@@ -228,6 +228,7 @@ pub trait FromIterator<A>: Sized {
 #[rustc_diagnostic_item = "IntoIterator"]
 #[rustc_skip_array_during_method_dispatch]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait IntoIterator {
     /// The type of the elements being iterated over.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -263,7 +264,7 @@ pub trait IntoIterator {
 
 #[rustc_const_unstable(feature = "const_intoiterator_identity", issue = "90603")]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<I: ~const Iterator> const IntoIterator for I {
+impl<I: Iterator> const IntoIterator for I {
     type Item = I::Item;
     type IntoIter = I;
 
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index b2d08f4b0..789a87968 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -692,7 +692,7 @@ pub trait Iterator {
     /// assert_eq!(it.next(), Some(NotClone(99))); // The separator.
     /// assert_eq!(it.next(), Some(NotClone(1)));  // The next element from `v`.
     /// assert_eq!(it.next(), Some(NotClone(99))); // The separator.
-    /// assert_eq!(it.next(), Some(NotClone(2)));  // The last element from from `v`.
+    /// assert_eq!(it.next(), Some(NotClone(2)));  // The last element from `v`.
     /// assert_eq!(it.next(), None);               // The iterator is finished.
     /// ```
     ///
@@ -2431,22 +2431,13 @@ pub trait Iterator {
     ///
     /// # Example
     ///
-    /// Find the maximum value:
-    ///
     /// ```
-    /// fn find_max<I>(iter: I) -> Option<I::Item>
-    ///     where I: Iterator,
-    ///           I::Item: Ord,
-    /// {
-    ///     iter.reduce(|accum, item| {
-    ///         if accum >= item { accum } else { item }
-    ///     })
-    /// }
-    /// let a = [10, 20, 5, -23, 0];
-    /// let b: [u32; 0] = [];
+    /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap();
+    /// assert_eq!(reduced, 45);
     ///
-    /// assert_eq!(find_max(a.iter()), Some(&20));
-    /// assert_eq!(find_max(b.iter()), None);
+    /// // Which is equivalent to doing it with `fold`:
+    /// let folded: i32 = (1..10).fold(0, |acc, e| acc + e);
+    /// assert_eq!(reduced, folded);
     /// ```
     #[inline]
     #[stable(feature = "iterator_fold_self", since = "1.51.0")]
@@ -2906,14 +2897,14 @@ pub trait Iterator {
     /// Stopping at the first `true`:
     ///
     /// ```
-    /// let a = [1, 2, 3];
+    /// let a = [-1, 2, 3, 4];
     ///
     /// let mut iter = a.iter();
     ///
-    /// assert_eq!(iter.rposition(|&x| x == 2), Some(1));
+    /// assert_eq!(iter.rposition(|&x| x >= 2), Some(3));
     ///
     /// // we can still use `iter`, as there are more elements.
-    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), Some(&-1));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -3461,36 +3452,27 @@ pub trait Iterator {
     /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater);
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
-    fn cmp_by<I, F>(mut self, other: I, mut cmp: F) -> Ordering
+    fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
     where
         Self: Sized,
         I: IntoIterator,
         F: FnMut(Self::Item, I::Item) -> Ordering,
     {
-        let mut other = other.into_iter();
-
-        loop {
-            let x = match self.next() {
-                None => {
-                    if other.next().is_none() {
-                        return Ordering::Equal;
-                    } else {
-                        return Ordering::Less;
-                    }
-                }
-                Some(val) => val,
-            };
-
-            let y = match other.next() {
-                None => return Ordering::Greater,
-                Some(val) => val,
-            };
-
-            match cmp(x, y) {
-                Ordering::Equal => (),
-                non_eq => return non_eq,
+        #[inline]
+        fn compare<X, Y, F>(mut cmp: F) -> impl FnMut(X, Y) -> ControlFlow<Ordering>
+        where
+            F: FnMut(X, Y) -> Ordering,
+        {
+            move |x, y| match cmp(x, y) {
+                Ordering::Equal => ControlFlow::CONTINUE,
+                non_eq => ControlFlow::Break(non_eq),
             }
         }
+
+        match iter_compare(self, other.into_iter(), compare(cmp)) {
+            ControlFlow::Continue(ord) => ord,
+            ControlFlow::Break(ord) => ord,
+        }
     }
 
     /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
@@ -3546,36 +3528,27 @@ pub trait Iterator {
     /// );
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
-    fn partial_cmp_by<I, F>(mut self, other: I, mut partial_cmp: F) -> Option<Ordering>
+    fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
     where
         Self: Sized,
         I: IntoIterator,
         F: FnMut(Self::Item, I::Item) -> Option<Ordering>,
     {
-        let mut other = other.into_iter();
-
-        loop {
-            let x = match self.next() {
-                None => {
-                    if other.next().is_none() {
-                        return Some(Ordering::Equal);
-                    } else {
-                        return Some(Ordering::Less);
-                    }
-                }
-                Some(val) => val,
-            };
-
-            let y = match other.next() {
-                None => return Some(Ordering::Greater),
-                Some(val) => val,
-            };
-
-            match partial_cmp(x, y) {
-                Some(Ordering::Equal) => (),
-                non_eq => return non_eq,
+        #[inline]
+        fn compare<X, Y, F>(mut partial_cmp: F) -> impl FnMut(X, Y) -> ControlFlow<Option<Ordering>>
+        where
+            F: FnMut(X, Y) -> Option<Ordering>,
+        {
+            move |x, y| match partial_cmp(x, y) {
+                Some(Ordering::Equal) => ControlFlow::CONTINUE,
+                non_eq => ControlFlow::Break(non_eq),
             }
         }
+
+        match iter_compare(self, other.into_iter(), compare(partial_cmp)) {
+            ControlFlow::Continue(ord) => Some(ord),
+            ControlFlow::Break(ord) => ord,
+        }
     }
 
     /// Determines if the elements of this [`Iterator`] are equal to those of
@@ -3613,29 +3586,26 @@ pub trait Iterator {
     /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y));
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
-    fn eq_by<I, F>(mut self, other: I, mut eq: F) -> bool
+    fn eq_by<I, F>(self, other: I, eq: F) -> bool
     where
         Self: Sized,
         I: IntoIterator,
         F: FnMut(Self::Item, I::Item) -> bool,
     {
-        let mut other = other.into_iter();
-
-        loop {
-            let x = match self.next() {
-                None => return other.next().is_none(),
-                Some(val) => val,
-            };
-
-            let y = match other.next() {
-                None => return false,
-                Some(val) => val,
-            };
-
-            if !eq(x, y) {
-                return false;
+        #[inline]
+        fn compare<X, Y, F>(mut eq: F) -> impl FnMut(X, Y) -> ControlFlow<()>
+        where
+            F: FnMut(X, Y) -> bool,
+        {
+            move |x, y| {
+                if eq(x, y) { ControlFlow::CONTINUE } else { ControlFlow::BREAK }
             }
         }
+
+        match iter_compare(self, other.into_iter(), compare(eq)) {
+            ControlFlow::Continue(ord) => ord == Ordering::Equal,
+            ControlFlow::Break(()) => false,
+        }
     }
 
     /// Determines if the elements of this [`Iterator`] are unequal to those of
@@ -3860,6 +3830,46 @@ pub trait Iterator {
     }
 }
 
+/// Compares two iterators element-wise using the given function.
+///
+/// If `ControlFlow::CONTINUE` is returned from the function, the comparison moves on to the next
+/// elements of both iterators. Returning `ControlFlow::Break(x)` short-circuits the iteration and
+/// returns `ControlFlow::Break(x)`. If one of the iterators runs out of elements,
+/// `ControlFlow::Continue(ord)` is returned where `ord` is the result of comparing the lengths of
+/// the iterators.
+///
+/// Isolates the logic shared by ['cmp_by'](Iterator::cmp_by),
+/// ['partial_cmp_by'](Iterator::partial_cmp_by), and ['eq_by'](Iterator::eq_by).
+#[inline]
+fn iter_compare<A, B, F, T>(mut a: A, mut b: B, f: F) -> ControlFlow<T, Ordering>
+where
+    A: Iterator,
+    B: Iterator,
+    F: FnMut(A::Item, B::Item) -> ControlFlow<T>,
+{
+    #[inline]
+    fn compare<'a, B, X, T>(
+        b: &'a mut B,
+        mut f: impl FnMut(X, B::Item) -> ControlFlow<T> + 'a,
+    ) -> impl FnMut(X) -> ControlFlow<ControlFlow<T, Ordering>> + 'a
+    where
+        B: Iterator,
+    {
+        move |x| match b.next() {
+            None => ControlFlow::Break(ControlFlow::Continue(Ordering::Greater)),
+            Some(y) => f(x, y).map_break(ControlFlow::Break),
+        }
+    }
+
+    match a.try_for_each(compare(&mut b, f)) {
+        ControlFlow::Continue(()) => ControlFlow::Continue(match b.next() {
+            None => Ordering::Equal,
+            Some(_) => Ordering::Less,
+        }),
+        ControlFlow::Break(x) => x,
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: Iterator + ?Sized> Iterator for &mut I {
     type Item = I::Item;
diff --git a/library/core/src/lazy.rs b/library/core/src/lazy.rs
deleted file mode 100644
index f8c06c3f9..000000000
--- a/library/core/src/lazy.rs
+++ /dev/null
@@ -1 +0,0 @@
-//! Lazy values and one-time initialization of static data.
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 5621d15c1..659409557 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -114,6 +114,7 @@
 #![feature(const_fmt_arguments_new)]
 #![feature(const_heap)]
 #![feature(const_convert)]
+#![feature(const_index_range_slice_index)]
 #![feature(const_inherent_unchecked_arith)]
 #![feature(const_int_unchecked_arith)]
 #![feature(const_intrinsic_forget)]
@@ -137,17 +138,21 @@
 #![feature(const_size_of_val)]
 #![feature(const_slice_from_raw_parts_mut)]
 #![feature(const_slice_ptr_len)]
+#![feature(const_slice_split_at_mut)]
 #![feature(const_str_from_utf8_unchecked_mut)]
 #![feature(const_swap)]
 #![feature(const_trait_impl)]
+#![feature(const_try)]
 #![feature(const_type_id)]
 #![feature(const_type_name)]
 #![feature(const_default_impls)]
 #![feature(const_unicode_case_lookup)]
 #![feature(const_unsafecell_get_mut)]
+#![feature(const_waker)]
 #![feature(core_panic)]
 #![feature(duration_consts_float)]
 #![feature(maybe_uninit_uninit_array)]
+#![feature(ptr_alignment_type)]
 #![feature(ptr_metadata)]
 #![feature(slice_ptr_get)]
 #![feature(slice_split_at_unchecked)]
@@ -160,6 +165,7 @@
 #![feature(const_slice_index)]
 #![feature(const_is_char_boundary)]
 #![feature(const_cstr_methods)]
+#![feature(is_ascii_octdigit)]
 //
 // Language features:
 #![feature(abi_unadjusted)]
@@ -168,6 +174,7 @@
 #![feature(allow_internal_unstable)]
 #![feature(associated_type_bounds)]
 #![feature(auto_traits)]
+#![feature(c_unwind)]
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(cfg_target_has_atomic_equal_alignment)]
@@ -185,13 +192,13 @@
 #![feature(extern_types)]
 #![feature(fundamental)]
 #![feature(if_let_guard)]
+#![feature(inline_const)]
 #![feature(intra_doc_pointers)]
 #![feature(intrinsics)]
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]
 #![feature(macro_metavar_expr)]
 #![feature(min_specialization)]
-#![feature(mixed_integer_ops)]
 #![feature(must_not_suspend)]
 #![feature(negative_impls)]
 #![feature(never_type)]
@@ -205,12 +212,14 @@
 #![feature(simd_ffi)]
 #![feature(staged_api)]
 #![feature(stmt_expr_attributes)]
+#![feature(target_feature_11)]
 #![feature(trait_alias)]
 #![feature(transparent_unions)]
 #![feature(try_blocks)]
 #![feature(unboxed_closures)]
 #![feature(unsized_fn_params)]
 #![feature(asm_const)]
+#![feature(const_transmute_copy)]
 //
 // Target features:
 #![feature(arm_target_feature)]
@@ -220,6 +229,7 @@
 #![feature(hexagon_target_feature)]
 #![feature(mips_target_feature)]
 #![feature(powerpc_target_feature)]
+#![feature(riscv_target_feature)]
 #![feature(rtm_target_feature)]
 #![feature(sse4a_target_feature)]
 #![feature(tbm_target_feature)]
@@ -306,7 +316,6 @@ pub mod clone;
 pub mod cmp;
 pub mod convert;
 pub mod default;
-#[cfg(not(bootstrap))]
 pub mod error;
 pub mod marker;
 pub mod ops;
@@ -323,8 +332,6 @@ pub mod cell;
 pub mod char;
 pub mod ffi;
 pub mod iter;
-#[unstable(feature = "once_cell", issue = "74465")]
-pub mod lazy;
 pub mod option;
 pub mod panic;
 pub mod panicking;
@@ -353,6 +360,8 @@ mod bool;
 mod tuple;
 mod unit;
 
+mod const_closure;
+
 #[stable(feature = "core_primitive", since = "1.43.0")]
 pub mod primitive;
 
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
index b8239ed88..ae4ebf444 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -44,6 +44,12 @@ impl<T: ?Sized> !Send for *const T {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> !Send for *mut T {}
 
+// Most instances arise automatically, but this instance is needed to link up `T: Sync` with
+// `&T: Send` (and it also removes the unsound default instance `T Send` -> `&T: Send` that would
+// otherwise exist).
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync + ?Sized> Send for &T {}
+
 /// Types with a constant size known at compile time.
 ///
 /// All type parameters have an implicit bound of `Sized`. The special syntax
@@ -81,6 +87,7 @@ impl<T: ?Sized> !Send for *mut T {}
 /// ```
 ///
 /// [trait object]: ../../book/ch17-02-trait-objects.html
+#[doc(alias = "?", alias = "?Sized")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[lang = "sized"]
 #[rustc_on_unimplemented(
@@ -482,64 +489,6 @@ impl<T: ?Sized> !Sync for *const T {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> !Sync for *mut T {}
 
-macro_rules! impls {
-    ($t: ident) => {
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> Hash for $t<T> {
-            #[inline]
-            fn hash<H: Hasher>(&self, _: &mut H) {}
-        }
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> cmp::PartialEq for $t<T> {
-            fn eq(&self, _other: &$t<T>) -> bool {
-                true
-            }
-        }
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> cmp::Eq for $t<T> {}
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> cmp::PartialOrd for $t<T> {
-            fn partial_cmp(&self, _other: &$t<T>) -> Option<cmp::Ordering> {
-                Option::Some(cmp::Ordering::Equal)
-            }
-        }
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> cmp::Ord for $t<T> {
-            fn cmp(&self, _other: &$t<T>) -> cmp::Ordering {
-                cmp::Ordering::Equal
-            }
-        }
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> Copy for $t<T> {}
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        impl<T: ?Sized> Clone for $t<T> {
-            fn clone(&self) -> Self {
-                Self
-            }
-        }
-
-        #[stable(feature = "rust1", since = "1.0.0")]
-        #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
-        impl<T: ?Sized> const Default for $t<T> {
-            fn default() -> Self {
-                Self
-            }
-        }
-
-        #[unstable(feature = "structural_match", issue = "31434")]
-        impl<T: ?Sized> StructuralPartialEq for $t<T> {}
-
-        #[unstable(feature = "structural_match", issue = "31434")]
-        impl<T: ?Sized> StructuralEq for $t<T> {}
-    };
-}
-
 /// Zero-sized type used to mark things that "act like" they own a `T`.
 ///
 /// Adding a `PhantomData<T>` field to your type tells the compiler that your
@@ -677,15 +626,60 @@ macro_rules! impls {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct PhantomData<T: ?Sized>;
 
-impls! { PhantomData }
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Hash for PhantomData<T> {
+    #[inline]
+    fn hash<H: Hasher>(&self, _: &mut H) {}
+}
 
-mod impls {
-    #[stable(feature = "rust1", since = "1.0.0")]
-    unsafe impl<T: Sync + ?Sized> Send for &T {}
-    #[stable(feature = "rust1", since = "1.0.0")]
-    unsafe impl<T: Send + ?Sized> Send for &mut T {}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> cmp::PartialEq for PhantomData<T> {
+    fn eq(&self, _other: &PhantomData<T>) -> bool {
+        true
+    }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> cmp::Eq for PhantomData<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> cmp::PartialOrd for PhantomData<T> {
+    fn partial_cmp(&self, _other: &PhantomData<T>) -> Option<cmp::Ordering> {
+        Option::Some(cmp::Ordering::Equal)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> cmp::Ord for PhantomData<T> {
+    fn cmp(&self, _other: &PhantomData<T>) -> cmp::Ordering {
+        cmp::Ordering::Equal
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Copy for PhantomData<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Clone for PhantomData<T> {
+    fn clone(&self) -> Self {
+        Self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T: ?Sized> const Default for PhantomData<T> {
+    fn default() -> Self {
+        Self
+    }
+}
+
+#[unstable(feature = "structural_match", issue = "31434")]
+impl<T: ?Sized> StructuralPartialEq for PhantomData<T> {}
+
+#[unstable(feature = "structural_match", issue = "31434")]
+impl<T: ?Sized> StructuralEq for PhantomData<T> {}
+
 /// Compiler-internal trait used to indicate the type of enum discriminants.
 ///
 /// This trait is automatically implemented for every type and does not add any
@@ -798,6 +792,7 @@ impl<T: ?Sized> Unpin for *mut T {}
 #[unstable(feature = "const_trait_impl", issue = "67792")]
 #[lang = "destruct"]
 #[rustc_on_unimplemented(message = "can't drop `{Self}`", append_const_msg)]
+#[const_trait]
 pub trait Destruct {}
 
 /// A marker for tuple types.
@@ -805,7 +800,7 @@ pub trait Destruct {}
 /// The implementation of this trait is built-in and cannot be implemented
 /// for any user type.
 #[unstable(feature = "tuple_trait", issue = "none")]
-#[cfg_attr(not(bootstrap), lang = "tuple_trait")]
+#[lang = "tuple_trait"]
 #[rustc_on_unimplemented(message = "`{Self}` is not a tuple")]
 pub trait Tuple {}
 
diff --git a/library/core/src/mem/maybe_uninit.rs b/library/core/src/mem/maybe_uninit.rs
index 2490c0767..7757c95de 100644
--- a/library/core/src/mem/maybe_uninit.rs
+++ b/library/core/src/mem/maybe_uninit.rs
@@ -146,7 +146,6 @@ use crate::slice;
 ///
 /// ```
 /// use std::mem::MaybeUninit;
-/// use std::ptr;
 ///
 /// // Create an uninitialized array of `MaybeUninit`. The `assume_init` is
 /// // safe because the type we are claiming to have initialized here is a
@@ -162,7 +161,7 @@ use crate::slice;
 ///
 /// // For each item in the array, drop if we allocated it.
 /// for elem in &mut data[0..data_len] {
-///     unsafe { ptr::drop_in_place(elem.as_mut_ptr()); }
+///     unsafe { elem.assume_init_drop(); }
 /// }
 /// ```
 ///
@@ -647,7 +646,7 @@ impl<T> MaybeUninit<T> {
     /// implements the [`Copy`] trait or not. When using multiple copies of the
     /// data (by calling `assume_init_read` multiple times, or first calling
     /// `assume_init_read` and then [`assume_init`]), it is your responsibility
-    /// to ensure that that data may indeed be duplicated.
+    /// to ensure that data may indeed be duplicated.
     ///
     /// [inv]: #initialization-invariant
     /// [`assume_init`]: MaybeUninit::assume_init
@@ -1284,3 +1283,42 @@ impl<T> MaybeUninit<T> {
         }
     }
 }
+
+impl<T, const N: usize> MaybeUninit<[T; N]> {
+    /// Transposes a `MaybeUninit<[T; N]>` into a `[MaybeUninit<T>; N]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(maybe_uninit_uninit_array_transpose)]
+    /// # use std::mem::MaybeUninit;
+    ///
+    /// let data: [MaybeUninit<u8>; 1000] = MaybeUninit::uninit().transpose();
+    /// ```
+    #[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
+    #[inline]
+    pub const fn transpose(self) -> [MaybeUninit<T>; N] {
+        // SAFETY: T and MaybeUninit<T> have the same layout
+        unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
+    }
+}
+
+impl<T, const N: usize> [MaybeUninit<T>; N] {
+    /// Transposes a `[MaybeUninit<T>; N]` into a `MaybeUninit<[T; N]>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(maybe_uninit_uninit_array_transpose)]
+    /// # use std::mem::MaybeUninit;
+    ///
+    /// let data = [MaybeUninit::<u8>::uninit(); 1000];
+    /// let data: MaybeUninit<[u8; 1000]> = data.transpose();
+    /// ```
+    #[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
+    #[inline]
+    pub const fn transpose(self) -> MaybeUninit<[T; N]> {
+        // SAFETY: T and MaybeUninit<T> have the same layout
+        unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
+    }
+}
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index d2dd2941d..9195da5a4 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -21,11 +21,10 @@ mod maybe_uninit;
 #[stable(feature = "maybe_uninit", since = "1.36.0")]
 pub use maybe_uninit::MaybeUninit;
 
-mod valid_align;
-// For now this type is left crate-local.  It could potentially make sense to expose
-// it publicly, as it would be a nice parameter type for methods which need to take
-// alignment as a parameter, such as `Layout::padding_needed_for`.
-pub(crate) use valid_align::ValidAlign;
+// FIXME: This is left here for now to avoid complications around pending reverts.
+// Once <https://github.com/rust-lang/rust/issues/101899> is fully resolved,
+// this should be removed and the references in `alloc::Layout` updated.
+pub(crate) use ptr::Alignment as ValidAlign;
 
 mod transmutability;
 #[unstable(feature = "transmutability", issue = "99571")]
@@ -1009,18 +1008,18 @@ pub fn copy<T: Copy>(x: &T) -> T {
     *x
 }
 
-/// Interprets `src` as having type `&U`, and then reads `src` without moving
+/// Interprets `src` as having type `&Dst`, and then reads `src` without moving
 /// the contained value.
 ///
-/// This function will unsafely assume the pointer `src` is valid for [`size_of::<U>`][size_of]
-/// bytes by transmuting `&T` to `&U` and then reading the `&U` (except that this is done in a way
-/// that is correct even when `&U` has stricter alignment requirements than `&T`). It will also
-/// unsafely create a copy of the contained value instead of moving out of `src`.
+/// This function will unsafely assume the pointer `src` is valid for [`size_of::<Dst>`][size_of]
+/// bytes by transmuting `&Src` to `&Dst` and then reading the `&Dst` (except that this is done
+/// in a way that is correct even when `&Dst` has stricter alignment requirements than `&Src`).
+/// It will also unsafely create a copy of the contained value instead of moving out of `src`.
 ///
-/// It is not a compile-time error if `T` and `U` have different sizes, but it
-/// is highly encouraged to only invoke this function where `T` and `U` have the
-/// same size. This function triggers [undefined behavior][ub] if `U` is larger than
-/// `T`.
+/// It is not a compile-time error if `Src` and `Dst` have different sizes, but it
+/// is highly encouraged to only invoke this function where `Src` and `Dst` have the
+/// same size. This function triggers [undefined behavior][ub] if `Dst` is larger than
+/// `Src`.
 ///
 /// [ub]: ../../reference/behavior-considered-undefined.html
 ///
@@ -1053,19 +1052,22 @@ pub fn copy<T: Copy>(x: &T) -> T {
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_transmute_copy", issue = "83165")]
-pub const unsafe fn transmute_copy<T, U>(src: &T) -> U {
-    assert!(size_of::<T>() >= size_of::<U>(), "cannot transmute_copy if U is larger than T");
+pub const unsafe fn transmute_copy<Src, Dst>(src: &Src) -> Dst {
+    assert!(
+        size_of::<Src>() >= size_of::<Dst>(),
+        "cannot transmute_copy if Dst is larger than Src"
+    );
 
-    // If U has a higher alignment requirement, src might not be suitably aligned.
-    if align_of::<U>() > align_of::<T>() {
+    // If Dst has a higher alignment requirement, src might not be suitably aligned.
+    if align_of::<Dst>() > align_of::<Src>() {
         // SAFETY: `src` is a reference which is guaranteed to be valid for reads.
         // The caller must guarantee that the actual transmutation is safe.
-        unsafe { ptr::read_unaligned(src as *const T as *const U) }
+        unsafe { ptr::read_unaligned(src as *const Src as *const Dst) }
     } else {
         // SAFETY: `src` is a reference which is guaranteed to be valid for reads.
-        // We just checked that `src as *const U` was properly aligned.
+        // We just checked that `src as *const Dst` was properly aligned.
         // The caller must guarantee that the actual transmutation is safe.
-        unsafe { ptr::read(src as *const T as *const U) }
+        unsafe { ptr::read(src as *const Src as *const Dst) }
     }
 }
 
@@ -1178,3 +1180,44 @@ pub const fn discriminant<T>(v: &T) -> Discriminant<T> {
 pub const fn variant_count<T>() -> usize {
     intrinsics::variant_count::<T>()
 }
+
+/// Provides associated constants for various useful properties of types,
+/// to give them a canonical form in our code and make them easier to read.
+///
+/// This is here only to simplify all the ZST checks we need in the library.
+/// It's not on a stabilization track right now.
+#[doc(hidden)]
+#[unstable(feature = "sized_type_properties", issue = "none")]
+pub trait SizedTypeProperties: Sized {
+    /// `true` if this type requires no storage.
+    /// `false` if its [size](size_of) is greater than zero.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(sized_type_properties)]
+    /// use core::mem::SizedTypeProperties;
+    ///
+    /// fn do_something_with<T>() {
+    ///     if T::IS_ZST {
+    ///         // ... special approach ...
+    ///     } else {
+    ///         // ... the normal thing ...
+    ///     }
+    /// }
+    ///
+    /// struct MyUnit;
+    /// assert!(MyUnit::IS_ZST);
+    ///
+    /// // For negative checks, consider using UFCS to emphasize the negation
+    /// assert!(!<i32>::IS_ZST);
+    /// // As it can sometimes hide in the type otherwise
+    /// assert!(!String::IS_ZST);
+    /// ```
+    #[doc(hidden)]
+    #[unstable(feature = "sized_type_properties", issue = "none")]
+    const IS_ZST: bool = size_of::<Self>() == 0;
+}
+#[doc(hidden)]
+#[unstable(feature = "sized_type_properties", issue = "none")]
+impl<T> SizedTypeProperties for T {}
diff --git a/library/core/src/mem/transmutability.rs b/library/core/src/mem/transmutability.rs
index 87a378631..3b98efff2 100644
--- a/library/core/src/mem/transmutability.rs
+++ b/library/core/src/mem/transmutability.rs
@@ -4,7 +4,7 @@
 /// any value of type `Self` are safely transmutable into a value of type `Dst`, in a given `Context`,
 /// notwithstanding whatever safety checks you have asked the compiler to [`Assume`] are satisfied.
 #[unstable(feature = "transmutability", issue = "99571")]
-#[cfg_attr(not(bootstrap), lang = "transmute_trait")]
+#[lang = "transmute_trait"]
 #[rustc_on_unimplemented(
     message = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`.",
     label = "`{Src}` cannot be safely transmuted into `{Self}` in the defining scope of `{Context}`."
@@ -17,7 +17,7 @@ where
 
 /// What transmutation safety conditions shall the compiler assume that *you* are checking?
 #[unstable(feature = "transmutability", issue = "99571")]
-#[cfg_attr(not(bootstrap), lang = "transmute_opts")]
+#[lang = "transmute_opts"]
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 pub struct Assume {
     /// When `true`, the compiler assumes that *you* are ensuring (either dynamically or statically) that
diff --git a/library/core/src/num/dec2flt/lemire.rs b/library/core/src/num/dec2flt/lemire.rs
index 75405f471..9f7594460 100644
--- a/library/core/src/num/dec2flt/lemire.rs
+++ b/library/core/src/num/dec2flt/lemire.rs
@@ -6,7 +6,7 @@ use crate::num::dec2flt::table::{
     LARGEST_POWER_OF_FIVE, POWER_OF_FIVE_128, SMALLEST_POWER_OF_FIVE,
 };
 
-/// Compute a float using an extended-precision representation.
+/// Compute w * 10^q using an extended-precision float representation.
 ///
 /// Fast conversion of a the significant digits and decimal exponent
 /// a float to an extended representation with a binary float. This
@@ -76,7 +76,7 @@ pub fn compute_float<F: RawFloat>(q: i64, mut w: u64) -> BiasedFp {
         return BiasedFp { f: mantissa, e: power2 };
     }
     // Need to handle rounding ties. Normally, we need to round up,
-    // but if we fall right in between and and we have an even basis, we
+    // but if we fall right in between and we have an even basis, we
     // need to round down.
     //
     // This will only occur if:
diff --git a/library/core/src/num/error.rs b/library/core/src/num/error.rs
index 1f6b40e5d..768dd8781 100644
--- a/library/core/src/num/error.rs
+++ b/library/core/src/num/error.rs
@@ -1,7 +1,6 @@
 //! Error types for conversion to integral types.
 
 use crate::convert::Infallible;
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 
@@ -147,7 +146,6 @@ impl fmt::Display for ParseIntError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for ParseIntError {
     #[allow(deprecated)]
@@ -156,7 +154,6 @@ impl Error for ParseIntError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "try_from", since = "1.34.0")]
 impl Error for TryFromIntError {
     #[allow(deprecated)]
diff --git a/library/core/src/num/flt2dec/strategy/grisu.rs b/library/core/src/num/flt2dec/strategy/grisu.rs
index a4cb51c62..ed3e0edaf 100644
--- a/library/core/src/num/flt2dec/strategy/grisu.rs
+++ b/library/core/src/num/flt2dec/strategy/grisu.rs
@@ -253,7 +253,6 @@ pub fn format_shortest_opt<'a>(
     let delta1frac = delta1 & ((1 << e) - 1);
 
     // render integral parts, while checking for the accuracy at each step.
-    let mut kappa = max_kappa as i16;
     let mut ten_kappa = max_ten_kappa; // 10^kappa
     let mut remainder = plus1int; // digits yet to be rendered
     loop {
@@ -290,12 +289,10 @@ pub fn format_shortest_opt<'a>(
         // the exact number of digits is `max_kappa + 1` as `plus1 < 10^(max_kappa+1)`.
         if i > max_kappa as usize {
             debug_assert_eq!(ten_kappa, 1);
-            debug_assert_eq!(kappa, 0);
             break;
         }
 
         // restore invariants
-        kappa -= 1;
         ten_kappa /= 10;
         remainder = r;
     }
@@ -338,7 +335,6 @@ pub fn format_shortest_opt<'a>(
         }
 
         // restore invariants
-        kappa -= 1;
         remainder = r;
     }
 
diff --git a/library/core/src/num/int_log10.rs b/library/core/src/num/int_log10.rs
index cc26c04a5..80472528f 100644
--- a/library/core/src/num/int_log10.rs
+++ b/library/core/src/num/int_log10.rs
@@ -1,5 +1,5 @@
 /// These functions compute the integer logarithm of their type, assuming
-/// that someone has already checked that the the value is strictly positive.
+/// that someone has already checked that the value is strictly positive.
 
 // 0 < val <= u8::MAX
 #[inline]
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index e7deb728d..914dca61b 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -464,12 +464,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".checked_add_unsigned(2), Some(3));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).checked_add_unsigned(3), None);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -533,12 +532,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".checked_sub_unsigned(2), Some(-1));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MIN + 2).checked_sub_unsigned(3), None);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -654,7 +652,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".checked_rem(2), Some(1));")]
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".checked_rem(0), None);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.checked_rem(-1), None);")]
@@ -706,7 +703,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".checked_neg(), Some(-5));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.checked_neg(), None);")]
         /// ```
@@ -822,7 +818,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!((-5", stringify!($SelfT), ").checked_abs(), Some(5));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.checked_abs(), None);")]
         /// ```
@@ -874,7 +869,7 @@ macro_rules! int_impl {
             // Deal with the final bit of the exponent separately, since
             // squaring the base afterwards is not necessary and may cause a
             // needless overflow.
-            Some(try_opt!(acc.checked_mul(base)))
+            acc.checked_mul(base)
         }
 
         /// Saturating integer addition. Computes `self + rhs`, saturating at the numeric
@@ -907,12 +902,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".saturating_add_unsigned(2), 3);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.saturating_add_unsigned(100), ", stringify!($SelfT), "::MAX);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -954,12 +948,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(100", stringify!($SelfT), ".saturating_sub_unsigned(127), -27);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.saturating_sub_unsigned(100), ", stringify!($SelfT), "::MIN);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1030,7 +1023,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(10", stringify!($SelfT), ".saturating_mul(12), 120);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.saturating_mul(10), ", stringify!($SelfT), "::MAX);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.saturating_mul(10), ", stringify!($SelfT), "::MIN);")]
@@ -1089,7 +1081,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!((-4", stringify!($SelfT), ").saturating_pow(3), -64);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.saturating_pow(2), ", stringify!($SelfT), "::MAX);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.saturating_pow(3), ", stringify!($SelfT), "::MIN);")]
@@ -1135,12 +1126,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(100", stringify!($SelfT), ".wrapping_add_unsigned(27), 127);")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.wrapping_add_unsigned(2), ", stringify!($SelfT), "::MIN + 1);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline(always)]
@@ -1176,12 +1166,11 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(0", stringify!($SelfT), ".wrapping_sub_unsigned(127), -127);")]
         #[doc = concat!("assert_eq!((-2", stringify!($SelfT), ").wrapping_sub_unsigned(", stringify!($UnsignedT), "::MAX), -1);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline(always)]
@@ -1504,7 +1493,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_add(2), (7, false));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.overflowing_add(1), (", stringify!($SelfT), "::MIN, true));")]
         /// ```
@@ -1574,13 +1562,12 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".overflowing_add_unsigned(2), (3, false));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MIN).overflowing_add_unsigned(", stringify!($UnsignedT), "::MAX), (", stringify!($SelfT), "::MAX, false));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).overflowing_add_unsigned(3), (", stringify!($SelfT), "::MIN, true));")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1600,7 +1587,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_sub(2), (3, false));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.overflowing_sub(1), (", stringify!($SelfT), "::MAX, true));")]
         /// ```
@@ -1658,13 +1644,12 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".overflowing_sub_unsigned(2), (-1, false));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX).overflowing_sub_unsigned(", stringify!($UnsignedT), "::MAX), (", stringify!($SelfT), "::MIN, false));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MIN + 2).overflowing_sub_unsigned(3), (", stringify!($SelfT), "::MAX, true));")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1711,7 +1696,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_div(2), (2, false));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.overflowing_div(-1), (", stringify!($SelfT), "::MIN, true));")]
         /// ```
@@ -1774,7 +1758,6 @@ macro_rules! int_impl {
         /// Basic usage:
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_rem(2), (1, false));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.overflowing_rem(-1), (0, true));")]
         /// ```
@@ -2287,9 +2270,8 @@ macro_rules! int_impl {
         ///
         /// # Panics
         ///
-        /// When the number is negative, zero, or if the base is not at least 2; it
-        /// panics in debug mode and the return value is 0 in release
-        /// mode.
+        /// This function will panic if `self` is less than or equal to zero,
+        /// or if `base` is less then 2.
         ///
         /// # Examples
         ///
@@ -2302,27 +2284,16 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog(self, base: Self) -> u32 {
-            match self.checked_ilog(base) {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            assert!(base >= 2, "base of integer logarithm must be at least 2");
+            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
         ///
         /// # Panics
         ///
-        /// When the number is negative or zero it panics in debug mode and the return value
-        /// is 0 in release mode.
+        /// This function will panic if `self` is less than or equal to zero.
         ///
         /// # Examples
         ///
@@ -2335,27 +2306,15 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog2(self) -> u32 {
-            match self.checked_ilog2() {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            self.checked_ilog2().expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
         ///
         /// # Panics
         ///
-        /// When the number is negative or zero it panics in debug mode and the return value
-        /// is 0 in release mode.
+        /// This function will panic if `self` is less than or equal to zero.
         ///
         /// # Example
         ///
@@ -2368,19 +2327,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog10(self) -> u32 {
-            match self.checked_ilog10() {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            self.checked_ilog10().expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,
diff --git a/library/core/src/num/mod.rs b/library/core/src/num/mod.rs
index ab17aa0c8..311c5fa5b 100644
--- a/library/core/src/num/mod.rs
+++ b/library/core/src/num/mod.rs
@@ -3,7 +3,6 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use crate::ascii;
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::intrinsics;
 use crate::mem;
@@ -59,7 +58,6 @@ pub use wrapping::Wrapping;
 #[cfg(not(no_fp_fmt_parse))]
 pub use dec2flt::ParseFloatError;
 
-#[cfg(not(bootstrap))]
 #[cfg(not(no_fp_fmt_parse))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for ParseFloatError {
@@ -113,6 +111,9 @@ macro_rules! widening_impl {
         /// This returns the low-order (wrapping) bits and the high-order (overflow) bits
         /// of the result as two separate values, in that order.
         ///
+        /// If you also need to add a carry to the wide result, then you want
+        /// [`Self::carrying_mul`] instead.
+        ///
         /// # Examples
         ///
         /// Basic usage:
@@ -148,6 +149,8 @@ macro_rules! widening_impl {
         /// additional amount of overflow. This allows for chaining together multiple
         /// multiplications to create "big integers" which represent larger values.
         ///
+        /// If you don't need the `carry`, then you can use [`Self::widening_mul`] instead.
+        ///
         /// # Examples
         ///
         /// Basic usage:
@@ -167,6 +170,31 @@ macro_rules! widening_impl {
         )]
         /// ```
         ///
+        /// This is the core operation needed for scalar multiplication when
+        /// implementing it for wider-than-native types.
+        ///
+        /// ```
+        /// #![feature(bigint_helper_methods)]
+        /// fn scalar_mul_eq(little_endian_digits: &mut Vec<u16>, multiplicand: u16) {
+        ///     let mut carry = 0;
+        ///     for d in little_endian_digits.iter_mut() {
+        ///         (*d, carry) = d.carrying_mul(multiplicand, carry);
+        ///     }
+        ///     if carry != 0 {
+        ///         little_endian_digits.push(carry);
+        ///     }
+        /// }
+        ///
+        /// let mut v = vec![10, 20];
+        /// scalar_mul_eq(&mut v, 3);
+        /// assert_eq!(v, [30, 60]);
+        ///
+        /// assert_eq!(0x87654321_u64 * 0xFEED, 0x86D3D159E38D);
+        /// let mut v = vec![0x4321, 0x8765];
+        /// scalar_mul_eq(&mut v, 0xFEED);
+        /// assert_eq!(v, [0xE38D, 0xD159, 0x86D3]);
+        /// ```
+        ///
         /// If `carry` is zero, this is similar to [`overflowing_mul`](Self::overflowing_mul),
         /// except that it gives the value of the overflow instead of just whether one happened:
         ///
@@ -594,6 +622,38 @@ impl u8 {
         matches!(*self, b'0'..=b'9')
     }
 
+    /// Checks if the value is an ASCII octal digit:
+    /// U+0030 '0' ..= U+0037 '7'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(is_ascii_octdigit)]
+    ///
+    /// let uppercase_a = b'A';
+    /// let a = b'a';
+    /// let zero = b'0';
+    /// let seven = b'7';
+    /// let nine = b'9';
+    /// let percent = b'%';
+    /// let lf = b'\n';
+    ///
+    /// assert!(!uppercase_a.is_ascii_octdigit());
+    /// assert!(!a.is_ascii_octdigit());
+    /// assert!(zero.is_ascii_octdigit());
+    /// assert!(seven.is_ascii_octdigit());
+    /// assert!(!nine.is_ascii_octdigit());
+    /// assert!(!percent.is_ascii_octdigit());
+    /// assert!(!lf.is_ascii_octdigit());
+    /// ```
+    #[must_use]
+    #[unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[rustc_const_unstable(feature = "is_ascii_octdigit", issue = "101288")]
+    #[inline]
+    pub const fn is_ascii_octdigit(&self) -> bool {
+        matches!(*self, b'0'..=b'7')
+    }
+
     /// Checks if the value is an ASCII hexadecimal digit:
     ///
     /// - U+0030 '0' ..= U+0039 '9', or
@@ -948,8 +1008,8 @@ impl usize {
 /// assert_eq!(num.classify(), FpCategory::Normal);
 /// assert_eq!(inf.classify(), FpCategory::Infinite);
 /// assert_eq!(zero.classify(), FpCategory::Zero);
-/// assert_eq!(nan.classify(), FpCategory::Nan);
 /// assert_eq!(sub.classify(), FpCategory::Subnormal);
+/// assert_eq!(nan.classify(), FpCategory::Nan);
 /// ```
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs
index 532a09736..6b6f3417f 100644
--- a/library/core/src/num/nonzero.rs
+++ b/library/core/src/num/nonzero.rs
@@ -56,7 +56,10 @@ macro_rules! nonzero_integers {
                 pub const unsafe fn new_unchecked(n: $Int) -> Self {
                     // SAFETY: this is guaranteed to be safe by the caller.
                     unsafe {
-                        core::intrinsics::assert_unsafe_precondition!((n: $Int) => n != 0);
+                        core::intrinsics::assert_unsafe_precondition!(
+                            concat!(stringify!($Ty), "::new_unchecked requires a non-zero argument"),
+                            (n: $Int) => n != 0
+                        );
                         Self(n)
                     }
                 }
@@ -721,6 +724,160 @@ macro_rules! nonzero_signed_operations {
                     // SAFETY: absolute value of nonzero cannot yield zero values.
                     unsafe { $Uty::new_unchecked(self.get().unsigned_abs()) }
                 }
+
+                /// Returns `true` if `self` is negative and `false` if the
+                /// number is positive.
+                ///
+                /// # Example
+                ///
+                /// ```
+                /// #![feature(nonzero_negation_ops)]
+                ///
+                #[doc = concat!("# use std::num::", stringify!($Ty), ";")]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("let pos_five = ", stringify!($Ty), "::new(5)?;")]
+                #[doc = concat!("let neg_five = ", stringify!($Ty), "::new(-5)?;")]
+                ///
+                /// assert!(neg_five.is_negative());
+                /// assert!(!pos_five.is_negative());
+                /// # Some(())
+                /// # }
+                /// ```
+                #[must_use]
+                #[inline]
+                #[unstable(feature = "nonzero_negation_ops", issue = "102443")]
+                pub const fn is_negative(self) -> bool {
+                    self.get().is_negative()
+                }
+
+                /// Checked negation. Computes `-self`, returning `None` if `self == i32::MIN`.
+                ///
+                /// # Example
+                ///
+                /// ```
+                /// #![feature(nonzero_negation_ops)]
+                ///
+                #[doc = concat!("# use std::num::", stringify!($Ty), ";")]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("let pos_five = ", stringify!($Ty), "::new(5)?;")]
+                #[doc = concat!("let neg_five = ", stringify!($Ty), "::new(-5)?;")]
+                #[doc = concat!("let min = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MIN)?;")]
+                ///
+                /// assert_eq!(pos_five.checked_neg(), Some(neg_five));
+                /// assert_eq!(min.checked_neg(), None);
+                /// # Some(())
+                /// # }
+                /// ```
+                #[inline]
+                #[unstable(feature = "nonzero_negation_ops", issue = "102443")]
+                pub const fn checked_neg(self) -> Option<$Ty> {
+                    if let Some(result) = self.get().checked_neg() {
+                        // SAFETY: negation of nonzero cannot yield zero values.
+                        return Some(unsafe { $Ty::new_unchecked(result) });
+                    }
+                    None
+                }
+
+                /// Negates self, overflowing if this is equal to the minimum value.
+                ///
+                #[doc = concat!("See [`", stringify!($Int), "::overflowing_neg`]")]
+                /// for documentation on overflow behaviour.
+                ///
+                /// # Example
+                ///
+                /// ```
+                /// #![feature(nonzero_negation_ops)]
+                ///
+                #[doc = concat!("# use std::num::", stringify!($Ty), ";")]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("let pos_five = ", stringify!($Ty), "::new(5)?;")]
+                #[doc = concat!("let neg_five = ", stringify!($Ty), "::new(-5)?;")]
+                #[doc = concat!("let min = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MIN)?;")]
+                ///
+                /// assert_eq!(pos_five.overflowing_neg(), (neg_five, false));
+                /// assert_eq!(min.overflowing_neg(), (min, true));
+                /// # Some(())
+                /// # }
+                /// ```
+                #[inline]
+                #[unstable(feature = "nonzero_negation_ops", issue = "102443")]
+                pub const fn overflowing_neg(self) -> ($Ty, bool) {
+                    let (result, overflow) = self.get().overflowing_neg();
+                    // SAFETY: negation of nonzero cannot yield zero values.
+                    ((unsafe { $Ty::new_unchecked(result) }), overflow)
+                }
+
+                /// Saturating negation. Computes `-self`, returning `MAX` if
+                /// `self == i32::MIN` instead of overflowing.
+                ///
+                /// # Example
+                ///
+                /// ```
+                /// #![feature(nonzero_negation_ops)]
+                ///
+                #[doc = concat!("# use std::num::", stringify!($Ty), ";")]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("let pos_five = ", stringify!($Ty), "::new(5)?;")]
+                #[doc = concat!("let neg_five = ", stringify!($Ty), "::new(-5)?;")]
+                #[doc = concat!("let min = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MIN)?;")]
+                #[doc = concat!("let min_plus_one = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MIN + 1)?;")]
+                #[doc = concat!("let max = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MAX)?;")]
+                ///
+                /// assert_eq!(pos_five.saturating_neg(), neg_five);
+                /// assert_eq!(min.saturating_neg(), max);
+                /// assert_eq!(max.saturating_neg(), min_plus_one);
+                /// # Some(())
+                /// # }
+                /// ```
+                #[inline]
+                #[unstable(feature = "nonzero_negation_ops", issue = "102443")]
+                pub const fn saturating_neg(self) -> $Ty {
+                    if let Some(result) = self.checked_neg() {
+                        return result;
+                    }
+                    $Ty::MAX
+                }
+
+                /// Wrapping (modular) negation. Computes `-self`, wrapping around at the boundary
+                /// of the type.
+                ///
+                #[doc = concat!("See [`", stringify!($Int), "::wrapping_neg`]")]
+                /// for documentation on overflow behaviour.
+                ///
+                /// # Example
+                ///
+                /// ```
+                /// #![feature(nonzero_negation_ops)]
+                ///
+                #[doc = concat!("# use std::num::", stringify!($Ty), ";")]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("let pos_five = ", stringify!($Ty), "::new(5)?;")]
+                #[doc = concat!("let neg_five = ", stringify!($Ty), "::new(-5)?;")]
+                #[doc = concat!("let min = ", stringify!($Ty), "::new(",
+                                stringify!($Int), "::MIN)?;")]
+                ///
+                /// assert_eq!(pos_five.wrapping_neg(), neg_five);
+                /// assert_eq!(min.wrapping_neg(), min);
+                /// # Some(())
+                /// # }
+                /// ```
+                #[inline]
+                #[unstable(feature = "nonzero_negation_ops", issue = "102443")]
+                pub const fn wrapping_neg(self) -> $Ty {
+                    let result = self.get().wrapping_neg();
+                    // SAFETY: negation of nonzero cannot yield zero values.
+                    unsafe { $Ty::new_unchecked(result) }
+                }
             }
         )+
     }
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 46fd7f2d0..335cc5124 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -474,13 +474,12 @@ macro_rules! uint_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".checked_add_signed(2), Some(3));")]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".checked_add_signed(-2), None);")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).checked_add_signed(3), None);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -693,8 +692,7 @@ macro_rules! uint_impl {
         ///
         /// # Panics
         ///
-        /// When the number is zero, or if the base is not at least 2;
-        /// it panics in debug mode and the return value is 0 in release mode.
+        /// This function will panic if `self` is zero, or if `base` is less then 2.
         ///
         /// # Examples
         ///
@@ -707,27 +705,16 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog(self, base: Self) -> u32 {
-            match self.checked_ilog(base) {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            assert!(base >= 2, "base of integer logarithm must be at least 2");
+            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
         ///
         /// # Panics
         ///
-        /// When the number is zero it panics in debug mode and
-        /// the return value is 0 in release mode.
+        /// This function will panic if `self` is zero.
         ///
         /// # Examples
         ///
@@ -740,27 +727,15 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog2(self) -> u32 {
-            match self.checked_ilog2() {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            self.checked_ilog2().expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
         ///
         /// # Panics
         ///
-        /// When the number is zero it panics in debug mode and the
-        /// return value is 0 in release mode.
+        /// This function will panic if `self` is zero.
         ///
         /// # Example
         ///
@@ -773,19 +748,8 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline]
         #[track_caller]
-        #[rustc_inherit_overflow_checks]
-        #[allow(arithmetic_overflow)]
         pub const fn ilog10(self) -> u32 {
-            match self.checked_ilog10() {
-                Some(n) => n,
-                None => {
-                    // In debug builds, trigger a panic on None.
-                    // This should optimize completely out in release builds.
-                    let _ = Self::MAX + 1;
-
-                    0
-                },
-            }
+            self.checked_ilog10().expect("argument of integer logarithm must be positive")
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,
@@ -1026,7 +990,7 @@ macro_rules! uint_impl {
             // squaring the base afterwards is not necessary and may cause a
             // needless overflow.
 
-            Some(try_opt!(acc.checked_mul(base)))
+            acc.checked_mul(base)
         }
 
         /// Saturating integer addition. Computes `self + rhs`, saturating at
@@ -1057,13 +1021,12 @@ macro_rules! uint_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".saturating_add_signed(2), 3);")]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".saturating_add_signed(-2), 0);")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).saturating_add_signed(4), ", stringify!($SelfT), "::MAX);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1198,13 +1161,12 @@ macro_rules! uint_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".wrapping_add_signed(2), 3);")]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".wrapping_add_signed(-2), ", stringify!($SelfT), "::MAX);")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).wrapping_add_signed(4), 1);")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1494,7 +1456,6 @@ macro_rules! uint_impl {
         /// Basic usage
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_add(2), (7, false));")]
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.overflowing_add(1), (0, true));")]
         /// ```
@@ -1508,37 +1469,42 @@ macro_rules! uint_impl {
             (a as Self, b)
         }
 
-        /// Calculates `self + rhs + carry` without the ability to overflow.
+        /// Calculates `self` + `rhs` + `carry` and returns a tuple containing
+        /// the sum and the output carry.
         ///
-        /// Performs "ternary addition" which takes in an extra bit to add, and may return an
-        /// additional bit of overflow. This allows for chaining together multiple additions
-        /// to create "big integers" which represent larger values.
+        /// Performs "ternary addition" of two integer operands and a carry-in
+        /// bit, and returns an output integer and a carry-out bit. This allows
+        /// chaining together multiple additions to create a wider addition, and
+        /// can be useful for bignum addition.
         ///
         #[doc = concat!("This can be thought of as a ", stringify!($BITS), "-bit \"full adder\", in the electronics sense.")]
         ///
-        /// # Examples
+        /// If the input carry is false, this method is equivalent to
+        /// [`overflowing_add`](Self::overflowing_add), and the output carry is
+        /// equal to the overflow flag. Note that although carry and overflow
+        /// flags are similar for unsigned integers, they are different for
+        /// signed integers.
         ///
-        /// Basic usage
+        /// # Examples
         ///
         /// ```
         /// #![feature(bigint_helper_methods)]
-        #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, false), (7, false));")]
-        #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, true), (8, false));")]
-        #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, false), (0, true));")]
-        #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(0, true), (0, true));")]
-        #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, true), (1, true));")]
-        #[doc = concat!("assert_eq!(",
-            stringify!($SelfT), "::MAX.carrying_add(", stringify!($SelfT), "::MAX, true), ",
-            "(", stringify!($SelfT), "::MAX, true));"
-        )]
-        /// ```
         ///
-        /// If `carry` is false, this method is equivalent to [`overflowing_add`](Self::overflowing_add):
+        #[doc = concat!("//    3  MAX    (a = 3 × 2^", stringify!($BITS), " + 2^", stringify!($BITS), " - 1)")]
+        #[doc = concat!("// +  5    7    (b = 5 × 2^", stringify!($BITS), " + 7)")]
+        /// // ---------
+        #[doc = concat!("//    9    6    (sum = 9 × 2^", stringify!($BITS), " + 6)")]
         ///
-        /// ```
-        /// #![feature(bigint_helper_methods)]
-        #[doc = concat!("assert_eq!(5_", stringify!($SelfT), ".carrying_add(2, false), 5_", stringify!($SelfT), ".overflowing_add(2));")]
-        #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, false), ", stringify!($SelfT), "::MAX.overflowing_add(1));")]
+        #[doc = concat!("let (a1, a0): (", stringify!($SelfT), ", ", stringify!($SelfT), ") = (3, ", stringify!($SelfT), "::MAX);")]
+        #[doc = concat!("let (b1, b0): (", stringify!($SelfT), ", ", stringify!($SelfT), ") = (5, 7);")]
+        /// let carry0 = false;
+        ///
+        /// let (sum0, carry1) = a0.carrying_add(b0, carry0);
+        /// assert_eq!(carry1, true);
+        /// let (sum1, carry2) = a1.carrying_add(b1, carry1);
+        /// assert_eq!(carry2, false);
+        ///
+        /// assert_eq!((sum1, sum0), (9, 6));
         /// ```
         #[unstable(feature = "bigint_helper_methods", issue = "85532")]
         #[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
@@ -1564,13 +1530,12 @@ macro_rules! uint_impl {
         /// Basic usage:
         ///
         /// ```
-        /// # #![feature(mixed_integer_ops)]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".overflowing_add_signed(2), (3, false));")]
         #[doc = concat!("assert_eq!(1", stringify!($SelfT), ".overflowing_add_signed(-2), (", stringify!($SelfT), "::MAX, true));")]
         #[doc = concat!("assert_eq!((", stringify!($SelfT), "::MAX - 2).overflowing_add_signed(4), (1, true));")]
         /// ```
-        #[unstable(feature = "mixed_integer_ops", issue = "87840")]
-        #[rustc_const_unstable(feature = "mixed_integer_ops", issue = "87840")]
+        #[stable(feature = "mixed_integer_ops", since = "1.66.0")]
+        #[rustc_const_stable(feature = "mixed_integer_ops", since = "1.66.0")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
@@ -1590,7 +1555,6 @@ macro_rules! uint_impl {
         /// Basic usage
         ///
         /// ```
-        ///
         #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".overflowing_sub(2), (3, false));")]
         #[doc = concat!("assert_eq!(0", stringify!($SelfT), ".overflowing_sub(1), (", stringify!($SelfT), "::MAX, true));")]
         /// ```
@@ -1604,22 +1568,35 @@ macro_rules! uint_impl {
             (a as Self, b)
         }
 
-        /// Calculates `self - rhs - borrow` without the ability to overflow.
+        /// Calculates `self` &minus; `rhs` &minus; `borrow` and returns a tuple
+        /// containing the difference and the output borrow.
         ///
-        /// Performs "ternary subtraction" which takes in an extra bit to subtract, and may return
-        /// an additional bit of overflow. This allows for chaining together multiple subtractions
-        /// to create "big integers" which represent larger values.
+        /// Performs "ternary subtraction" by subtracting both an integer
+        /// operand and a borrow-in bit from `self`, and returns an output
+        /// integer and a borrow-out bit. This allows chaining together multiple
+        /// subtractions to create a wider subtraction, and can be useful for
+        /// bignum subtraction.
         ///
         /// # Examples
         ///
-        /// Basic usage
-        ///
         /// ```
         /// #![feature(bigint_helper_methods)]
-        #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, false), (3, false));")]
-        #[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, true), (2, false));")]
-        #[doc = concat!("assert_eq!(0", stringify!($SelfT), ".borrowing_sub(1, false), (", stringify!($SelfT), "::MAX, true));")]
-        #[doc = concat!("assert_eq!(0", stringify!($SelfT), ".borrowing_sub(1, true), (", stringify!($SelfT), "::MAX - 1, true));")]
+        ///
+        #[doc = concat!("//    9    6    (a = 9 × 2^", stringify!($BITS), " + 6)")]
+        #[doc = concat!("// -  5    7    (b = 5 × 2^", stringify!($BITS), " + 7)")]
+        /// // ---------
+        #[doc = concat!("//    3  MAX    (diff = 3 × 2^", stringify!($BITS), " + 2^", stringify!($BITS), " - 1)")]
+        ///
+        #[doc = concat!("let (a1, a0): (", stringify!($SelfT), ", ", stringify!($SelfT), ") = (9, 6);")]
+        #[doc = concat!("let (b1, b0): (", stringify!($SelfT), ", ", stringify!($SelfT), ") = (5, 7);")]
+        /// let borrow0 = false;
+        ///
+        /// let (diff0, borrow1) = a0.borrowing_sub(b0, borrow0);
+        /// assert_eq!(borrow1, true);
+        /// let (diff1, borrow2) = a1.borrowing_sub(b1, borrow1);
+        /// assert_eq!(borrow2, false);
+        ///
+        #[doc = concat!("assert_eq!((diff1, diff0), (3, ", stringify!($SelfT), "::MAX));")]
         /// ```
         #[unstable(feature = "bigint_helper_methods", issue = "85532")]
         #[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
diff --git a/library/core/src/ops/arith.rs b/library/core/src/ops/arith.rs
index e367be8c1..75c52d3ec 100644
--- a/library/core/src/ops/arith.rs
+++ b/library/core/src/ops/arith.rs
@@ -65,38 +65,15 @@
 /// ```
 #[lang = "add"]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(
-    bootstrap,
-    rustc_on_unimplemented(
-        on(
-            all(_Self = "{integer}", Rhs = "{float}"),
-            message = "cannot add a float to an integer",
-        ),
-        on(
-            all(_Self = "{float}", Rhs = "{integer}"),
-            message = "cannot add an integer to a float",
-        ),
-        message = "cannot add `{Rhs}` to `{Self}`",
-        label = "no implementation for `{Self} + {Rhs}`"
-    )
-)]
-#[cfg_attr(
-    not(bootstrap),
-    rustc_on_unimplemented(
-        on(
-            all(_Self = "{integer}", Rhs = "{float}"),
-            message = "cannot add a float to an integer",
-        ),
-        on(
-            all(_Self = "{float}", Rhs = "{integer}"),
-            message = "cannot add an integer to a float",
-        ),
-        message = "cannot add `{Rhs}` to `{Self}`",
-        label = "no implementation for `{Self} + {Rhs}`",
-        append_const_msg,
-    )
+#[rustc_on_unimplemented(
+    on(all(_Self = "{integer}", Rhs = "{float}"), message = "cannot add a float to an integer",),
+    on(all(_Self = "{float}", Rhs = "{integer}"), message = "cannot add an integer to a float",),
+    message = "cannot add `{Rhs}` to `{Self}`",
+    label = "no implementation for `{Self} + {Rhs}`",
+    append_const_msg
 )]
 #[doc(alias = "+")]
+#[const_trait]
 pub trait Add<Rhs = Self> {
     /// The resulting type after applying the `+` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -201,9 +178,11 @@ add_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
     message = "cannot subtract `{Rhs}` from `{Self}`",
-    label = "no implementation for `{Self} - {Rhs}`"
+    label = "no implementation for `{Self} - {Rhs}`",
+    append_const_msg
 )]
 #[doc(alias = "-")]
+#[const_trait]
 pub trait Sub<Rhs = Self> {
     /// The resulting type after applying the `-` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -333,6 +312,7 @@ sub_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
     label = "no implementation for `{Self} * {Rhs}`"
 )]
 #[doc(alias = "*")]
+#[const_trait]
 pub trait Mul<Rhs = Self> {
     /// The resulting type after applying the `*` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -466,6 +446,7 @@ mul_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
     label = "no implementation for `{Self} / {Rhs}`"
 )]
 #[doc(alias = "/")]
+#[const_trait]
 pub trait Div<Rhs = Self> {
     /// The resulting type after applying the `/` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -568,6 +549,7 @@ div_impl_float! { f32 f64 }
     label = "no implementation for `{Self} % {Rhs}`"
 )]
 #[doc(alias = "%")]
+#[const_trait]
 pub trait Rem<Rhs = Self> {
     /// The resulting type after applying the `%` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -682,6 +664,7 @@ rem_impl_float! { f32 f64 }
 #[lang = "neg"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(alias = "-")]
+#[const_trait]
 pub trait Neg {
     /// The resulting type after applying the `-` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -755,6 +738,7 @@ neg_impl! { isize i8 i16 i32 i64 i128 f32 f64 }
 )]
 #[doc(alias = "+")]
 #[doc(alias = "+=")]
+#[const_trait]
 pub trait AddAssign<Rhs = Self> {
     /// Performs the `+=` operation.
     ///
@@ -822,6 +806,7 @@ add_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 )]
 #[doc(alias = "-")]
 #[doc(alias = "-=")]
+#[const_trait]
 pub trait SubAssign<Rhs = Self> {
     /// Performs the `-=` operation.
     ///
@@ -880,6 +865,7 @@ sub_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 )]
 #[doc(alias = "*")]
 #[doc(alias = "*=")]
+#[const_trait]
 pub trait MulAssign<Rhs = Self> {
     /// Performs the `*=` operation.
     ///
@@ -938,6 +924,7 @@ mul_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 )]
 #[doc(alias = "/")]
 #[doc(alias = "/=")]
+#[const_trait]
 pub trait DivAssign<Rhs = Self> {
     /// Performs the `/=` operation.
     ///
@@ -999,6 +986,7 @@ div_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 )]
 #[doc(alias = "%")]
 #[doc(alias = "%=")]
+#[const_trait]
 pub trait RemAssign<Rhs = Self> {
     /// Performs the `%=` operation.
     ///
diff --git a/library/core/src/ops/bit.rs b/library/core/src/ops/bit.rs
index 7c664226f..327009801 100644
--- a/library/core/src/ops/bit.rs
+++ b/library/core/src/ops/bit.rs
@@ -31,6 +31,7 @@
 #[lang = "not"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(alias = "!")]
+#[const_trait]
 pub trait Not {
     /// The resulting type after applying the `!` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -143,6 +144,7 @@ impl const Not for ! {
     message = "no implementation for `{Self} & {Rhs}`",
     label = "no implementation for `{Self} & {Rhs}`"
 )]
+#[const_trait]
 pub trait BitAnd<Rhs = Self> {
     /// The resulting type after applying the `&` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -244,6 +246,7 @@ bitand_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} | {Rhs}`",
     label = "no implementation for `{Self} | {Rhs}`"
 )]
+#[const_trait]
 pub trait BitOr<Rhs = Self> {
     /// The resulting type after applying the `|` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -345,6 +348,7 @@ bitor_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} ^ {Rhs}`",
     label = "no implementation for `{Self} ^ {Rhs}`"
 )]
+#[const_trait]
 pub trait BitXor<Rhs = Self> {
     /// The resulting type after applying the `^` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -445,6 +449,7 @@ bitxor_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} << {Rhs}`",
     label = "no implementation for `{Self} << {Rhs}`"
 )]
+#[const_trait]
 pub trait Shl<Rhs = Self> {
     /// The resulting type after applying the `<<` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -564,6 +569,7 @@ shl_impl_all! { u8 u16 u32 u64 u128 usize i8 i16 i32 i64 isize i128 }
     message = "no implementation for `{Self} >> {Rhs}`",
     label = "no implementation for `{Self} >> {Rhs}`"
 )]
+#[const_trait]
 pub trait Shr<Rhs = Self> {
     /// The resulting type after applying the `>>` operator.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -692,6 +698,7 @@ shr_impl_all! { u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize }
     message = "no implementation for `{Self} &= {Rhs}`",
     label = "no implementation for `{Self} &= {Rhs}`"
 )]
+#[const_trait]
 pub trait BitAndAssign<Rhs = Self> {
     /// Performs the `&=` operation.
     ///
@@ -764,6 +771,7 @@ bitand_assign_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} |= {Rhs}`",
     label = "no implementation for `{Self} |= {Rhs}`"
 )]
+#[const_trait]
 pub trait BitOrAssign<Rhs = Self> {
     /// Performs the `|=` operation.
     ///
@@ -836,6 +844,7 @@ bitor_assign_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} ^= {Rhs}`",
     label = "no implementation for `{Self} ^= {Rhs}`"
 )]
+#[const_trait]
 pub trait BitXorAssign<Rhs = Self> {
     /// Performs the `^=` operation.
     ///
@@ -906,6 +915,7 @@ bitxor_assign_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
     message = "no implementation for `{Self} <<= {Rhs}`",
     label = "no implementation for `{Self} <<= {Rhs}`"
 )]
+#[const_trait]
 pub trait ShlAssign<Rhs = Self> {
     /// Performs the `<<=` operation.
     ///
@@ -989,6 +999,7 @@ shl_assign_impl_all! { u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize }
     message = "no implementation for `{Self} >>= {Rhs}`",
     label = "no implementation for `{Self} >>= {Rhs}`"
 )]
+#[const_trait]
 pub trait ShrAssign<Rhs = Self> {
     /// Performs the `>>=` operation.
     ///
diff --git a/library/core/src/ops/control_flow.rs b/library/core/src/ops/control_flow.rs
index b1f5559dc..72ebe653c 100644
--- a/library/core/src/ops/control_flow.rs
+++ b/library/core/src/ops/control_flow.rs
@@ -95,7 +95,8 @@ pub enum ControlFlow<B, C = ()> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<B, C> ops::Try for ControlFlow<B, C> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<B, C> const ops::Try for ControlFlow<B, C> {
     type Output = C;
     type Residual = ControlFlow<B, convert::Infallible>;
 
@@ -114,7 +115,8 @@ impl<B, C> ops::Try for ControlFlow<B, C> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<B, C> ops::FromResidual for ControlFlow<B, C> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<B, C> const ops::FromResidual for ControlFlow<B, C> {
     #[inline]
     fn from_residual(residual: ControlFlow<B, convert::Infallible>) -> Self {
         match residual {
@@ -124,7 +126,8 @@ impl<B, C> ops::FromResidual for ControlFlow<B, C> {
 }
 
 #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
-impl<B, C> ops::Residual<C> for ControlFlow<B, convert::Infallible> {
+#[rustc_const_unstable(feature = "const_try", issue = "74935")]
+impl<B, C> const ops::Residual<C> for ControlFlow<B, convert::Infallible> {
     type TryType = ControlFlow<B, C>;
 }
 
diff --git a/library/core/src/ops/deref.rs b/library/core/src/ops/deref.rs
index d68932402..4f4c99c4a 100644
--- a/library/core/src/ops/deref.rs
+++ b/library/core/src/ops/deref.rs
@@ -61,6 +61,7 @@
 #[doc(alias = "&*")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Deref"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Deref {
     /// The resulting type after dereferencing.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -169,6 +170,7 @@ impl<T: ?Sized> const Deref for &mut T {
 #[lang = "deref_mut"]
 #[doc(alias = "*")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait DerefMut: Deref {
     /// Mutably dereferences the value.
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/core/src/ops/drop.rs b/library/core/src/ops/drop.rs
index de9ddb852..a2c3d978c 100644
--- a/library/core/src/ops/drop.rs
+++ b/library/core/src/ops/drop.rs
@@ -134,6 +134,7 @@
 /// these types cannot have destructors.
 #[lang = "drop"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[const_trait]
 pub trait Drop {
     /// Executes the destructor for this type.
     ///
diff --git a/library/core/src/ops/function.rs b/library/core/src/ops/function.rs
index 8fdf22cf6..2e0a752c8 100644
--- a/library/core/src/ops/function.rs
+++ b/library/core/src/ops/function.rs
@@ -71,6 +71,7 @@
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Fn<Args>: FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -158,6 +159,7 @@ pub trait Fn<Args>: FnMut<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait FnMut<Args>: FnOnce<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -237,6 +239,7 @@ pub trait FnMut<Args>: FnOnce<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait FnOnce<Args> {
     /// The returned type after the call operator is used.
     #[lang = "fn_once_output"]
diff --git a/library/core/src/ops/generator.rs b/library/core/src/ops/generator.rs
index 3ebd6f8cd..fee4beb1e 100644
--- a/library/core/src/ops/generator.rs
+++ b/library/core/src/ops/generator.rs
@@ -83,7 +83,6 @@ pub trait Generator<R = ()> {
     /// `return` statement or implicitly as the last expression of a generator
     /// literal. For example futures would use this as `Result<T, E>` as it
     /// represents a completed future.
-    #[cfg_attr(bootstrap, lang = "generator_return")]
     type Return;
 
     /// Resumes the execution of this generator.
diff --git a/library/core/src/ops/index.rs b/library/core/src/ops/index.rs
index e2e569cb7..dd4e3ac1c 100644
--- a/library/core/src/ops/index.rs
+++ b/library/core/src/ops/index.rs
@@ -55,6 +55,7 @@
 #[doc(alias = "]")]
 #[doc(alias = "[")]
 #[doc(alias = "[]")]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Index<Idx: ?Sized> {
     /// The returned type after indexing.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -163,6 +164,7 @@ see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#ind
 #[doc(alias = "[")]
 #[doc(alias = "]")]
 #[doc(alias = "[]")]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
     /// Performs the mutable indexing (`container[index]`) operation.
     ///
diff --git a/library/core/src/ops/index_range.rs b/library/core/src/ops/index_range.rs
new file mode 100644
index 000000000..3e06776d2
--- /dev/null
+++ b/library/core/src/ops/index_range.rs
@@ -0,0 +1,171 @@
+use crate::intrinsics::{assert_unsafe_precondition, unchecked_add, unchecked_sub};
+use crate::iter::{FusedIterator, TrustedLen};
+
+/// Like a `Range<usize>`, but with a safety invariant that `start <= end`.
+///
+/// This means that `end - start` cannot overflow, allowing some μoptimizations.
+///
+/// (Normal `Range` code needs to handle degenerate ranges like `10..0`,
+///  which takes extra checks compared to only handling the canonical form.)
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) struct IndexRange {
+    start: usize,
+    end: usize,
+}
+
+impl IndexRange {
+    /// # Safety
+    /// - `start <= end`
+    #[inline]
+    pub const unsafe fn new_unchecked(start: usize, end: usize) -> Self {
+        // SAFETY: comparisons on usize are pure
+        unsafe {
+            assert_unsafe_precondition!(
+               "IndexRange::new_unchecked requires `start <= end`",
+                (start: usize, end: usize) => start <= end
+            )
+        };
+        IndexRange { start, end }
+    }
+
+    #[inline]
+    pub const fn zero_to(end: usize) -> Self {
+        IndexRange { start: 0, end }
+    }
+
+    #[inline]
+    pub const fn start(&self) -> usize {
+        self.start
+    }
+
+    #[inline]
+    pub const fn end(&self) -> usize {
+        self.end
+    }
+
+    #[inline]
+    pub const fn len(&self) -> usize {
+        // SAFETY: By invariant, this cannot wrap
+        unsafe { unchecked_sub(self.end, self.start) }
+    }
+
+    /// # Safety
+    /// - Can only be called when `start < end`, aka when `len > 0`.
+    #[inline]
+    unsafe fn next_unchecked(&mut self) -> usize {
+        debug_assert!(self.start < self.end);
+
+        let value = self.start;
+        // SAFETY: The range isn't empty, so this cannot overflow
+        self.start = unsafe { unchecked_add(value, 1) };
+        value
+    }
+
+    /// # Safety
+    /// - Can only be called when `start < end`, aka when `len > 0`.
+    #[inline]
+    unsafe fn next_back_unchecked(&mut self) -> usize {
+        debug_assert!(self.start < self.end);
+
+        // SAFETY: The range isn't empty, so this cannot overflow
+        let value = unsafe { unchecked_sub(self.end, 1) };
+        self.end = value;
+        value
+    }
+
+    /// Removes the first `n` items from this range, returning them as an `IndexRange`.
+    /// If there are fewer than `n`, then the whole range is returned and
+    /// `self` is left empty.
+    ///
+    /// This is designed to help implement `Iterator::advance_by`.
+    #[inline]
+    pub fn take_prefix(&mut self, n: usize) -> Self {
+        let mid = if n <= self.len() {
+            // SAFETY: We just checked that this will be between start and end,
+            // and thus the addition cannot overflow.
+            unsafe { unchecked_add(self.start, n) }
+        } else {
+            self.end
+        };
+        let prefix = Self { start: self.start, end: mid };
+        self.start = mid;
+        prefix
+    }
+
+    /// Removes the last `n` items from this range, returning them as an `IndexRange`.
+    /// If there are fewer than `n`, then the whole range is returned and
+    /// `self` is left empty.
+    ///
+    /// This is designed to help implement `Iterator::advance_back_by`.
+    #[inline]
+    pub fn take_suffix(&mut self, n: usize) -> Self {
+        let mid = if n <= self.len() {
+            // SAFETY: We just checked that this will be between start and end,
+            // and thus the addition cannot overflow.
+            unsafe { unchecked_sub(self.end, n) }
+        } else {
+            self.start
+        };
+        let suffix = Self { start: mid, end: self.end };
+        self.end = mid;
+        suffix
+    }
+}
+
+impl Iterator for IndexRange {
+    type Item = usize;
+
+    #[inline]
+    fn next(&mut self) -> Option<usize> {
+        if self.len() > 0 {
+            // SAFETY: We just checked that the range is non-empty
+            unsafe { Some(self.next_unchecked()) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len();
+        (len, Some(len))
+    }
+
+    #[inline]
+    fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+        let original_len = self.len();
+        self.take_prefix(n);
+        if n > original_len { Err(original_len) } else { Ok(()) }
+    }
+}
+
+impl DoubleEndedIterator for IndexRange {
+    #[inline]
+    fn next_back(&mut self) -> Option<usize> {
+        if self.len() > 0 {
+            // SAFETY: We just checked that the range is non-empty
+            unsafe { Some(self.next_back_unchecked()) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        let original_len = self.len();
+        self.take_suffix(n);
+        if n > original_len { Err(original_len) } else { Ok(()) }
+    }
+}
+
+impl ExactSizeIterator for IndexRange {
+    #[inline]
+    fn len(&self) -> usize {
+        self.len()
+    }
+}
+
+// SAFETY: Because we only deal in `usize`, our `len` is always perfect.
+unsafe impl TrustedLen for IndexRange {}
+
+impl FusedIterator for IndexRange {}
diff --git a/library/core/src/ops/mod.rs b/library/core/src/ops/mod.rs
index 31c1a1d09..a5e5b13b3 100644
--- a/library/core/src/ops/mod.rs
+++ b/library/core/src/ops/mod.rs
@@ -146,6 +146,7 @@ mod drop;
 mod function;
 mod generator;
 mod index;
+mod index_range;
 mod range;
 mod try_trait;
 mod unsize;
@@ -178,6 +179,8 @@ pub use self::index::{Index, IndexMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};
 
+pub(crate) use self::index_range::IndexRange;
+
 #[stable(feature = "inclusive_range", since = "1.26.0")]
 pub use self::range::{Bound, RangeBounds, RangeInclusive, RangeToInclusive};
 
diff --git a/library/core/src/ops/try_trait.rs b/library/core/src/ops/try_trait.rs
index 10f041344..84a690468 100644
--- a/library/core/src/ops/try_trait.rs
+++ b/library/core/src/ops/try_trait.rs
@@ -128,7 +128,8 @@ use crate::ops::ControlFlow;
 )]
 #[doc(alias = "?")]
 #[lang = "Try"]
-pub trait Try: FromResidual {
+#[const_trait]
+pub trait Try: ~const FromResidual {
     /// The type of the value produced by `?` when *not* short-circuiting.
     #[unstable(feature = "try_trait_v2", issue = "84277")]
     type Output;
@@ -222,7 +223,7 @@ pub trait Try: FromResidual {
 /// Every `Try` type needs to be recreatable from its own associated
 /// `Residual` type, but can also have additional `FromResidual` implementations
 /// to support interconversion with other `Try` types.
-#[cfg_attr(not(bootstrap), rustc_on_unimplemented(
+#[rustc_on_unimplemented(
     on(
         all(
             from_desugaring = "QuestionMark",
@@ -301,89 +302,10 @@ pub trait Try: FromResidual {
         label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`",
         parent_label = "this function should return `Result` or `Option` to accept `?`"
     ),
-))]
-#[cfg_attr(bootstrap, rustc_on_unimplemented(
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::result::Result<T, E>",
-            R = "std::option::Option<std::convert::Infallible>"
-        ),
-        message = "the `?` operator can only be used on `Result`s, not `Option`s, \
-            in {ItemContext} that returns `Result`",
-        label = "use `.ok_or(...)?` to provide an error compatible with `{Self}`",
-        enclosing_scope = "this function returns a `Result`"
-    ),
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::result::Result<T, E>",
-        ),
-        // There's a special error message in the trait selection code for
-        // `From` in `?`, so this is not shown for result-in-result errors,
-        // and thus it can be phrased more strongly than `ControlFlow`'s.
-        message = "the `?` operator can only be used on `Result`s \
-            in {ItemContext} that returns `Result`",
-        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
-        enclosing_scope = "this function returns a `Result`"
-    ),
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::option::Option<T>",
-            R = "std::result::Result<T, E>",
-        ),
-        message = "the `?` operator can only be used on `Option`s, not `Result`s, \
-            in {ItemContext} that returns `Option`",
-        label = "use `.ok()?` if you want to discard the `{R}` error information",
-        enclosing_scope = "this function returns an `Option`"
-    ),
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::option::Option<T>",
-        ),
-        // `Option`-in-`Option` always works, as there's only one possible
-        // residual, so this can also be phrased strongly.
-        message = "the `?` operator can only be used on `Option`s \
-            in {ItemContext} that returns `Option`",
-        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
-        enclosing_scope = "this function returns an `Option`"
-    ),
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::ops::ControlFlow<B, C>",
-            R = "std::ops::ControlFlow<B, C>",
-        ),
-        message = "the `?` operator in {ItemContext} that returns `ControlFlow<B, _>` \
-            can only be used on other `ControlFlow<B, _>`s (with the same Break type)",
-        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
-        enclosing_scope = "this function returns a `ControlFlow`",
-        note = "unlike `Result`, there's no `From`-conversion performed for `ControlFlow`"
-    ),
-    on(
-        all(
-            from_desugaring = "QuestionMark",
-            _Self = "std::ops::ControlFlow<B, C>",
-            // `R` is not a `ControlFlow`, as that case was matched previously
-        ),
-        message = "the `?` operator can only be used on `ControlFlow`s \
-            in {ItemContext} that returns `ControlFlow`",
-        label = "this `?` produces `{R}`, which is incompatible with `{Self}`",
-        enclosing_scope = "this function returns a `ControlFlow`",
-    ),
-    on(
-        all(from_desugaring = "QuestionMark"),
-        message = "the `?` operator can only be used in {ItemContext} \
-                    that returns `Result` or `Option` \
-                    (or another type that implements `{FromResidual}`)",
-        label = "cannot use the `?` operator in {ItemContext} that returns `{Self}`",
-        enclosing_scope = "this function should return `Result` or `Option` to accept `?`"
-    ),
-))]
+)]
 #[rustc_diagnostic_item = "FromResidual"]
 #[unstable(feature = "try_trait_v2", issue = "84277")]
+#[const_trait]
 pub trait FromResidual<R = <Self as Try>::Residual> {
     /// Constructs the type from a compatible `Residual` type.
     ///
@@ -436,10 +358,11 @@ where
 /// and in the other direction,
 /// `<Result<Infallible, E> as Residual<T>>::TryType = Result<T, E>`.
 #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
+#[const_trait]
 pub trait Residual<O> {
     /// The "return" type of this meta-function.
     #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
-    type TryType: Try<Output = O, Residual = Self>;
+    type TryType: ~const Try<Output = O, Residual = Self>;
 }
 
 #[unstable(feature = "pub_crate_should_not_need_unstable_attr", issue = "none")]
@@ -456,16 +379,19 @@ pub(crate) type ChangeOutputType<T, V> = <<T as Try>::Residual as Residual<V>>::
 pub(crate) struct NeverShortCircuit<T>(pub T);
 
 impl<T> NeverShortCircuit<T> {
-    /// Wrap a binary `FnMut` to return its result wrapped in a `NeverShortCircuit`.
+    /// Implementation for building `ConstFnMutClosure` for wrapping the output of a ~const FnMut in a `NeverShortCircuit`.
     #[inline]
-    pub fn wrap_mut_2<A, B>(mut f: impl FnMut(A, B) -> T) -> impl FnMut(A, B) -> Self {
-        move |a, b| NeverShortCircuit(f(a, b))
+    pub const fn wrap_mut_2_imp<A, B, F: ~const FnMut(A, B) -> T>(
+        f: &mut F,
+        (a, b): (A, B),
+    ) -> NeverShortCircuit<T> {
+        NeverShortCircuit(f(a, b))
     }
 }
 
 pub(crate) enum NeverShortCircuitResidual {}
 
-impl<T> Try for NeverShortCircuit<T> {
+impl<T> const Try for NeverShortCircuit<T> {
     type Output = T;
     type Residual = NeverShortCircuitResidual;
 
@@ -480,14 +406,14 @@ impl<T> Try for NeverShortCircuit<T> {
     }
 }
 
-impl<T> FromResidual for NeverShortCircuit<T> {
+impl<T> const FromResidual for NeverShortCircuit<T> {
     #[inline]
     fn from_residual(never: NeverShortCircuitResidual) -> Self {
         match never {}
     }
 }
 
-impl<T> Residual<T> for NeverShortCircuitResidual {
+impl<T> const Residual<T> for NeverShortCircuitResidual {
     type TryType = NeverShortCircuit<T>;
 }
 
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index 934175863..f284b4359 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -559,22 +559,25 @@ impl<T> Option<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(is_some_with)]
+    /// #![feature(is_some_and)]
     ///
     /// let x: Option<u32> = Some(2);
-    /// assert_eq!(x.is_some_and(|&x| x > 1), true);
+    /// assert_eq!(x.is_some_and(|x| x > 1), true);
     ///
     /// let x: Option<u32> = Some(0);
-    /// assert_eq!(x.is_some_and(|&x| x > 1), false);
+    /// assert_eq!(x.is_some_and(|x| x > 1), false);
     ///
     /// let x: Option<u32> = None;
-    /// assert_eq!(x.is_some_and(|&x| x > 1), false);
+    /// assert_eq!(x.is_some_and(|x| x > 1), false);
     /// ```
     #[must_use]
     #[inline]
-    #[unstable(feature = "is_some_with", issue = "93050")]
-    pub fn is_some_and(&self, f: impl FnOnce(&T) -> bool) -> bool {
-        matches!(self, Some(x) if f(x))
+    #[unstable(feature = "is_some_and", issue = "93050")]
+    pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool {
+        match self {
+            None => false,
+            Some(x) => f(x),
+        }
     }
 
     /// Returns `true` if the option is a [`None`] value.
@@ -834,19 +837,12 @@ impl<T> Option<T> {
     ///
     /// # Examples
     ///
-    /// Converts a string to an integer, turning poorly-formed strings
-    /// into 0 (the default value for integers). [`parse`] converts
-    /// a string to any other type that implements [`FromStr`], returning
-    /// [`None`] on error.
-    ///
     /// ```
-    /// let good_year_from_input = "1909";
-    /// let bad_year_from_input = "190blarg";
-    /// let good_year = good_year_from_input.parse().ok().unwrap_or_default();
-    /// let bad_year = bad_year_from_input.parse().ok().unwrap_or_default();
+    /// let x: Option<u32> = None;
+    /// let y: Option<u32> = Some(12);
     ///
-    /// assert_eq!(1909, good_year);
-    /// assert_eq!(0, bad_year);
+    /// assert_eq!(x.unwrap_or_default(), 0);
+    /// assert_eq!(y.unwrap_or_default(), 12);
     /// ```
     ///
     /// [default value]: Default::default
@@ -1717,8 +1713,6 @@ impl<T, U> Option<(T, U)> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(unzip_option)]
-    ///
     /// let x = Some((1, "hi"));
     /// let y = None::<(u8, u32)>;
     ///
@@ -1726,8 +1720,13 @@ impl<T, U> Option<(T, U)> {
     /// assert_eq!(y.unzip(), (None, None));
     /// ```
     #[inline]
-    #[unstable(feature = "unzip_option", issue = "87800", reason = "recently added")]
-    pub const fn unzip(self) -> (Option<T>, Option<U>) {
+    #[stable(feature = "unzip_option", since = "1.66.0")]
+    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    pub const fn unzip(self) -> (Option<T>, Option<U>)
+    where
+        T: ~const Destruct,
+        U: ~const Destruct,
+    {
         match self {
             Some((a, b)) => (Some(a), Some(b)),
             None => (None, None),
@@ -2321,7 +2320,8 @@ impl<T> ops::FromResidual<ops::Yeet<()>> for Option<T> {
 }
 
 #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
-impl<T> ops::Residual<T> for Option<convert::Infallible> {
+#[rustc_const_unstable(feature = "const_try", issue = "74935")]
+impl<T> const ops::Residual<T> for Option<convert::Infallible> {
     type TryType = Option<T>;
 }
 
diff --git a/library/core/src/panic/location.rs b/library/core/src/panic/location.rs
index 8eefd9ff2..6dcf23dde 100644
--- a/library/core/src/panic/location.rs
+++ b/library/core/src/panic/location.rs
@@ -123,8 +123,9 @@ impl<'a> Location<'a> {
     /// ```
     #[must_use]
     #[stable(feature = "panic_hooks", since = "1.10.0")]
+    #[rustc_const_unstable(feature = "const_location_fields", issue = "102911")]
     #[inline]
-    pub fn file(&self) -> &str {
+    pub const fn file(&self) -> &str {
         self.file
     }
 
@@ -147,8 +148,9 @@ impl<'a> Location<'a> {
     /// ```
     #[must_use]
     #[stable(feature = "panic_hooks", since = "1.10.0")]
+    #[rustc_const_unstable(feature = "const_location_fields", issue = "102911")]
     #[inline]
-    pub fn line(&self) -> u32 {
+    pub const fn line(&self) -> u32 {
         self.line
     }
 
@@ -171,8 +173,9 @@ impl<'a> Location<'a> {
     /// ```
     #[must_use]
     #[stable(feature = "panic_col", since = "1.25.0")]
+    #[rustc_const_unstable(feature = "const_location_fields", issue = "102911")]
     #[inline]
-    pub fn column(&self) -> u32 {
+    pub const fn column(&self) -> u32 {
         self.col
     }
 }
diff --git a/library/core/src/panicking.rs b/library/core/src/panicking.rs
index d4afe0f53..a9de7c94e 100644
--- a/library/core/src/panicking.rs
+++ b/library/core/src/panicking.rs
@@ -29,6 +29,73 @@
 use crate::fmt;
 use crate::panic::{Location, PanicInfo};
 
+// First we define the two main entry points that all panics go through.
+// In the end both are just convenience wrappers around `panic_impl`.
+
+/// The entry point for panicking with a formatted message.
+///
+/// This is designed to reduce the amount of code required at the call
+/// site as much as possible (so that `panic!()` has as low an impact
+/// on (e.g.) the inlining of other functions as possible), by moving
+/// the actual formatting into this shared place.
+#[cold]
+// If panic_immediate_abort, inline the abort call,
+// otherwise avoid inlining because of it is cold path.
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[track_caller]
+#[lang = "panic_fmt"] // needed for const-evaluated panics
+#[rustc_do_not_const_check] // hooked by const-eval
+#[rustc_const_unstable(feature = "core_panic", issue = "none")]
+pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        super::intrinsics::abort()
+    }
+
+    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+    // that gets resolved to the `#[panic_handler]` function.
+    extern "Rust" {
+        #[lang = "panic_impl"]
+        fn panic_impl(pi: &PanicInfo<'_>) -> !;
+    }
+
+    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
+
+    // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
+    unsafe { panic_impl(&pi) }
+}
+
+/// Like panic_fmt, but without unwinding and track_caller to reduce the impact on codesize.
+/// Also just works on `str`, as a `fmt::Arguments` needs more space to be passed.
+#[cold]
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[cfg_attr(not(bootstrap), rustc_nounwind)]
+#[cfg_attr(bootstrap, rustc_allocator_nounwind)]
+pub fn panic_str_nounwind(msg: &'static str) -> ! {
+    if cfg!(feature = "panic_immediate_abort") {
+        super::intrinsics::abort()
+    }
+
+    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+    // that gets resolved to the `#[panic_handler]` function.
+    extern "Rust" {
+        #[lang = "panic_impl"]
+        fn panic_impl(pi: &PanicInfo<'_>) -> !;
+    }
+
+    // PanicInfo with the `can_unwind` flag set to false forces an abort.
+    let pieces = [msg];
+    let fmt = fmt::Arguments::new_v1(&pieces, &[]);
+    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
+
+    // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
+    unsafe { panic_impl(&pi) }
+}
+
+// Next we define a bunch of higher-level wrappers that all bottom out in the two core functions
+// above.
+
 /// The underlying implementation of libcore's `panic!` macro when no formatting is used.
 #[cold]
 // never inline unless panic_immediate_abort to avoid code
@@ -84,62 +151,17 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
     panic!("index out of bounds: the len is {len} but the index is {index}")
 }
 
-// This function is called directly by the codegen backend, and must not have
-// any extra arguments (including those synthesized by track_caller).
+/// Panic because we cannot unwind out of a function.
+///
+/// This function is called directly by the codegen backend, and must not have
+/// any extra arguments (including those synthesized by track_caller).
 #[cold]
 #[inline(never)]
 #[lang = "panic_no_unwind"] // needed by codegen for panic in nounwind function
+#[cfg_attr(not(bootstrap), rustc_nounwind)]
+#[cfg_attr(bootstrap, rustc_allocator_nounwind)]
 fn panic_no_unwind() -> ! {
-    if cfg!(feature = "panic_immediate_abort") {
-        super::intrinsics::abort()
-    }
-
-    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
-    // that gets resolved to the `#[panic_handler]` function.
-    extern "Rust" {
-        #[lang = "panic_impl"]
-        fn panic_impl(pi: &PanicInfo<'_>) -> !;
-    }
-
-    // PanicInfo with the `can_unwind` flag set to false forces an abort.
-    let fmt = format_args!("panic in a function that cannot unwind");
-    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
-
-    // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
-    unsafe { panic_impl(&pi) }
-}
-
-/// The entry point for panicking with a formatted message.
-///
-/// This is designed to reduce the amount of code required at the call
-/// site as much as possible (so that `panic!()` has as low an impact
-/// on (e.g.) the inlining of other functions as possible), by moving
-/// the actual formatting into this shared place.
-#[cold]
-// If panic_immediate_abort, inline the abort call,
-// otherwise avoid inlining because of it is cold path.
-#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
-#[cfg_attr(feature = "panic_immediate_abort", inline)]
-#[track_caller]
-#[lang = "panic_fmt"] // needed for const-evaluated panics
-#[rustc_do_not_const_check] // hooked by const-eval
-#[rustc_const_unstable(feature = "core_panic", issue = "none")]
-pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
-    if cfg!(feature = "panic_immediate_abort") {
-        super::intrinsics::abort()
-    }
-
-    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
-    // that gets resolved to the `#[panic_handler]` function.
-    extern "Rust" {
-        #[lang = "panic_impl"]
-        fn panic_impl(pi: &PanicInfo<'_>) -> !;
-    }
-
-    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
-
-    // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
-    unsafe { panic_impl(&pi) }
+    panic_str_nounwind("panic in a function that cannot unwind")
 }
 
 /// This function is used instead of panic_fmt in const eval.
diff --git a/library/core/src/primitive_docs.rs b/library/core/src/primitive_docs.rs
index 242f44ade..331714a99 100644
--- a/library/core/src/primitive_docs.rs
+++ b/library/core/src/primitive_docs.rs
@@ -611,7 +611,19 @@ mod prim_pointer {}
 ///
 /// Arrays coerce to [slices (`[T]`)][slice], so a slice method may be called on
 /// an array. Indeed, this provides most of the API for working with arrays.
-/// Slices have a dynamic size and do not coerce to arrays.
+///
+/// Slices have a dynamic size and do not coerce to arrays. Instead, use
+/// `slice.try_into().unwrap()` or `<ArrayType>::try_from(slice).unwrap()`.
+///
+/// Array's `try_from(slice)` implementations (and the corresponding `slice.try_into()`
+/// array implementations) succeed if the input slice length is the same as the result
+/// array length. They optimize especially well when the optimizer can easily determine
+/// the slice length, e.g. `<[u8; 4]>::try_from(&slice[4..8]).unwrap()`. Array implements
+/// [TryFrom](crate::convert::TryFrom) returning:
+///
+/// - `[T; N]` copies from the slice's elements
+/// - `&[T; N]` references the original slice's elements
+/// - `&mut [T; N]` references the original slice's elements
 ///
 /// You can move elements out of an array with a [slice pattern]. If you want
 /// one element, see [`mem::replace`].
@@ -640,6 +652,15 @@ mod prim_pointer {}
 /// for x in &array { }
 /// ```
 ///
+/// You can use `<ArrayType>::try_from(slice)` or `slice.try_into()` to get an array from
+/// a slice:
+///
+/// ```
+/// let bytes: [u8; 3] = [1, 0, 2];
+/// assert_eq!(1, u16::from_le_bytes(<[u8; 2]>::try_from(&bytes[0..2]).unwrap()));
+/// assert_eq!(512, u16::from_le_bytes(bytes[1..3].try_into().unwrap()));
+/// ```
+///
 /// You can use a [slice pattern] to move elements out of an array:
 ///
 /// ```
diff --git a/library/core/src/mem/valid_align.rs b/library/core/src/ptr/alignment.rs
index 32b2afb72..1390e09dd 100644
--- a/library/core/src/mem/valid_align.rs
+++ b/library/core/src/ptr/alignment.rs
@@ -1,4 +1,4 @@
-use crate::convert::TryFrom;
+use crate::convert::{TryFrom, TryInto};
 use crate::intrinsics::assert_unsafe_precondition;
 use crate::num::NonZeroUsize;
 use crate::{cmp, fmt, hash, mem, num};
@@ -8,16 +8,62 @@ use crate::{cmp, fmt, hash, mem, num};
 ///
 /// Note that particularly large alignments, while representable in this type,
 /// are likely not to be supported by actual allocators and linkers.
-#[derive(Copy, Clone)]
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+#[derive(Copy, Clone, Eq, PartialEq)]
 #[repr(transparent)]
-pub(crate) struct ValidAlign(ValidAlignEnum);
+pub struct Alignment(AlignmentEnum);
 
-// ValidAlign is `repr(usize)`, but via extra steps.
-const _: () = assert!(mem::size_of::<ValidAlign>() == mem::size_of::<usize>());
-const _: () = assert!(mem::align_of::<ValidAlign>() == mem::align_of::<usize>());
+// Alignment is `repr(usize)`, but via extra steps.
+const _: () = assert!(mem::size_of::<Alignment>() == mem::size_of::<usize>());
+const _: () = assert!(mem::align_of::<Alignment>() == mem::align_of::<usize>());
 
-impl ValidAlign {
-    /// Creates a `ValidAlign` from a power-of-two `usize`.
+fn _alignment_can_be_structurally_matched(a: Alignment) -> bool {
+    matches!(a, Alignment::MIN)
+}
+
+impl Alignment {
+    /// The smallest possible alignment, 1.
+    ///
+    /// All addresses are always aligned at least this much.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ptr_alignment_type)]
+    /// use std::ptr::Alignment;
+    ///
+    /// assert_eq!(Alignment::MIN.as_usize(), 1);
+    /// ```
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    pub const MIN: Self = Self(AlignmentEnum::_Align1Shl0);
+
+    /// Returns the alignment for a type.
+    ///
+    /// This provides the same numerical value as [`mem::align_of`],
+    /// but in an `Alignment` instead of a `usize.
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[inline]
+    pub const fn of<T>() -> Self {
+        // SAFETY: rustc ensures that type alignment is always a power of two.
+        unsafe { Alignment::new_unchecked(mem::align_of::<T>()) }
+    }
+
+    /// Creates an `Alignment` from a `usize`, or returns `None` if it's
+    /// not a power of two.
+    ///
+    /// Note that `0` is not a power of two, nor a valid alignment.
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[inline]
+    pub const fn new(align: usize) -> Option<Self> {
+        if align.is_power_of_two() {
+            // SAFETY: Just checked it only has one bit set
+            Some(unsafe { Self::new_unchecked(align) })
+        } else {
+            None
+        }
+    }
+
+    /// Creates an `Alignment` from a power-of-two `usize`.
     ///
     /// # Safety
     ///
@@ -25,101 +71,120 @@ impl ValidAlign {
     ///
     /// Equivalently, it must be `1 << exp` for some `exp` in `0..usize::BITS`.
     /// It must *not* be zero.
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
-    pub(crate) const unsafe fn new_unchecked(align: usize) -> Self {
+    pub const unsafe fn new_unchecked(align: usize) -> Self {
         // SAFETY: Precondition passed to the caller.
-        unsafe { assert_unsafe_precondition!((align: usize) => align.is_power_of_two()) };
+        unsafe {
+            assert_unsafe_precondition!(
+               "Alignment::new_unchecked requires a power of two",
+                (align: usize) => align.is_power_of_two()
+            )
+        };
 
         // SAFETY: By precondition, this must be a power of two, and
         // our variants encompass all possible powers of two.
-        unsafe { mem::transmute::<usize, ValidAlign>(align) }
+        unsafe { mem::transmute::<usize, Alignment>(align) }
     }
 
+    /// Returns the alignment as a [`usize`]
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
-    pub(crate) const fn as_usize(self) -> usize {
+    pub const fn as_usize(self) -> usize {
         self.0 as usize
     }
 
+    /// Returns the alignment as a [`NonZeroUsize`]
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
-    pub(crate) const fn as_nonzero(self) -> NonZeroUsize {
+    pub const fn as_nonzero(self) -> NonZeroUsize {
         // SAFETY: All the discriminants are non-zero.
         unsafe { NonZeroUsize::new_unchecked(self.as_usize()) }
     }
 
-    /// Returns the base 2 logarithm of the alignment.
+    /// Returns the base-2 logarithm of the alignment.
     ///
     /// This is always exact, as `self` represents a power of two.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ptr_alignment_type)]
+    /// use std::ptr::Alignment;
+    ///
+    /// assert_eq!(Alignment::of::<u8>().log2(), 0);
+    /// assert_eq!(Alignment::new(1024).unwrap().log2(), 10);
+    /// ```
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
-    pub(crate) fn log2(self) -> u32 {
+    pub fn log2(self) -> u32 {
         self.as_nonzero().trailing_zeros()
     }
-
-    /// Returns the alignment for a type.
-    #[inline]
-    pub(crate) fn of<T>() -> Self {
-        // SAFETY: rustc ensures that type alignment is always a power of two.
-        unsafe { ValidAlign::new_unchecked(mem::align_of::<T>()) }
-    }
 }
 
-impl fmt::Debug for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::Debug for Alignment {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{:?} (1 << {:?})", self.as_nonzero(), self.log2())
     }
 }
 
-impl TryFrom<NonZeroUsize> for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl TryFrom<NonZeroUsize> for Alignment {
     type Error = num::TryFromIntError;
 
     #[inline]
-    fn try_from(align: NonZeroUsize) -> Result<ValidAlign, Self::Error> {
-        if align.is_power_of_two() {
-            // SAFETY: Just checked for power-of-two
-            unsafe { Ok(ValidAlign::new_unchecked(align.get())) }
-        } else {
-            Err(num::TryFromIntError(()))
-        }
+    fn try_from(align: NonZeroUsize) -> Result<Alignment, Self::Error> {
+        align.get().try_into()
     }
 }
 
-impl TryFrom<usize> for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl TryFrom<usize> for Alignment {
     type Error = num::TryFromIntError;
 
     #[inline]
-    fn try_from(align: usize) -> Result<ValidAlign, Self::Error> {
-        if align.is_power_of_two() {
-            // SAFETY: Just checked for power-of-two
-            unsafe { Ok(ValidAlign::new_unchecked(align)) }
-        } else {
-            Err(num::TryFromIntError(()))
-        }
+    fn try_from(align: usize) -> Result<Alignment, Self::Error> {
+        Self::new(align).ok_or(num::TryFromIntError(()))
     }
 }
 
-impl cmp::Eq for ValidAlign {}
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl From<Alignment> for NonZeroUsize {
+    #[inline]
+    fn from(align: Alignment) -> NonZeroUsize {
+        align.as_nonzero()
+    }
+}
 
-impl cmp::PartialEq for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl From<Alignment> for usize {
     #[inline]
-    fn eq(&self, other: &Self) -> bool {
-        self.as_nonzero() == other.as_nonzero()
+    fn from(align: Alignment) -> usize {
+        align.as_usize()
     }
 }
 
-impl cmp::Ord for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl cmp::Ord for Alignment {
     #[inline]
     fn cmp(&self, other: &Self) -> cmp::Ordering {
         self.as_nonzero().cmp(&other.as_nonzero())
     }
 }
 
-impl cmp::PartialOrd for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl cmp::PartialOrd for Alignment {
     #[inline]
     fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
         Some(self.cmp(other))
     }
 }
 
-impl hash::Hash for ValidAlign {
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl hash::Hash for Alignment {
     #[inline]
     fn hash<H: hash::Hasher>(&self, state: &mut H) {
         self.as_nonzero().hash(state)
@@ -127,15 +192,15 @@ impl hash::Hash for ValidAlign {
 }
 
 #[cfg(target_pointer_width = "16")]
-type ValidAlignEnum = ValidAlignEnum16;
+type AlignmentEnum = AlignmentEnum16;
 #[cfg(target_pointer_width = "32")]
-type ValidAlignEnum = ValidAlignEnum32;
+type AlignmentEnum = AlignmentEnum32;
 #[cfg(target_pointer_width = "64")]
-type ValidAlignEnum = ValidAlignEnum64;
+type AlignmentEnum = AlignmentEnum64;
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 #[repr(u16)]
-enum ValidAlignEnum16 {
+enum AlignmentEnum16 {
     _Align1Shl0 = 1 << 0,
     _Align1Shl1 = 1 << 1,
     _Align1Shl2 = 1 << 2,
@@ -154,9 +219,9 @@ enum ValidAlignEnum16 {
     _Align1Shl15 = 1 << 15,
 }
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 #[repr(u32)]
-enum ValidAlignEnum32 {
+enum AlignmentEnum32 {
     _Align1Shl0 = 1 << 0,
     _Align1Shl1 = 1 << 1,
     _Align1Shl2 = 1 << 2,
@@ -191,9 +256,9 @@ enum ValidAlignEnum32 {
     _Align1Shl31 = 1 << 31,
 }
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 #[repr(u64)]
-enum ValidAlignEnum64 {
+enum AlignmentEnum64 {
     _Align1Shl0 = 1 << 0,
     _Align1Shl1 = 1 << 1,
     _Align1Shl2 = 1 << 2,
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index 43e883b8b..5a083227b 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -568,7 +568,6 @@ impl<T: ?Sized> *const T {
     ///
     /// For non-`Sized` pointees this operation changes only the data pointer,
     /// leaving the metadata untouched.
-    #[cfg(not(bootstrap))]
     #[unstable(feature = "ptr_mask", issue = "98290")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
     #[inline(always)]
@@ -695,7 +694,7 @@ impl<T: ?Sized> *const T {
     /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
     ///
     /// This computes the same value that [`offset_from`](#method.offset_from)
-    /// would compute, but with the added precondition that that the offset is
+    /// would compute, but with the added precondition that the offset is
     /// guaranteed to be non-negative.  This method is equivalent to
     /// `usize::from(self.offset_from(origin)).unwrap_unchecked()`,
     /// but it provides slightly more information to the optimizer, which can
@@ -762,7 +761,10 @@ impl<T: ?Sized> *const T {
         // SAFETY: The comparison has no side-effects, and the intrinsic
         // does this check internally in the CTFE implementation.
         unsafe {
-            assert_unsafe_precondition!([T](this: *const T, origin: *const T) => this >= origin)
+            assert_unsafe_precondition!(
+                "ptr::sub_ptr requires `this >= origin`",
+                [T](this: *const T, origin: *const T) => this >= origin
+            )
         };
 
         let pointee_size = mem::size_of::<T>();
@@ -803,7 +805,7 @@ impl<T: ?Sized> *const T {
 
     /// Returns whether two pointers are guaranteed to be inequal.
     ///
-    /// At runtime this function behaves like `Some(self == other)`.
+    /// At runtime this function behaves like `Some(self != other)`.
     /// However, in some contexts (e.g., compile-time evaluation),
     /// it is not always possible to determine inequality of two pointers, so this function may
     /// spuriously return `None` for pointers that later actually turn out to have its inequality known.
diff --git a/library/core/src/ptr/metadata.rs b/library/core/src/ptr/metadata.rs
index 8865c834c..caa10f181 100644
--- a/library/core/src/ptr/metadata.rs
+++ b/library/core/src/ptr/metadata.rs
@@ -135,16 +135,16 @@ pub const fn from_raw_parts_mut<T: ?Sized>(
 }
 
 #[repr(C)]
-pub(crate) union PtrRepr<T: ?Sized> {
-    pub(crate) const_ptr: *const T,
-    pub(crate) mut_ptr: *mut T,
-    pub(crate) components: PtrComponents<T>,
+union PtrRepr<T: ?Sized> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: PtrComponents<T>,
 }
 
 #[repr(C)]
-pub(crate) struct PtrComponents<T: ?Sized> {
-    pub(crate) data_address: *const (),
-    pub(crate) metadata: <T as Pointee>::Metadata,
+struct PtrComponents<T: ?Sized> {
+    data_address: *const (),
+    metadata: <T as Pointee>::Metadata,
 }
 
 // Manual impl needed to avoid `T: Copy` bound.
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index e976abed7..565c38d22 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -377,6 +377,10 @@ use crate::intrinsics::{
 
 use crate::mem::{self, MaybeUninit};
 
+mod alignment;
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+pub use alignment::Alignment;
+
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(inline)]
 pub use crate::intrinsics::copy_nonoverlapping;
@@ -390,7 +394,6 @@ pub use crate::intrinsics::copy;
 pub use crate::intrinsics::write_bytes;
 
 mod metadata;
-pub(crate) use metadata::PtrRepr;
 #[unstable(feature = "ptr_metadata", issue = "81513")]
 pub use metadata::{from_raw_parts, from_raw_parts_mut, metadata, DynMetadata, Pointee, Thin};
 
@@ -578,12 +581,21 @@ pub const fn invalid_mut<T>(addr: usize) -> *mut T {
 /// Convert an address back to a pointer, picking up a previously 'exposed' provenance.
 ///
 /// This is equivalent to `addr as *const T`. The provenance of the returned pointer is that of *any*
-/// pointer that was previously passed to [`expose_addr`][pointer::expose_addr] or a `ptr as usize`
-/// cast. If there is no previously 'exposed' provenance that justifies the way this pointer will be
-/// used, the program has undefined behavior. Note that there is no algorithm that decides which
-/// provenance will be used. You can think of this as "guessing" the right provenance, and the guess
-/// will be "maximally in your favor", in the sense that if there is any way to avoid undefined
-/// behavior, then that is the guess that will be taken.
+/// pointer that was previously exposed by passing it to [`expose_addr`][pointer::expose_addr],
+/// or a `ptr as usize` cast. In addition, memory which is outside the control of the Rust abstract
+/// machine (MMIO registers, for example) is always considered to be exposed, so long as this memory
+/// is disjoint from memory that will be used by the abstract machine such as the stack, heap,
+/// and statics.
+///
+/// If there is no 'exposed' provenance that justifies the way this pointer will be used,
+/// the program has undefined behavior. In particular, the aliasing rules still apply: pointers
+/// and references that have been invalidated due to aliasing accesses cannot be used any more,
+/// even if they have been exposed!
+///
+/// Note that there is no algorithm that decides which provenance will be used. You can think of this
+/// as "guessing" the right provenance, and the guess will be "maximally in your favor", in the sense
+/// that if there is any way to avoid undefined behavior (while upholding all aliasing requirements),
+/// then that is the guess that will be taken.
 ///
 /// On platforms with multiple address spaces, it is your responsibility to ensure that the
 /// address makes sense in the address space that this pointer will be used with.
@@ -886,7 +898,10 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
     // SAFETY: the caller must guarantee that `x` and `y` are
     // valid for writes and properly aligned.
     unsafe {
-        assert_unsafe_precondition!([T](x: *mut T, y: *mut T, count: usize) =>
+        assert_unsafe_precondition!(
+            "ptr::swap_nonoverlapping requires that both pointer arguments are aligned and non-null \
+            and the specified memory ranges do not overlap",
+            [T](x: *mut T, y: *mut T, count: usize) =>
             is_aligned_and_not_null(x)
                 && is_aligned_and_not_null(y)
                 && is_nonoverlapping(x, y, count)
@@ -983,7 +998,10 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
     // and cannot overlap `src` since `dst` must point to a distinct
     // allocated object.
     unsafe {
-        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!(
+            "ptr::replace requires that the pointer argument is aligned and non-null",
+            [T](dst: *mut T) => is_aligned_and_not_null(dst)
+        );
         mem::swap(&mut *dst, &mut src); // cannot overlap
     }
     src
@@ -1114,6 +1132,10 @@ pub const unsafe fn read<T>(src: *const T) -> T {
     // Also, since we just wrote a valid value into `tmp`, it is guaranteed
     // to be properly initialized.
     unsafe {
+        assert_unsafe_precondition!(
+            "ptr::read requires that the pointer argument is aligned and non-null",
+            [T](src: *const T) => is_aligned_and_not_null(src)
+        );
         copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
         tmp.assume_init()
     }
@@ -1307,6 +1329,10 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
     // `dst` cannot overlap `src` because the caller has mutable access
     // to `dst` while `src` is owned by this function.
     unsafe {
+        assert_unsafe_precondition!(
+            "ptr::write requires that the pointer argument is aligned and non-null",
+            [T](dst: *mut T) => is_aligned_and_not_null(dst)
+        );
         copy_nonoverlapping(&src as *const T, dst, 1);
         intrinsics::forget(src);
     }
@@ -1470,7 +1496,10 @@ pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 pub unsafe fn read_volatile<T>(src: *const T) -> T {
     // SAFETY: the caller must uphold the safety contract for `volatile_load`.
     unsafe {
-        assert_unsafe_precondition!([T](src: *const T) => is_aligned_and_not_null(src));
+        assert_unsafe_precondition!(
+            "ptr::read_volatile requires that the pointer argument is aligned and non-null",
+            [T](src: *const T) => is_aligned_and_not_null(src)
+        );
         intrinsics::volatile_load(src)
     }
 }
@@ -1541,7 +1570,10 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
     // SAFETY: the caller must uphold the safety contract for `volatile_store`.
     unsafe {
-        assert_unsafe_precondition!([T](dst: *mut T) => is_aligned_and_not_null(dst));
+        assert_unsafe_precondition!(
+            "ptr::write_volatile requires that the pointer argument is aligned and non-null",
+            [T](dst: *mut T) => is_aligned_and_not_null(dst)
+        );
         intrinsics::volatile_store(dst, src);
     }
 }
@@ -1728,6 +1760,12 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
 /// by their address rather than comparing the values they point to
 /// (which is what the `PartialEq for &T` implementation does).
 ///
+/// When comparing wide pointers, both the address and the metadata are tested for equality.
+/// However, note that comparing trait object pointers (`*const dyn Trait`) is unrealiable: pointers
+/// to values of the same underlying type can compare inequal (because vtables are duplicated in
+/// multiple codegen units), and pointers to values of *different* underlying type can compare equal
+/// (since identical vtables can be deduplicated within a codegen unit).
+///
 /// # Examples
 ///
 /// ```
@@ -1754,41 +1792,6 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
 /// assert!(!std::ptr::eq(&a[..2], &a[..3]));
 /// assert!(!std::ptr::eq(&a[0..2], &a[1..3]));
 /// ```
-///
-/// Traits are also compared by their implementation:
-///
-/// ```
-/// #[repr(transparent)]
-/// struct Wrapper { member: i32 }
-///
-/// trait Trait {}
-/// impl Trait for Wrapper {}
-/// impl Trait for i32 {}
-///
-/// let wrapper = Wrapper { member: 10 };
-///
-/// // Pointers have equal addresses.
-/// assert!(std::ptr::eq(
-///     &wrapper as *const Wrapper as *const u8,
-///     &wrapper.member as *const i32 as *const u8
-/// ));
-///
-/// // Objects have equal addresses, but `Trait` has different implementations.
-/// assert!(!std::ptr::eq(
-///     &wrapper as &dyn Trait,
-///     &wrapper.member as &dyn Trait,
-/// ));
-/// assert!(!std::ptr::eq(
-///     &wrapper as &dyn Trait as *const dyn Trait,
-///     &wrapper.member as &dyn Trait as *const dyn Trait,
-/// ));
-///
-/// // Converting the reference to a `*const u8` compares by address.
-/// assert!(std::ptr::eq(
-///     &wrapper as &dyn Trait as *const dyn Trait as *const u8,
-///     &wrapper.member as &dyn Trait as *const dyn Trait as *const u8,
-/// ));
-/// ```
 #[stable(feature = "ptr_eq", since = "1.17.0")]
 #[inline]
 pub fn eq<T: ?Sized>(a: *const T, b: *const T) -> bool {
@@ -1856,9 +1859,16 @@ macro_rules! maybe_fnptr_doc {
 // Impls for function pointers
 macro_rules! fnptr_impls_safety_abi {
     ($FnTy: ty, $($Arg: ident),*) => {
+        fnptr_impls_safety_abi! { #[stable(feature = "fnptr_impls", since = "1.4.0")] $FnTy, $($Arg),* }
+    };
+    (@c_unwind $FnTy: ty, $($Arg: ident),*) => {
+        #[cfg(not(bootstrap))]
+        fnptr_impls_safety_abi! { #[unstable(feature = "c_unwind", issue = "74990")] $FnTy, $($Arg),* }
+    };
+    (#[$meta:meta] $FnTy: ty, $($Arg: ident),*) => {
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> PartialEq for $FnTy {
                 #[inline]
                 fn eq(&self, other: &Self) -> bool {
@@ -1869,13 +1879,13 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> Eq for $FnTy {}
         }
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> PartialOrd for $FnTy {
                 #[inline]
                 fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
@@ -1886,7 +1896,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> Ord for $FnTy {
                 #[inline]
                 fn cmp(&self, other: &Self) -> Ordering {
@@ -1897,7 +1907,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> hash::Hash for $FnTy {
                 fn hash<HH: hash::Hasher>(&self, state: &mut HH) {
                     state.write_usize(*self as usize)
@@ -1907,7 +1917,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> fmt::Pointer for $FnTy {
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     fmt::pointer_fmt_inner(*self as usize, f)
@@ -1917,7 +1927,7 @@ macro_rules! fnptr_impls_safety_abi {
 
         maybe_fnptr_doc! {
             $($Arg)* @
-            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            #[$meta]
             impl<Ret, $($Arg),*> fmt::Debug for $FnTy {
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     fmt::pointer_fmt_inner(*self as usize, f)
@@ -1932,16 +1942,22 @@ macro_rules! fnptr_impls_args {
         fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
         fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
     };
     () => {
         // No variadic functions with 0 parameters
         fnptr_impls_safety_abi! { extern "Rust" fn() -> Ret, }
         fnptr_impls_safety_abi! { extern "C" fn() -> Ret, }
+        fnptr_impls_safety_abi! { @c_unwind extern "C-unwind" fn() -> Ret, }
         fnptr_impls_safety_abi! { unsafe extern "Rust" fn() -> Ret, }
         fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, }
+        fnptr_impls_safety_abi! { @c_unwind unsafe extern "C-unwind" fn() -> Ret, }
     };
 }
 
diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index e277b8181..6764002bc 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -80,10 +80,14 @@ impl<T: ?Sized> *mut T {
     #[unstable(feature = "set_ptr_value", issue = "75091")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
     #[inline]
-    pub fn with_metadata_of<U>(self, mut val: *mut U) -> *mut U
+    pub fn with_metadata_of<U>(self, val: *const U) -> *mut U
     where
         U: ?Sized,
     {
+        // Prepare in the type system that we will replace the pointer value with a mutable
+        // pointer, taking the mutable provenance from the `self` pointer.
+        let mut val = val as *mut U;
+        // Pointer to the pointer value within the value.
         let target = &mut val as *mut *mut U as *mut *mut u8;
         // SAFETY: In case of a thin pointer, this operations is identical
         // to a simple assignment. In case of a fat pointer, with the current
@@ -584,7 +588,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// For non-`Sized` pointees this operation changes only the data pointer,
     /// leaving the metadata untouched.
-    #[cfg(not(bootstrap))]
     #[unstable(feature = "ptr_mask", issue = "98290")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
     #[inline(always)]
@@ -727,7 +730,7 @@ impl<T: ?Sized> *mut T {
 
     /// Returns whether two pointers are guaranteed to be inequal.
     ///
-    /// At runtime this function behaves like `Some(self == other)`.
+    /// At runtime this function behaves like `Some(self != other)`.
     /// However, in some contexts (e.g., compile-time evaluation),
     /// it is not always possible to determine inequality of two pointers, so this function may
     /// spuriously return `None` for pointers that later actually turn out to have its inequality known.
@@ -868,7 +871,7 @@ impl<T: ?Sized> *mut T {
     /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
     ///
     /// This computes the same value that [`offset_from`](#method.offset_from)
-    /// would compute, but with the added precondition that that the offset is
+    /// would compute, but with the added precondition that the offset is
     /// guaranteed to be non-negative.  This method is equivalent to
     /// `usize::from(self.offset_from(origin)).unwrap_unchecked()`,
     /// but it provides slightly more information to the optimizer, which can
diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index f3ef094cb..c18264d13 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -2,6 +2,7 @@ use crate::cmp::Ordering;
 use crate::convert::From;
 use crate::fmt;
 use crate::hash;
+use crate::intrinsics::assert_unsafe_precondition;
 use crate::marker::Unsize;
 use crate::mem::{self, MaybeUninit};
 use crate::num::NonZeroUsize;
@@ -195,7 +196,10 @@ impl<T: ?Sized> NonNull<T> {
     #[inline]
     pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
         // SAFETY: the caller must guarantee that `ptr` is non-null.
-        unsafe { NonNull { pointer: ptr as _ } }
+        unsafe {
+            assert_unsafe_precondition!("NonNull::new_unchecked requires that the pointer is non-null", [T: ?Sized](ptr: *mut T) => !ptr.is_null());
+            NonNull { pointer: ptr as _ }
+        }
     }
 
     /// Creates a new `NonNull` if `ptr` is non-null.
diff --git a/library/core/src/result.rs b/library/core/src/result.rs
index 76eaa191f..3f33c5fd6 100644
--- a/library/core/src/result.rs
+++ b/library/core/src/result.rs
@@ -548,22 +548,25 @@ impl<T, E> Result<T, E> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(is_some_with)]
+    /// #![feature(is_some_and)]
     ///
     /// let x: Result<u32, &str> = Ok(2);
-    /// assert_eq!(x.is_ok_and(|&x| x > 1), true);
+    /// assert_eq!(x.is_ok_and(|x| x > 1), true);
     ///
     /// let x: Result<u32, &str> = Ok(0);
-    /// assert_eq!(x.is_ok_and(|&x| x > 1), false);
+    /// assert_eq!(x.is_ok_and(|x| x > 1), false);
     ///
     /// let x: Result<u32, &str> = Err("hey");
-    /// assert_eq!(x.is_ok_and(|&x| x > 1), false);
+    /// assert_eq!(x.is_ok_and(|x| x > 1), false);
     /// ```
     #[must_use]
     #[inline]
-    #[unstable(feature = "is_some_with", issue = "93050")]
-    pub fn is_ok_and(&self, f: impl FnOnce(&T) -> bool) -> bool {
-        matches!(self, Ok(x) if f(x))
+    #[unstable(feature = "is_some_and", issue = "93050")]
+    pub fn is_ok_and(self, f: impl FnOnce(T) -> bool) -> bool {
+        match self {
+            Err(_) => false,
+            Ok(x) => f(x),
+        }
     }
 
     /// Returns `true` if the result is [`Err`].
@@ -592,7 +595,7 @@ impl<T, E> Result<T, E> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(is_some_with)]
+    /// #![feature(is_some_and)]
     /// use std::io::{Error, ErrorKind};
     ///
     /// let x: Result<u32, Error> = Err(Error::new(ErrorKind::NotFound, "!"));
@@ -606,9 +609,12 @@ impl<T, E> Result<T, E> {
     /// ```
     #[must_use]
     #[inline]
-    #[unstable(feature = "is_some_with", issue = "93050")]
-    pub fn is_err_and(&self, f: impl FnOnce(&E) -> bool) -> bool {
-        matches!(self, Err(x) if f(x))
+    #[unstable(feature = "is_some_and", issue = "93050")]
+    pub fn is_err_and(self, f: impl FnOnce(E) -> bool) -> bool {
+        match self {
+            Ok(_) => false,
+            Err(e) => f(e),
+        }
     }
 
     /////////////////////////////////////////////////////////////////////////
@@ -2066,9 +2072,6 @@ impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E> {
     /// so the final value of `shared` is 6 (= `3 + 2 + 1`), not 16.
     #[inline]
     fn from_iter<I: IntoIterator<Item = Result<A, E>>>(iter: I) -> Result<V, E> {
-        // FIXME(#11084): This could be replaced with Iterator::scan when this
-        // performance bug is closed.
-
         iter::try_process(iter.into_iter(), |i| i.collect())
     }
 }
@@ -2116,6 +2119,7 @@ impl<T, E, F: From<E>> ops::FromResidual<ops::Yeet<E>> for Result<T, F> {
 }
 
 #[unstable(feature = "try_trait_v2_residual", issue = "91285")]
-impl<T, E> ops::Residual<T> for Result<convert::Infallible, E> {
+#[rustc_const_unstable(feature = "const_try", issue = "74935")]
+impl<T, E> const ops::Residual<T> for Result<convert::Infallible, E> {
     type TryType = Result<T, E>;
 }
diff --git a/library/core/src/slice/index.rs b/library/core/src/slice/index.rs
index 3403a5a86..6d2f7330d 100644
--- a/library/core/src/slice/index.rs
+++ b/library/core/src/slice/index.rs
@@ -139,6 +139,8 @@ mod private_slice_index {
     impl Sealed for ops::RangeToInclusive<usize> {}
     #[stable(feature = "slice_index_with_ops_bound_pair", since = "1.53.0")]
     impl Sealed for (ops::Bound<usize>, ops::Bound<usize>) {}
+
+    impl Sealed for ops::IndexRange {}
 }
 
 /// A helper trait used for indexing operations.
@@ -158,6 +160,7 @@ mod private_slice_index {
     message = "the type `{T}` cannot be indexed by `{Self}`",
     label = "slice indices are of type `usize` or ranges of `usize`"
 )]
+#[const_trait]
 pub unsafe trait SliceIndex<T: ?Sized>: private_slice_index::Sealed {
     /// The output type returned by methods.
     #[stable(feature = "slice_get_slice", since = "1.28.0")]
@@ -229,7 +232,10 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
         // so the call to `add` is safe.
         unsafe {
-            assert_unsafe_precondition!([T](this: usize, slice: *const [T]) => this < slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the index is within the slice",
+                [T](this: usize, slice: *const [T]) => this < slice.len()
+            );
             slice.as_ptr().add(self)
         }
     }
@@ -239,7 +245,10 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
         let this = self;
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!([T](this: usize, slice: *mut [T]) => this < slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the index is within the slice",
+                [T](this: usize, slice: *mut [T]) => this < slice.len()
+            );
             slice.as_mut_ptr().add(self)
         }
     }
@@ -257,6 +266,83 @@ unsafe impl<T> const SliceIndex<[T]> for usize {
     }
 }
 
+/// Because `IndexRange` guarantees `start <= end`, fewer checks are needed here
+/// than there are for a general `Range<usize>` (which might be `100..3`).
+#[rustc_const_unstable(feature = "const_index_range_slice_index", issue = "none")]
+unsafe impl<T> const SliceIndex<[T]> for ops::IndexRange {
+    type Output = [T];
+
+    #[inline]
+    fn get(self, slice: &[T]) -> Option<&[T]> {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&*self.get_unchecked(slice)) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { Some(&mut *self.get_unchecked_mut(slice)) }
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked(self, slice: *const [T]) -> *const [T] {
+        let end = self.end();
+        // SAFETY: the caller guarantees that `slice` is not dangling, so it
+        // cannot be longer than `isize::MAX`. They also guarantee that
+        // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
+        // so the call to `add` is safe.
+
+        unsafe {
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the index is within the slice",
+                [T](end: usize, slice: *const [T]) => end <= slice.len()
+            );
+            ptr::slice_from_raw_parts(slice.as_ptr().add(self.start()), self.len())
+        }
+    }
+
+    #[inline]
+    unsafe fn get_unchecked_mut(self, slice: *mut [T]) -> *mut [T] {
+        let end = self.end();
+        // SAFETY: see comments for `get_unchecked` above.
+        unsafe {
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the index is within the slice",
+                [T](end: usize, slice: *mut [T]) => end <= slice.len()
+            );
+            ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start()), self.len())
+        }
+    }
+
+    #[inline]
+    fn index(self, slice: &[T]) -> &[T] {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { &*self.get_unchecked(slice) }
+        } else {
+            slice_end_index_len_fail(self.end(), slice.len())
+        }
+    }
+
+    #[inline]
+    fn index_mut(self, slice: &mut [T]) -> &mut [T] {
+        if self.end() <= slice.len() {
+            // SAFETY: `self` is checked to be valid and in bounds above.
+            unsafe { &mut *self.get_unchecked_mut(slice) }
+        } else {
+            slice_end_index_len_fail(self.end(), slice.len())
+        }
+    }
+}
+
 #[stable(feature = "slice_get_slice_impls", since = "1.15.0")]
 #[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
 unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
@@ -291,8 +377,11 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
         // so the call to `add` is safe.
 
         unsafe {
-            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *const [T]) =>
-            this.end >= this.start && this.end <= slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked requires that the range is within the slice",
+                [T](this: ops::Range<usize>, slice: *const [T]) =>
+                this.end >= this.start && this.end <= slice.len()
+            );
             ptr::slice_from_raw_parts(slice.as_ptr().add(self.start), self.end - self.start)
         }
     }
@@ -302,8 +391,11 @@ unsafe impl<T> const SliceIndex<[T]> for ops::Range<usize> {
         let this = ops::Range { start: self.start, end: self.end };
         // SAFETY: see comments for `get_unchecked` above.
         unsafe {
-            assert_unsafe_precondition!([T](this: ops::Range<usize>, slice: *mut [T]) =>
-                this.end >= this.start && this.end <= slice.len());
+            assert_unsafe_precondition!(
+                "slice::get_unchecked_mut requires that the range is within the slice",
+                [T](this: ops::Range<usize>, slice: *mut [T]) =>
+                this.end >= this.start && this.end <= slice.len()
+            );
             ptr::slice_from_raw_parts_mut(slice.as_mut_ptr().add(self.start), self.end - self.start)
         }
     }
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index 395c56784..8a8962828 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -9,7 +9,7 @@ use crate::fmt;
 use crate::intrinsics::{assume, exact_div, unchecked_sub};
 use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
 use crate::marker::{PhantomData, Send, Sized, Sync};
-use crate::mem;
+use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
 use crate::ptr::NonNull;
 
@@ -91,11 +91,8 @@ impl<'a, T> Iter<'a, T> {
         unsafe {
             assume(!ptr.is_null());
 
-            let end = if mem::size_of::<T>() == 0 {
-                ptr.wrapping_byte_add(slice.len())
-            } else {
-                ptr.add(slice.len())
-            };
+            let end =
+                if T::IS_ZST { ptr.wrapping_byte_add(slice.len()) } else { ptr.add(slice.len()) };
 
             Self { ptr: NonNull::new_unchecked(ptr as *mut T), end, _marker: PhantomData }
         }
@@ -127,6 +124,7 @@ impl<'a, T> Iter<'a, T> {
     /// ```
     #[must_use]
     #[stable(feature = "iter_to_slice", since = "1.4.0")]
+    #[inline]
     pub fn as_slice(&self) -> &'a [T] {
         self.make_slice()
     }
@@ -146,6 +144,7 @@ iterator! {struct Iter -> *const T, &'a T, const, {/* no mut */}, {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Clone for Iter<'_, T> {
+    #[inline]
     fn clone(&self) -> Self {
         Iter { ptr: self.ptr, end: self.end, _marker: self._marker }
     }
@@ -153,6 +152,7 @@ impl<T> Clone for Iter<'_, T> {
 
 #[stable(feature = "slice_iter_as_ref", since = "1.13.0")]
 impl<T> AsRef<[T]> for Iter<'_, T> {
+    #[inline]
     fn as_ref(&self) -> &[T] {
         self.as_slice()
     }
@@ -227,11 +227,8 @@ impl<'a, T> IterMut<'a, T> {
         unsafe {
             assume(!ptr.is_null());
 
-            let end = if mem::size_of::<T>() == 0 {
-                ptr.wrapping_byte_add(slice.len())
-            } else {
-                ptr.add(slice.len())
-            };
+            let end =
+                if T::IS_ZST { ptr.wrapping_byte_add(slice.len()) } else { ptr.add(slice.len()) };
 
             Self { ptr: NonNull::new_unchecked(ptr), end, _marker: PhantomData }
         }
@@ -303,6 +300,7 @@ impl<'a, T> IterMut<'a, T> {
     /// ```
     #[must_use]
     #[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
+    #[inline]
     pub fn as_slice(&self) -> &[T] {
         self.make_slice()
     }
@@ -351,6 +349,7 @@ impl<'a, T> IterMut<'a, T> {
 
 #[stable(feature = "slice_iter_mut_as_slice", since = "1.53.0")]
 impl<T> AsRef<[T]> for IterMut<'_, T> {
+    #[inline]
     fn as_ref(&self) -> &[T] {
         self.as_slice()
     }
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
index 6c9e7574e..ce51d48e3 100644
--- a/library/core/src/slice/iter/macros.rs
+++ b/library/core/src/slice/iter/macros.rs
@@ -100,7 +100,7 @@ macro_rules! iterator {
             // Unsafe because the offset must not exceed `self.len()`.
             #[inline(always)]
             unsafe fn pre_dec_end(&mut self, offset: usize) -> * $raw_mut T {
-                if mem::size_of::<T>() == 0 {
+                if T::IS_ZST {
                     zst_shrink!(self, offset);
                     self.ptr.as_ptr()
                 } else {
@@ -140,7 +140,7 @@ macro_rules! iterator {
                 // since we check if the iterator is empty first.
                 unsafe {
                     assume(!self.ptr.as_ptr().is_null());
-                    if mem::size_of::<T>() != 0 {
+                    if !<T>::IS_ZST {
                         assume(!self.end.is_null());
                     }
                     if is_empty!(self) {
@@ -166,7 +166,7 @@ macro_rules! iterator {
             fn nth(&mut self, n: usize) -> Option<$elem> {
                 if n >= len!(self) {
                     // This iterator is now empty.
-                    if mem::size_of::<T>() == 0 {
+                    if T::IS_ZST {
                         // We have to do it this way as `ptr` may never be 0, but `end`
                         // could be (due to wrapping).
                         self.end = self.ptr.as_ptr();
@@ -355,7 +355,7 @@ macro_rules! iterator {
                 // empty first.
                 unsafe {
                     assume(!self.ptr.as_ptr().is_null());
-                    if mem::size_of::<T>() != 0 {
+                    if !<T>::IS_ZST {
                         assume(!self.end.is_null());
                     }
                     if is_empty!(self) {
diff --git a/library/core/src/slice/memchr.rs b/library/core/src/slice/memchr.rs
index 7de1f48e6..c848c2e18 100644
--- a/library/core/src/slice/memchr.rs
+++ b/library/core/src/slice/memchr.rs
@@ -141,8 +141,8 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
         // SAFETY: offset starts at len - suffix.len(), as long as it is greater than
         // min_aligned_offset (prefix.len()) the remaining distance is at least 2 * chunk_bytes.
         unsafe {
-            let u = *(ptr.offset(offset as isize - 2 * chunk_bytes as isize) as *const Chunk);
-            let v = *(ptr.offset(offset as isize - chunk_bytes as isize) as *const Chunk);
+            let u = *(ptr.add(offset - 2 * chunk_bytes) as *const Chunk);
+            let v = *(ptr.add(offset - chunk_bytes) as *const Chunk);
 
             // Break if there is a matching byte.
             let zu = contains_zero_byte(u ^ repeated_x);
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 6a7150d29..4f1bb1734 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -9,7 +9,7 @@
 use crate::cmp::Ordering::{self, Greater, Less};
 use crate::intrinsics::{assert_unsafe_precondition, exact_div};
 use crate::marker::Copy;
-use crate::mem;
+use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
 use crate::ops::{Bound, FnMut, OneSidedRange, Range, RangeBounds};
 use crate::option::Option;
@@ -123,18 +123,11 @@ impl<T> [T] {
     #[lang = "slice_len_fn"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+    #[rustc_allow_const_fn_unstable(ptr_metadata)]
     #[inline]
     #[must_use]
-    // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
     pub const fn len(&self) -> usize {
-        // FIXME: Replace with `crate::ptr::metadata(self)` when that is const-stable.
-        // As of this writing this causes a "Const-stable functions can only call other
-        // const-stable functions" error.
-
-        // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
-        // and PtrComponents<T> have the same memory layouts. Only std can make this
-        // guarantee.
-        unsafe { crate::ptr::PtrRepr { const_ptr: self }.components.metadata }
+        ptr::metadata(self)
     }
 
     /// Returns `true` if the slice has a length of 0.
@@ -660,7 +653,10 @@ impl<T> [T] {
         let ptr = this.as_mut_ptr();
         // SAFETY: caller has to guarantee that `a < self.len()` and `b < self.len()`
         unsafe {
-            assert_unsafe_precondition!([T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len());
+            assert_unsafe_precondition!(
+                "slice::swap_unchecked requires that the indices are within the slice",
+                [T](a: usize, b: usize, this: &mut [T]) => a < this.len() && b < this.len()
+            );
             ptr::swap(ptr.add(a), ptr.add(b));
         }
     }
@@ -976,7 +972,10 @@ impl<T> [T] {
         let this = self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            assert_unsafe_precondition!(
+                "slice::as_chunks_unchecked requires `N != 0` and the slice to split exactly into `N`-element chunks",
+                [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+            );
             exact_div(self.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1116,7 +1115,10 @@ impl<T> [T] {
         let this = &*self;
         // SAFETY: Caller must guarantee that `N` is nonzero and exactly divides the slice length
         let new_len = unsafe {
-            assert_unsafe_precondition!([T](this: &[T], N: usize) => N != 0 && this.len() % N == 0);
+            assert_unsafe_precondition!(
+                "slice::as_chunks_unchecked_mut requires `N != 0` and the slice to split exactly into `N`-element chunks",
+                [T](this: &[T], N: usize) => N != 0 && this.len() % N == 0
+            );
             exact_div(this.len(), N)
         };
         // SAFETY: We cast a slice of `new_len * N` elements into
@@ -1580,7 +1582,8 @@ impl<T> [T] {
     #[inline]
     #[track_caller]
     #[must_use]
-    pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+    #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
+    pub const fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
         assert!(mid <= self.len());
         // SAFETY: `[ptr; mid]` and `[mid; len]` are inside `self`, which
         // fulfills the requirements of `from_raw_parts_mut`.
@@ -1679,9 +1682,10 @@ impl<T> [T] {
     /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
     /// ```
     #[unstable(feature = "slice_split_at_unchecked", reason = "new API", issue = "76014")]
+    #[rustc_const_unstable(feature = "const_slice_split_at_mut", issue = "101804")]
     #[inline]
     #[must_use]
-    pub unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
+    pub const unsafe fn split_at_mut_unchecked(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
         let len = self.len();
         let ptr = self.as_mut_ptr();
 
@@ -1690,7 +1694,10 @@ impl<T> [T] {
         // `[ptr; mid]` and `[mid; len]` are not overlapping, so returning a mutable reference
         // is fine.
         unsafe {
-            assert_unsafe_precondition!((mid: usize, len: usize) => mid <= len);
+            assert_unsafe_precondition!(
+                "slice::split_at_mut_unchecked requires the index to be within the slice",
+                (mid: usize, len: usize) => mid <= len
+            );
             (from_raw_parts_mut(ptr, mid), from_raw_parts_mut(ptr.add(mid), len - mid))
         }
     }
@@ -2074,7 +2081,7 @@ impl<T> [T] {
         SplitN::new(self.split(pred), n)
     }
 
-    /// Returns an iterator over subslices separated by elements that match
+    /// Returns an iterator over mutable subslices separated by elements that match
     /// `pred`, limited to returning at most `n` items. The matched element is
     /// not contained in the subslices.
     ///
@@ -2357,6 +2364,28 @@ impl<T> [T] {
     /// assert!(match r { Ok(1..=4) => true, _ => false, });
     /// ```
     ///
+    /// If you want to find that whole *range* of matching items, rather than
+    /// an arbitrary matching one, that can be done using [`partition_point`]:
+    /// ```
+    /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    ///
+    /// let low = s.partition_point(|x| x < &1);
+    /// assert_eq!(low, 1);
+    /// let high = s.partition_point(|x| x <= &1);
+    /// assert_eq!(high, 5);
+    /// let r = s.binary_search(&1);
+    /// assert!((low..high).contains(&r.unwrap()));
+    ///
+    /// assert!(s[..low].iter().all(|&x| x < 1));
+    /// assert!(s[low..high].iter().all(|&x| x == 1));
+    /// assert!(s[high..].iter().all(|&x| x > 1));
+    ///
+    /// // For something not found, the "range" of equal items is empty
+    /// assert_eq!(s.partition_point(|x| x < &11), 9);
+    /// assert_eq!(s.partition_point(|x| x <= &11), 9);
+    /// assert_eq!(s.binary_search(&11), Err(9));
+    /// ```
+    ///
     /// If you want to insert an item to a sorted vector, while maintaining
     /// sort order, consider using [`partition_point`]:
     ///
@@ -2424,15 +2453,20 @@ impl<T> [T] {
     where
         F: FnMut(&'a T) -> Ordering,
     {
+        // INVARIANTS:
+        // - 0 <= left <= left + size = right <= self.len()
+        // - f returns Less for everything in self[..left]
+        // - f returns Greater for everything in self[right..]
         let mut size = self.len();
         let mut left = 0;
         let mut right = size;
         while left < right {
             let mid = left + size / 2;
 
-            // SAFETY: the call is made safe by the following invariants:
-            // - `mid >= 0`
-            // - `mid < size`: `mid` is limited by `[left; right)` bound.
+            // SAFETY: the while condition means `size` is strictly positive, so
+            // `size/2 < size`.  Thus `left + size/2 < left + size`, which
+            // coupled with the `left + size <= self.len()` invariant means
+            // we have `left + size/2 < self.len()`, and this is in-bounds.
             let cmp = f(unsafe { self.get_unchecked(mid) });
 
             // The reason why we use if/else control flow rather than match
@@ -2450,6 +2484,10 @@ impl<T> [T] {
 
             size = right - left;
         }
+
+        // SAFETY: directly true from the overall invariant.
+        // Note that this is `<=`, unlike the assume in the `Ok` path.
+        unsafe { crate::intrinsics::assume(left <= self.len()) };
         Err(left)
     }
 
@@ -2540,7 +2578,7 @@ impl<T> [T] {
     where
         T: Ord,
     {
-        sort::quicksort(self, |a, b| a.lt(b));
+        sort::quicksort(self, T::lt);
     }
 
     /// Sorts the slice with a comparator function, but might not preserve the order of equal
@@ -2643,9 +2681,10 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index`. Additionally, this reordering is
     /// unstable (i.e. any number of equal elements may end up at position `index`), in-place
     /// (i.e. does not allocate), and *O*(*n*) worst-case. This function is also/ known as "kth
-    /// element" in other libraries. It returns a triplet of the following values: all elements less
-    /// than the one at the given index, the value at the given index, and all elements greater than
-    /// the one at the given index.
+    /// element" in other libraries. It returns a triplet of the following from the reordered slice:
+    /// the subslice prior to `index`, the element at `index`, and the subslice after `index`;
+    /// accordingly, the values in those two subslices will respectively all be less-than-or-equal-to
+    /// and greater-than-or-equal-to the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2679,8 +2718,7 @@ impl<T> [T] {
     where
         T: Ord,
     {
-        let mut f = |a: &T, b: &T| a.lt(b);
-        sort::partition_at_index(self, index, &mut f)
+        sort::partition_at_index(self, index, T::lt)
     }
 
     /// Reorder the slice with a comparator function such that the element at `index` is at its
@@ -2690,10 +2728,11 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index` using the comparator function.
     /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
     /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
-    /// is also known as "kth element" in other libraries. It returns a triplet of the following
-    /// values: all elements less than the one at the given index, the value at the given index,
-    /// and all elements greater than the one at the given index, using the provided comparator
-    /// function.
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+    /// the slice reordered according to the provided comparator function: the subslice prior to
+    /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+    /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+    /// the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2731,8 +2770,7 @@ impl<T> [T] {
     where
         F: FnMut(&T, &T) -> Ordering,
     {
-        let mut f = |a: &T, b: &T| compare(a, b) == Less;
-        sort::partition_at_index(self, index, &mut f)
+        sort::partition_at_index(self, index, |a: &T, b: &T| compare(a, b) == Less)
     }
 
     /// Reorder the slice with a key extraction function such that the element at `index` is at its
@@ -2742,10 +2780,11 @@ impl<T> [T] {
     /// less than or equal to any value at a position `j > index` using the key extraction function.
     /// Additionally, this reordering is unstable (i.e. any number of equal elements may end up at
     /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) worst-case. This function
-    /// is also known as "kth element" in other libraries. It returns a triplet of the following
-    /// values: all elements less than the one at the given index, the value at the given index, and
-    /// all elements greater than the one at the given index, using the provided key extraction
-    /// function.
+    /// is also known as "kth element" in other libraries. It returns a triplet of the following from
+    /// the slice reordered according to the provided key extraction function: the subslice prior to
+    /// `index`, the element at `index`, and the subslice after `index`; accordingly, the values in
+    /// those two subslices will respectively all be less-than-or-equal-to and greater-than-or-equal-to
+    /// the value of the element at `index`.
     ///
     /// # Current implementation
     ///
@@ -2784,8 +2823,7 @@ impl<T> [T] {
         F: FnMut(&T) -> K,
         K: Ord,
     {
-        let mut g = |a: &T, b: &T| f(a).lt(&f(b));
-        sort::partition_at_index(self, index, &mut g)
+        sort::partition_at_index(self, index, |a: &T, b: &T| f(a).lt(&f(b)))
     }
 
     /// Moves all consecutive repeated elements to the end of the slice according to the
@@ -3459,7 +3497,7 @@ impl<T> [T] {
     #[must_use]
     pub unsafe fn align_to<U>(&self) -> (&[T], &[U], &[T]) {
         // Note that most of this function will be constant-evaluated,
-        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+        if U::IS_ZST || T::IS_ZST {
             // handle ZSTs specially, which is – don't handle them at all.
             return (self, &[], &[]);
         }
@@ -3520,7 +3558,7 @@ impl<T> [T] {
     #[must_use]
     pub unsafe fn align_to_mut<U>(&mut self) -> (&mut [T], &mut [U], &mut [T]) {
         // Note that most of this function will be constant-evaluated,
-        if mem::size_of::<U>() == 0 || mem::size_of::<T>() == 0 {
+        if U::IS_ZST || T::IS_ZST {
             // handle ZSTs specially, which is – don't handle them at all.
             return (self, &mut [], &mut []);
         }
@@ -3776,6 +3814,16 @@ impl<T> [T] {
     /// assert!(v[i..].iter().all(|&x| !(x < 5)));
     /// ```
     ///
+    /// If all elements of the slice match the predicate, including if the slice
+    /// is empty, then the length of the slice will be returned:
+    ///
+    /// ```
+    /// let a = [2, 4, 8];
+    /// assert_eq!(a.partition_point(|x| x < &100), a.len());
+    /// let a: [i32; 0] = [];
+    /// assert_eq!(a.partition_point(|x| x < &100), 0);
+    /// ```
+    ///
     /// If you want to insert an item to a sorted vector, while maintaining
     /// sort order:
     ///
@@ -4066,7 +4114,7 @@ impl<T, const N: usize> [[T; N]] {
     /// ```
     #[unstable(feature = "slice_flatten", issue = "95629")]
     pub fn flatten(&self) -> &[T] {
-        let len = if crate::mem::size_of::<T>() == 0 {
+        let len = if T::IS_ZST {
             self.len().checked_mul(N).expect("slice len overflow")
         } else {
             // SAFETY: `self.len() * N` cannot overflow because `self` is
@@ -4104,7 +4152,7 @@ impl<T, const N: usize> [[T; N]] {
     /// ```
     #[unstable(feature = "slice_flatten", issue = "95629")]
     pub fn flatten_mut(&mut self) -> &mut [T] {
-        let len = if crate::mem::size_of::<T>() == 0 {
+        let len = if T::IS_ZST {
             self.len().checked_mul(N).expect("slice len overflow")
         } else {
             // SAFETY: `self.len() * N` cannot overflow because `self` is
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
index f1e8bc79b..052fd34d0 100644
--- a/library/core/src/slice/raw.rs
+++ b/library/core/src/slice/raw.rs
@@ -1,7 +1,9 @@
 //! Free functions to create `&[T]` and `&mut [T]`.
 
 use crate::array;
-use crate::intrinsics::{assert_unsafe_precondition, is_aligned_and_not_null};
+use crate::intrinsics::{
+    assert_unsafe_precondition, is_aligned_and_not_null, is_valid_allocation_size,
+};
 use crate::ops::Range;
 use crate::ptr;
 
@@ -90,9 +92,10 @@ use crate::ptr;
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
     unsafe {
-        assert_unsafe_precondition!([T](data: *const T, len: usize) =>
-            is_aligned_and_not_null(data)
-                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        assert_unsafe_precondition!(
+            "slice::from_raw_parts requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
+            [T](data: *const T, len: usize) => is_aligned_and_not_null(data)
+                && is_valid_allocation_size::<T>(len)
         );
         &*ptr::slice_from_raw_parts(data, len)
     }
@@ -134,9 +137,10 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
     unsafe {
-        assert_unsafe_precondition!([T](data: *mut T, len: usize) =>
-            is_aligned_and_not_null(data)
-                && crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize
+        assert_unsafe_precondition!(
+            "slice::from_raw_parts_mut requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
+            [T](data: *mut T, len: usize) => is_aligned_and_not_null(data)
+                && is_valid_allocation_size::<T>(len)
         );
         &mut *ptr::slice_from_raw_parts_mut(data, len)
     }
@@ -188,6 +192,10 @@ pub const fn from_mut<T>(s: &mut T) -> &mut [T] {
 ///
 /// Note that a range created from [`slice::as_ptr_range`] fulfills these requirements.
 ///
+/// # Panics
+///
+/// This function panics if `T` is a Zero-Sized Type (“ZST”).
+///
 /// # Caveat
 ///
 /// The lifetime for the returned slice is inferred from its usage. To
@@ -219,9 +227,15 @@ pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
 }
 
-/// Performs the same functionality as [`from_ptr_range`], except that a
+/// Forms a mutable slice from a pointer range.
+///
+/// This is the same functionality as [`from_ptr_range`], except that a
 /// mutable slice is returned.
 ///
+/// This function is useful for interacting with foreign interfaces which
+/// use two pointers to refer to a range of elements in memory, as is
+/// common in C++.
+///
 /// # Safety
 ///
 /// Behavior is undefined if any of the following conditions are violated:
@@ -247,6 +261,18 @@ pub const unsafe fn from_ptr_range<'a, T>(range: Range<*const T>) -> &'a [T] {
 ///
 /// Note that a range created from [`slice::as_mut_ptr_range`] fulfills these requirements.
 ///
+/// # Panics
+///
+/// This function panics if `T` is a Zero-Sized Type (“ZST”).
+///
+/// # Caveat
+///
+/// The lifetime for the returned slice is inferred from its usage. To
+/// prevent accidental misuse, it's suggested to tie the lifetime to whichever
+/// source lifetime is safe in the context, such as by providing a helper
+/// function taking the lifetime of a host value for the slice, or by explicit
+/// annotation.
+///
 /// # Examples
 ///
 /// ```
diff --git a/library/core/src/slice/rotate.rs b/library/core/src/slice/rotate.rs
index 4589c6c0f..fa8c238f8 100644
--- a/library/core/src/slice/rotate.rs
+++ b/library/core/src/slice/rotate.rs
@@ -1,5 +1,5 @@
 use crate::cmp;
-use crate::mem::{self, MaybeUninit};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::ptr;
 
 /// Rotates the range `[mid-left, mid+right)` such that the element at `mid` becomes the first
@@ -63,7 +63,7 @@ use crate::ptr;
 /// when `left < right` the swapping happens from the left instead.
 pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize) {
     type BufType = [usize; 32];
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         return;
     }
     loop {
diff --git a/library/core/src/slice/sort.rs b/library/core/src/slice/sort.rs
index c6c03c0b0..87f77b7f2 100644
--- a/library/core/src/slice/sort.rs
+++ b/library/core/src/slice/sort.rs
@@ -7,7 +7,7 @@
 //! stable sorting implementation.
 
 use crate::cmp;
-use crate::mem::{self, MaybeUninit};
+use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::ptr;
 
 /// When dropped, copies from `src` into `dest`.
@@ -813,7 +813,7 @@ where
     F: FnMut(&T, &T) -> bool,
 {
     // Sorting has no meaningful behavior on zero-sized types.
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         return;
     }
 
@@ -898,7 +898,7 @@ where
         panic!("partition_at_index index {} greater than length of slice {}", index, v.len());
     }
 
-    if mem::size_of::<T>() == 0 {
+    if T::IS_ZST {
         // Sorting has no meaningful behavior on zero-sized types. Do nothing.
     } else if index == v.len() - 1 {
         // Find max element and place it in the last position of the array. We're free to use
diff --git a/library/core/src/str/error.rs b/library/core/src/str/error.rs
index 343889b69..a11b5add4 100644
--- a/library/core/src/str/error.rs
+++ b/library/core/src/str/error.rs
@@ -1,6 +1,5 @@
 //! Defines utf8 error type.
 
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt;
 
@@ -124,7 +123,6 @@ impl fmt::Display for Utf8Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for Utf8Error {
     #[allow(deprecated)]
@@ -148,7 +146,6 @@ impl fmt::Display for ParseBoolError {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Error for ParseBoolError {
     #[allow(deprecated)]
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index f673aa2a4..fbc0fc397 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -2642,5 +2642,4 @@ impl_fn_for_zst! {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg(not(bootstrap))]
 impl !crate::error::Error for &str {}
diff --git a/library/core/src/str/pattern.rs b/library/core/src/str/pattern.rs
index 031fb8e8b..ec2cb429e 100644
--- a/library/core/src/str/pattern.rs
+++ b/library/core/src/str/pattern.rs
@@ -267,7 +267,7 @@ pub unsafe trait Searcher<'a> {
 /// The index ranges returned by this trait are not required
 /// to exactly match those of the forward search in reverse.
 ///
-/// For the reason why this trait is marked unsafe, see them
+/// For the reason why this trait is marked unsafe, see the
 /// parent trait [`Searcher`].
 pub unsafe trait ReverseSearcher<'a>: Searcher<'a> {
     /// Performs the next search step starting from the back.
diff --git a/library/core/src/str/traits.rs b/library/core/src/str/traits.rs
index e9649fc91..d3ed811b1 100644
--- a/library/core/src/str/traits.rs
+++ b/library/core/src/str/traits.rs
@@ -507,7 +507,6 @@ unsafe impl const SliceIndex<str> for ops::RangeToInclusive<usize> {
 ///
 /// ```
 /// use std::str::FromStr;
-/// use std::num::ParseIntError;
 ///
 /// #[derive(Debug, PartialEq)]
 /// struct Point {
@@ -515,18 +514,21 @@ unsafe impl const SliceIndex<str> for ops::RangeToInclusive<usize> {
 ///     y: i32
 /// }
 ///
+/// #[derive(Debug, PartialEq, Eq)]
+/// struct ParsePointError;
+///
 /// impl FromStr for Point {
-///     type Err = ParseIntError;
+///     type Err = ParsePointError;
 ///
 ///     fn from_str(s: &str) -> Result<Self, Self::Err> {
 ///         let (x, y) = s
 ///             .strip_prefix('(')
 ///             .and_then(|s| s.strip_suffix(')'))
 ///             .and_then(|s| s.split_once(','))
-///             .unwrap();
+///             .ok_or(ParsePointError)?;
 ///
-///         let x_fromstr = x.parse::<i32>()?;
-///         let y_fromstr = y.parse::<i32>()?;
+///         let x_fromstr = x.parse::<i32>().map_err(|_| ParsePointError)?;
+///         let y_fromstr = y.parse::<i32>().map_err(|_| ParsePointError)?;
 ///
 ///         Ok(Point { x: x_fromstr, y: y_fromstr })
 ///     }
@@ -538,6 +540,8 @@ unsafe impl const SliceIndex<str> for ops::RangeToInclusive<usize> {
 /// // Implicit calls, through parse
 /// assert_eq!("(1,2)".parse(), expected);
 /// assert_eq!("(1,2)".parse::<Point>(), expected);
+/// // Invalid input string
+/// assert!(Point::from_str("(1 2)").is_err());
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait FromStr: Sized {
@@ -573,8 +577,8 @@ impl FromStr for bool {
 
     /// Parse a `bool` from a string.
     ///
-    /// Yields a `Result<bool, ParseBoolError>`, because `s` may or may not
-    /// actually be parseable.
+    /// The only accepted values are `"true"` and `"false"`. Any other input
+    /// will return an error.
     ///
     /// # Examples
     ///
diff --git a/library/core/src/sync/atomic.rs b/library/core/src/sync/atomic.rs
index 3c96290fc..edc68d6fa 100644
--- a/library/core/src/sync/atomic.rs
+++ b/library/core/src/sync/atomic.rs
@@ -294,7 +294,7 @@ impl AtomicBool {
     /// ```
     /// use std::sync::atomic::AtomicBool;
     ///
-    /// let atomic_true  = AtomicBool::new(true);
+    /// let atomic_true = AtomicBool::new(true);
     /// let atomic_false = AtomicBool::new(false);
     /// ```
     #[inline]
@@ -955,6 +955,14 @@ impl AtomicBool {
     /// **Note:** This method is only available on platforms that support atomic
     /// operations on `u8`.
     ///
+    /// # Considerations
+    ///
+    /// This method is not magic;  it is not provided by the hardware.
+    /// It is implemented in terms of [`AtomicBool::compare_exchange_weak`], and suffers from the same drawbacks.
+    /// In particular, this method will not circumvent the [ABA Problem].
+    ///
+    /// [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -1171,7 +1179,7 @@ impl<T> AtomicPtr<T> {
     /// use std::sync::atomic::{AtomicPtr, Ordering};
     ///
     /// let ptr = &mut 5;
-    /// let some_ptr  = AtomicPtr::new(ptr);
+    /// let some_ptr = AtomicPtr::new(ptr);
     ///
     /// let value = some_ptr.load(Ordering::Relaxed);
     /// ```
@@ -1198,7 +1206,7 @@ impl<T> AtomicPtr<T> {
     /// use std::sync::atomic::{AtomicPtr, Ordering};
     ///
     /// let ptr = &mut 5;
-    /// let some_ptr  = AtomicPtr::new(ptr);
+    /// let some_ptr = AtomicPtr::new(ptr);
     ///
     /// let other_ptr = &mut 10;
     ///
@@ -1230,7 +1238,7 @@ impl<T> AtomicPtr<T> {
     /// use std::sync::atomic::{AtomicPtr, Ordering};
     ///
     /// let ptr = &mut 5;
-    /// let some_ptr  = AtomicPtr::new(ptr);
+    /// let some_ptr = AtomicPtr::new(ptr);
     ///
     /// let other_ptr = &mut 10;
     ///
@@ -1282,9 +1290,9 @@ impl<T> AtomicPtr<T> {
     /// use std::sync::atomic::{AtomicPtr, Ordering};
     ///
     /// let ptr = &mut 5;
-    /// let some_ptr  = AtomicPtr::new(ptr);
+    /// let some_ptr = AtomicPtr::new(ptr);
     ///
-    /// let other_ptr   = &mut 10;
+    /// let other_ptr = &mut 10;
     ///
     /// let value = some_ptr.compare_and_swap(ptr, other_ptr, Ordering::Relaxed);
     /// ```
@@ -1325,9 +1333,9 @@ impl<T> AtomicPtr<T> {
     /// use std::sync::atomic::{AtomicPtr, Ordering};
     ///
     /// let ptr = &mut 5;
-    /// let some_ptr  = AtomicPtr::new(ptr);
+    /// let some_ptr = AtomicPtr::new(ptr);
     ///
-    /// let other_ptr   = &mut 10;
+    /// let other_ptr = &mut 10;
     ///
     /// let value = some_ptr.compare_exchange(ptr, other_ptr,
     ///                                       Ordering::SeqCst, Ordering::Relaxed);
@@ -1422,6 +1430,14 @@ impl<T> AtomicPtr<T> {
     /// **Note:** This method is only available on platforms that support atomic
     /// operations on pointers.
     ///
+    /// # Considerations
+    ///
+    /// This method is not magic;  it is not provided by the hardware.
+    /// It is implemented in terms of [`AtomicPtr::compare_exchange_weak`], and suffers from the same drawbacks.
+    /// In particular, this method will not circumvent the [ABA Problem].
+    ///
+    /// [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -1626,8 +1642,8 @@ impl<T> AtomicPtr<T> {
     /// and the argument `val`, and stores a pointer with provenance of the
     /// current pointer and the resulting address.
     ///
-    /// This is equivalent equivalent to using [`map_addr`] to atomically
-    /// perform `ptr = ptr.map_addr(|a| a | val)`. This can be used in tagged
+    /// This is equivalent to using [`map_addr`] to atomically perform
+    /// `ptr = ptr.map_addr(|a| a | val)`. This can be used in tagged
     /// pointer schemes to atomically set tag bits.
     ///
     /// **Caveat**: This operation returns the previous value. To compute the
@@ -1677,8 +1693,8 @@ impl<T> AtomicPtr<T> {
     /// pointer, and the argument `val`, and stores a pointer with provenance of
     /// the current pointer and the resulting address.
     ///
-    /// This is equivalent equivalent to using [`map_addr`] to atomically
-    /// perform `ptr = ptr.map_addr(|a| a & val)`. This can be used in tagged
+    /// This is equivalent to using [`map_addr`] to atomically perform
+    /// `ptr = ptr.map_addr(|a| a & val)`. This can be used in tagged
     /// pointer schemes to atomically unset tag bits.
     ///
     /// **Caveat**: This operation returns the previous value. To compute the
@@ -1727,8 +1743,8 @@ impl<T> AtomicPtr<T> {
     /// pointer, and the argument `val`, and stores a pointer with provenance of
     /// the current pointer and the resulting address.
     ///
-    /// This is equivalent equivalent to using [`map_addr`] to atomically
-    /// perform `ptr = ptr.map_addr(|a| a ^ val)`. This can be used in tagged
+    /// This is equivalent to using [`map_addr`] to atomically perform
+    /// `ptr = ptr.map_addr(|a| a ^ val)`. This can be used in tagged
     /// pointer schemes to atomically toggle tag bits.
     ///
     /// **Caveat**: This operation returns the previous value. To compute the
@@ -2510,6 +2526,16 @@ macro_rules! atomic_int {
             /// **Note**: This method is only available on platforms that support atomic operations on
             #[doc = concat!("[`", $s_int_type, "`].")]
             ///
+            /// # Considerations
+            ///
+            /// This method is not magic;  it is not provided by the hardware.
+            /// It is implemented in terms of
+            #[doc = concat!("[`", stringify!($atomic_type), "::compare_exchange_weak`],")]
+            /// and suffers from the same drawbacks.
+            /// In particular, this method will not circumvent the [ABA Problem].
+            ///
+            /// [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
+            ///
             /// # Examples
             ///
             /// ```rust
diff --git a/library/core/src/sync/exclusive.rs b/library/core/src/sync/exclusive.rs
index a7519ab5a..c65c27500 100644
--- a/library/core/src/sync/exclusive.rs
+++ b/library/core/src/sync/exclusive.rs
@@ -100,6 +100,7 @@ impl<T: Sized> Exclusive<T> {
     /// Wrap a value in an `Exclusive`
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn new(t: T) -> Self {
         Self { inner: t }
     }
@@ -107,6 +108,7 @@ impl<T: Sized> Exclusive<T> {
     /// Unwrap the value contained in the `Exclusive`
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn into_inner(self) -> T {
         self.inner
     }
@@ -116,6 +118,7 @@ impl<T: ?Sized> Exclusive<T> {
     /// Get exclusive access to the underlying value.
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn get_mut(&mut self) -> &mut T {
         &mut self.inner
     }
@@ -128,6 +131,7 @@ impl<T: ?Sized> Exclusive<T> {
     /// produce _pinned_ access to the underlying value.
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T> {
         // SAFETY: `Exclusive` can only produce `&mut T` if itself is unpinned
         // `Pin::map_unchecked_mut` is not const, so we do this conversion manually
@@ -139,6 +143,7 @@ impl<T: ?Sized> Exclusive<T> {
     /// building an `Exclusive` with [`Exclusive::new`].
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn from_mut(r: &'_ mut T) -> &'_ mut Exclusive<T> {
         // SAFETY: repr is ≥ C, so refs have the same layout; and `Exclusive` properties are `&mut`-agnostic
         unsafe { &mut *(r as *mut T as *mut Exclusive<T>) }
@@ -149,6 +154,7 @@ impl<T: ?Sized> Exclusive<T> {
     /// building an `Exclusive` with [`Exclusive::new`].
     #[unstable(feature = "exclusive_wrapper", issue = "98407")]
     #[must_use]
+    #[inline]
     pub const fn from_pin_mut(r: Pin<&'_ mut T>) -> Pin<&'_ mut Exclusive<T>> {
         // SAFETY: `Exclusive` can only produce `&mut T` if itself is unpinned
         // `Pin::map_unchecked_mut` is not const, so we do this conversion manually
@@ -158,6 +164,7 @@ impl<T: ?Sized> Exclusive<T> {
 
 #[unstable(feature = "exclusive_wrapper", issue = "98407")]
 impl<T> From<T> for Exclusive<T> {
+    #[inline]
     fn from(t: T) -> Self {
         Self::new(t)
     }
@@ -166,7 +173,7 @@ impl<T> From<T> for Exclusive<T> {
 #[unstable(feature = "exclusive_wrapper", issue = "98407")]
 impl<T: Future + ?Sized> Future for Exclusive<T> {
     type Output = T::Output;
-
+    #[inline]
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         self.get_pin_mut().poll(cx)
     }
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index 60ecc9c0b..0cff972df 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -186,17 +186,19 @@ pub struct Context<'a> {
 impl<'a> Context<'a> {
     /// Create a new `Context` from a [`&Waker`](Waker).
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
     #[must_use]
     #[inline]
-    pub fn from_waker(waker: &'a Waker) -> Self {
+    pub const fn from_waker(waker: &'a Waker) -> Self {
         Context { waker, _marker: PhantomData }
     }
 
     /// Returns a reference to the [`Waker`] for the current task.
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
     #[must_use]
     #[inline]
-    pub fn waker(&self) -> &'a Waker {
+    pub const fn waker(&self) -> &'a Waker {
         &self.waker
     }
 }
@@ -311,7 +313,8 @@ impl Waker {
     #[inline]
     #[must_use]
     #[stable(feature = "futures_api", since = "1.36.0")]
-    pub unsafe fn from_raw(waker: RawWaker) -> Waker {
+    #[rustc_const_unstable(feature = "const_waker", issue = "102012")]
+    pub const unsafe fn from_raw(waker: RawWaker) -> Waker {
         Waker { waker }
     }
 
diff --git a/library/core/src/time.rs b/library/core/src/time.rs
index 4f29ecc0f..ba1cb6efa 100644
--- a/library/core/src/time.rs
+++ b/library/core/src/time.rs
@@ -29,6 +29,20 @@ const NANOS_PER_MICRO: u32 = 1_000;
 const MILLIS_PER_SEC: u64 = 1_000;
 const MICROS_PER_SEC: u64 = 1_000_000;
 
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[repr(transparent)]
+#[rustc_layout_scalar_valid_range_start(0)]
+#[rustc_layout_scalar_valid_range_end(999_999_999)]
+struct Nanoseconds(u32);
+
+impl Default for Nanoseconds {
+    #[inline]
+    fn default() -> Self {
+        // SAFETY: 0 is within the valid range
+        unsafe { Nanoseconds(0) }
+    }
+}
+
 /// A `Duration` type to represent a span of time, typically used for system
 /// timeouts.
 ///
@@ -71,7 +85,7 @@ const MICROS_PER_SEC: u64 = 1_000_000;
 #[cfg_attr(not(test), rustc_diagnostic_item = "Duration")]
 pub struct Duration {
     secs: u64,
-    nanos: u32, // Always 0 <= nanos < NANOS_PER_SEC
+    nanos: Nanoseconds, // Always 0 <= nanos < NANOS_PER_SEC
 }
 
 impl Duration {
@@ -188,7 +202,8 @@ impl Duration {
             None => panic!("overflow in Duration::new"),
         };
         let nanos = nanos % NANOS_PER_SEC;
-        Duration { secs, nanos }
+        // SAFETY: nanos % NANOS_PER_SEC < NANOS_PER_SEC, therefore nanos is within the valid range
+        Duration { secs, nanos: unsafe { Nanoseconds(nanos) } }
     }
 
     /// Creates a new `Duration` from the specified number of whole seconds.
@@ -208,7 +223,7 @@ impl Duration {
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_secs(secs: u64) -> Duration {
-        Duration { secs, nanos: 0 }
+        Duration::new(secs, 0)
     }
 
     /// Creates a new `Duration` from the specified number of milliseconds.
@@ -228,10 +243,7 @@ impl Duration {
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_millis(millis: u64) -> Duration {
-        Duration {
-            secs: millis / MILLIS_PER_SEC,
-            nanos: ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI,
-        }
+        Duration::new(millis / MILLIS_PER_SEC, ((millis % MILLIS_PER_SEC) as u32) * NANOS_PER_MILLI)
     }
 
     /// Creates a new `Duration` from the specified number of microseconds.
@@ -251,10 +263,7 @@ impl Duration {
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_micros(micros: u64) -> Duration {
-        Duration {
-            secs: micros / MICROS_PER_SEC,
-            nanos: ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO,
-        }
+        Duration::new(micros / MICROS_PER_SEC, ((micros % MICROS_PER_SEC) as u32) * NANOS_PER_MICRO)
     }
 
     /// Creates a new `Duration` from the specified number of nanoseconds.
@@ -274,10 +283,7 @@ impl Duration {
     #[inline]
     #[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
     pub const fn from_nanos(nanos: u64) -> Duration {
-        Duration {
-            secs: nanos / (NANOS_PER_SEC as u64),
-            nanos: (nanos % (NANOS_PER_SEC as u64)) as u32,
-        }
+        Duration::new(nanos / (NANOS_PER_SEC as u64), (nanos % (NANOS_PER_SEC as u64)) as u32)
     }
 
     /// Returns true if this `Duration` spans no time.
@@ -301,7 +307,7 @@ impl Duration {
     #[rustc_const_stable(feature = "duration_zero", since = "1.53.0")]
     #[inline]
     pub const fn is_zero(&self) -> bool {
-        self.secs == 0 && self.nanos == 0
+        self.secs == 0 && self.nanos.0 == 0
     }
 
     /// Returns the number of _whole_ seconds contained by this `Duration`.
@@ -352,7 +358,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn subsec_millis(&self) -> u32 {
-        self.nanos / NANOS_PER_MILLI
+        self.nanos.0 / NANOS_PER_MILLI
     }
 
     /// Returns the fractional part of this `Duration`, in whole microseconds.
@@ -375,7 +381,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn subsec_micros(&self) -> u32 {
-        self.nanos / NANOS_PER_MICRO
+        self.nanos.0 / NANOS_PER_MICRO
     }
 
     /// Returns the fractional part of this `Duration`, in nanoseconds.
@@ -398,7 +404,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn subsec_nanos(&self) -> u32 {
-        self.nanos
+        self.nanos.0
     }
 
     /// Returns the total number of whole milliseconds contained by this `Duration`.
@@ -416,7 +422,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn as_millis(&self) -> u128 {
-        self.secs as u128 * MILLIS_PER_SEC as u128 + (self.nanos / NANOS_PER_MILLI) as u128
+        self.secs as u128 * MILLIS_PER_SEC as u128 + (self.nanos.0 / NANOS_PER_MILLI) as u128
     }
 
     /// Returns the total number of whole microseconds contained by this `Duration`.
@@ -434,7 +440,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn as_micros(&self) -> u128 {
-        self.secs as u128 * MICROS_PER_SEC as u128 + (self.nanos / NANOS_PER_MICRO) as u128
+        self.secs as u128 * MICROS_PER_SEC as u128 + (self.nanos.0 / NANOS_PER_MICRO) as u128
     }
 
     /// Returns the total number of nanoseconds contained by this `Duration`.
@@ -452,7 +458,7 @@ impl Duration {
     #[must_use]
     #[inline]
     pub const fn as_nanos(&self) -> u128 {
-        self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos as u128
+        self.secs as u128 * NANOS_PER_SEC as u128 + self.nanos.0 as u128
     }
 
     /// Checked `Duration` addition. Computes `self + other`, returning [`None`]
@@ -475,7 +481,7 @@ impl Duration {
     #[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
     pub const fn checked_add(self, rhs: Duration) -> Option<Duration> {
         if let Some(mut secs) = self.secs.checked_add(rhs.secs) {
-            let mut nanos = self.nanos + rhs.nanos;
+            let mut nanos = self.nanos.0 + rhs.nanos.0;
             if nanos >= NANOS_PER_SEC {
                 nanos -= NANOS_PER_SEC;
                 if let Some(new_secs) = secs.checked_add(1) {
@@ -485,7 +491,7 @@ impl Duration {
                 }
             }
             debug_assert!(nanos < NANOS_PER_SEC);
-            Some(Duration { secs, nanos })
+            Some(Duration::new(secs, nanos))
         } else {
             None
         }
@@ -535,16 +541,16 @@ impl Duration {
     #[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
     pub const fn checked_sub(self, rhs: Duration) -> Option<Duration> {
         if let Some(mut secs) = self.secs.checked_sub(rhs.secs) {
-            let nanos = if self.nanos >= rhs.nanos {
-                self.nanos - rhs.nanos
+            let nanos = if self.nanos.0 >= rhs.nanos.0 {
+                self.nanos.0 - rhs.nanos.0
             } else if let Some(sub_secs) = secs.checked_sub(1) {
                 secs = sub_secs;
-                self.nanos + NANOS_PER_SEC - rhs.nanos
+                self.nanos.0 + NANOS_PER_SEC - rhs.nanos.0
             } else {
                 return None;
             };
             debug_assert!(nanos < NANOS_PER_SEC);
-            Some(Duration { secs, nanos })
+            Some(Duration::new(secs, nanos))
         } else {
             None
         }
@@ -593,13 +599,13 @@ impl Duration {
     #[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
     pub const fn checked_mul(self, rhs: u32) -> Option<Duration> {
         // Multiply nanoseconds as u64, because it cannot overflow that way.
-        let total_nanos = self.nanos as u64 * rhs as u64;
+        let total_nanos = self.nanos.0 as u64 * rhs as u64;
         let extra_secs = total_nanos / (NANOS_PER_SEC as u64);
         let nanos = (total_nanos % (NANOS_PER_SEC as u64)) as u32;
         if let Some(s) = self.secs.checked_mul(rhs as u64) {
             if let Some(secs) = s.checked_add(extra_secs) {
                 debug_assert!(nanos < NANOS_PER_SEC);
-                return Some(Duration { secs, nanos });
+                return Some(Duration::new(secs, nanos));
             }
         }
         None
@@ -653,9 +659,9 @@ impl Duration {
             let secs = self.secs / (rhs as u64);
             let carry = self.secs - secs * (rhs as u64);
             let extra_nanos = carry * (NANOS_PER_SEC as u64) / (rhs as u64);
-            let nanos = self.nanos / rhs + (extra_nanos as u32);
+            let nanos = self.nanos.0 / rhs + (extra_nanos as u32);
             debug_assert!(nanos < NANOS_PER_SEC);
-            Some(Duration { secs, nanos })
+            Some(Duration::new(secs, nanos))
         } else {
             None
         }
@@ -677,7 +683,7 @@ impl Duration {
     #[inline]
     #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     pub const fn as_secs_f64(&self) -> f64 {
-        (self.secs as f64) + (self.nanos as f64) / (NANOS_PER_SEC as f64)
+        (self.secs as f64) + (self.nanos.0 as f64) / (NANOS_PER_SEC as f64)
     }
 
     /// Returns the number of seconds contained by this `Duration` as `f32`.
@@ -696,7 +702,7 @@ impl Duration {
     #[inline]
     #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     pub const fn as_secs_f32(&self) -> f32 {
-        (self.secs as f32) + (self.nanos as f32) / (NANOS_PER_SEC as f32)
+        (self.secs as f32) + (self.nanos.0 as f32) / (NANOS_PER_SEC as f32)
     }
 
     /// Creates a new `Duration` from the specified number of seconds represented
@@ -987,13 +993,13 @@ macro_rules! sum_durations {
         for entry in $iter {
             total_secs =
                 total_secs.checked_add(entry.secs).expect("overflow in iter::sum over durations");
-            total_nanos = match total_nanos.checked_add(entry.nanos as u64) {
+            total_nanos = match total_nanos.checked_add(entry.nanos.0 as u64) {
                 Some(n) => n,
                 None => {
                     total_secs = total_secs
                         .checked_add(total_nanos / NANOS_PER_SEC as u64)
                         .expect("overflow in iter::sum over durations");
-                    (total_nanos % NANOS_PER_SEC as u64) + entry.nanos as u64
+                    (total_nanos % NANOS_PER_SEC as u64) + entry.nanos.0 as u64
                 }
             };
         }
@@ -1001,7 +1007,7 @@ macro_rules! sum_durations {
             .checked_add(total_nanos / NANOS_PER_SEC as u64)
             .expect("overflow in iter::sum over durations");
         total_nanos = total_nanos % NANOS_PER_SEC as u64;
-        Duration { secs: total_secs, nanos: total_nanos as u32 }
+        Duration::new(total_secs, total_nanos as u32)
     }};
 }
 
@@ -1037,7 +1043,7 @@ impl fmt::Debug for Duration {
         /// to the formatter's `width`, if specified.
         fn fmt_decimal(
             f: &mut fmt::Formatter<'_>,
-            mut integer_part: u64,
+            integer_part: u64,
             mut fractional_part: u32,
             mut divisor: u32,
             prefix: &str,
@@ -1069,7 +1075,7 @@ impl fmt::Debug for Duration {
             // normal floating point numbers. However, we only need to do work
             // when rounding up. This happens if the first digit of the
             // remaining ones is >= 5.
-            if fractional_part > 0 && fractional_part >= divisor * 5 {
+            let integer_part = if fractional_part > 0 && fractional_part >= divisor * 5 {
                 // Round up the number contained in the buffer. We go through
                 // the buffer backwards and keep track of the carry.
                 let mut rev_pos = pos;
@@ -1093,9 +1099,18 @@ impl fmt::Debug for Duration {
                 // the whole buffer to '0's and need to increment the integer
                 // part.
                 if carry {
-                    integer_part += 1;
+                    // If `integer_part == u64::MAX` and precision < 9, any
+                    // carry of the overflow during rounding of the
+                    // `fractional_part` into the `integer_part` will cause the
+                    // `integer_part` itself to overflow. Avoid this by using an
+                    // `Option<u64>`, with `None` representing `u64::MAX + 1`.
+                    integer_part.checked_add(1)
+                } else {
+                    Some(integer_part)
                 }
-            }
+            } else {
+                Some(integer_part)
+            };
 
             // Determine the end of the buffer: if precision is set, we just
             // use as many digits from the buffer (capped to 9). If it isn't
@@ -1105,7 +1120,12 @@ impl fmt::Debug for Duration {
             // This closure emits the formatted duration without emitting any
             // padding (padding is calculated below).
             let emit_without_padding = |f: &mut fmt::Formatter<'_>| {
-                write!(f, "{}{}", prefix, integer_part)?;
+                if let Some(integer_part) = integer_part {
+                    write!(f, "{}{}", prefix, integer_part)?;
+                } else {
+                    // u64::MAX + 1 == 18446744073709551616
+                    write!(f, "{}18446744073709551616", prefix)?;
+                }
 
                 // Write the decimal point and the fractional part (if any).
                 if end > 0 {
@@ -1135,12 +1155,17 @@ impl fmt::Debug for Duration {
                     // 2. The postfix: can be "µs" so we have to count UTF8 characters.
                     let mut actual_w = prefix.len() + postfix.chars().count();
                     // 3. The integer part:
-                    if let Some(log) = integer_part.checked_ilog10() {
-                        // integer_part is > 0, so has length log10(x)+1
-                        actual_w += 1 + log as usize;
+                    if let Some(integer_part) = integer_part {
+                        if let Some(log) = integer_part.checked_ilog10() {
+                            // integer_part is > 0, so has length log10(x)+1
+                            actual_w += 1 + log as usize;
+                        } else {
+                            // integer_part is 0, so has length 1.
+                            actual_w += 1;
+                        }
                     } else {
-                        // integer_part is 0, so has length 1.
-                        actual_w += 1;
+                        // integer_part is u64::MAX + 1, so has length 20
+                        actual_w += 20;
                     }
                     // 4. The fractional part (if any):
                     if end > 0 {
@@ -1166,27 +1191,27 @@ impl fmt::Debug for Duration {
         let prefix = if f.sign_plus() { "+" } else { "" };
 
         if self.secs > 0 {
-            fmt_decimal(f, self.secs, self.nanos, NANOS_PER_SEC / 10, prefix, "s")
-        } else if self.nanos >= NANOS_PER_MILLI {
+            fmt_decimal(f, self.secs, self.nanos.0, NANOS_PER_SEC / 10, prefix, "s")
+        } else if self.nanos.0 >= NANOS_PER_MILLI {
             fmt_decimal(
                 f,
-                (self.nanos / NANOS_PER_MILLI) as u64,
-                self.nanos % NANOS_PER_MILLI,
+                (self.nanos.0 / NANOS_PER_MILLI) as u64,
+                self.nanos.0 % NANOS_PER_MILLI,
                 NANOS_PER_MILLI / 10,
                 prefix,
                 "ms",
             )
-        } else if self.nanos >= NANOS_PER_MICRO {
+        } else if self.nanos.0 >= NANOS_PER_MICRO {
             fmt_decimal(
                 f,
-                (self.nanos / NANOS_PER_MICRO) as u64,
-                self.nanos % NANOS_PER_MICRO,
+                (self.nanos.0 / NANOS_PER_MICRO) as u64,
+                self.nanos.0 % NANOS_PER_MICRO,
                 NANOS_PER_MICRO / 10,
                 prefix,
                 "µs",
             )
         } else {
-            fmt_decimal(f, self.nanos as u64, 0, 1, prefix, "ns")
+            fmt_decimal(f, self.nanos.0 as u64, 0, 1, prefix, "ns")
         }
     }
 }
@@ -1200,7 +1225,6 @@ impl fmt::Debug for Duration {
 /// # Example
 ///
 /// ```
-/// #![feature(duration_checked_float)]
 /// use std::time::Duration;
 ///
 /// if let Err(e) = Duration::try_from_secs_f32(-1.0) {
@@ -1208,33 +1232,33 @@ impl fmt::Debug for Duration {
 /// }
 /// ```
 #[derive(Debug, Clone, PartialEq, Eq)]
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-pub struct FromFloatSecsError {
-    kind: FromFloatSecsErrorKind,
+#[stable(feature = "duration_checked_float", since = "1.66.0")]
+pub struct TryFromFloatSecsError {
+    kind: TryFromFloatSecsErrorKind,
 }
 
-impl FromFloatSecsError {
+impl TryFromFloatSecsError {
     const fn description(&self) -> &'static str {
         match self.kind {
-            FromFloatSecsErrorKind::Negative => {
+            TryFromFloatSecsErrorKind::Negative => {
                 "can not convert float seconds to Duration: value is negative"
             }
-            FromFloatSecsErrorKind::OverflowOrNan => {
+            TryFromFloatSecsErrorKind::OverflowOrNan => {
                 "can not convert float seconds to Duration: value is either too big or NaN"
             }
         }
     }
 }
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-impl fmt::Display for FromFloatSecsError {
+#[stable(feature = "duration_checked_float", since = "1.66.0")]
+impl fmt::Display for TryFromFloatSecsError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.description().fmt(f)
     }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-enum FromFloatSecsErrorKind {
+enum TryFromFloatSecsErrorKind {
     // Value is negative.
     Negative,
     // Value is either too big to be represented as `Duration` or `NaN`.
@@ -1254,8 +1278,8 @@ macro_rules! try_from_secs {
         const MANT_MASK: $bits_ty = (1 << $mant_bits) - 1;
         const EXP_MASK: $bits_ty = (1 << $exp_bits) - 1;
 
-        if $secs.is_sign_negative() {
-            return Err(FromFloatSecsError { kind: FromFloatSecsErrorKind::Negative });
+        if $secs < 0.0 {
+            return Err(TryFromFloatSecsError { kind: TryFromFloatSecsErrorKind::Negative });
         }
 
         let bits = $secs.to_bits();
@@ -1314,10 +1338,10 @@ macro_rules! try_from_secs {
             let secs = u64::from(mant) << (exp - $mant_bits);
             (secs, 0)
         } else {
-            return Err(FromFloatSecsError { kind: FromFloatSecsErrorKind::OverflowOrNan });
+            return Err(TryFromFloatSecsError { kind: TryFromFloatSecsErrorKind::OverflowOrNan });
         };
 
-        Ok(Duration { secs, nanos })
+        Ok(Duration::new(secs, nanos))
     }};
 }
 
@@ -1330,8 +1354,6 @@ impl Duration {
     ///
     /// # Examples
     /// ```
-    /// #![feature(duration_checked_float)]
-    ///
     /// use std::time::Duration;
     ///
     /// let res = Duration::try_from_secs_f32(0.0);
@@ -1379,9 +1401,10 @@ impl Duration {
     /// let res = Duration::try_from_secs_f32(val);
     /// assert_eq!(res, Ok(Duration::new(1, 2_929_688)));
     /// ```
-    #[unstable(feature = "duration_checked_float", issue = "83400")]
+    #[stable(feature = "duration_checked_float", since = "1.66.0")]
+    #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     #[inline]
-    pub const fn try_from_secs_f32(secs: f32) -> Result<Duration, FromFloatSecsError> {
+    pub const fn try_from_secs_f32(secs: f32) -> Result<Duration, TryFromFloatSecsError> {
         try_from_secs!(
             secs = secs,
             mantissa_bits = 23,
@@ -1400,8 +1423,6 @@ impl Duration {
     ///
     /// # Examples
     /// ```
-    /// #![feature(duration_checked_float)]
-    ///
     /// use std::time::Duration;
     ///
     /// let res = Duration::try_from_secs_f64(0.0);
@@ -1457,9 +1478,10 @@ impl Duration {
     /// let res = Duration::try_from_secs_f64(val);
     /// assert_eq!(res, Ok(Duration::new(1, 2_929_688)));
     /// ```
-    #[unstable(feature = "duration_checked_float", issue = "83400")]
+    #[stable(feature = "duration_checked_float", since = "1.66.0")]
+    #[rustc_const_unstable(feature = "duration_consts_float", issue = "72440")]
     #[inline]
-    pub const fn try_from_secs_f64(secs: f64) -> Result<Duration, FromFloatSecsError> {
+    pub const fn try_from_secs_f64(secs: f64) -> Result<Duration, TryFromFloatSecsError> {
         try_from_secs!(
             secs = secs,
             mantissa_bits = 52,
diff --git a/library/core/src/tuple.rs b/library/core/src/tuple.rs
index aa8a2425b..fc91fe468 100644
--- a/library/core/src/tuple.rs
+++ b/library/core/src/tuple.rs
@@ -93,7 +93,8 @@ macro_rules! tuple_impls {
         maybe_tuple_doc! {
             $($T)+ @
             #[stable(feature = "rust1", since = "1.0.0")]
-            impl<$($T:Default),+> Default for ($($T,)+) {
+            #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+            impl<$($T: ~const Default),+> const Default for ($($T,)+) {
                 #[inline]
                 fn default() -> ($($T,)+) {
                     ($({ let x: $T = Default::default(); x},)+)
diff --git a/library/core/src/unicode/printable.rs b/library/core/src/unicode/printable.rs
index 31cf88a41..ffb18a5ba 100644
--- a/library/core/src/unicode/printable.rs
+++ b/library/core/src/unicode/printable.rs
@@ -54,7 +54,7 @@ pub(crate) fn is_printable(x: char) -> bool {
         if 0x2a6e0 <= x && x < 0x2a700 {
             return false;
         }
-        if 0x2b739 <= x && x < 0x2b740 {
+        if 0x2b73a <= x && x < 0x2b740 {
             return false;
         }
         if 0x2b81e <= x && x < 0x2b820 {
@@ -69,7 +69,10 @@ pub(crate) fn is_printable(x: char) -> bool {
         if 0x2fa1e <= x && x < 0x30000 {
             return false;
         }
-        if 0x3134b <= x && x < 0xe0100 {
+        if 0x3134b <= x && x < 0x31350 {
+            return false;
+        }
+        if 0x323b0 <= x && x < 0xe0100 {
             return false;
         }
         if 0xe01f0 <= x && x < 0x110000 {
@@ -92,7 +95,7 @@ const SINGLETONS0U: &[(u8, u8)] = &[
     (0x0b, 25),
     (0x0c, 26),
     (0x0d, 16),
-    (0x0e, 13),
+    (0x0e, 12),
     (0x0f, 4),
     (0x10, 3),
     (0x12, 18),
@@ -142,24 +145,24 @@ const SINGLETONS0L: &[u8] = &[
     0xe4, 0xe5, 0xf0, 0x0d, 0x11, 0x45, 0x49, 0x64,
     0x65, 0x80, 0x84, 0xb2, 0xbc, 0xbe, 0xbf, 0xd5,
     0xd7, 0xf0, 0xf1, 0x83, 0x85, 0x8b, 0xa4, 0xa6,
-    0xbe, 0xbf, 0xc5, 0xc7, 0xce, 0xcf, 0xda, 0xdb,
-    0x48, 0x98, 0xbd, 0xcd, 0xc6, 0xce, 0xcf, 0x49,
-    0x4e, 0x4f, 0x57, 0x59, 0x5e, 0x5f, 0x89, 0x8e,
-    0x8f, 0xb1, 0xb6, 0xb7, 0xbf, 0xc1, 0xc6, 0xc7,
-    0xd7, 0x11, 0x16, 0x17, 0x5b, 0x5c, 0xf6, 0xf7,
-    0xfe, 0xff, 0x80, 0x6d, 0x71, 0xde, 0xdf, 0x0e,
-    0x1f, 0x6e, 0x6f, 0x1c, 0x1d, 0x5f, 0x7d, 0x7e,
-    0xae, 0xaf, 0x7f, 0xbb, 0xbc, 0x16, 0x17, 0x1e,
-    0x1f, 0x46, 0x47, 0x4e, 0x4f, 0x58, 0x5a, 0x5c,
-    0x5e, 0x7e, 0x7f, 0xb5, 0xc5, 0xd4, 0xd5, 0xdc,
-    0xf0, 0xf1, 0xf5, 0x72, 0x73, 0x8f, 0x74, 0x75,
-    0x96, 0x26, 0x2e, 0x2f, 0xa7, 0xaf, 0xb7, 0xbf,
-    0xc7, 0xcf, 0xd7, 0xdf, 0x9a, 0x40, 0x97, 0x98,
-    0x30, 0x8f, 0x1f, 0xd2, 0xd4, 0xce, 0xff, 0x4e,
-    0x4f, 0x5a, 0x5b, 0x07, 0x08, 0x0f, 0x10, 0x27,
-    0x2f, 0xee, 0xef, 0x6e, 0x6f, 0x37, 0x3d, 0x3f,
-    0x42, 0x45, 0x90, 0x91, 0x53, 0x67, 0x75, 0xc8,
-    0xc9, 0xd0, 0xd1, 0xd8, 0xd9, 0xe7, 0xfe, 0xff,
+    0xbe, 0xbf, 0xc5, 0xc7, 0xcf, 0xda, 0xdb, 0x48,
+    0x98, 0xbd, 0xcd, 0xc6, 0xce, 0xcf, 0x49, 0x4e,
+    0x4f, 0x57, 0x59, 0x5e, 0x5f, 0x89, 0x8e, 0x8f,
+    0xb1, 0xb6, 0xb7, 0xbf, 0xc1, 0xc6, 0xc7, 0xd7,
+    0x11, 0x16, 0x17, 0x5b, 0x5c, 0xf6, 0xf7, 0xfe,
+    0xff, 0x80, 0x6d, 0x71, 0xde, 0xdf, 0x0e, 0x1f,
+    0x6e, 0x6f, 0x1c, 0x1d, 0x5f, 0x7d, 0x7e, 0xae,
+    0xaf, 0x7f, 0xbb, 0xbc, 0x16, 0x17, 0x1e, 0x1f,
+    0x46, 0x47, 0x4e, 0x4f, 0x58, 0x5a, 0x5c, 0x5e,
+    0x7e, 0x7f, 0xb5, 0xc5, 0xd4, 0xd5, 0xdc, 0xf0,
+    0xf1, 0xf5, 0x72, 0x73, 0x8f, 0x74, 0x75, 0x96,
+    0x26, 0x2e, 0x2f, 0xa7, 0xaf, 0xb7, 0xbf, 0xc7,
+    0xcf, 0xd7, 0xdf, 0x9a, 0x40, 0x97, 0x98, 0x30,
+    0x8f, 0x1f, 0xd2, 0xd4, 0xce, 0xff, 0x4e, 0x4f,
+    0x5a, 0x5b, 0x07, 0x08, 0x0f, 0x10, 0x27, 0x2f,
+    0xee, 0xef, 0x6e, 0x6f, 0x37, 0x3d, 0x3f, 0x42,
+    0x45, 0x90, 0x91, 0x53, 0x67, 0x75, 0xc8, 0xc9,
+    0xd0, 0xd1, 0xd8, 0xd9, 0xe7, 0xfe, 0xff,
 ];
 #[rustfmt::skip]
 const SINGLETONS1U: &[(u8, u8)] = &[
@@ -184,10 +187,12 @@ const SINGLETONS1U: &[(u8, u8)] = &[
     (0x19, 13),
     (0x1c, 5),
     (0x1d, 8),
+    (0x1f, 1),
     (0x24, 1),
     (0x6a, 4),
     (0x6b, 2),
     (0xaf, 3),
+    (0xb1, 2),
     (0xbc, 2),
     (0xcf, 2),
     (0xd1, 2),
@@ -203,7 +208,7 @@ const SINGLETONS1U: &[(u8, u8)] = &[
     (0xee, 32),
     (0xf0, 4),
     (0xf8, 2),
-    (0xfa, 2),
+    (0xfa, 3),
     (0xfb, 1),
 ];
 #[rustfmt::skip]
@@ -220,18 +225,19 @@ const SINGLETONS1L: &[u8] = &[
     0x0a, 0x0b, 0x14, 0x17, 0x36, 0x39, 0x3a, 0xa8,
     0xa9, 0xd8, 0xd9, 0x09, 0x37, 0x90, 0x91, 0xa8,
     0x07, 0x0a, 0x3b, 0x3e, 0x66, 0x69, 0x8f, 0x92,
-    0x6f, 0x5f, 0xbf, 0xee, 0xef, 0x5a, 0x62, 0xf4,
-    0xfc, 0xff, 0x9a, 0x9b, 0x2e, 0x2f, 0x27, 0x28,
-    0x55, 0x9d, 0xa0, 0xa1, 0xa3, 0xa4, 0xa7, 0xa8,
-    0xad, 0xba, 0xbc, 0xc4, 0x06, 0x0b, 0x0c, 0x15,
-    0x1d, 0x3a, 0x3f, 0x45, 0x51, 0xa6, 0xa7, 0xcc,
-    0xcd, 0xa0, 0x07, 0x19, 0x1a, 0x22, 0x25, 0x3e,
-    0x3f, 0xe7, 0xec, 0xef, 0xff, 0xc5, 0xc6, 0x04,
-    0x20, 0x23, 0x25, 0x26, 0x28, 0x33, 0x38, 0x3a,
-    0x48, 0x4a, 0x4c, 0x50, 0x53, 0x55, 0x56, 0x58,
-    0x5a, 0x5c, 0x5e, 0x60, 0x63, 0x65, 0x66, 0x6b,
-    0x73, 0x78, 0x7d, 0x7f, 0x8a, 0xa4, 0xaa, 0xaf,
-    0xb0, 0xc0, 0xd0, 0xae, 0xaf, 0x6e, 0x6f, 0x93,
+    0x11, 0x6f, 0x5f, 0xbf, 0xee, 0xef, 0x5a, 0x62,
+    0xf4, 0xfc, 0xff, 0x53, 0x54, 0x9a, 0x9b, 0x2e,
+    0x2f, 0x27, 0x28, 0x55, 0x9d, 0xa0, 0xa1, 0xa3,
+    0xa4, 0xa7, 0xa8, 0xad, 0xba, 0xbc, 0xc4, 0x06,
+    0x0b, 0x0c, 0x15, 0x1d, 0x3a, 0x3f, 0x45, 0x51,
+    0xa6, 0xa7, 0xcc, 0xcd, 0xa0, 0x07, 0x19, 0x1a,
+    0x22, 0x25, 0x3e, 0x3f, 0xe7, 0xec, 0xef, 0xff,
+    0xc5, 0xc6, 0x04, 0x20, 0x23, 0x25, 0x26, 0x28,
+    0x33, 0x38, 0x3a, 0x48, 0x4a, 0x4c, 0x50, 0x53,
+    0x55, 0x56, 0x58, 0x5a, 0x5c, 0x5e, 0x60, 0x63,
+    0x65, 0x66, 0x6b, 0x73, 0x78, 0x7d, 0x7f, 0x8a,
+    0xa4, 0xaa, 0xaf, 0xb0, 0xc0, 0xd0, 0xae, 0xaf,
+    0x6e, 0x6f, 0xbe, 0x93,
 ];
 #[rustfmt::skip]
 const NORMAL0: &[u8] = &[
@@ -272,7 +278,7 @@ const NORMAL0: &[u8] = &[
     0x1b, 0x07,
     0x57, 0x07,
     0x02, 0x06,
-    0x16, 0x0d,
+    0x17, 0x0c,
     0x50, 0x04,
     0x43, 0x03,
     0x2d, 0x03,
@@ -424,8 +430,8 @@ const NORMAL1: &[u8] = &[
     0x33, 0x07,
     0x2e, 0x08,
     0x0a, 0x81, 0x26,
-    0x52, 0x4e,
-    0x28, 0x08,
+    0x52, 0x4b,
+    0x2b, 0x08,
     0x2a, 0x16,
     0x1a, 0x26,
     0x1c, 0x14,
@@ -438,7 +444,7 @@ const NORMAL1: &[u8] = &[
     0x48, 0x08,
     0x27, 0x09,
     0x75, 0x0b,
-    0x3f, 0x41,
+    0x42, 0x3e,
     0x2a, 0x06,
     0x3b, 0x05,
     0x0a, 0x06,
@@ -464,7 +470,8 @@ const NORMAL1: &[u8] = &[
     0x45, 0x1b,
     0x48, 0x08,
     0x53, 0x0d,
-    0x49, 0x81, 0x07,
+    0x49, 0x07,
+    0x0a, 0x80, 0xf6,
     0x46, 0x0a,
     0x1d, 0x03,
     0x47, 0x49,
@@ -473,14 +480,17 @@ const NORMAL1: &[u8] = &[
     0x0a, 0x06,
     0x39, 0x07,
     0x0a, 0x81, 0x36,
-    0x19, 0x80, 0xb7,
+    0x19, 0x07,
+    0x3b, 0x03,
+    0x1c, 0x56,
     0x01, 0x0f,
     0x32, 0x0d,
     0x83, 0x9b, 0x66,
     0x75, 0x0b,
     0x80, 0xc4, 0x8a, 0x4c,
     0x63, 0x0d,
-    0x84, 0x2f, 0x8f, 0xd1,
+    0x84, 0x30, 0x10,
+    0x16, 0x8f, 0xaa,
     0x82, 0x47, 0xa1, 0xb9,
     0x82, 0x39, 0x07,
     0x2a, 0x04,
@@ -498,8 +508,9 @@ const NORMAL1: &[u8] = &[
     0x97, 0xf8, 0x08,
     0x84, 0xd6, 0x2a,
     0x09, 0xa2, 0xe7,
-    0x81, 0x33, 0x2d,
-    0x03, 0x11,
+    0x81, 0x33, 0x0f,
+    0x01, 0x1d,
+    0x06, 0x0e,
     0x04, 0x08,
     0x81, 0x8c, 0x89, 0x04,
     0x6b, 0x05,
@@ -511,21 +522,26 @@ const NORMAL1: &[u8] = &[
     0x80, 0xf6, 0x0a,
     0x73, 0x08,
     0x70, 0x15,
-    0x46, 0x80, 0x9a,
+    0x46, 0x7a,
+    0x14, 0x0c,
     0x14, 0x0c,
     0x57, 0x09,
     0x19, 0x80, 0x87,
     0x81, 0x47, 0x03,
     0x85, 0x42, 0x0f,
     0x15, 0x84, 0x50,
-    0x1f, 0x80, 0xe1,
-    0x2b, 0x80, 0xd5,
+    0x1f, 0x06,
+    0x06, 0x80, 0xd5,
+    0x2b, 0x05,
+    0x3e, 0x21,
+    0x01, 0x70,
     0x2d, 0x03,
     0x1a, 0x04,
     0x02, 0x81, 0x40,
     0x1f, 0x11,
     0x3a, 0x05,
-    0x01, 0x84, 0xe0,
+    0x01, 0x81, 0xd0,
+    0x2a, 0x82, 0xe6,
     0x80, 0xf7, 0x29,
     0x4c, 0x04,
     0x0a, 0x04,
@@ -546,11 +562,11 @@ const NORMAL1: &[u8] = &[
     0x09, 0x07,
     0x02, 0x0e,
     0x06, 0x80, 0x9a,
-    0x83, 0xd8, 0x05,
-    0x10, 0x03,
+    0x83, 0xd8, 0x04,
+    0x11, 0x03,
     0x0d, 0x03,
-    0x74, 0x0c,
-    0x59, 0x07,
+    0x77, 0x04,
+    0x5f, 0x06,
     0x0c, 0x04,
     0x01, 0x0f,
     0x0c, 0x04,
@@ -559,15 +575,12 @@ const NORMAL1: &[u8] = &[
     0x28, 0x08,
     0x22, 0x4e,
     0x81, 0x54, 0x0c,
-    0x15, 0x03,
-    0x05, 0x03,
-    0x07, 0x09,
     0x1d, 0x03,
-    0x0b, 0x05,
-    0x06, 0x0a,
-    0x0a, 0x06,
-    0x08, 0x08,
-    0x07, 0x09,
+    0x09, 0x07,
+    0x36, 0x08,
+    0x0e, 0x04,
+    0x09, 0x07,
+    0x09, 0x07,
     0x80, 0xcb, 0x25,
     0x0a, 0x84, 0x06,
 ];
diff --git a/library/core/src/unicode/unicode_data.rs b/library/core/src/unicode/unicode_data.rs
index 7301da2af..bd69ca520 100644
--- a/library/core/src/unicode/unicode_data.rs
+++ b/library/core/src/unicode/unicode_data.rs
@@ -99,21 +99,21 @@ fn skip_search<const SOR: usize, const OFFSETS: usize>(
     offset_idx % 2 == 1
 }
 
-pub const UNICODE_VERSION: (u8, u8, u8) = (14, 0, 0);
+pub const UNICODE_VERSION: (u8, u8, u8) = (15, 0, 0);
 
 #[rustfmt::skip]
 pub mod alphabetic {
-    static SHORT_OFFSET_RUNS: [u32; 51] = [
-        706, 33559113, 876615277, 956309270, 1166025910, 1314925568, 1319120901, 1398813696,
-        1449151936, 1451271309, 1455465997, 1463867300, 1652619520, 1663105646, 1665203518,
-        1711342208, 1797326647, 1891700352, 2044795904, 2397118176, 2485199770, 2495688592,
-        2506175535, 2512471040, 2514568775, 2516674560, 2518772281, 2520870464, 2552334328,
-        2583792854, 2587996144, 2594287907, 2608968444, 2621553664, 2623656960, 2644629158,
-        2722225920, 2770461328, 2808211424, 2816601600, 2850156848, 2988572672, 3001198304,
-        3003299641, 3007499938, 3015896033, 3020093440, 3022191134, 3024289792, 3026391883,
-        3029603147,
+    static SHORT_OFFSET_RUNS: [u32; 53] = [
+        706, 33559113, 872420973, 952114966, 1161831606, 1310731264, 1314926597, 1394619392,
+        1444957632, 1447077005, 1451271693, 1459672996, 1648425216, 1658911342, 1661009214,
+        1707147904, 1793132343, 1887506048, 2040601600, 2392923872, 2481005466, 2504077200,
+        2514564144, 2520859648, 2527151687, 2529257472, 2531355193, 2533453376, 2564917240,
+        2596375766, 2600579056, 2606870819, 2621551356, 2642525184, 2644628480, 2665600678,
+        2743197440, 2791432848, 2841765072, 2850154464, 2854350336, 2887905584, 3026321408,
+        3038947040, 3041048378, 3045248674, 3053644769, 3057842176, 3059939870, 3062038528,
+        3064140619, 3066241968, 3071550384,
     ];
-    static OFFSETS: [u8; 1445] = [
+    static OFFSETS: [u8; 1465] = [
         65, 26, 6, 26, 47, 1, 10, 1, 4, 1, 5, 23, 1, 31, 1, 0, 4, 12, 14, 5, 7, 1, 1, 1, 86, 1, 42,
         5, 1, 2, 2, 4, 1, 1, 6, 1, 1, 3, 1, 1, 1, 20, 1, 83, 1, 139, 8, 166, 1, 38, 2, 1, 6, 41, 39,
         14, 1, 1, 1, 2, 1, 2, 1, 1, 8, 27, 4, 4, 29, 11, 5, 56, 1, 7, 14, 102, 1, 8, 4, 8, 4, 3, 10,
@@ -123,50 +123,51 @@ pub mod alphabetic {
         2, 1, 2, 4, 5, 4, 2, 2, 2, 4, 1, 7, 4, 1, 1, 17, 6, 11, 3, 1, 9, 1, 3, 1, 22, 1, 7, 1, 2, 1,
         5, 3, 9, 1, 3, 1, 2, 3, 1, 15, 4, 21, 4, 4, 3, 1, 8, 2, 2, 2, 22, 1, 7, 1, 2, 1, 5, 3, 8, 2,
         2, 2, 2, 9, 2, 4, 2, 1, 5, 13, 1, 16, 2, 1, 6, 3, 3, 1, 4, 3, 2, 1, 1, 1, 2, 3, 2, 3, 3, 3,
-        12, 4, 5, 3, 3, 1, 3, 3, 1, 6, 1, 40, 4, 1, 8, 1, 3, 1, 23, 1, 16, 3, 8, 1, 3, 1, 3, 8, 2,
-        1, 3, 2, 1, 2, 4, 28, 4, 1, 8, 1, 3, 1, 23, 1, 10, 1, 5, 3, 8, 1, 3, 1, 3, 8, 2, 6, 2, 1, 4,
-        13, 2, 13, 13, 1, 3, 1, 41, 2, 8, 1, 3, 1, 3, 1, 1, 5, 4, 7, 5, 22, 6, 1, 3, 1, 18, 3, 24,
-        1, 9, 1, 1, 2, 7, 8, 6, 1, 1, 1, 8, 18, 2, 13, 58, 5, 7, 6, 1, 51, 2, 1, 1, 1, 5, 1, 24, 1,
-        1, 1, 19, 1, 3, 2, 5, 1, 1, 6, 1, 14, 4, 32, 1, 63, 8, 1, 36, 4, 17, 6, 16, 1, 36, 67, 55,
-        1, 1, 2, 5, 16, 64, 10, 4, 2, 38, 1, 1, 5, 1, 2, 43, 1, 0, 1, 4, 2, 7, 1, 1, 1, 4, 2, 41, 1,
-        4, 2, 33, 1, 4, 2, 7, 1, 1, 1, 4, 2, 15, 1, 57, 1, 4, 2, 67, 37, 16, 16, 86, 2, 6, 3, 0, 2,
-        17, 1, 26, 5, 75, 3, 11, 7, 20, 11, 21, 12, 20, 12, 13, 1, 3, 1, 2, 12, 52, 2, 19, 14, 1, 4,
-        1, 67, 89, 7, 43, 5, 70, 10, 31, 1, 12, 4, 9, 23, 30, 2, 5, 11, 44, 4, 26, 54, 28, 4, 63, 2,
-        20, 50, 1, 23, 2, 11, 3, 49, 52, 1, 15, 1, 8, 51, 42, 2, 4, 10, 44, 1, 11, 14, 55, 22, 3,
-        10, 36, 2, 9, 7, 43, 2, 3, 41, 4, 1, 6, 1, 2, 3, 1, 5, 192, 39, 14, 11, 0, 2, 6, 2, 38, 2,
-        6, 2, 8, 1, 1, 1, 1, 1, 1, 1, 31, 2, 53, 1, 7, 1, 1, 3, 3, 1, 7, 3, 4, 2, 6, 4, 13, 5, 3, 1,
-        7, 116, 1, 13, 1, 16, 13, 101, 1, 4, 1, 2, 10, 1, 1, 3, 5, 6, 1, 1, 1, 1, 1, 1, 4, 1, 11, 2,
-        4, 5, 5, 4, 1, 17, 41, 0, 52, 0, 229, 6, 4, 3, 2, 12, 38, 1, 1, 5, 1, 2, 56, 7, 1, 16, 23,
-        9, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 32, 47, 1, 0, 3, 25, 9, 7, 5, 2, 5, 4,
-        86, 6, 3, 1, 90, 1, 4, 5, 43, 1, 94, 17, 32, 48, 16, 0, 0, 64, 0, 67, 46, 2, 0, 3, 16, 10,
-        2, 20, 47, 5, 8, 3, 113, 39, 9, 2, 103, 2, 64, 5, 2, 1, 1, 1, 5, 24, 20, 1, 33, 24, 52, 12,
-        68, 1, 1, 44, 6, 3, 1, 1, 3, 10, 33, 5, 35, 13, 29, 3, 51, 1, 12, 15, 1, 16, 16, 10, 5, 1,
-        55, 9, 14, 18, 23, 3, 69, 1, 1, 1, 1, 24, 3, 2, 16, 2, 4, 11, 6, 2, 6, 2, 6, 9, 7, 1, 7, 1,
-        43, 1, 14, 6, 123, 21, 0, 12, 23, 4, 49, 0, 0, 2, 106, 38, 7, 12, 5, 5, 12, 1, 13, 1, 5, 1,
-        1, 1, 2, 1, 2, 1, 108, 33, 0, 18, 64, 2, 54, 40, 12, 116, 5, 1, 135, 36, 26, 6, 26, 11, 89,
-        3, 6, 2, 6, 2, 6, 2, 3, 35, 12, 1, 26, 1, 19, 1, 2, 1, 15, 2, 14, 34, 123, 69, 53, 0, 29, 3,
+        12, 4, 5, 3, 3, 1, 3, 3, 1, 6, 1, 40, 13, 1, 3, 1, 23, 1, 16, 3, 8, 1, 3, 1, 3, 8, 2, 1, 3,
+        2, 1, 2, 4, 28, 4, 1, 8, 1, 3, 1, 23, 1, 10, 1, 5, 3, 8, 1, 3, 1, 3, 8, 2, 6, 2, 1, 4, 13,
+        3, 12, 13, 1, 3, 1, 41, 2, 8, 1, 3, 1, 3, 1, 1, 5, 4, 7, 5, 22, 6, 1, 3, 1, 18, 3, 24, 1, 9,
+        1, 1, 2, 7, 8, 6, 1, 1, 1, 8, 18, 2, 13, 58, 5, 7, 6, 1, 51, 2, 1, 1, 1, 5, 1, 24, 1, 1, 1,
+        19, 1, 3, 2, 5, 1, 1, 6, 1, 14, 4, 32, 1, 63, 8, 1, 36, 4, 19, 4, 16, 1, 36, 67, 55, 1, 1,
+        2, 5, 16, 64, 10, 4, 2, 38, 1, 1, 5, 1, 2, 43, 1, 0, 1, 4, 2, 7, 1, 1, 1, 4, 2, 41, 1, 4, 2,
+        33, 1, 4, 2, 7, 1, 1, 1, 4, 2, 15, 1, 57, 1, 4, 2, 67, 37, 16, 16, 86, 2, 6, 3, 0, 2, 17, 1,
+        26, 5, 75, 3, 11, 7, 20, 11, 21, 12, 20, 12, 13, 1, 3, 1, 2, 12, 52, 2, 19, 14, 1, 4, 1, 67,
+        89, 7, 43, 5, 70, 10, 31, 1, 12, 4, 9, 23, 30, 2, 5, 11, 44, 4, 26, 54, 28, 4, 63, 2, 20,
+        50, 1, 23, 2, 11, 3, 49, 52, 1, 15, 1, 8, 51, 42, 2, 4, 10, 44, 1, 11, 14, 55, 22, 3, 10,
+        36, 2, 9, 7, 43, 2, 3, 41, 4, 1, 6, 1, 2, 3, 1, 5, 192, 39, 14, 11, 0, 2, 6, 2, 38, 2, 6, 2,
+        8, 1, 1, 1, 1, 1, 1, 1, 31, 2, 53, 1, 7, 1, 1, 3, 3, 1, 7, 3, 4, 2, 6, 4, 13, 5, 3, 1, 7,
+        116, 1, 13, 1, 16, 13, 101, 1, 4, 1, 2, 10, 1, 1, 3, 5, 6, 1, 1, 1, 1, 1, 1, 4, 1, 11, 2, 4,
+        5, 5, 4, 1, 17, 41, 0, 52, 0, 229, 6, 4, 3, 2, 12, 38, 1, 1, 5, 1, 2, 56, 7, 1, 16, 23, 9,
+        7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 7, 1, 32, 47, 1, 0, 3, 25, 9, 7, 5, 2, 5, 4, 86,
+        6, 3, 1, 90, 1, 4, 5, 43, 1, 94, 17, 32, 48, 16, 0, 0, 64, 0, 67, 46, 2, 0, 3, 16, 10, 2,
+        20, 47, 5, 8, 3, 113, 39, 9, 2, 103, 2, 64, 5, 2, 1, 1, 1, 5, 24, 20, 1, 33, 24, 52, 12, 68,
+        1, 1, 44, 6, 3, 1, 1, 3, 10, 33, 5, 35, 13, 29, 3, 51, 1, 12, 15, 1, 16, 16, 10, 5, 1, 55,
+        9, 14, 18, 23, 3, 69, 1, 1, 1, 1, 24, 3, 2, 16, 2, 4, 11, 6, 2, 6, 2, 6, 9, 7, 1, 7, 1, 43,
+        1, 14, 6, 123, 21, 0, 12, 23, 4, 49, 0, 0, 2, 106, 38, 7, 12, 5, 5, 12, 1, 13, 1, 5, 1, 1,
+        1, 2, 1, 2, 1, 108, 33, 0, 18, 64, 2, 54, 40, 12, 116, 5, 1, 135, 36, 26, 6, 26, 11, 89, 3,
+        6, 2, 6, 2, 6, 2, 3, 35, 12, 1, 26, 1, 19, 1, 2, 1, 15, 2, 14, 34, 123, 69, 53, 0, 29, 3,
         49, 47, 32, 13, 30, 5, 43, 5, 30, 2, 36, 4, 8, 1, 5, 42, 158, 18, 36, 4, 36, 4, 40, 8, 52,
         12, 11, 1, 15, 1, 7, 1, 2, 1, 11, 1, 15, 1, 7, 1, 2, 67, 0, 9, 22, 10, 8, 24, 6, 1, 42, 1,
         9, 69, 6, 2, 1, 1, 44, 1, 2, 3, 1, 2, 23, 10, 23, 9, 31, 65, 19, 1, 2, 10, 22, 10, 26, 70,
         56, 6, 2, 64, 4, 1, 2, 5, 8, 1, 3, 1, 29, 42, 29, 3, 29, 35, 8, 1, 28, 27, 54, 10, 22, 10,
         19, 13, 18, 110, 73, 55, 51, 13, 51, 13, 40, 0, 42, 1, 2, 3, 2, 78, 29, 10, 1, 8, 22, 42,
-        18, 46, 21, 27, 23, 9, 70, 43, 5, 12, 55, 9, 1, 13, 25, 23, 51, 17, 4, 8, 35, 3, 1, 9, 64,
-        1, 4, 9, 2, 10, 1, 1, 1, 35, 18, 1, 34, 2, 1, 6, 1, 65, 7, 1, 1, 1, 4, 1, 15, 1, 10, 7, 57,
+        18, 46, 21, 27, 23, 9, 70, 43, 5, 10, 57, 9, 1, 13, 25, 23, 51, 17, 4, 8, 35, 3, 1, 9, 64,
+        1, 4, 9, 2, 10, 1, 1, 1, 35, 18, 1, 34, 2, 1, 6, 4, 62, 7, 1, 1, 1, 4, 1, 15, 1, 10, 7, 57,
         23, 4, 1, 8, 2, 2, 2, 22, 1, 7, 1, 2, 1, 5, 3, 8, 2, 2, 2, 2, 3, 1, 6, 1, 5, 7, 156, 66, 1,
         3, 1, 4, 20, 3, 30, 66, 2, 2, 1, 1, 184, 54, 2, 7, 25, 6, 34, 63, 1, 1, 3, 1, 59, 54, 2, 1,
         71, 27, 2, 14, 21, 7, 185, 57, 103, 64, 31, 8, 2, 1, 2, 8, 1, 2, 1, 30, 1, 2, 2, 2, 2, 4,
         93, 8, 2, 46, 2, 6, 1, 1, 1, 2, 27, 51, 2, 10, 17, 72, 5, 1, 18, 73, 0, 9, 1, 45, 1, 7, 1,
         1, 49, 30, 2, 22, 1, 14, 73, 7, 1, 2, 1, 44, 3, 1, 1, 2, 1, 3, 1, 1, 2, 2, 24, 6, 1, 2, 1,
-        37, 1, 2, 1, 4, 1, 1, 0, 23, 185, 1, 79, 0, 102, 111, 17, 196, 0, 97, 15, 0, 0, 0, 0, 0, 7,
-        31, 17, 79, 17, 30, 18, 48, 16, 4, 31, 21, 5, 19, 0, 64, 128, 75, 4, 57, 7, 17, 64, 2, 1, 1,
-        12, 2, 14, 0, 8, 0, 42, 9, 0, 4, 1, 7, 1, 2, 1, 0, 45, 3, 17, 4, 8, 0, 0, 107, 5, 13, 3, 9,
-        7, 10, 4, 1, 0, 85, 1, 71, 1, 2, 2, 1, 2, 2, 2, 4, 1, 12, 1, 1, 1, 7, 1, 65, 1, 4, 2, 8, 1,
-        7, 1, 28, 1, 4, 1, 5, 1, 1, 3, 7, 1, 0, 2, 25, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1,
-        25, 1, 31, 1, 25, 1, 8, 0, 31, 225, 7, 1, 17, 2, 7, 1, 2, 1, 5, 213, 45, 10, 7, 16, 1, 0,
-        30, 18, 44, 0, 7, 1, 4, 1, 2, 1, 15, 1, 197, 59, 68, 3, 1, 3, 1, 0, 4, 1, 27, 1, 2, 1, 1, 2,
-        1, 1, 10, 1, 4, 1, 1, 1, 1, 6, 1, 4, 1, 1, 1, 1, 1, 1, 3, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1,
-        1, 1, 1, 1, 2, 1, 1, 2, 4, 1, 7, 1, 4, 1, 4, 1, 1, 1, 10, 1, 17, 5, 3, 1, 5, 1, 17, 0, 26,
-        6, 26, 6, 26, 0, 0, 32, 0, 7, 222, 2, 0, 14, 0, 0, 0, 0, 0, 0,
+        37, 1, 2, 1, 4, 1, 1, 0, 23, 9, 17, 1, 41, 3, 3, 111, 1, 79, 0, 102, 111, 17, 196, 0, 97,
+        15, 0, 17, 6, 0, 0, 0, 0, 7, 31, 17, 79, 17, 30, 18, 48, 16, 4, 31, 21, 5, 19, 0, 64, 128,
+        75, 4, 57, 7, 17, 64, 2, 1, 1, 12, 2, 14, 0, 8, 0, 42, 9, 0, 4, 1, 7, 1, 2, 1, 0, 15, 1, 29,
+        3, 2, 1, 14, 4, 8, 0, 0, 107, 5, 13, 3, 9, 7, 10, 4, 1, 0, 85, 1, 71, 1, 2, 2, 1, 2, 2, 2,
+        4, 1, 12, 1, 1, 1, 7, 1, 65, 1, 4, 2, 8, 1, 7, 1, 28, 1, 4, 1, 5, 1, 1, 3, 7, 1, 0, 2, 25,
+        1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 8, 0, 31, 6, 6, 213, 7, 1,
+        17, 2, 7, 1, 2, 1, 5, 5, 62, 33, 1, 112, 45, 10, 7, 16, 1, 0, 30, 18, 44, 0, 28, 0, 7, 1, 4,
+        1, 2, 1, 15, 1, 197, 59, 68, 3, 1, 3, 1, 0, 4, 1, 27, 1, 2, 1, 1, 2, 1, 1, 10, 1, 4, 1, 1,
+        1, 1, 6, 1, 4, 1, 1, 1, 1, 1, 1, 3, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2,
+        4, 1, 7, 1, 4, 1, 4, 1, 1, 1, 10, 1, 17, 5, 3, 1, 5, 1, 17, 0, 26, 6, 26, 6, 26, 0, 0, 32,
+        0, 6, 222, 2, 0, 14, 0, 0, 0, 0, 0, 5, 0, 0,
     ];
     pub fn lookup(c: char) -> bool {
         super::skip_search(
@@ -182,11 +183,11 @@ pub mod case_ignorable {
     static SHORT_OFFSET_RUNS: [u32; 35] = [
         688, 44045149, 572528402, 576724925, 807414908, 878718981, 903913493, 929080568, 933275148,
         937491230, 1138818560, 1147208189, 1210124160, 1222707713, 1235291428, 1260457643,
-        1264654383, 1491147067, 1499536432, 1558257395, 1621177392, 1625385712, 1629581135,
-        1642180592, 1658961053, 1671548672, 1679937895, 1688328704, 1709301760, 1734467888,
-        1755439790, 1759635664, 1768027131, 1777205249, 1782514160,
+        1264654383, 1499535675, 1507925040, 1566646003, 1629566000, 1650551536, 1658941263,
+        1671540720, 1688321181, 1700908800, 1709298023, 1717688832, 1738661888, 1763828398,
+        1797383403, 1805773008, 1809970171, 1819148289, 1824457200,
     ];
-    static OFFSETS: [u8; 855] = [
+    static OFFSETS: [u8; 875] = [
         39, 1, 6, 1, 11, 1, 35, 1, 1, 1, 71, 1, 4, 1, 1, 1, 4, 1, 2, 2, 0, 192, 4, 2, 4, 1, 9, 2,
         1, 1, 251, 7, 207, 1, 5, 1, 49, 45, 1, 1, 1, 2, 1, 2, 1, 1, 44, 1, 11, 6, 10, 11, 1, 1, 35,
         1, 10, 21, 16, 1, 101, 8, 1, 10, 1, 4, 33, 1, 1, 1, 30, 27, 91, 11, 58, 11, 4, 1, 2, 1, 24,
@@ -195,7 +196,7 @@ pub mod case_ignorable {
         57, 1, 4, 5, 1, 2, 4, 1, 20, 2, 22, 6, 1, 1, 58, 1, 2, 1, 1, 4, 8, 1, 7, 2, 11, 2, 30, 1,
         61, 1, 12, 1, 50, 1, 3, 1, 55, 1, 1, 3, 5, 3, 1, 4, 7, 2, 11, 2, 29, 1, 58, 1, 2, 1, 6, 1,
         5, 2, 20, 2, 28, 2, 57, 2, 4, 4, 8, 1, 20, 2, 29, 1, 72, 1, 7, 3, 1, 1, 90, 1, 2, 7, 11, 9,
-        98, 1, 2, 9, 9, 1, 1, 6, 74, 2, 27, 1, 1, 1, 1, 1, 55, 14, 1, 5, 1, 2, 5, 11, 1, 36, 9, 1,
+        98, 1, 2, 9, 9, 1, 1, 7, 73, 2, 27, 1, 1, 1, 1, 1, 55, 14, 1, 5, 1, 2, 5, 11, 1, 36, 9, 1,
         102, 4, 1, 6, 1, 2, 2, 2, 25, 2, 4, 3, 16, 4, 13, 1, 2, 2, 6, 1, 15, 1, 94, 1, 0, 3, 0, 3,
         29, 2, 30, 2, 30, 2, 64, 2, 1, 7, 8, 1, 2, 11, 3, 1, 5, 1, 45, 5, 51, 1, 65, 2, 34, 1, 118,
         3, 4, 2, 9, 1, 6, 3, 219, 2, 2, 1, 58, 1, 1, 7, 1, 1, 1, 1, 2, 8, 6, 10, 2, 1, 39, 1, 8, 31,
@@ -209,15 +210,16 @@ pub mod case_ignorable {
         1, 1, 27, 1, 14, 2, 5, 2, 1, 1, 100, 5, 9, 3, 121, 1, 2, 1, 4, 1, 0, 1, 147, 17, 0, 16, 3,
         1, 12, 16, 34, 1, 2, 1, 169, 1, 7, 1, 6, 1, 11, 1, 35, 1, 1, 1, 47, 1, 45, 2, 67, 1, 21, 3,
         0, 1, 226, 1, 149, 5, 0, 6, 1, 42, 1, 9, 0, 3, 1, 2, 5, 4, 40, 3, 4, 1, 165, 2, 0, 4, 0, 2,
-        153, 11, 49, 4, 123, 1, 54, 15, 41, 1, 2, 2, 10, 3, 49, 4, 2, 2, 2, 1, 4, 1, 10, 1, 50, 3,
-        36, 5, 1, 8, 62, 1, 12, 2, 52, 9, 10, 4, 2, 1, 95, 3, 2, 1, 1, 2, 6, 1, 160, 1, 3, 8, 21, 2,
-        57, 2, 3, 1, 37, 7, 3, 5, 195, 8, 2, 3, 1, 1, 23, 1, 84, 6, 1, 1, 4, 2, 1, 2, 238, 4, 6, 2,
-        1, 2, 27, 2, 85, 8, 2, 1, 1, 2, 106, 1, 1, 1, 2, 6, 1, 1, 101, 3, 2, 4, 1, 5, 0, 9, 1, 2, 0,
-        2, 1, 1, 4, 1, 144, 4, 2, 2, 4, 1, 32, 10, 40, 6, 2, 4, 8, 1, 9, 6, 2, 3, 46, 13, 1, 2, 0,
-        7, 1, 6, 1, 1, 82, 22, 2, 7, 1, 2, 1, 2, 122, 6, 3, 1, 1, 2, 1, 7, 1, 1, 72, 2, 3, 1, 1, 1,
-        0, 2, 0, 9, 0, 5, 59, 7, 9, 4, 0, 1, 63, 17, 64, 2, 1, 2, 0, 4, 1, 7, 1, 2, 0, 2, 1, 4, 0,
-        46, 2, 23, 0, 3, 9, 16, 2, 7, 30, 4, 148, 3, 0, 55, 4, 50, 8, 1, 14, 1, 22, 5, 1, 15, 0, 7,
-        1, 17, 2, 7, 1, 2, 1, 5, 0, 14, 0, 1, 61, 4, 0, 7, 109, 8, 0, 5, 0, 1, 30, 96, 128, 240, 0,
+        80, 3, 70, 11, 49, 4, 123, 1, 54, 15, 41, 1, 2, 2, 10, 3, 49, 4, 2, 2, 2, 1, 4, 1, 10, 1,
+        50, 3, 36, 5, 1, 8, 62, 1, 12, 2, 52, 9, 10, 4, 2, 1, 95, 3, 2, 1, 1, 2, 6, 1, 2, 1, 157, 1,
+        3, 8, 21, 2, 57, 2, 3, 1, 37, 7, 3, 5, 195, 8, 2, 3, 1, 1, 23, 1, 84, 6, 1, 1, 4, 2, 1, 2,
+        238, 4, 6, 2, 1, 2, 27, 2, 85, 8, 2, 1, 1, 2, 106, 1, 1, 1, 2, 6, 1, 1, 101, 3, 2, 4, 1, 5,
+        0, 9, 1, 2, 0, 2, 1, 1, 4, 1, 144, 4, 2, 2, 4, 1, 32, 10, 40, 6, 2, 4, 8, 1, 9, 6, 2, 3, 46,
+        13, 1, 2, 0, 7, 1, 6, 1, 1, 82, 22, 2, 7, 1, 2, 1, 2, 122, 6, 3, 1, 1, 2, 1, 7, 1, 1, 72, 2,
+        3, 1, 1, 1, 0, 2, 11, 2, 52, 5, 5, 1, 1, 1, 0, 17, 6, 15, 0, 5, 59, 7, 9, 4, 0, 1, 63, 17,
+        64, 2, 1, 2, 0, 4, 1, 7, 1, 2, 0, 2, 1, 4, 0, 46, 2, 23, 0, 3, 9, 16, 2, 7, 30, 4, 148, 3,
+        0, 55, 4, 50, 8, 1, 14, 1, 22, 5, 1, 15, 0, 7, 1, 17, 2, 7, 1, 2, 1, 5, 5, 62, 33, 1, 160,
+        14, 0, 1, 61, 4, 0, 5, 0, 7, 109, 8, 0, 5, 0, 1, 30, 96, 128, 240, 0,
     ];
     pub fn lookup(c: char) -> bool {
         super::skip_search(
@@ -230,24 +232,24 @@ pub mod case_ignorable {
 
 #[rustfmt::skip]
 pub mod cased {
-    static SHORT_OFFSET_RUNS: [u32; 21] = [
+    static SHORT_OFFSET_RUNS: [u32; 22] = [
         4256, 115348384, 136322176, 144711446, 163587254, 320875520, 325101120, 350268208,
         392231680, 404815649, 413205504, 421595008, 467733632, 484513952, 492924480, 497144832,
-        501339814, 578936576, 627173632, 635564336, 640872842,
+        501339814, 578936576, 627171376, 639756544, 643952944, 649261450,
     ];
-    static OFFSETS: [u8; 311] = [
+    static OFFSETS: [u8; 315] = [
         65, 26, 6, 26, 47, 1, 10, 1, 4, 1, 5, 23, 1, 31, 1, 195, 1, 4, 4, 208, 1, 36, 7, 2, 30, 5,
         96, 1, 42, 4, 2, 2, 2, 4, 1, 1, 6, 1, 1, 3, 1, 1, 1, 20, 1, 83, 1, 139, 8, 166, 1, 38, 9,
-        41, 0, 38, 1, 1, 5, 1, 2, 43, 2, 3, 0, 86, 2, 6, 0, 9, 7, 43, 2, 3, 64, 192, 64, 0, 2, 6, 2,
+        41, 0, 38, 1, 1, 5, 1, 2, 43, 1, 4, 0, 86, 2, 6, 0, 9, 7, 43, 2, 3, 64, 192, 64, 0, 2, 6, 2,
         38, 2, 6, 2, 8, 1, 1, 1, 1, 1, 1, 1, 31, 2, 53, 1, 7, 1, 1, 3, 3, 1, 7, 3, 4, 2, 6, 4, 13,
         5, 3, 1, 7, 116, 1, 13, 1, 16, 13, 101, 1, 4, 1, 2, 10, 1, 1, 3, 5, 6, 1, 1, 1, 1, 1, 1, 4,
         1, 6, 4, 1, 2, 4, 5, 5, 4, 1, 17, 32, 3, 2, 0, 52, 0, 229, 6, 4, 3, 2, 12, 38, 1, 1, 5, 1,
-        0, 46, 18, 30, 132, 102, 3, 4, 1, 59, 5, 2, 1, 1, 1, 5, 27, 2, 1, 3, 0, 43, 1, 13, 7, 80, 0,
+        0, 46, 18, 30, 132, 102, 3, 4, 1, 59, 5, 2, 1, 1, 1, 5, 24, 5, 1, 3, 0, 43, 1, 14, 6, 80, 0,
         7, 12, 5, 0, 26, 6, 26, 0, 80, 96, 36, 4, 36, 116, 11, 1, 15, 1, 7, 1, 2, 1, 11, 1, 15, 1,
         7, 1, 2, 0, 1, 2, 3, 1, 42, 1, 9, 0, 51, 13, 51, 0, 64, 0, 64, 0, 85, 1, 71, 1, 2, 2, 1, 2,
         2, 2, 4, 1, 12, 1, 1, 1, 7, 1, 65, 1, 4, 2, 8, 1, 7, 1, 28, 1, 4, 1, 5, 1, 1, 3, 7, 1, 0, 2,
-        25, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 8, 0, 10, 1, 20, 0,
-        68, 0, 26, 6, 26, 6, 26, 0,
+        25, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 31, 1, 25, 1, 8, 0, 10, 1, 20, 6, 6,
+        0, 62, 0, 68, 0, 26, 6, 26, 6, 26, 0,
     ];
     pub fn lookup(c: char) -> bool {
         super::skip_search(
@@ -277,14 +279,14 @@ pub mod cc {
 
 #[rustfmt::skip]
 pub mod grapheme_extend {
-    static SHORT_OFFSET_RUNS: [u32; 32] = [
+    static SHORT_OFFSET_RUNS: [u32; 33] = [
         768, 2098307, 6292881, 10490717, 522196754, 526393356, 731917551, 740306986, 752920175,
         761309186, 778107678, 908131840, 912326558, 920715773, 924912129, 937495844, 962662059,
-        966858799, 1205935152, 1277239027, 1340173040, 1344368463, 1352776861, 1365364480,
-        1369559397, 1377950208, 1407311872, 1432478000, 1453449902, 1457645776, 1466826784,
-        1476329968,
+        966858799, 1214323760, 1285627635, 1348547648, 1369533168, 1377922895, 1386331293,
+        1398918912, 1403113829, 1411504640, 1440866304, 1466032814, 1495393516, 1503783120,
+        1508769824, 1518273008,
     ];
-    static OFFSETS: [u8; 707] = [
+    static OFFSETS: [u8; 727] = [
         0, 112, 0, 7, 0, 45, 1, 1, 1, 2, 1, 2, 1, 1, 72, 11, 48, 21, 16, 1, 101, 7, 2, 6, 2, 2, 1,
         4, 35, 1, 30, 27, 91, 11, 58, 9, 9, 1, 24, 4, 1, 9, 1, 3, 1, 5, 43, 3, 60, 8, 42, 24, 1, 32,
         55, 1, 1, 1, 4, 8, 4, 1, 3, 7, 10, 2, 29, 1, 58, 1, 1, 1, 2, 4, 8, 1, 9, 1, 10, 2, 26, 1, 2,
@@ -292,7 +294,7 @@ pub mod grapheme_extend {
         1, 1, 58, 1, 1, 2, 1, 4, 8, 1, 7, 3, 10, 2, 30, 1, 59, 1, 1, 1, 12, 1, 9, 1, 40, 1, 3, 1,
         55, 1, 1, 3, 5, 3, 1, 4, 7, 2, 11, 2, 29, 1, 58, 1, 2, 1, 2, 1, 3, 1, 5, 2, 7, 2, 11, 2, 28,
         2, 57, 2, 1, 1, 2, 4, 8, 1, 9, 1, 10, 2, 29, 1, 72, 1, 4, 1, 2, 3, 1, 1, 8, 1, 81, 1, 2, 7,
-        12, 8, 98, 1, 2, 9, 11, 6, 74, 2, 27, 1, 1, 1, 1, 1, 55, 14, 1, 5, 1, 2, 5, 11, 1, 36, 9, 1,
+        12, 8, 98, 1, 2, 9, 11, 7, 73, 2, 27, 1, 1, 1, 1, 1, 55, 14, 1, 5, 1, 2, 5, 11, 1, 36, 9, 1,
         102, 4, 1, 6, 1, 2, 2, 2, 25, 2, 4, 3, 16, 4, 13, 1, 2, 2, 6, 1, 15, 1, 0, 3, 0, 3, 29, 2,
         30, 2, 30, 2, 64, 2, 1, 7, 8, 1, 2, 11, 9, 1, 45, 3, 1, 1, 117, 2, 34, 1, 118, 3, 4, 2, 9,
         1, 6, 3, 219, 2, 2, 1, 58, 1, 1, 7, 1, 1, 1, 1, 2, 8, 6, 10, 2, 1, 48, 31, 49, 4, 48, 7, 1,
@@ -301,16 +303,17 @@ pub mod grapheme_extend {
         4, 1, 10, 32, 2, 80, 2, 0, 1, 3, 1, 4, 1, 25, 2, 5, 1, 151, 2, 26, 18, 13, 1, 38, 8, 25, 11,
         46, 3, 48, 1, 2, 4, 2, 2, 39, 1, 67, 6, 2, 2, 2, 2, 12, 1, 8, 1, 47, 1, 51, 1, 1, 3, 2, 2,
         5, 2, 1, 1, 42, 2, 8, 1, 238, 1, 2, 1, 4, 1, 0, 1, 0, 16, 16, 16, 0, 2, 0, 1, 226, 1, 149,
-        5, 0, 3, 1, 2, 5, 4, 40, 3, 4, 1, 165, 2, 0, 4, 0, 2, 153, 11, 49, 4, 123, 1, 54, 15, 41, 1,
-        2, 2, 10, 3, 49, 4, 2, 2, 7, 1, 61, 3, 36, 5, 1, 8, 62, 1, 12, 2, 52, 9, 10, 4, 2, 1, 95, 3,
-        2, 1, 1, 2, 6, 1, 160, 1, 3, 8, 21, 2, 57, 2, 1, 1, 1, 1, 22, 1, 14, 7, 3, 5, 195, 8, 2, 3,
-        1, 1, 23, 1, 81, 1, 2, 6, 1, 1, 2, 1, 1, 2, 1, 2, 235, 1, 2, 4, 6, 2, 1, 2, 27, 2, 85, 8, 2,
-        1, 1, 2, 106, 1, 1, 1, 2, 6, 1, 1, 101, 3, 2, 4, 1, 5, 0, 9, 1, 2, 245, 1, 10, 2, 1, 1, 4,
-        1, 144, 4, 2, 2, 4, 1, 32, 10, 40, 6, 2, 4, 8, 1, 9, 6, 2, 3, 46, 13, 1, 2, 0, 7, 1, 6, 1,
-        1, 82, 22, 2, 7, 1, 2, 1, 2, 122, 6, 3, 1, 1, 2, 1, 7, 1, 1, 72, 2, 3, 1, 1, 1, 0, 2, 0, 5,
-        59, 7, 0, 1, 63, 4, 81, 1, 0, 2, 0, 46, 2, 23, 0, 1, 1, 3, 4, 5, 8, 8, 2, 7, 30, 4, 148, 3,
-        0, 55, 4, 50, 8, 1, 14, 1, 22, 5, 1, 15, 0, 7, 1, 17, 2, 7, 1, 2, 1, 5, 0, 7, 0, 1, 61, 4,
-        0, 7, 109, 7, 0, 96, 128, 240, 0,
+        5, 0, 3, 1, 2, 5, 4, 40, 3, 4, 1, 165, 2, 0, 4, 0, 2, 80, 3, 70, 11, 49, 4, 123, 1, 54, 15,
+        41, 1, 2, 2, 10, 3, 49, 4, 2, 2, 7, 1, 61, 3, 36, 5, 1, 8, 62, 1, 12, 2, 52, 9, 10, 4, 2, 1,
+        95, 3, 2, 1, 1, 2, 6, 1, 2, 1, 157, 1, 3, 8, 21, 2, 57, 2, 1, 1, 1, 1, 22, 1, 14, 7, 3, 5,
+        195, 8, 2, 3, 1, 1, 23, 1, 81, 1, 2, 6, 1, 1, 2, 1, 1, 2, 1, 2, 235, 1, 2, 4, 6, 2, 1, 2,
+        27, 2, 85, 8, 2, 1, 1, 2, 106, 1, 1, 1, 2, 6, 1, 1, 101, 3, 2, 4, 1, 5, 0, 9, 1, 2, 245, 1,
+        10, 2, 1, 1, 4, 1, 144, 4, 2, 2, 4, 1, 32, 10, 40, 6, 2, 4, 8, 1, 9, 6, 2, 3, 46, 13, 1, 2,
+        0, 7, 1, 6, 1, 1, 82, 22, 2, 7, 1, 2, 1, 2, 122, 6, 3, 1, 1, 2, 1, 7, 1, 1, 72, 2, 3, 1, 1,
+        1, 0, 2, 11, 2, 52, 5, 5, 1, 1, 1, 0, 1, 6, 15, 0, 5, 59, 7, 0, 1, 63, 4, 81, 1, 0, 2, 0,
+        46, 2, 23, 0, 1, 1, 3, 4, 5, 8, 8, 2, 7, 30, 4, 148, 3, 0, 55, 4, 50, 8, 1, 14, 1, 22, 5, 1,
+        15, 0, 7, 1, 17, 2, 7, 1, 2, 1, 5, 100, 1, 160, 7, 0, 1, 61, 4, 0, 4, 0, 7, 109, 7, 0, 96,
+        128, 240, 0,
     ];
     pub fn lookup(c: char) -> bool {
         super::skip_search(
@@ -327,50 +330,52 @@ pub mod lowercase {
         14, 17, 0, 0, 9, 0, 0, 12, 13, 10, 0, 16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
         0, 0, 0, 4, 1, 0, 15, 0, 8, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-        0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 18, 0,
-        3, 0, 0, 7,
+        0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 19, 0,
+        3, 18, 0, 7,
     ];
-    const BITSET_INDEX_CHUNKS: &'static [[u8; 16]; 19] = &[
+    const BITSET_INDEX_CHUNKS: &'static [[u8; 16]; 20] = &[
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 59, 0, 0],
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 16, 14, 55, 0],
-        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 41, 0, 0, 0],
-        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 43, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 40, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 44, 0, 0, 0],
         [0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 0, 0],
-        [0, 0, 0, 0, 0, 0, 0, 0, 0, 65, 42, 0, 50, 46, 48, 32],
+        [0, 0, 0, 0, 0, 0, 0, 0, 0, 65, 43, 0, 51, 47, 49, 33],
         [0, 0, 0, 0, 10, 56, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [0, 0, 0, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [0, 0, 0, 53, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 26],
+        [0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 19, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 27],
         [0, 0, 0, 60, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [0, 0, 0, 70, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [0, 0, 57, 0, 55, 55, 55, 0, 21, 21, 67, 21, 35, 24, 23, 36],
-        [0, 5, 74, 0, 28, 15, 72, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [0, 64, 33, 17, 22, 51, 52, 47, 45, 8, 34, 40, 0, 27, 13, 30],
-        [11, 58, 0, 4, 0, 0, 29, 0, 0, 0, 0, 0, 0, 0, 31, 0],
-        [16, 25, 21, 37, 38, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [16, 49, 2, 20, 66, 9, 57, 0, 0, 0, 0, 0, 0, 0, 0, 0],
-        [63, 39, 54, 12, 73, 61, 18, 1, 6, 62, 71, 19, 68, 69, 3, 44],
+        [0, 0, 0, 69, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 57, 0, 55, 55, 55, 0, 22, 22, 67, 22, 36, 25, 24, 37],
+        [0, 5, 68, 0, 29, 15, 73, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [0, 64, 34, 17, 23, 52, 53, 48, 46, 8, 35, 42, 0, 28, 13, 31],
+        [11, 58, 0, 6, 0, 0, 30, 0, 0, 0, 0, 0, 0, 0, 32, 0],
+        [16, 26, 22, 38, 39, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [16, 50, 2, 21, 66, 9, 57, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [16, 70, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        [63, 41, 54, 12, 75, 61, 18, 1, 7, 62, 74, 20, 71, 72, 4, 45],
     ];
     const BITSET_CANONICAL: &'static [u64; 55] = &[
         0b0000000000000000000000000000000000000000000000000000000000000000,
         0b1111111111111111110000000000000000000000000011111111111111111111,
         0b1010101010101010101010101010101010101010101010101010100000000010,
+        0b0000000000000111111111111111111111111111111111111111111111111111,
         0b1111111111111111111111000000000000000000000000001111110111111111,
-        0b0000111111111111111111111111111111111111000000000000000000000000,
         0b1000000000000010000000000000000000000000000000000000000000000000,
+        0b0000111111111111111111111111111111111111000000000000000000000000,
         0b0000111111111111111111111111110000000000000000000000000011111111,
-        0b0000000000000111111111111111111111111111111111111111111111111111,
         0b1111111111111111111111111111111111111111111111111010101010000101,
         0b1111111111111111111111111111111100000000000000000000000000000000,
         0b1111111111111111111111111111110000000000000000000000000000000000,
         0b1111111111111111111111110000000000000000000000000000000000000000,
         0b1111111111111111111111000000000000000000000000001111111111101111,
         0b1111111111111111111100000000000000000000000000010000000000000000,
-        0b1111111111111111000000011111111111110111111111111111111111111111,
+        0b1111111111111111000000111111111111110111111111111111111111111111,
         0b1111111111111111000000000000000000000000000000000100001111000000,
         0b1111111111111111000000000000000000000000000000000000000000000000,
         0b1111111101111111111111111111111110000000000000000000000000000000,
         0b1111110000000000000000000000000011111111111111111111111111000000,
+        0b1111011111111111111111111111111111111111111111110000000000000000,
         0b1111000000000000000000000000001111110111111111111111111111111100,
         0b1010101010101010101010101010101010101010101010101101010101010100,
         0b1010101010101010101010101010101010101010101010101010101010101010,
@@ -384,16 +389,16 @@ pub mod lowercase {
         0b0001101111111011111111111111101111111111100000000000000000000000,
         0b0001100100101111101010101010101010101010111000110111111111111111,
         0b0000011111111101111111111111111111111111111111111111111110111001,
-        0b0000011101000000000000000000000000000010101010100000010100001010,
+        0b0000011101011100000000000000000000000010101010100000010100001010,
         0b0000010000100000000001000000000000000000000000000000000000000000,
         0b0000000111111111111111111111111111111111111011111111111111111111,
         0b0000000011111111000000001111111100000000001111110000000011111111,
         0b0000000011011100000000001111111100000000110011110000000011011100,
         0b0000000000001000010100000001101010101010101010101010101010101010,
         0b0000000000000000001000001011111111111111111111111111111111111111,
+        0b0000000000000000000001111110000001111111111111111111101111111111,
         0b0000000000000000000000001111111111111111110111111100000000000000,
         0b0000000000000000000000000001111100000000000000000000000000000011,
-        0b0000000000000000000000000000000001111111111111111111101111111111,
         0b0000000000000000000000000000000000111010101010101010101010101010,
         0b0000000000000000000000000000000000000000111110000000000001111111,
         0b0000000000000000000000000000000000000000000000000000101111110111,
@@ -405,13 +410,12 @@ pub mod lowercase {
         0b1010101010101011101010101010100000000000000000000000000000000000,
         0b1101010010101010101010101010101010101010101010101010101101010101,
         0b1110011001010001001011010010101001001110001001000011000100101001,
-        0b1110011111111111111111111111111111111111111111110000000000000000,
         0b1110101111000000000000000000000000001111111111111111111111111100,
     ];
-    const BITSET_MAPPING: &'static [(u8, u8); 20] = &[
+    const BITSET_MAPPING: &'static [(u8, u8); 21] = &[
         (0, 64), (1, 188), (1, 183), (1, 176), (1, 109), (1, 124), (1, 126), (1, 66), (1, 70),
-        (1, 77), (2, 146), (2, 144), (2, 83), (3, 12), (3, 6), (4, 156), (4, 78), (5, 187),
-        (6, 132), (7, 93),
+        (1, 77), (2, 146), (2, 144), (2, 83), (3, 93), (3, 147), (3, 133), (4, 12), (4, 6),
+        (5, 187), (6, 78), (7, 132),
     ];
 
     #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
@@ -428,14 +432,14 @@ pub mod lowercase {
 
 #[rustfmt::skip]
 pub mod n {
-    static SHORT_OFFSET_RUNS: [u32; 38] = [
+    static SHORT_OFFSET_RUNS: [u32; 39] = [
         1632, 18876774, 31461440, 102765417, 111154926, 115349830, 132128880, 165684320, 186656630,
         195046653, 199241735, 203436434, 216049184, 241215536, 249605104, 274792208, 278987015,
         283181793, 295766104, 320933114, 383848032, 392238160, 434181712, 442570976, 455154768,
-        463544256, 476128256, 480340576, 484535936, 501338848, 505534414, 513925440, 518120176,
-        522315975, 526511217, 534900992, 555875312, 561183738,
+        463544144, 476128256, 484534880, 488730240, 505533120, 509728718, 522314048, 526508784,
+        530703600, 534898887, 539094129, 547483904, 568458224, 573766650,
     ];
-    static OFFSETS: [u8; 269] = [
+    static OFFSETS: [u8; 275] = [
         48, 10, 120, 2, 5, 1, 2, 3, 0, 10, 134, 10, 198, 10, 0, 10, 118, 10, 4, 6, 108, 10, 118,
         10, 118, 10, 2, 6, 110, 13, 115, 10, 8, 7, 103, 10, 104, 7, 7, 19, 109, 10, 96, 10, 118, 10,
         70, 20, 0, 10, 70, 10, 0, 20, 0, 3, 239, 10, 6, 10, 22, 10, 0, 10, 128, 11, 165, 10, 6, 10,
@@ -445,9 +449,9 @@ pub mod n {
         29, 1, 8, 1, 134, 5, 202, 10, 0, 8, 25, 7, 39, 9, 75, 5, 22, 6, 160, 2, 2, 16, 2, 46, 64, 9,
         52, 2, 30, 3, 75, 5, 104, 8, 24, 8, 41, 7, 0, 6, 48, 10, 0, 31, 158, 10, 42, 4, 112, 7, 134,
         30, 128, 10, 60, 10, 144, 10, 7, 20, 251, 10, 0, 10, 118, 10, 0, 10, 102, 10, 102, 12, 0,
-        19, 93, 10, 0, 29, 227, 10, 70, 10, 0, 21, 0, 111, 0, 10, 86, 10, 134, 10, 1, 7, 0, 23, 0,
-        20, 108, 25, 0, 50, 0, 10, 0, 10, 0, 9, 128, 10, 0, 59, 1, 3, 1, 4, 76, 45, 1, 15, 0, 13, 0,
-        10, 0,
+        19, 93, 10, 0, 29, 227, 10, 70, 10, 0, 10, 102, 21, 0, 111, 0, 10, 86, 10, 134, 10, 1, 7, 0,
+        23, 0, 20, 12, 20, 108, 25, 0, 50, 0, 10, 0, 10, 0, 10, 0, 9, 128, 10, 0, 59, 1, 3, 1, 4,
+        76, 45, 1, 15, 0, 13, 0, 10, 0,
     ];
     pub fn lookup(c: char) -> bool {
         super::skip_search(
diff --git a/library/core/tests/ascii.rs b/library/core/tests/ascii.rs
index 6d2cf3e83..f5f2dd047 100644
--- a/library/core/tests/ascii.rs
+++ b/library/core/tests/ascii.rs
@@ -252,6 +252,23 @@ fn test_is_ascii_digit() {
 }
 
 #[test]
+fn test_is_ascii_octdigit() {
+    assert_all!(is_ascii_octdigit, "", "01234567");
+    assert_none!(
+        is_ascii_octdigit,
+        "abcdefghijklmnopqrstuvwxyz",
+        "ABCDEFGHIJKLMNOQPRSTUVWXYZ",
+        "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~",
+        " \t\n\x0c\r",
+        "\x00\x01\x02\x03\x04\x05\x06\x07",
+        "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+        "\x10\x11\x12\x13\x14\x15\x16\x17",
+        "\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f",
+        "\x7f",
+    );
+}
+
+#[test]
 fn test_is_ascii_hexdigit() {
     assert_all!(is_ascii_hexdigit, "", "0123456789", "abcdefABCDEF",);
     assert_none!(
@@ -454,6 +471,7 @@ fn ascii_ctype_const() {
         is_ascii_lowercase    => [true,  false, false, false, false];
         is_ascii_alphanumeric => [true,  true,  true,  false, false];
         is_ascii_digit        => [false, false, true,  false, false];
+        is_ascii_octdigit     => [false, false, false, false, false];
         is_ascii_hexdigit     => [true,  true,  true,  false, false];
         is_ascii_punctuation  => [false, false, false, true,  false];
         is_ascii_graphic      => [true,  true,  true,  true,  false];
diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
index 4a0e162bc..51f858ade 100644
--- a/library/core/tests/lib.rs
+++ b/library/core/tests/lib.rs
@@ -2,12 +2,12 @@
 #![feature(array_chunks)]
 #![feature(array_methods)]
 #![feature(array_windows)]
-#![feature(bench_black_box)]
 #![feature(bigint_helper_methods)]
 #![feature(cell_update)]
 #![feature(const_assume)]
 #![feature(const_black_box)]
 #![feature(const_bool_to_option)]
+#![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
 #![feature(const_heap)]
@@ -21,6 +21,7 @@
 #![feature(const_ptr_write)]
 #![feature(const_trait_impl)]
 #![feature(const_likely)]
+#![feature(const_location_fields)]
 #![feature(core_intrinsics)]
 #![feature(core_private_bignum)]
 #![feature(core_private_diy_float)]
@@ -48,8 +49,8 @@
 #![feature(slice_from_ptr_range)]
 #![feature(split_as_slice)]
 #![feature(maybe_uninit_uninit_array)]
-#![feature(maybe_uninit_array_assume_init)]
 #![feature(maybe_uninit_write_slice)]
+#![feature(maybe_uninit_uninit_array_transpose)]
 #![feature(min_specialization)]
 #![feature(numfmt)]
 #![feature(step_trait)]
@@ -74,6 +75,7 @@
 #![feature(iterator_try_reduce)]
 #![feature(const_mut_refs)]
 #![feature(const_pin)]
+#![feature(const_waker)]
 #![feature(never_type)]
 #![feature(unwrap_infallible)]
 #![feature(pointer_byte_offsets)]
@@ -93,13 +95,13 @@
 #![feature(strict_provenance_atomic_ptr)]
 #![feature(trusted_random_access)]
 #![feature(unsize)]
-#![feature(unzip_option)]
 #![feature(const_array_from_ref)]
 #![feature(const_slice_from_ref)]
 #![feature(waker_getters)]
 #![feature(slice_flatten)]
 #![feature(provide_any)]
 #![feature(utf8_chunks)]
+#![feature(is_ascii_octdigit)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 extern crate test;
@@ -130,6 +132,7 @@ mod nonzero;
 mod num;
 mod ops;
 mod option;
+mod panic;
 mod pattern;
 mod pin;
 mod pin_macro;
diff --git a/library/core/tests/mem.rs b/library/core/tests/mem.rs
index 6856d1a1f..0362e1c8a 100644
--- a/library/core/tests/mem.rs
+++ b/library/core/tests/mem.rs
@@ -130,7 +130,11 @@ fn test_transmute_copy_grow_panics() {
             payload
                 .downcast::<&'static str>()
                 .and_then(|s| {
-                    if *s == "cannot transmute_copy if U is larger than T" { Ok(s) } else { Err(s) }
+                    if *s == "cannot transmute_copy if Dst is larger than Src" {
+                        Ok(s)
+                    } else {
+                        Err(s)
+                    }
                 })
                 .unwrap_or_else(|p| panic::resume_unwind(p));
         }
@@ -163,18 +167,18 @@ fn assume_init_good() {
 
 #[test]
 fn uninit_array_assume_init() {
-    let mut array: [MaybeUninit<i16>; 5] = MaybeUninit::uninit_array();
+    let mut array = [MaybeUninit::<i16>::uninit(); 5];
     array[0].write(3);
     array[1].write(1);
     array[2].write(4);
     array[3].write(1);
     array[4].write(5);
 
-    let array = unsafe { MaybeUninit::array_assume_init(array) };
+    let array = unsafe { array.transpose().assume_init() };
 
     assert_eq!(array, [3, 1, 4, 1, 5]);
 
-    let [] = unsafe { MaybeUninit::<!>::array_assume_init([]) };
+    let [] = unsafe { [MaybeUninit::<!>::uninit(); 0].transpose().assume_init() };
 }
 
 #[test]
diff --git a/library/core/tests/num/int_log.rs b/library/core/tests/num/int_log.rs
index be203fb5c..a1edb1a51 100644
--- a/library/core/tests/num/int_log.rs
+++ b/library/core/tests/num/int_log.rs
@@ -164,3 +164,33 @@ fn ilog10_u64() {
 fn ilog10_u128() {
     ilog10_loop! { u128, 38 }
 }
+
+#[test]
+#[should_panic(expected = "argument of integer logarithm must be positive")]
+fn ilog2_of_0_panic() {
+    let _ = 0u32.ilog2();
+}
+
+#[test]
+#[should_panic(expected = "argument of integer logarithm must be positive")]
+fn ilog10_of_0_panic() {
+    let _ = 0u32.ilog10();
+}
+
+#[test]
+#[should_panic(expected = "argument of integer logarithm must be positive")]
+fn ilog3_of_0_panic() {
+    let _ = 0u32.ilog(3);
+}
+
+#[test]
+#[should_panic(expected = "base of integer logarithm must be at least 2")]
+fn ilog0_of_1_panic() {
+    let _ = 1u32.ilog(0);
+}
+
+#[test]
+#[should_panic(expected = "base of integer logarithm must be at least 2")]
+fn ilog1_of_1_panic() {
+    let _ = 1u32.ilog(1);
+}
diff --git a/library/core/tests/num/mod.rs b/library/core/tests/num/mod.rs
index 49580cdcc..c79e909e4 100644
--- a/library/core/tests/num/mod.rs
+++ b/library/core/tests/num/mod.rs
@@ -172,7 +172,7 @@ fn test_can_not_overflow() {
 
            // Calcutate the string length for the smallest overflowing number:
            let max_len_string = format_radix(num, base as u128);
-           // Ensure that that string length is deemed to potentially overflow:
+           // Ensure that string length is deemed to potentially overflow:
            assert!(can_overflow::<$t>(base, &max_len_string));
         }
         )*)
diff --git a/library/core/tests/num/wrapping.rs b/library/core/tests/num/wrapping.rs
index 8ded139a1..c5a719883 100644
--- a/library/core/tests/num/wrapping.rs
+++ b/library/core/tests/num/wrapping.rs
@@ -75,8 +75,6 @@ wrapping_test!(test_wrapping_u64, u64, u64::MIN, u64::MAX);
 wrapping_test!(test_wrapping_u128, u128, u128::MIN, u128::MAX);
 wrapping_test!(test_wrapping_usize, usize, usize::MIN, usize::MAX);
 
-// Don't warn about overflowing ops on 32-bit platforms
-#[cfg_attr(target_pointer_width = "32", allow(const_err))]
 #[test]
 fn wrapping_int_api() {
     assert_eq!(i8::MAX.wrapping_add(1), i8::MIN);
diff --git a/library/core/tests/option.rs b/library/core/tests/option.rs
index 9f5e537dc..f36f7c268 100644
--- a/library/core/tests/option.rs
+++ b/library/core/tests/option.rs
@@ -57,6 +57,7 @@ fn test_get_resource() {
 }
 
 #[test]
+#[cfg_attr(not(bootstrap), allow(for_loops_over_fallibles))]
 fn test_option_dance() {
     let x = Some(());
     let mut y = Some(5);
diff --git a/library/core/tests/panic.rs b/library/core/tests/panic.rs
new file mode 100644
index 000000000..24b6c56b3
--- /dev/null
+++ b/library/core/tests/panic.rs
@@ -0,0 +1 @@
+mod location;
diff --git a/library/core/tests/panic/location.rs b/library/core/tests/panic/location.rs
new file mode 100644
index 000000000..d20241d83
--- /dev/null
+++ b/library/core/tests/panic/location.rs
@@ -0,0 +1,31 @@
+use core::panic::Location;
+
+// Note: Some of the following tests depend on the source location,
+// so please be careful when editing this file.
+
+#[test]
+fn location_const_caller() {
+    const _CALLER_REFERENCE: &Location<'static> = Location::caller();
+    const _CALLER: Location<'static> = *Location::caller();
+}
+
+#[test]
+fn location_const_file() {
+    const CALLER: &Location<'static> = Location::caller();
+    const FILE: &str = CALLER.file();
+    assert_eq!(FILE, file!());
+}
+
+#[test]
+fn location_const_line() {
+    const CALLER: &Location<'static> = Location::caller();
+    const LINE: u32 = CALLER.line();
+    assert_eq!(LINE, 21);
+}
+
+#[test]
+fn location_const_column() {
+    const CALLER: &Location<'static> = Location::caller();
+    const COLUMN: u32 = CALLER.column();
+    assert_eq!(COLUMN, 40);
+}
diff --git a/library/core/tests/slice.rs b/library/core/tests/slice.rs
index b8f6fe696..9e1fbea79 100644
--- a/library/core/tests/slice.rs
+++ b/library/core/tests/slice.rs
@@ -1284,7 +1284,6 @@ fn test_windows_zip() {
 }
 
 #[test]
-#[allow(const_err)]
 fn test_iter_ref_consistency() {
     use std::fmt::Debug;
 
diff --git a/library/core/tests/task.rs b/library/core/tests/task.rs
index d71fef9e5..56be30e92 100644
--- a/library/core/tests/task.rs
+++ b/library/core/tests/task.rs
@@ -1,4 +1,4 @@
-use core::task::Poll;
+use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 
 #[test]
 fn poll_const() {
@@ -12,3 +12,18 @@ fn poll_const() {
     const IS_PENDING: bool = POLL.is_pending();
     assert!(IS_PENDING);
 }
+
+#[test]
+fn waker_const() {
+    const VOID_TABLE: RawWakerVTable = RawWakerVTable::new(|_| VOID_WAKER, |_| {}, |_| {}, |_| {});
+
+    const VOID_WAKER: RawWaker = RawWaker::new(&(), &VOID_TABLE);
+
+    static WAKER: Waker = unsafe { Waker::from_raw(VOID_WAKER) };
+
+    static CONTEXT: Context<'static> = Context::from_waker(&WAKER);
+
+    static WAKER_REF: &'static Waker = CONTEXT.waker();
+
+    WAKER_REF.wake_by_ref();
+}
diff --git a/library/core/tests/time.rs b/library/core/tests/time.rs
index fe2d2f241..a05128de4 100644
--- a/library/core/tests/time.rs
+++ b/library/core/tests/time.rs
@@ -197,9 +197,31 @@ fn correct_sum() {
 #[test]
 fn debug_formatting_extreme_values() {
     assert_eq!(
-        format!("{:?}", Duration::new(18_446_744_073_709_551_615, 123_456_789)),
+        format!("{:?}", Duration::new(u64::MAX, 123_456_789)),
         "18446744073709551615.123456789s"
     );
+    assert_eq!(format!("{:.0?}", Duration::MAX), "18446744073709551616s");
+    assert_eq!(format!("{:.0?}", Duration::new(u64::MAX, 500_000_000)), "18446744073709551616s");
+    assert_eq!(format!("{:.0?}", Duration::new(u64::MAX, 499_999_999)), "18446744073709551615s");
+    assert_eq!(
+        format!("{:.3?}", Duration::new(u64::MAX, 999_500_000)),
+        "18446744073709551616.000s"
+    );
+    assert_eq!(
+        format!("{:.3?}", Duration::new(u64::MAX, 999_499_999)),
+        "18446744073709551615.999s"
+    );
+    assert_eq!(
+        format!("{:.8?}", Duration::new(u64::MAX, 999_999_995)),
+        "18446744073709551616.00000000s"
+    );
+    assert_eq!(
+        format!("{:.8?}", Duration::new(u64::MAX, 999_999_994)),
+        "18446744073709551615.99999999s"
+    );
+    assert_eq!(format!("{:21.0?}", Duration::MAX), "18446744073709551616s");
+    assert_eq!(format!("{:22.0?}", Duration::MAX), "18446744073709551616s ");
+    assert_eq!(format!("{:24.0?}", Duration::MAX), "18446744073709551616s   ");
 }
 
 #[test]
@@ -445,3 +467,11 @@ fn duration_const() {
     const SATURATING_MUL: Duration = MAX.saturating_mul(2);
     assert_eq!(SATURATING_MUL, MAX);
 }
+
+#[test]
+fn from_neg_zero() {
+    assert_eq!(Duration::try_from_secs_f32(-0.0), Ok(Duration::ZERO));
+    assert_eq!(Duration::try_from_secs_f64(-0.0), Ok(Duration::ZERO));
+    assert_eq!(Duration::from_secs_f32(-0.0), Duration::ZERO);
+    assert_eq!(Duration::from_secs_f64(-0.0), Duration::ZERO);
+}
diff --git a/library/panic_unwind/src/emcc.rs b/library/panic_unwind/src/emcc.rs
index 7c233c7c3..c6d423085 100644
--- a/library/panic_unwind/src/emcc.rs
+++ b/library/panic_unwind/src/emcc.rs
@@ -47,7 +47,12 @@ static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
     name: b"rust_panic\0".as_ptr(),
 };
 
+// NOTE(nbdd0121): The `canary` field will be part of stable ABI after `c_unwind` stabilization.
+#[repr(C)]
 struct Exception {
+    // See `gcc.rs` on why this is present. We already have a static here so just use it.
+    canary: *const TypeInfo,
+
     // This is necessary because C++ code can capture our exception with
     // std::exception_ptr and rethrow it multiple times, possibly even in
     // another thread.
@@ -70,27 +75,38 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     let catch_data = &*(ptr as *mut CatchData);
 
     let adjusted_ptr = __cxa_begin_catch(catch_data.ptr as *mut libc::c_void) as *mut Exception;
-    let out = if catch_data.is_rust_panic {
-        let was_caught = (*adjusted_ptr).caught.swap(true, Ordering::SeqCst);
-        if was_caught {
-            // Since cleanup() isn't allowed to panic, we just abort instead.
-            intrinsics::abort();
-        }
-        (*adjusted_ptr).data.take().unwrap()
-    } else {
+    if !catch_data.is_rust_panic {
         super::__rust_foreign_exception();
-    };
+    }
+
+    let canary = ptr::addr_of!((*adjusted_ptr).canary).read();
+    if !ptr::eq(canary, &EXCEPTION_TYPE_INFO) {
+        super::__rust_foreign_exception();
+    }
+
+    let was_caught = (*adjusted_ptr).caught.swap(true, Ordering::SeqCst);
+    if was_caught {
+        // Since cleanup() isn't allowed to panic, we just abort instead.
+        intrinsics::abort();
+    }
+    let out = (*adjusted_ptr).data.take().unwrap();
     __cxa_end_catch();
     out
 }
 
 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
-    let sz = mem::size_of_val(&data);
-    let exception = __cxa_allocate_exception(sz) as *mut Exception;
+    let exception = __cxa_allocate_exception(mem::size_of::<Exception>()) as *mut Exception;
     if exception.is_null() {
         return uw::_URC_FATAL_PHASE1_ERROR as u32;
     }
-    ptr::write(exception, Exception { caught: AtomicBool::new(false), data: Some(data) });
+    ptr::write(
+        exception,
+        Exception {
+            canary: &EXCEPTION_TYPE_INFO,
+            caught: AtomicBool::new(false),
+            data: Some(data),
+        },
+    );
     __cxa_throw(exception as *mut _, &EXCEPTION_TYPE_INFO, exception_cleanup);
 }
 
diff --git a/library/panic_unwind/src/gcc.rs b/library/panic_unwind/src/gcc.rs
index 261404e87..0b7a873a6 100644
--- a/library/panic_unwind/src/gcc.rs
+++ b/library/panic_unwind/src/gcc.rs
@@ -38,12 +38,23 @@
 
 use alloc::boxed::Box;
 use core::any::Any;
+use core::ptr;
 
 use unwind as uw;
 
+// In case where multiple copies of std exist in a single process,
+// we use address of this static variable to distinguish an exception raised by
+// this copy and some other copy (which needs to be treated as foreign exception).
+static CANARY: u8 = 0;
+
+// NOTE(nbdd0121)
+// Once `c_unwind` feature is stabilized, there will be ABI stability requirement
+// on this struct. The first two field must be `_Unwind_Exception` and `canary`,
+// as it may be accessed by a different version of the std with a different compiler.
 #[repr(C)]
 struct Exception {
     _uwe: uw::_Unwind_Exception,
+    canary: *const u8,
     cause: Box<dyn Any + Send>,
 }
 
@@ -54,6 +65,7 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
             exception_cleanup,
             private: [0; uw::unwinder_private_data_size],
         },
+        canary: &CANARY,
         cause: data,
     });
     let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
@@ -75,10 +87,22 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     if (*exception).exception_class != rust_exception_class() {
         uw::_Unwind_DeleteException(exception);
         super::__rust_foreign_exception();
-    } else {
-        let exception = Box::from_raw(exception as *mut Exception);
-        exception.cause
     }
+
+    let exception = exception.cast::<Exception>();
+    // Just access the canary field, avoid accessing the entire `Exception` as
+    // it can be a foreign Rust exception.
+    let canary = ptr::addr_of!((*exception).canary).read();
+    if !ptr::eq(canary, &CANARY) {
+        // A foreign Rust exception, treat it slightly differently from other
+        // foreign exceptions, because call into `_Unwind_DeleteException` will
+        // call into `__rust_drop_panic` which produces a confusing
+        // "Rust panic must be rethrown" message.
+        super::__rust_foreign_exception();
+    }
+
+    let exception = Box::from_raw(exception as *mut Exception);
+    exception.cause
 }
 
 // Rust's exception class identifier.  This is used by personality routines to
diff --git a/library/panic_unwind/src/lib.rs b/library/panic_unwind/src/lib.rs
index 1eb4f3789..7e7180a38 100644
--- a/library/panic_unwind/src/lib.rs
+++ b/library/panic_unwind/src/lib.rs
@@ -42,7 +42,8 @@ cfg_if::cfg_if! {
         // L4Re is unix family but does not yet support unwinding.
         #[path = "dummy.rs"]
         mod real_imp;
-    } else if #[cfg(target_env = "msvc")] {
+    } else if #[cfg(all(target_env = "msvc", not(target_arch = "arm")))] {
+        // LLVM does not support unwinding on 32 bit ARM msvc (thumbv7a-pc-windows-msvc)
         #[path = "seh.rs"]
         mod real_imp;
     } else if #[cfg(any(
diff --git a/library/panic_unwind/src/seh.rs b/library/panic_unwind/src/seh.rs
index 6b8d06568..651115a82 100644
--- a/library/panic_unwind/src/seh.rs
+++ b/library/panic_unwind/src/seh.rs
@@ -49,9 +49,15 @@
 use alloc::boxed::Box;
 use core::any::Any;
 use core::mem::{self, ManuallyDrop};
+use core::ptr;
 use libc::{c_int, c_uint, c_void};
 
+// NOTE(nbdd0121): The `canary` field will be part of stable ABI after `c_unwind` stabilization.
+#[repr(C)]
 struct Exception {
+    // See `gcc.rs` on why this is present. We already have a static here so just use it.
+    canary: *const _TypeDescriptor,
+
     // This needs to be an Option because we catch the exception by reference
     // and its destructor is executed by the C++ runtime. When we take the Box
     // out of the exception, we need to leave the exception in a valid state
@@ -235,7 +241,7 @@ static mut TYPE_DESCRIPTOR: _TypeDescriptor = _TypeDescriptor {
 macro_rules! define_cleanup {
     ($abi:tt $abi2:tt) => {
         unsafe extern $abi fn exception_cleanup(e: *mut Exception) {
-            if let Exception { data: Some(b) } = e.read() {
+            if let Exception { data: Some(b), .. } = e.read() {
                 drop(b);
                 super::__rust_drop_panic();
             }
@@ -265,7 +271,7 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     // The ManuallyDrop is needed here since we don't want Exception to be
     // dropped when unwinding. Instead it will be dropped by exception_cleanup
     // which is invoked by the C++ runtime.
-    let mut exception = ManuallyDrop::new(Exception { data: Some(data) });
+    let mut exception = ManuallyDrop::new(Exception { canary: &TYPE_DESCRIPTOR, data: Some(data) });
     let throw_ptr = &mut exception as *mut _ as *mut _;
 
     // This... may seems surprising, and justifiably so. On 32-bit MSVC the
@@ -321,8 +327,12 @@ pub unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send> {
     // __rust_try. This happens when a non-Rust foreign exception is caught.
     if payload.is_null() {
         super::__rust_foreign_exception();
-    } else {
-        let exception = &mut *(payload as *mut Exception);
-        exception.data.take().unwrap()
     }
+    let exception = payload as *mut Exception;
+    let canary = ptr::addr_of!((*exception).canary).read();
+    if !ptr::eq(canary, &TYPE_DESCRIPTOR) {
+        // A foreign Rust exception.
+        super::__rust_foreign_exception();
+    }
+    (*exception).data.take().unwrap()
 }
diff --git a/library/proc_macro/src/bridge/client.rs b/library/proc_macro/src/bridge/client.rs
index 4461b2180..506b2a773 100644
--- a/library/proc_macro/src/bridge/client.rs
+++ b/library/proc_macro/src/bridge/client.rs
@@ -223,10 +223,10 @@ pub(crate) use super::symbol::Symbol;
 
 macro_rules! define_client_side {
     ($($name:ident {
-        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)*;)*
+        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
     }),* $(,)?) => {
         $(impl $name {
-            $(pub(crate) fn $method($($arg: $arg_ty),*) $(-> $ret_ty)* {
+            $(pub(crate) fn $method($($arg: $arg_ty),*) $(-> $ret_ty)? {
                 Bridge::with(|bridge| {
                     let mut buf = bridge.cached_buffer.take();
 
diff --git a/library/proc_macro/src/lib.rs b/library/proc_macro/src/lib.rs
index 495c1c5ae..0d3fc2c52 100644
--- a/library/proc_macro/src/lib.rs
+++ b/library/proc_macro/src/lib.rs
@@ -533,7 +533,7 @@ impl Span {
         other.resolved_at(*self)
     }
 
-    /// Compares to spans to see if they're equal.
+    /// Compares two spans to see if they're equal.
     #[unstable(feature = "proc_macro_span", issue = "54725")]
     pub fn eq(&self, other: &Span) -> bool {
         self.0 == other.0
@@ -546,7 +546,7 @@ impl Span {
     /// Note: The observable result of a macro should only rely on the tokens and
     /// not on this source text. The result of this function is a best effort to
     /// be used for diagnostics only.
-    #[unstable(feature = "proc_macro_span", issue = "54725")]
+    #[stable(feature = "proc_macro_source_text", since = "1.66.0")]
     pub fn source_text(&self) -> Option<String> {
         self.0.source_text()
     }
diff --git a/library/std/Cargo.toml b/library/std/Cargo.toml
index 324ecc804..bc10b12ec 100644
--- a/library/std/Cargo.toml
+++ b/library/std/Cargo.toml
@@ -11,11 +11,11 @@ crate-type = ["dylib", "rlib"]
 
 [dependencies]
 alloc = { path = "../alloc" }
-cfg-if = { version = "0.1.8", features = ['rustc-dep-of-std'] }
+cfg-if = { version = "1.0", features = ['rustc-dep-of-std'] }
 panic_unwind = { path = "../panic_unwind", optional = true }
 panic_abort = { path = "../panic_abort" }
 core = { path = "../core" }
-libc = { version = "0.2.126", default-features = false, features = ['rustc-dep-of-std'] }
+libc = { version = "0.2.135", default-features = false, features = ['rustc-dep-of-std'] }
 compiler_builtins = { version = "0.1.73" }
 profiler_builtins = { path = "../profiler_builtins", optional = true }
 unwind = { path = "../unwind" }
diff --git a/library/std/src/backtrace.rs b/library/std/src/backtrace.rs
index 5cf6ec817..9cb74f951 100644
--- a/library/std/src/backtrace.rs
+++ b/library/std/src/backtrace.rs
@@ -14,8 +14,8 @@
 //! Backtraces are attempted to be as accurate as possible, but no guarantees
 //! are provided about the exact accuracy of a backtrace. Instruction pointers,
 //! symbol names, filenames, line numbers, etc, may all be incorrect when
-//! reported. Accuracy is attempted on a best-effort basis, however, and bugs
-//! are always welcome to indicate areas of improvement!
+//! reported. Accuracy is attempted on a best-effort basis, however, any bug
+//! reports are always welcome to indicate areas of improvement!
 //!
 //! For most platforms a backtrace with a filename/line number requires that
 //! programs be compiled with debug information. Without debug information
@@ -39,7 +39,7 @@
 //! default. Its behavior is governed by two environment variables:
 //!
 //! * `RUST_LIB_BACKTRACE` - if this is set to `0` then `Backtrace::capture`
-//!   will never capture a backtrace. Any other value this is set to will enable
+//!   will never capture a backtrace. Any other value set will enable
 //!   `Backtrace::capture`.
 //!
 //! * `RUST_BACKTRACE` - if `RUST_LIB_BACKTRACE` is not set, then this variable
@@ -325,8 +325,7 @@ impl Backtrace {
     // Capture a backtrace which start just before the function addressed by
     // `ip`
     fn create(ip: usize) -> Backtrace {
-        // SAFETY: We don't attempt to lock this reentrantly.
-        let _lock = unsafe { lock() };
+        let _lock = lock();
         let mut frames = Vec::new();
         let mut actual_start = None;
         unsafe {
@@ -469,8 +468,7 @@ impl Capture {
         // Use the global backtrace lock to synchronize this as it's a
         // requirement of the `backtrace` crate, and then actually resolve
         // everything.
-        // SAFETY: We don't attempt to lock this reentrantly.
-        let _lock = unsafe { lock() };
+        let _lock = lock();
         for frame in self.frames.iter_mut() {
             let symbols = &mut frame.symbols;
             let frame = match &frame.frame {
diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index 9845d1faf..708edc5de 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/library/std/src/collections/hash/map.rs
@@ -9,7 +9,6 @@ use crate::borrow::Borrow;
 use crate::cell::Cell;
 use crate::collections::TryReserveError;
 use crate::collections::TryReserveErrorKind;
-#[cfg(not(bootstrap))]
 use crate::error::Error;
 use crate::fmt::{self, Debug};
 #[allow(deprecated)]
@@ -281,7 +280,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
+    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
         HashMap { base: base::HashMap::with_hasher(hash_builder) }
     }
 
@@ -759,7 +759,7 @@ where
 
     /// Tries to reserve capacity for at least `additional` more elements to be inserted
     /// in the `HashMap`. The collection may reserve more space to speculatively
-    /// avoid frequent reallocations. After calling `reserve`,
+    /// avoid frequent reallocations. After calling `try_reserve`,
     /// capacity will be greater than or equal to `self.len() + additional` if
     /// it returns `Ok(())`.
     /// Does nothing if capacity is already sufficient.
@@ -2160,7 +2160,6 @@ impl<'a, K: Debug, V: Debug> fmt::Display for OccupiedError<'a, K, V> {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[unstable(feature = "map_try_insert", issue = "82766")]
 impl<'a, K: fmt::Debug, V: fmt::Debug> Error for OccupiedError<'a, K, V> {
     #[allow(deprecated)]
diff --git a/library/std/src/collections/hash/map/tests.rs b/library/std/src/collections/hash/map/tests.rs
index cb3032719..65634f206 100644
--- a/library/std/src/collections/hash/map/tests.rs
+++ b/library/std/src/collections/hash/map/tests.rs
@@ -1115,3 +1115,9 @@ fn from_array() {
     // that's a problem!
     let _must_not_require_type_annotation = HashMap::from([(1, 2)]);
 }
+
+#[test]
+fn const_with_hasher() {
+    const X: HashMap<(), (), ()> = HashMap::with_hasher(());
+    assert_eq!(X.len(), 0);
+}
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index 5b6a415fa..cee884145 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/library/std/src/collections/hash/set.rs
@@ -376,7 +376,8 @@ impl<T, S> HashSet<T, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn with_hasher(hasher: S) -> HashSet<T, S> {
+    #[rustc_const_unstable(feature = "const_collections_with_hasher", issue = "102575")]
+    pub const fn with_hasher(hasher: S) -> HashSet<T, S> {
         HashSet { base: base::HashSet::with_hasher(hasher) }
     }
 
@@ -461,7 +462,7 @@ where
 
     /// Tries to reserve capacity for at least `additional` more elements to be inserted
     /// in the `HashSet`. The collection may reserve more space to speculatively
-    /// avoid frequent reallocations. After calling `reserve`,
+    /// avoid frequent reallocations. After calling `try_reserve`,
     /// capacity will be greater than or equal to `self.len() + additional` if
     /// it returns `Ok(())`.
     /// Does nothing if capacity is already sufficient.
diff --git a/library/std/src/collections/hash/set/tests.rs b/library/std/src/collections/hash/set/tests.rs
index 233db276b..941a0450c 100644
--- a/library/std/src/collections/hash/set/tests.rs
+++ b/library/std/src/collections/hash/set/tests.rs
@@ -496,3 +496,9 @@ fn from_array() {
     // that's a problem!
     let _must_not_require_type_annotation = HashSet::from([1, 2]);
 }
+
+#[test]
+fn const_with_hasher() {
+    const X: HashSet<(), ()> = HashSet::with_hasher(());
+    assert_eq!(X.len(), 0);
+}
diff --git a/library/std/src/env.rs b/library/std/src/env.rs
index 463f71406..6eb7cbea6 100644
--- a/library/std/src/env.rs
+++ b/library/std/src/env.rs
@@ -603,7 +603,7 @@ pub fn home_dir() -> Option<PathBuf> {
 /// # Platform-specific behavior
 ///
 /// On Unix, returns the value of the `TMPDIR` environment variable if it is
-/// set, otherwise for non-Android it returns `/tmp`. If Android, since there
+/// set, otherwise for non-Android it returns `/tmp`. On Android, since there
 /// is no global temporary folder (it is usually allocated per-app), it returns
 /// `/data/local/tmp`.
 /// On Windows, the behavior is equivalent to that of [`GetTempPath2`][GetTempPath2] /
diff --git a/library/std/src/error.rs b/library/std/src/error.rs
index e45059595..05f8fd8de 100644
--- a/library/std/src/error.rs
+++ b/library/std/src/error.rs
@@ -4,242 +4,12 @@
 #[cfg(test)]
 mod tests;
 
-#[cfg(bootstrap)]
-use core::array;
-#[cfg(bootstrap)]
-use core::convert::Infallible;
-
-#[cfg(bootstrap)]
-use crate::alloc::{AllocError, LayoutError};
-#[cfg(bootstrap)]
-use crate::any::Demand;
-#[cfg(bootstrap)]
-use crate::any::{Provider, TypeId};
 use crate::backtrace::Backtrace;
-#[cfg(bootstrap)]
-use crate::borrow::Cow;
-#[cfg(bootstrap)]
-use crate::cell;
-#[cfg(bootstrap)]
-use crate::char;
-#[cfg(bootstrap)]
-use crate::fmt::Debug;
-#[cfg(bootstrap)]
-use crate::fmt::Display;
 use crate::fmt::{self, Write};
-#[cfg(bootstrap)]
-use crate::io;
-#[cfg(bootstrap)]
-use crate::mem::transmute;
-#[cfg(bootstrap)]
-use crate::num;
-#[cfg(bootstrap)]
-use crate::str;
-#[cfg(bootstrap)]
-use crate::string;
-#[cfg(bootstrap)]
-use crate::sync::Arc;
-#[cfg(bootstrap)]
-use crate::time;
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::error::Error;
 
-/// `Error` is a trait representing the basic expectations for error values,
-/// i.e., values of type `E` in [`Result<T, E>`].
-///
-/// Errors must describe themselves through the [`Display`] and [`Debug`]
-/// traits. Error messages are typically concise lowercase sentences without
-/// trailing punctuation:
-///
-/// ```
-/// let err = "NaN".parse::<u32>().unwrap_err();
-/// assert_eq!(err.to_string(), "invalid digit found in string");
-/// ```
-///
-/// Errors may provide cause information. [`Error::source()`] is generally
-/// used when errors cross "abstraction boundaries". If one module must report
-/// an error that is caused by an error from a lower-level module, it can allow
-/// accessing that error via [`Error::source()`]. This makes it possible for the
-/// high-level module to provide its own errors while also revealing some of the
-/// implementation for debugging.
-#[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(test), rustc_diagnostic_item = "Error")]
-#[cfg(bootstrap)]
-pub trait Error: Debug + Display {
-    /// The lower-level source of this error, if any.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::fmt;
-    ///
-    /// #[derive(Debug)]
-    /// struct SuperError {
-    ///     source: SuperErrorSideKick,
-    /// }
-    ///
-    /// impl fmt::Display for SuperError {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "SuperError is here!")
-    ///     }
-    /// }
-    ///
-    /// impl Error for SuperError {
-    ///     fn source(&self) -> Option<&(dyn Error + 'static)> {
-    ///         Some(&self.source)
-    ///     }
-    /// }
-    ///
-    /// #[derive(Debug)]
-    /// struct SuperErrorSideKick;
-    ///
-    /// impl fmt::Display for SuperErrorSideKick {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "SuperErrorSideKick is here!")
-    ///     }
-    /// }
-    ///
-    /// impl Error for SuperErrorSideKick {}
-    ///
-    /// fn get_super_error() -> Result<(), SuperError> {
-    ///     Err(SuperError { source: SuperErrorSideKick })
-    /// }
-    ///
-    /// fn main() {
-    ///     match get_super_error() {
-    ///         Err(e) => {
-    ///             println!("Error: {e}");
-    ///             println!("Caused by: {}", e.source().unwrap());
-    ///         }
-    ///         _ => println!("No error"),
-    ///     }
-    /// }
-    /// ```
-    #[stable(feature = "error_source", since = "1.30.0")]
-    fn source(&self) -> Option<&(dyn Error + 'static)> {
-        None
-    }
-
-    /// Gets the `TypeId` of `self`.
-    #[doc(hidden)]
-    #[unstable(
-        feature = "error_type_id",
-        reason = "this is memory-unsafe to override in user code",
-        issue = "60784"
-    )]
-    fn type_id(&self, _: private::Internal) -> TypeId
-    where
-        Self: 'static,
-    {
-        TypeId::of::<Self>()
-    }
-
-    /// ```
-    /// if let Err(e) = "xc".parse::<u32>() {
-    ///     // Print `e` itself, no need for description().
-    ///     eprintln!("Error: {e}");
-    /// }
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[deprecated(since = "1.42.0", note = "use the Display impl or to_string()")]
-    fn description(&self) -> &str {
-        "description() is deprecated; use Display"
-    }
-
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[deprecated(
-        since = "1.33.0",
-        note = "replaced by Error::source, which can support downcasting"
-    )]
-    #[allow(missing_docs)]
-    fn cause(&self) -> Option<&dyn Error> {
-        self.source()
-    }
-
-    /// Provides type based access to context intended for error reports.
-    ///
-    /// Used in conjunction with [`Demand::provide_value`] and [`Demand::provide_ref`] to extract
-    /// references to member variables from `dyn Error` trait objects.
-    ///
-    /// # Example
-    ///
-    /// ```rust
-    /// #![feature(provide_any)]
-    /// #![feature(error_generic_member_access)]
-    /// use core::fmt;
-    /// use core::any::Demand;
-    ///
-    /// #[derive(Debug)]
-    /// struct MyBacktrace {
-    ///     // ...
-    /// }
-    ///
-    /// impl MyBacktrace {
-    ///     fn new() -> MyBacktrace {
-    ///         // ...
-    ///         # MyBacktrace {}
-    ///     }
-    /// }
-    ///
-    /// #[derive(Debug)]
-    /// struct SourceError {
-    ///     // ...
-    /// }
-    ///
-    /// impl fmt::Display for SourceError {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "Example Source Error")
-    ///     }
-    /// }
-    ///
-    /// impl std::error::Error for SourceError {}
-    ///
-    /// #[derive(Debug)]
-    /// struct Error {
-    ///     source: SourceError,
-    ///     backtrace: MyBacktrace,
-    /// }
-    ///
-    /// impl fmt::Display for Error {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "Example Error")
-    ///     }
-    /// }
-    ///
-    /// impl std::error::Error for Error {
-    ///     fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
-    ///         demand
-    ///             .provide_ref::<MyBacktrace>(&self.backtrace)
-    ///             .provide_ref::<dyn std::error::Error + 'static>(&self.source);
-    ///     }
-    /// }
-    ///
-    /// fn main() {
-    ///     let backtrace = MyBacktrace::new();
-    ///     let source = SourceError {};
-    ///     let error = Error { source, backtrace };
-    ///     let dyn_error = &error as &dyn std::error::Error;
-    ///     let backtrace_ref = dyn_error.request_ref::<MyBacktrace>().unwrap();
-    ///
-    ///     assert!(core::ptr::eq(&error.backtrace, backtrace_ref));
-    /// }
-    /// ```
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    #[allow(unused_variables)]
-    fn provide<'a>(&'a self, demand: &mut Demand<'a>) {}
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "error_generic_member_access", issue = "99301")]
-impl<'b> Provider for dyn Error + 'b {
-    fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
-        self.provide(demand)
-    }
-}
-
 mod private {
     // This is a hack to prevent `type_id` from being overridden by `Error`
     // implementations, since that can enable unsound downcasting.
@@ -248,799 +18,6 @@ mod private {
     pub struct Internal;
 }
 
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
-    /// Converts a type of [`Error`] into a box of dyn [`Error`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::fmt;
-    /// use std::mem;
-    ///
-    /// #[derive(Debug)]
-    /// struct AnError;
-    ///
-    /// impl fmt::Display for AnError {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "An error")
-    ///     }
-    /// }
-    ///
-    /// impl Error for AnError {}
-    ///
-    /// let an_error = AnError;
-    /// assert!(0 == mem::size_of_val(&an_error));
-    /// let a_boxed_error = Box::<dyn Error>::from(an_error);
-    /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(err: E) -> Box<dyn Error + 'a> {
-        Box::new(err)
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a type of [`Error`] + [`Send`] + [`Sync`] into a box of
-    /// dyn [`Error`] + [`Send`] + [`Sync`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::fmt;
-    /// use std::mem;
-    ///
-    /// #[derive(Debug)]
-    /// struct AnError;
-    ///
-    /// impl fmt::Display for AnError {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "An error")
-    ///     }
-    /// }
-    ///
-    /// impl Error for AnError {}
-    ///
-    /// unsafe impl Send for AnError {}
-    ///
-    /// unsafe impl Sync for AnError {}
-    ///
-    /// let an_error = AnError;
-    /// assert!(0 == mem::size_of_val(&an_error));
-    /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
-    /// assert!(
-    ///     mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
-        Box::new(err)
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl From<String> for Box<dyn Error + Send + Sync> {
-    /// Converts a [`String`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    ///
-    /// let a_string_error = "a string error".to_string();
-    /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
-    /// assert!(
-    ///     mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    #[inline]
-    fn from(err: String) -> Box<dyn Error + Send + Sync> {
-        struct StringError(String);
-
-        impl Error for StringError {
-            #[allow(deprecated)]
-            fn description(&self) -> &str {
-                &self.0
-            }
-        }
-
-        impl Display for StringError {
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                Display::fmt(&self.0, f)
-            }
-        }
-
-        // Purposefully skip printing "StringError(..)"
-        impl Debug for StringError {
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                Debug::fmt(&self.0, f)
-            }
-        }
-
-        Box::new(StringError(err))
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "string_box_error", since = "1.6.0")]
-impl From<String> for Box<dyn Error> {
-    /// Converts a [`String`] into a box of dyn [`Error`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    ///
-    /// let a_string_error = "a string error".to_string();
-    /// let a_boxed_error = Box::<dyn Error>::from(a_string_error);
-    /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(str_err: String) -> Box<dyn Error> {
-        let err1: Box<dyn Error + Send + Sync> = From::from(str_err);
-        let err2: Box<dyn Error> = err1;
-        err2
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a> From<&str> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a [`str`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
-    ///
-    /// [`str`]: prim@str
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    ///
-    /// let a_str_error = "a str error";
-    /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
-    /// assert!(
-    ///     mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    #[inline]
-    fn from(err: &str) -> Box<dyn Error + Send + Sync + 'a> {
-        From::from(String::from(err))
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "string_box_error", since = "1.6.0")]
-impl From<&str> for Box<dyn Error> {
-    /// Converts a [`str`] into a box of dyn [`Error`].
-    ///
-    /// [`str`]: prim@str
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    ///
-    /// let a_str_error = "a str error";
-    /// let a_boxed_error = Box::<dyn Error>::from(a_str_error);
-    /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(err: &str) -> Box<dyn Error> {
-        From::from(String::from(err))
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "cow_box_error", since = "1.22.0")]
-impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a> {
-    /// Converts a [`Cow`] into a box of dyn [`Error`] + [`Send`] + [`Sync`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    /// use std::borrow::Cow;
-    ///
-    /// let a_cow_str_error = Cow::from("a str error");
-    /// let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
-    /// assert!(
-    ///     mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a> {
-        From::from(String::from(err))
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "cow_box_error", since = "1.22.0")]
-impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
-    /// Converts a [`Cow`] into a box of dyn [`Error`].
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::error::Error;
-    /// use std::mem;
-    /// use std::borrow::Cow;
-    ///
-    /// let a_cow_str_error = Cow::from("a str error");
-    /// let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
-    /// assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))
-    /// ```
-    fn from(err: Cow<'a, str>) -> Box<dyn Error> {
-        From::from(String::from(err))
-    }
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "never_type", issue = "35121")]
-impl Error for ! {}
-
-#[cfg(bootstrap)]
-#[unstable(
-    feature = "allocator_api",
-    reason = "the precise API and guarantees it provides may be tweaked.",
-    issue = "32838"
-)]
-impl Error for AllocError {}
-
-#[cfg(bootstrap)]
-#[stable(feature = "alloc_layout", since = "1.28.0")]
-impl Error for LayoutError {}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for str::ParseBoolError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "failed to parse bool"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for str::Utf8Error {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "invalid utf-8: corrupt contents"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for num::ParseIntError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_from", since = "1.34.0")]
-impl Error for num::TryFromIntError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_from", since = "1.34.0")]
-impl Error for array::TryFromSliceError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for num::ParseFloatError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for string::FromUtf8Error {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "invalid utf-8"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for string::FromUtf16Error {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "invalid utf-16"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "str_parse_error2", since = "1.8.0")]
-impl Error for Infallible {
-    fn description(&self) -> &str {
-        match *self {}
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "decode_utf16", since = "1.9.0")]
-impl Error for char::DecodeUtf16Error {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "unpaired surrogate found"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "u8_from_char", since = "1.59.0")]
-impl Error for char::TryFromCharError {}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "map_try_insert", issue = "82766")]
-impl<'a, K: Debug + Ord, V: Debug> Error
-    for crate::collections::btree_map::OccupiedError<'a, K, V>
-{
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "key already exists"
-    }
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "map_try_insert", issue = "82766")]
-impl<'a, K: Debug, V: Debug> Error for crate::collections::hash_map::OccupiedError<'a, K, V> {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "key already exists"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "box_error", since = "1.8.0")]
-impl<T: Error> Error for Box<T> {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        Error::description(&**self)
-    }
-
-    #[allow(deprecated)]
-    fn cause(&self) -> Option<&dyn Error> {
-        Error::cause(&**self)
-    }
-
-    fn source(&self) -> Option<&(dyn Error + 'static)> {
-        Error::source(&**self)
-    }
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "thin_box", issue = "92791")]
-impl<T: ?Sized + crate::error::Error> crate::error::Error for crate::boxed::ThinBox<T> {
-    fn source(&self) -> Option<&(dyn crate::error::Error + 'static)> {
-        use core::ops::Deref;
-        self.deref().source()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "error_by_ref", since = "1.51.0")]
-impl<'a, T: Error + ?Sized> Error for &'a T {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        Error::description(&**self)
-    }
-
-    #[allow(deprecated)]
-    fn cause(&self) -> Option<&dyn Error> {
-        Error::cause(&**self)
-    }
-
-    fn source(&self) -> Option<&(dyn Error + 'static)> {
-        Error::source(&**self)
-    }
-
-    fn provide<'b>(&'b self, demand: &mut Demand<'b>) {
-        Error::provide(&**self, demand);
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "arc_error", since = "1.52.0")]
-impl<T: Error + ?Sized> Error for Arc<T> {
-    #[allow(deprecated, deprecated_in_future)]
-    fn description(&self) -> &str {
-        Error::description(&**self)
-    }
-
-    #[allow(deprecated)]
-    fn cause(&self) -> Option<&dyn Error> {
-        Error::cause(&**self)
-    }
-
-    fn source(&self) -> Option<&(dyn Error + 'static)> {
-        Error::source(&**self)
-    }
-
-    fn provide<'a>(&'a self, demand: &mut Demand<'a>) {
-        Error::provide(&**self, demand);
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "fmt_error", since = "1.11.0")]
-impl Error for fmt::Error {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "an error occurred when formatting an argument"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_borrow", since = "1.13.0")]
-impl Error for cell::BorrowError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "already mutably borrowed"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_borrow", since = "1.13.0")]
-impl Error for cell::BorrowMutError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "already borrowed"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_from", since = "1.34.0")]
-impl Error for char::CharTryFromError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "converted integer out of range for `char`"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "char_from_str", since = "1.20.0")]
-impl Error for char::ParseCharError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "try_reserve", since = "1.57.0")]
-impl Error for alloc::collections::TryReserveError {}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-impl Error for time::FromFloatSecsError {}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for alloc::ffi::NulError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "nul byte found in data"
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl From<alloc::ffi::NulError> for io::Error {
-    /// Converts a [`alloc::ffi::NulError`] into a [`io::Error`].
-    fn from(_: alloc::ffi::NulError) -> io::Error {
-        io::const_io_error!(io::ErrorKind::InvalidInput, "data provided contains a nul byte")
-    }
-}
-
-#[cfg(bootstrap)]
-#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
-impl Error for core::ffi::FromBytesWithNulError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
-impl Error for core::ffi::FromBytesUntilNulError {}
-
-#[cfg(bootstrap)]
-#[stable(feature = "cstring_from_vec_with_nul", since = "1.58.0")]
-impl Error for alloc::ffi::FromVecWithNulError {}
-
-#[cfg(bootstrap)]
-#[stable(feature = "cstring_into", since = "1.7.0")]
-impl Error for alloc::ffi::IntoStringError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        "C string contained non-utf8 bytes"
-    }
-
-    fn source(&self) -> Option<&(dyn Error + 'static)> {
-        Some(self.__source())
-    }
-}
-
-#[cfg(bootstrap)]
-impl<'a> dyn Error + 'a {
-    /// Request a reference of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_ref<T: ?Sized + 'static>(&'a self) -> Option<&'a T> {
-        core::any::request_ref(self)
-    }
-
-    /// Request a value of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_value<T: 'static>(&'a self) -> Option<T> {
-        core::any::request_value(self)
-    }
-}
-
-// Copied from `any.rs`.
-#[cfg(bootstrap)]
-impl dyn Error + 'static {
-    /// Returns `true` if the inner type is the same as `T`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn is<T: Error + 'static>(&self) -> bool {
-        // Get `TypeId` of the type this function is instantiated with.
-        let t = TypeId::of::<T>();
-
-        // Get `TypeId` of the type in the trait object (`self`).
-        let concrete = self.type_id(private::Internal);
-
-        // Compare both `TypeId`s on equality.
-        t == concrete
-    }
-
-    /// Returns some reference to the inner value if it is of type `T`, or
-    /// `None` if it isn't.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
-        if self.is::<T>() {
-            unsafe { Some(&*(self as *const dyn Error as *const T)) }
-        } else {
-            None
-        }
-    }
-
-    /// Returns some mutable reference to the inner value if it is of type `T`, or
-    /// `None` if it isn't.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
-        if self.is::<T>() {
-            unsafe { Some(&mut *(self as *mut dyn Error as *mut T)) }
-        } else {
-            None
-        }
-    }
-}
-
-#[cfg(bootstrap)]
-impl dyn Error + 'static + Send {
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn is<T: Error + 'static>(&self) -> bool {
-        <dyn Error + 'static>::is::<T>(self)
-    }
-
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
-        <dyn Error + 'static>::downcast_ref::<T>(self)
-    }
-
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
-        <dyn Error + 'static>::downcast_mut::<T>(self)
-    }
-
-    /// Request a reference of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
-        <dyn Error>::request_ref(self)
-    }
-
-    /// Request a value of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_value<T: 'static>(&self) -> Option<T> {
-        <dyn Error>::request_value(self)
-    }
-}
-
-#[cfg(bootstrap)]
-impl dyn Error + 'static + Send + Sync {
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn is<T: Error + 'static>(&self) -> bool {
-        <dyn Error + 'static>::is::<T>(self)
-    }
-
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
-        <dyn Error + 'static>::downcast_ref::<T>(self)
-    }
-
-    /// Forwards to the method defined on the type `dyn Error`.
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    #[inline]
-    pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
-        <dyn Error + 'static>::downcast_mut::<T>(self)
-    }
-
-    /// Request a reference of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_ref<T: ?Sized + 'static>(&self) -> Option<&T> {
-        <dyn Error>::request_ref(self)
-    }
-
-    /// Request a value of type `T` as context about this error.
-    #[unstable(feature = "error_generic_member_access", issue = "99301")]
-    pub fn request_value<T: 'static>(&self) -> Option<T> {
-        <dyn Error>::request_value(self)
-    }
-}
-
-#[cfg(bootstrap)]
-impl dyn Error {
-    #[inline]
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    /// Attempts to downcast the box to a concrete type.
-    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error>> {
-        if self.is::<T>() {
-            unsafe {
-                let raw: *mut dyn Error = Box::into_raw(self);
-                Ok(Box::from_raw(raw as *mut T))
-            }
-        } else {
-            Err(self)
-        }
-    }
-
-    /// Returns an iterator starting with the current error and continuing with
-    /// recursively calling [`Error::source`].
-    ///
-    /// If you want to omit the current error and only use its sources,
-    /// use `skip(1)`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(error_iter)]
-    /// use std::error::Error;
-    /// use std::fmt;
-    ///
-    /// #[derive(Debug)]
-    /// struct A;
-    ///
-    /// #[derive(Debug)]
-    /// struct B(Option<Box<dyn Error + 'static>>);
-    ///
-    /// impl fmt::Display for A {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "A")
-    ///     }
-    /// }
-    ///
-    /// impl fmt::Display for B {
-    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-    ///         write!(f, "B")
-    ///     }
-    /// }
-    ///
-    /// impl Error for A {}
-    ///
-    /// impl Error for B {
-    ///     fn source(&self) -> Option<&(dyn Error + 'static)> {
-    ///         self.0.as_ref().map(|e| e.as_ref())
-    ///     }
-    /// }
-    ///
-    /// let b = B(Some(Box::new(A)));
-    ///
-    /// // let err : Box<Error> = b.into(); // or
-    /// let err = &b as &(dyn Error);
-    ///
-    /// let mut iter = err.sources();
-    ///
-    /// assert_eq!("B".to_string(), iter.next().unwrap().to_string());
-    /// assert_eq!("A".to_string(), iter.next().unwrap().to_string());
-    /// assert!(iter.next().is_none());
-    /// assert!(iter.next().is_none());
-    /// ```
-    #[unstable(feature = "error_iter", issue = "58520")]
-    #[inline]
-    pub fn sources(&self) -> Sources<'_> {
-        // You may think this method would be better in the Error trait, and you'd be right.
-        // Unfortunately that doesn't work, not because of the object safety rules but because we
-        // save a reference to self in Sources below as a trait object. If this method was
-        // declared in Error, then self would have the type &T where T is some concrete type which
-        // implements Error. We would need to coerce self to have type &dyn Error, but that requires
-        // that Self has a known size (i.e., Self: Sized). We can't put that bound on Error
-        // since that would forbid Error trait objects, and we can't put that bound on the method
-        // because that means the method can't be called on trait objects (we'd also need the
-        // 'static bound, but that isn't allowed because methods with bounds on Self other than
-        // Sized are not object-safe). Requiring an Unsize bound is not backwards compatible.
-
-        Sources { current: Some(self) }
-    }
-}
-
-/// An iterator over an [`Error`] and its sources.
-///
-/// If you want to omit the initial error and only process
-/// its sources, use `skip(1)`.
-#[unstable(feature = "error_iter", issue = "58520")]
-#[derive(Clone, Debug)]
-#[cfg(bootstrap)]
-pub struct Sources<'a> {
-    current: Option<&'a (dyn Error + 'static)>,
-}
-
-#[cfg(bootstrap)]
-#[unstable(feature = "error_iter", issue = "58520")]
-impl<'a> Iterator for Sources<'a> {
-    type Item = &'a (dyn Error + 'static);
-
-    fn next(&mut self) -> Option<Self::Item> {
-        let current = self.current;
-        self.current = self.current.and_then(Error::source);
-        current
-    }
-}
-
-#[cfg(bootstrap)]
-impl dyn Error + Send {
-    #[inline]
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    /// Attempts to downcast the box to a concrete type.
-    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<dyn Error + Send>> {
-        let err: Box<dyn Error> = self;
-        <dyn Error>::downcast(err).map_err(|s| unsafe {
-            // Reapply the `Send` marker.
-            transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
-        })
-    }
-}
-
-#[cfg(bootstrap)]
-impl dyn Error + Send + Sync {
-    #[inline]
-    #[stable(feature = "error_downcast", since = "1.3.0")]
-    /// Attempts to downcast the box to a concrete type.
-    pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
-        let err: Box<dyn Error> = self;
-        <dyn Error>::downcast(err).map_err(|s| unsafe {
-            // Reapply the `Send + Sync` marker.
-            transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
-        })
-    }
-}
-
 /// An error reporter that prints an error and its sources.
 ///
 /// Report also exposes configuration options for formatting the error sources, either entirely on a
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index c6c78dc39..188ff00e1 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -1365,6 +1365,34 @@ impl FileTimes {
 impl Permissions {
     /// Returns `true` if these permissions describe a readonly (unwritable) file.
     ///
+    /// # Note
+    ///
+    /// This function does not take Access Control Lists (ACLs) or Unix group
+    /// membership into account.
+    ///
+    /// # Windows
+    ///
+    /// On Windows this returns [`FILE_ATTRIBUTE_READONLY`](https://docs.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants).
+    /// If `FILE_ATTRIBUTE_READONLY` is set then writes to the file will fail
+    /// but the user may still have permission to change this flag. If
+    /// `FILE_ATTRIBUTE_READONLY` is *not* set then writes may still fail due
+    /// to lack of write permission.
+    /// The behavior of this attribute for directories depends on the Windows
+    /// version.
+    ///
+    /// # Unix (including macOS)
+    ///
+    /// On Unix-based platforms this checks if *any* of the owner, group or others
+    /// write permission bits are set. It does not check if the current
+    /// user is in the file's assigned group. It also does not check ACLs.
+    /// Therefore even if this returns true you may not be able to write to the
+    /// file, and vice versa. The [`PermissionsExt`] trait gives direct access
+    /// to the permission bits but also does not read ACLs. If you need to
+    /// accurately know whether or not a file is writable use the `access()`
+    /// function from libc.
+    ///
+    /// [`PermissionsExt`]: crate::os::unix::fs::PermissionsExt
+    ///
     /// # Examples
     ///
     /// ```no_run
@@ -1390,8 +1418,40 @@ impl Permissions {
     /// using the resulting `Permission` will update file permissions to allow
     /// writing.
     ///
-    /// This operation does **not** modify the filesystem. To modify the
-    /// filesystem use the [`set_permissions`] function.
+    /// This operation does **not** modify the files attributes. This only
+    /// changes the in-memory value of these attributes for this `Permissions`
+    /// instance. To modify the files attributes use the [`set_permissions`]
+    /// function which commits these attribute changes to the file.
+    ///
+    /// # Note
+    ///
+    /// `set_readonly(false)` makes the file *world-writable* on Unix.
+    /// You can use the [`PermissionsExt`] trait on Unix to avoid this issue.
+    ///
+    /// It also does not take Access Control Lists (ACLs) or Unix group
+    /// membership into account.
+    ///
+    /// # Windows
+    ///
+    /// On Windows this sets or clears [`FILE_ATTRIBUTE_READONLY`](https://docs.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants).
+    /// If `FILE_ATTRIBUTE_READONLY` is set then writes to the file will fail
+    /// but the user may still have permission to change this flag. If
+    /// `FILE_ATTRIBUTE_READONLY` is *not* set then the write may still fail if
+    /// the user does not have permission to write to the file.
+    ///
+    /// In Windows 7 and earlier this attribute prevents deleting empty
+    /// directories. It does not prevent modifying the directory contents.
+    /// On later versions of Windows this attribute is ignored for directories.
+    ///
+    /// # Unix (including macOS)
+    ///
+    /// On Unix-based platforms this sets or clears the write access bit for
+    /// the owner, group *and* others, equivalent to `chmod a+w <file>`
+    /// or `chmod a-w <file>` respectively. The latter will grant write access
+    /// to all users! You can use the [`PermissionsExt`] trait on Unix
+    /// to avoid this issue.
+    ///
+    /// [`PermissionsExt`]: crate::os::unix::fs::PermissionsExt
     ///
     /// # Examples
     ///
@@ -1405,7 +1465,8 @@ impl Permissions {
     ///
     ///     permissions.set_readonly(true);
     ///
-    ///     // filesystem doesn't change
+    ///     // filesystem doesn't change, only the in memory state of the
+    ///     // readonly permission
     ///     assert_eq!(false, metadata.permissions().readonly());
     ///
     ///     // just this particular `permissions`.
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 29b09fcc5..3cabf2449 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -76,7 +76,6 @@ impl fmt::Debug for Error {
     }
 }
 
-#[cfg(not(bootstrap))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl From<alloc::ffi::NulError> for Error {
     /// Converts a [`alloc::ffi::NulError`] into a [`Error`].
@@ -388,7 +387,7 @@ pub enum ErrorKind {
 impl ErrorKind {
     pub(crate) fn as_str(&self) -> &'static str {
         use ErrorKind::*;
-        // Strictly alphabetical, please.  (Sadly rustfmt cannot do this yet.)
+        // tidy-alphabetical-start
         match *self {
             AddrInUse => "address in use",
             AddrNotAvailable => "address not available",
@@ -432,6 +431,7 @@ impl ErrorKind {
             WouldBlock => "operation would block",
             WriteZero => "write zero",
         }
+        // tidy-alphabetical-end
     }
 }
 
@@ -482,6 +482,7 @@ impl Error {
     /// originate from the OS itself. The `error` argument is an arbitrary
     /// payload which will be contained in this [`Error`].
     ///
+    /// Note that this function allocates memory on the heap.
     /// If no extra payload is required, use the `From` conversion from
     /// `ErrorKind`.
     ///
@@ -496,7 +497,7 @@ impl Error {
     /// // errors can also be created from other errors
     /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
     ///
-    /// // creating an error without payload
+    /// // creating an error without payload (and without memory allocation)
     /// let eof_error = Error::from(ErrorKind::UnexpectedEof);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/std/src/io/error/tests.rs b/library/std/src/io/error/tests.rs
index c897a5e87..16c634e9a 100644
--- a/library/std/src/io/error/tests.rs
+++ b/library/std/src/io/error/tests.rs
@@ -86,7 +86,7 @@ fn test_errorkind_packing() {
     assert_eq!(Error::from(ErrorKind::NotFound).kind(), ErrorKind::NotFound);
     assert_eq!(Error::from(ErrorKind::PermissionDenied).kind(), ErrorKind::PermissionDenied);
     assert_eq!(Error::from(ErrorKind::Uncategorized).kind(), ErrorKind::Uncategorized);
-    // Check that the innards look like like what we want.
+    // Check that the innards look like what we want.
     assert_matches!(
         Error::from(ErrorKind::OutOfMemory).repr.data(),
         ErrorData::Simple(ErrorKind::OutOfMemory),
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index eeace2c43..23a13523f 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -262,9 +262,12 @@ use crate::sys_common::memchr;
 
 #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 pub use self::buffered::WriterPanicked;
+pub(crate) use self::stdio::attempt_print_to_stderr;
 #[unstable(feature = "internal_output_capture", issue = "none")]
 #[doc(no_inline, hidden)]
 pub use self::stdio::set_output_capture;
+#[unstable(feature = "is_terminal", issue = "98070")]
+pub use self::stdio::IsTerminal;
 #[unstable(feature = "print_internals", issue = "none")]
 pub use self::stdio::{_eprint, _print};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -580,7 +583,7 @@ pub trait Read {
     /// `n > buf.len()`.
     ///
     /// No guarantees are provided about the contents of `buf` when this
-    /// function is called, implementations cannot rely on any property of the
+    /// function is called, so implementations cannot rely on any property of the
     /// contents of `buf` being true. It is recommended that *implementations*
     /// only write data to `buf` instead of reading its contents.
     ///
@@ -756,7 +759,7 @@ pub trait Read {
     /// specified buffer `buf`.
     ///
     /// No guarantees are provided about the contents of `buf` when this
-    /// function is called, implementations cannot rely on any property of the
+    /// function is called, so implementations cannot rely on any property of the
     /// contents of `buf` being true. It is recommended that implementations
     /// only write data to `buf` instead of reading its contents. The
     /// documentation on [`read`] has a more detailed explanation on this
diff --git a/library/std/src/io/readbuf.rs b/library/std/src/io/readbuf.rs
index b1a84095f..4800eeda0 100644
--- a/library/std/src/io/readbuf.rs
+++ b/library/std/src/io/readbuf.rs
@@ -3,10 +3,10 @@
 #[cfg(test)]
 mod tests;
 
-use crate::cmp;
 use crate::fmt::{self, Debug, Formatter};
 use crate::io::{Result, Write};
 use crate::mem::{self, MaybeUninit};
+use crate::{cmp, ptr};
 
 /// A borrowed byte buffer which is incrementally filled and initialized.
 ///
@@ -250,8 +250,11 @@ impl<'a> BorrowedCursor<'a> {
     /// Initializes all bytes in the cursor.
     #[inline]
     pub fn ensure_init(&mut self) -> &mut Self {
-        for byte in self.uninit_mut() {
-            byte.write(0);
+        let uninit = self.uninit_mut();
+        // SAFETY: 0 is a valid value for MaybeUninit<u8> and the length matches the allocation
+        // since it is comes from a slice reference.
+        unsafe {
+            ptr::write_bytes(uninit.as_mut_ptr(), 0, uninit.len());
         }
         self.buf.init = self.buf.capacity();
 
diff --git a/library/std/src/io/stdio.rs b/library/std/src/io/stdio.rs
index 2dc12a18a..1141a957d 100644
--- a/library/std/src/io/stdio.rs
+++ b/library/std/src/io/stdio.rs
@@ -7,6 +7,7 @@ use crate::io::prelude::*;
 
 use crate::cell::{Cell, RefCell};
 use crate::fmt;
+use crate::fs::File;
 use crate::io::{self, BufReader, IoSlice, IoSliceMut, LineWriter, Lines};
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::{Arc, Mutex, MutexGuard, OnceLock};
@@ -999,7 +1000,18 @@ fn print_to<T>(args: fmt::Arguments<'_>, global_s: fn() -> T, label: &str)
 where
     T: Write,
 {
-    if OUTPUT_CAPTURE_USED.load(Ordering::Relaxed)
+    if print_to_buffer_if_capture_used(args) {
+        // Successfully wrote to capture buffer.
+        return;
+    }
+
+    if let Err(e) = global_s().write_fmt(args) {
+        panic!("failed printing to {label}: {e}");
+    }
+}
+
+fn print_to_buffer_if_capture_used(args: fmt::Arguments<'_>) -> bool {
+    OUTPUT_CAPTURE_USED.load(Ordering::Relaxed)
         && OUTPUT_CAPTURE.try_with(|s| {
             // Note that we completely remove a local sink to write to in case
             // our printing recursively panics/prints, so the recursive
@@ -1009,16 +1021,49 @@ where
                 s.set(Some(w));
             })
         }) == Ok(Some(()))
-    {
-        // Successfully wrote to capture buffer.
+}
+
+/// Used by impl Termination for Result to print error after `main` or a test
+/// has returned. Should avoid panicking, although we can't help it if one of
+/// the Display impls inside args decides to.
+pub(crate) fn attempt_print_to_stderr(args: fmt::Arguments<'_>) {
+    if print_to_buffer_if_capture_used(args) {
         return;
     }
 
-    if let Err(e) = global_s().write_fmt(args) {
-        panic!("failed printing to {label}: {e}");
-    }
+    // Ignore error if the write fails, for example because stderr is already
+    // closed. There is not much point panicking at this point.
+    let _ = stderr().write_fmt(args);
 }
 
+/// Trait to determine if a descriptor/handle refers to a terminal/tty.
+#[unstable(feature = "is_terminal", issue = "98070")]
+pub trait IsTerminal: crate::sealed::Sealed {
+    /// Returns `true` if the descriptor/handle refers to a terminal/tty.
+    ///
+    /// On platforms where Rust does not know how to detect a terminal yet, this will return
+    /// `false`. This will also return `false` if an unexpected error occurred, such as from
+    /// passing an invalid file descriptor.
+    fn is_terminal(&self) -> bool;
+}
+
+macro_rules! impl_is_terminal {
+    ($($t:ty),*$(,)?) => {$(
+        #[unstable(feature = "sealed", issue = "none")]
+        impl crate::sealed::Sealed for $t {}
+
+        #[unstable(feature = "is_terminal", issue = "98070")]
+        impl IsTerminal for $t {
+            #[inline]
+            fn is_terminal(&self) -> bool {
+                crate::sys::io::is_terminal(self)
+            }
+        }
+    )*}
+}
+
+impl_is_terminal!(File, Stdin, StdinLock<'_>, Stdout, StdoutLock<'_>, Stderr, StderrLock<'_>);
+
 #[unstable(
     feature = "print_internals",
     reason = "implementation detail which may disappear or be replaced at any time",
diff --git a/library/std/src/keyword_docs.rs b/library/std/src/keyword_docs.rs
index a4b0522b0..e35145c4a 100644
--- a/library/std/src/keyword_docs.rs
+++ b/library/std/src/keyword_docs.rs
@@ -1867,11 +1867,15 @@ mod type_keyword {}
 /// Code or interfaces whose [memory safety] cannot be verified by the type
 /// system.
 ///
-/// The `unsafe` keyword has two uses: to declare the existence of contracts the
-/// compiler can't check (`unsafe fn` and `unsafe trait`), and to declare that a
-/// programmer has checked that these contracts have been upheld (`unsafe {}`
-/// and `unsafe impl`, but also `unsafe fn` -- see below). They are not mutually
-/// exclusive, as can be seen in `unsafe fn`.
+/// The `unsafe` keyword has two uses:
+/// - to declare the existence of contracts the compiler can't check (`unsafe fn` and `unsafe
+/// trait`),
+/// - and to declare that a programmer has checked that these contracts have been upheld (`unsafe
+/// {}` and `unsafe impl`, but also `unsafe fn` -- see below).
+///
+/// They are not mutually exclusive, as can be seen in `unsafe fn`: the body of an `unsafe fn` is,
+/// by default, treated like an unsafe block. The `unsafe_op_in_unsafe_fn` lint can be enabled to
+/// change that.
 ///
 /// # Unsafe abilities
 ///
@@ -1914,12 +1918,12 @@ mod type_keyword {}
 /// - `unsafe impl`: the contract necessary to implement the trait has been
 /// checked by the programmer and is guaranteed to be respected.
 ///
-/// `unsafe fn` also acts like an `unsafe {}` block
+/// By default, `unsafe fn` also acts like an `unsafe {}` block
 /// around the code inside the function. This means it is not just a signal to
 /// the caller, but also promises that the preconditions for the operations
-/// inside the function are upheld. Mixing these two meanings can be confusing
-/// and [proposal]s exist to use `unsafe {}` blocks inside such functions when
-/// making `unsafe` operations.
+/// inside the function are upheld. Mixing these two meanings can be confusing, so the
+/// `unsafe_op_in_unsafe_fn` lint can be enabled to warn against that and require explicit unsafe
+/// blocks even inside `unsafe fn`.
 ///
 /// See the [Rustnomicon] and the [Reference] for more information.
 ///
@@ -1987,13 +1991,16 @@ mod type_keyword {}
 ///
 /// ```rust
 /// # #![allow(dead_code)]
+/// #![deny(unsafe_op_in_unsafe_fn)]
+///
 /// /// Dereference the given pointer.
 /// ///
 /// /// # Safety
 /// ///
 /// /// `ptr` must be aligned and must not be dangling.
 /// unsafe fn deref_unchecked(ptr: *const i32) -> i32 {
-///     *ptr
+///     // SAFETY: the caller is required to ensure that `ptr` is aligned and dereferenceable.
+///     unsafe { *ptr }
 /// }
 ///
 /// let a = 3;
@@ -2003,35 +2010,118 @@ mod type_keyword {}
 /// unsafe { assert_eq!(*b, deref_unchecked(b)); };
 /// ```
 ///
-/// Traits marked as `unsafe` must be [`impl`]emented using `unsafe impl`. This
-/// makes a guarantee to other `unsafe` code that the implementation satisfies
-/// the trait's safety contract. The [Send] and [Sync] traits are examples of
-/// this behaviour in the standard library.
+/// ## `unsafe` and traits
+///
+/// The interactions of `unsafe` and traits can be surprising, so let us contrast the
+/// two combinations of safe `fn` in `unsafe trait` and `unsafe fn` in safe trait using two
+/// examples:
+///
+/// ```rust
+/// /// # Safety
+/// ///
+/// /// `make_even` must return an even number.
+/// unsafe trait MakeEven {
+///     fn make_even(&self) -> i32;
+/// }
+///
+/// // SAFETY: Our `make_even` always returns something even.
+/// unsafe impl MakeEven for i32 {
+///     fn make_even(&self) -> i32 {
+///         self << 1
+///     }
+/// }
+///
+/// fn use_make_even(x: impl MakeEven) {
+///     if x.make_even() % 2 == 1 {
+///         // SAFETY: this can never happen, because all `MakeEven` implementations
+///         // ensure that `make_even` returns something even.
+///         unsafe { std::hint::unreachable_unchecked() };
+///     }
+/// }
+/// ```
+///
+/// Note how the safety contract of the trait is upheld by the implementation, and is itself used to
+/// uphold the safety contract of the unsafe function `unreachable_unchecked` called by
+/// `use_make_even`. `make_even` itself is a safe function because its *callers* do not have to
+/// worry about any contract, only the *implementation* of `MakeEven` is required to uphold a
+/// certain contract. `use_make_even` is safe because it can use the promise made by `MakeEven`
+/// implementations to uphold the safety contract of the `unsafe fn unreachable_unchecked` it calls.
+///
+/// It is also possible to have `unsafe fn` in a regular safe `trait`:
 ///
 /// ```rust
-/// /// Implementors of this trait must guarantee an element is always
-/// /// accessible with index 3.
-/// unsafe trait ThreeIndexable<T> {
-///     /// Returns a reference to the element with index 3 in `&self`.
-///     fn three(&self) -> &T;
+/// # #![feature(never_type)]
+/// #![deny(unsafe_op_in_unsafe_fn)]
+///
+/// trait Indexable {
+///     const LEN: usize;
+///
+///     /// # Safety
+///     ///
+///     /// The caller must ensure that `idx < LEN`.
+///     unsafe fn idx_unchecked(&self, idx: usize) -> i32;
 /// }
 ///
-/// // The implementation of `ThreeIndexable` for `[T; 4]` is `unsafe`
-/// // because the implementor must abide by a contract the compiler cannot
-/// // check but as a programmer we know there will always be a valid element
-/// // at index 3 to access.
-/// unsafe impl<T> ThreeIndexable<T> for [T; 4] {
-///     fn three(&self) -> &T {
-///         // SAFETY: implementing the trait means there always is an element
-///         // with index 3 accessible.
-///         unsafe { self.get_unchecked(3) }
+/// // The implementation for `i32` doesn't need to do any contract reasoning.
+/// impl Indexable for i32 {
+///     const LEN: usize = 1;
+///
+///     unsafe fn idx_unchecked(&self, idx: usize) -> i32 {
+///         debug_assert_eq!(idx, 0);
+///         *self
 ///     }
 /// }
 ///
-/// let a = [1, 2, 4, 8];
-/// assert_eq!(a.three(), &8);
+/// // The implementation for arrays exploits the function contract to
+/// // make use of `get_unchecked` on slices and avoid a run-time check.
+/// impl Indexable for [i32; 42] {
+///     const LEN: usize = 42;
+///
+///     unsafe fn idx_unchecked(&self, idx: usize) -> i32 {
+///         // SAFETY: As per this trait's documentation, the caller ensures
+///         // that `idx < 42`.
+///         unsafe { *self.get_unchecked(idx) }
+///     }
+/// }
+///
+/// // The implementation for the never type declares a length of 0,
+/// // which means `idx_unchecked` can never be called.
+/// impl Indexable for ! {
+///     const LEN: usize = 0;
+///
+///     unsafe fn idx_unchecked(&self, idx: usize) -> i32 {
+///         // SAFETY: As per this trait's documentation, the caller ensures
+///         // that `idx < 0`, which is impossible, so this is dead code.
+///         unsafe { std::hint::unreachable_unchecked() }
+///     }
+/// }
+///
+/// fn use_indexable<I: Indexable>(x: I, idx: usize) -> i32 {
+///     if idx < I::LEN {
+///         // SAFETY: We have checked that `idx < I::LEN`.
+///         unsafe { x.idx_unchecked(idx) }
+///     } else {
+///         panic!("index out-of-bounds")
+///     }
+/// }
 /// ```
 ///
+/// This time, `use_indexable` is safe because it uses a run-time check to discharge the safety
+/// contract of `idx_unchecked`. Implementing `Indexable` is safe because when writing
+/// `idx_unchecked`, we don't have to worry: our *callers* need to discharge a proof obligation
+/// (like `use_indexable` does), but the *implementation* of `get_unchecked` has no proof obligation
+/// to contend with. Of course, the implementation of `Indexable` may choose to call other unsafe
+/// operations, and then it needs an `unsafe` *block* to indicate it discharged the proof
+/// obligations of its callees. (We enabled `unsafe_op_in_unsafe_fn`, so the body of `idx_unchecked`
+/// is not implicitly an unsafe block.) For that purpose it can make use of the contract that all
+/// its callers must uphold -- the fact that `idx < LEN`.
+///
+/// Formally speaking, an `unsafe fn` in a trait is a function with *preconditions* that go beyond
+/// those encoded by the argument types (such as `idx < LEN`), whereas an `unsafe trait` can declare
+/// that some of its functions have *postconditions* that go beyond those encoded in the return type
+/// (such as returning an even integer). If a trait needs a function with both extra precondition
+/// and extra postcondition, then it needs an `unsafe fn` in an `unsafe trait`.
+///
 /// [`extern`]: keyword.extern.html
 /// [`trait`]: keyword.trait.html
 /// [`static`]: keyword.static.html
@@ -2043,7 +2133,6 @@ mod type_keyword {}
 /// [nomicon-soundness]: ../nomicon/safe-unsafe-meaning.html
 /// [soundness]: https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#soundness-of-code--of-a-library
 /// [Reference]: ../reference/unsafety.html
-/// [proposal]: https://github.com/rust-lang/rfcs/pull/2585
 /// [discussion on Rust Internals]: https://internals.rust-lang.org/t/what-does-unsafe-mean/6696
 mod unsafe_keyword {}
 
diff --git a/library/std/src/lazy.rs b/library/std/src/lazy.rs
deleted file mode 100644
index f8c06c3f9..000000000
--- a/library/std/src/lazy.rs
+++ /dev/null
@@ -1 +0,0 @@
-//! Lazy values and one-time initialization of static data.
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index bc4f1b27c..385585dad 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -145,8 +145,8 @@
 //! abstracting over differences in common platforms, most notably Windows and
 //! Unix derivatives.
 //!
-//! Common types of I/O, including [files], [TCP], [UDP], are defined in the
-//! [`io`], [`fs`], and [`net`] modules.
+//! Common types of I/O, including [files], [TCP], and [UDP], are defined in
+//! the [`io`], [`fs`], and [`net`] modules.
 //!
 //! The [`thread`] module contains Rust's threading abstractions. [`sync`]
 //! contains further primitive shared memory types, including [`atomic`] and
@@ -251,11 +251,11 @@
 #![feature(doc_notable_trait)]
 #![feature(dropck_eyepatch)]
 #![feature(exhaustive_patterns)]
+#![feature(if_let_guard)]
 #![feature(intra_doc_pointers)]
-#![cfg_attr(bootstrap, feature(label_break_value))]
+#![feature(is_terminal)]
 #![feature(lang_items)]
 #![feature(let_chains)]
-#![cfg_attr(bootstrap, feature(let_else))]
 #![feature(linkage)]
 #![feature(link_cfg)]
 #![feature(min_specialization)]
@@ -280,11 +280,10 @@
 #![feature(core_intrinsics)]
 #![feature(cstr_from_bytes_until_nul)]
 #![feature(cstr_internals)]
-#![feature(duration_checked_float)]
 #![feature(duration_constants)]
-#![cfg_attr(not(bootstrap), feature(error_generic_member_access))]
-#![cfg_attr(not(bootstrap), feature(error_in_core))]
-#![cfg_attr(not(bootstrap), feature(error_iter))]
+#![feature(error_generic_member_access)]
+#![feature(error_in_core)]
+#![feature(error_iter)]
 #![feature(exact_size_is_empty)]
 #![feature(exclusive_wrapper)]
 #![feature(extend_one)]
@@ -293,10 +292,9 @@
 #![feature(hasher_prefixfree_extras)]
 #![feature(hashmap_internals)]
 #![feature(int_error_internals)]
-#![feature(is_some_with)]
+#![feature(is_some_and)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_write_slice)]
-#![feature(mixed_integer_ops)]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(panic_can_unwind)]
 #![feature(panic_info_message)]
@@ -315,6 +313,7 @@
 #![feature(strict_provenance)]
 #![feature(maybe_uninit_uninit_array)]
 #![feature(const_maybe_uninit_uninit_array)]
+#![feature(const_waker)]
 //
 // Library features (alloc):
 #![feature(alloc_layout_extra)]
@@ -350,9 +349,9 @@
 #![feature(trace_macros)]
 //
 // Only used in tests/benchmarks:
-#![feature(bench_black_box)]
 //
 // Only for const-ness:
+#![feature(const_collections_with_hasher)]
 #![feature(const_io_structs)]
 #![feature(const_ip)]
 #![feature(const_ipv4)]
@@ -530,9 +529,6 @@ pub mod process;
 pub mod sync;
 pub mod time;
 
-#[unstable(feature = "once_cell", issue = "74465")]
-pub mod lazy;
-
 // Pull in `std_float` crate  into libstd. The contents of
 // `std_float` are in a different repository: rust-lang/portable-simd.
 #[path = "../../portable-simd/crates/std_float/src/lib.rs"]
diff --git a/library/std/src/os/fd/mod.rs b/library/std/src/os/fd/mod.rs
index a45694753..c6aa7c77d 100644
--- a/library/std/src/os/fd/mod.rs
+++ b/library/std/src/os/fd/mod.rs
@@ -1,16 +1,25 @@
 //! Owned and borrowed Unix-like file descriptors.
+//!
+//! This module is supported on Unix platforms and WASI, which both use a
+//! similar file descriptor system for referencing OS resources.
 
 #![stable(feature = "io_safety", since = "1.63.0")]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 // `RawFd`, `AsRawFd`, etc.
-pub mod raw;
+mod raw;
 
 // `OwnedFd`, `AsFd`, etc.
-pub mod owned;
+mod owned;
 
 // Implementations for `AsRawFd` etc. for network types.
 mod net;
 
 #[cfg(test)]
 mod tests;
+
+// Export the types and traits for the public API.
+#[unstable(feature = "os_fd", issue = "98699")]
+pub use owned::*;
+#[unstable(feature = "os_fd", issue = "98699")]
+pub use raw::*;
diff --git a/library/std/src/os/fd/owned.rs b/library/std/src/os/fd/owned.rs
index 71e33fb9e..c16518577 100644
--- a/library/std/src/os/fd/owned.rs
+++ b/library/std/src/os/fd/owned.rs
@@ -6,6 +6,7 @@
 use super::raw::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 use crate::fmt;
 use crate::fs;
+use crate::io;
 use crate::marker::PhantomData;
 use crate::mem::forget;
 #[cfg(not(any(target_arch = "wasm32", target_env = "sgx")))]
@@ -192,6 +193,23 @@ impl fmt::Debug for OwnedFd {
     }
 }
 
+macro_rules! impl_is_terminal {
+    ($($t:ty),*$(,)?) => {$(
+        #[unstable(feature = "sealed", issue = "none")]
+        impl crate::sealed::Sealed for $t {}
+
+        #[unstable(feature = "is_terminal", issue = "98070")]
+        impl crate::io::IsTerminal for $t {
+            #[inline]
+            fn is_terminal(&self) -> bool {
+                crate::sys::io::is_terminal(self)
+            }
+        }
+    )*}
+}
+
+impl_is_terminal!(BorrowedFd<'_>, OwnedFd);
+
 /// A trait to borrow the file descriptor from an underlying object.
 ///
 /// This is only available on unix platforms and must be imported in order to
@@ -206,10 +224,8 @@ pub trait AsFd {
     /// ```rust,no_run
     /// use std::fs::File;
     /// # use std::io;
-    /// # #[cfg(target_os = "wasi")]
-    /// # use std::os::wasi::io::{AsFd, BorrowedFd};
-    /// # #[cfg(unix)]
-    /// # use std::os::unix::io::{AsFd, BorrowedFd};
+    /// # #[cfg(any(unix, target_os = "wasi"))]
+    /// # use std::os::fd::{AsFd, BorrowedFd};
     ///
     /// let mut f = File::open("foo.txt")?;
     /// # #[cfg(any(unix, target_os = "wasi"))]
@@ -387,3 +403,54 @@ impl<T: AsFd> AsFd for Box<T> {
         (**self).as_fd()
     }
 }
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl AsFd for io::Stdin {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        unsafe { BorrowedFd::borrow_raw(0) }
+    }
+}
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl<'a> AsFd for io::StdinLock<'a> {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        // SAFETY: user code should not close stdin out from under the standard library
+        unsafe { BorrowedFd::borrow_raw(0) }
+    }
+}
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl AsFd for io::Stdout {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        unsafe { BorrowedFd::borrow_raw(1) }
+    }
+}
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl<'a> AsFd for io::StdoutLock<'a> {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        // SAFETY: user code should not close stdout out from under the standard library
+        unsafe { BorrowedFd::borrow_raw(1) }
+    }
+}
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl AsFd for io::Stderr {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        unsafe { BorrowedFd::borrow_raw(2) }
+    }
+}
+
+#[stable(feature = "io_safety", since = "1.63.0")]
+impl<'a> AsFd for io::StderrLock<'a> {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        // SAFETY: user code should not close stderr out from under the standard library
+        unsafe { BorrowedFd::borrow_raw(2) }
+    }
+}
diff --git a/library/std/src/os/fd/raw.rs b/library/std/src/os/fd/raw.rs
index 1b3d11042..f92a05066 100644
--- a/library/std/src/os/fd/raw.rs
+++ b/library/std/src/os/fd/raw.rs
@@ -42,10 +42,8 @@ pub trait AsRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
-    /// #[cfg(unix)]
-    /// use std::os::unix::io::{AsRawFd, RawFd};
-    /// #[cfg(target_os = "wasi")]
-    /// use std::os::wasi::io::{AsRawFd, RawFd};
+    /// #[cfg(any(unix, target_os = "wasi"))]
+    /// use std::os::fd::{AsRawFd, RawFd};
     ///
     /// let mut f = File::open("foo.txt")?;
     /// // Note that `raw_fd` is only valid as long as `f` exists.
@@ -83,10 +81,8 @@ pub trait FromRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
-    /// #[cfg(unix)]
-    /// use std::os::unix::io::{FromRawFd, IntoRawFd, RawFd};
-    /// #[cfg(target_os = "wasi")]
-    /// use std::os::wasi::io::{FromRawFd, IntoRawFd, RawFd};
+    /// #[cfg(any(unix, target_os = "wasi"))]
+    /// use std::os::fd::{FromRawFd, IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;
     /// # #[cfg(any(unix, target_os = "wasi"))]
@@ -121,10 +117,8 @@ pub trait IntoRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
-    /// #[cfg(unix)]
-    /// use std::os::unix::io::{IntoRawFd, RawFd};
-    /// #[cfg(target_os = "wasi")]
-    /// use std::os::wasi::io::{IntoRawFd, RawFd};
+    /// #[cfg(any(unix, target_os = "wasi"))]
+    /// use std::os::fd::{IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;
     /// #[cfg(any(unix, target_os = "wasi"))]
diff --git a/library/std/src/os/mod.rs b/library/std/src/os/mod.rs
index 18c64b510..42773805c 100644
--- a/library/std/src/os/mod.rs
+++ b/library/std/src/os/mod.rs
@@ -145,9 +145,11 @@ pub mod solaris;
 pub mod solid;
 #[cfg(target_os = "vxworks")]
 pub mod vxworks;
+#[cfg(target_os = "watchos")]
+pub(crate) mod watchos;
 
 #[cfg(any(unix, target_os = "wasi", doc))]
-mod fd;
+pub mod fd;
 
 #[cfg(any(target_os = "linux", target_os = "android", doc))]
 mod net;
diff --git a/library/std/src/os/unix/io/fd.rs b/library/std/src/os/unix/io/fd.rs
deleted file mode 100644
index d4cb69645..000000000
--- a/library/std/src/os/unix/io/fd.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-//! Owned and borrowed file descriptors.
-
-// Tests for this module
-#[cfg(test)]
-mod tests;
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-pub use crate::os::fd::owned::*;
diff --git a/library/std/src/os/unix/io/mod.rs b/library/std/src/os/unix/io/mod.rs
index 3ab5606f8..25b5dbff1 100644
--- a/library/std/src/os/unix/io/mod.rs
+++ b/library/std/src/os/unix/io/mod.rs
@@ -77,10 +77,9 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-mod fd;
-mod raw;
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-pub use fd::*;
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use raw::*;
+pub use crate::os::fd::*;
+
+// Tests for this module
+#[cfg(test)]
+mod tests;
diff --git a/library/std/src/os/unix/io/raw.rs b/library/std/src/os/unix/io/raw.rs
deleted file mode 100644
index a4d2ba797..000000000
--- a/library/std/src/os/unix/io/raw.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-//! Unix-specific extensions to general I/O primitives.
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use crate::os::fd::raw::*;
diff --git a/library/std/src/os/unix/io/fd/tests.rs b/library/std/src/os/unix/io/tests.rs
index 84d2a7a1a..84d2a7a1a 100644
--- a/library/std/src/os/unix/io/fd/tests.rs
+++ b/library/std/src/os/unix/io/tests.rs
diff --git a/library/std/src/os/unix/mod.rs b/library/std/src/os/unix/mod.rs
index 411cc0925..f97fa0fb0 100644
--- a/library/std/src/os/unix/mod.rs
+++ b/library/std/src/os/unix/mod.rs
@@ -73,6 +73,8 @@ mod platform {
     pub use crate::os::solaris::*;
     #[cfg(target_os = "vxworks")]
     pub use crate::os::vxworks::*;
+    #[cfg(target_os = "watchos")]
+    pub use crate::os::watchos::*;
 }
 
 pub mod ffi;
diff --git a/library/std/src/os/wasi/io/fd.rs b/library/std/src/os/wasi/io/fd.rs
index 75703af6a..930aca887 100644
--- a/library/std/src/os/wasi/io/fd.rs
+++ b/library/std/src/os/wasi/io/fd.rs
@@ -1,10 +1,9 @@
 //! Owned and borrowed file descriptors.
 
-#![stable(feature = "io_safety_wasi", since = "1.65.0")]
+#![unstable(feature = "wasi_ext", issue = "71213")]
 
 // Tests for this module
 #[cfg(test)]
 mod tests;
 
-#[stable(feature = "io_safety_wasi", since = "1.65.0")]
 pub use crate::os::fd::owned::*;
diff --git a/library/std/src/os/wasi/io/mod.rs b/library/std/src/os/wasi/io/mod.rs
index 4f5cfbf9a..57bd842a5 100644
--- a/library/std/src/os/wasi/io/mod.rs
+++ b/library/std/src/os/wasi/io/mod.rs
@@ -1,12 +1,6 @@
 //! WASI-specific extensions to general I/O primitives.
 
-#![deny(unsafe_op_in_unsafe_fn)]
-#![stable(feature = "io_safety_wasi", since = "1.65.0")]
+#![stable(feature = "io_safety", since = "1.63.0")]
 
-mod fd;
-mod raw;
-
-#[stable(feature = "io_safety_wasi", since = "1.65.0")]
-pub use fd::*;
-#[stable(feature = "io_safety_wasi", since = "1.65.0")]
-pub use raw::*;
+#[stable(feature = "io_safety", since = "1.63.0")]
+pub use crate::os::fd::*;
diff --git a/library/std/src/os/wasi/io/raw.rs b/library/std/src/os/wasi/io/raw.rs
index 4ac792ee8..da3b36ada 100644
--- a/library/std/src/os/wasi/io/raw.rs
+++ b/library/std/src/os/wasi/io/raw.rs
@@ -1,6 +1,20 @@
 //! WASI-specific extensions to general I/O primitives.
 
-#![stable(feature = "io_safety_wasi", since = "1.65.0")]
+#![unstable(feature = "wasi_ext", issue = "71213")]
 
-#[stable(feature = "io_safety_wasi", since = "1.65.0")]
+// NOTE: despite the fact that this module is unstable,
+// stable Rust had the capability to access the stable
+// re-exported items from os::fd::raw through this
+// unstable module.
+// In PR #95956 the stability checker was changed to check
+// all path segments of an item rather than just the last,
+// which caused the aforementioned stable usage to regress
+// (see issue #99502).
+// As a result, the items in os::fd::raw were given the
+// rustc_allowed_through_unstable_modules attribute.
+// No regression tests were added to ensure this property,
+// as CI is not configured to test wasm32-wasi.
+// If this module is stabilized,
+// you may want to remove those attributes
+// (assuming no other unstable modules need them).
 pub use crate::os::fd::raw::*;
diff --git a/library/std/src/os/watchos/fs.rs b/library/std/src/os/watchos/fs.rs
new file mode 100644
index 000000000..a14fe35a7
--- /dev/null
+++ b/library/std/src/os/watchos/fs.rs
@@ -0,0 +1,142 @@
+#![stable(feature = "metadata_ext", since = "1.1.0")]
+
+use crate::fs::Metadata;
+use crate::sys_common::AsInner;
+
+#[allow(deprecated)]
+use crate::os::watchos::raw;
+
+/// OS-specific extensions to [`fs::Metadata`].
+///
+/// [`fs::Metadata`]: crate::fs::Metadata
+#[stable(feature = "metadata_ext", since = "1.1.0")]
+pub trait MetadataExt {
+    /// Gain a reference to the underlying `stat` structure which contains
+    /// the raw information returned by the OS.
+    ///
+    /// The contents of the returned `stat` are **not** consistent across
+    /// Unix platforms. The `os::unix::fs::MetadataExt` trait contains the
+    /// cross-Unix abstractions contained within the raw stat.
+    #[stable(feature = "metadata_ext", since = "1.1.0")]
+    #[deprecated(
+        since = "1.8.0",
+        note = "deprecated in favor of the accessor \
+                  methods of this trait"
+    )]
+    #[allow(deprecated)]
+    fn as_raw_stat(&self) -> &raw::stat;
+
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_dev(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_ino(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_mode(&self) -> u32;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_nlink(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_uid(&self) -> u32;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_gid(&self) -> u32;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_rdev(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_size(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_atime(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_atime_nsec(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_mtime(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_mtime_nsec(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_ctime(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_ctime_nsec(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_birthtime(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_birthtime_nsec(&self) -> i64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_blksize(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_blocks(&self) -> u64;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_flags(&self) -> u32;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_gen(&self) -> u32;
+    #[stable(feature = "metadata_ext2", since = "1.8.0")]
+    fn st_lspare(&self) -> u32;
+}
+
+#[stable(feature = "metadata_ext", since = "1.1.0")]
+impl MetadataExt for Metadata {
+    #[allow(deprecated)]
+    fn as_raw_stat(&self) -> &raw::stat {
+        unsafe { &*(self.as_inner().as_inner() as *const libc::stat as *const raw::stat) }
+    }
+    fn st_dev(&self) -> u64 {
+        self.as_inner().as_inner().st_dev as u64
+    }
+    fn st_ino(&self) -> u64 {
+        self.as_inner().as_inner().st_ino as u64
+    }
+    fn st_mode(&self) -> u32 {
+        self.as_inner().as_inner().st_mode as u32
+    }
+    fn st_nlink(&self) -> u64 {
+        self.as_inner().as_inner().st_nlink as u64
+    }
+    fn st_uid(&self) -> u32 {
+        self.as_inner().as_inner().st_uid as u32
+    }
+    fn st_gid(&self) -> u32 {
+        self.as_inner().as_inner().st_gid as u32
+    }
+    fn st_rdev(&self) -> u64 {
+        self.as_inner().as_inner().st_rdev as u64
+    }
+    fn st_size(&self) -> u64 {
+        self.as_inner().as_inner().st_size as u64
+    }
+    fn st_atime(&self) -> i64 {
+        self.as_inner().as_inner().st_atime as i64
+    }
+    fn st_atime_nsec(&self) -> i64 {
+        self.as_inner().as_inner().st_atime_nsec as i64
+    }
+    fn st_mtime(&self) -> i64 {
+        self.as_inner().as_inner().st_mtime as i64
+    }
+    fn st_mtime_nsec(&self) -> i64 {
+        self.as_inner().as_inner().st_mtime_nsec as i64
+    }
+    fn st_ctime(&self) -> i64 {
+        self.as_inner().as_inner().st_ctime as i64
+    }
+    fn st_ctime_nsec(&self) -> i64 {
+        self.as_inner().as_inner().st_ctime_nsec as i64
+    }
+    fn st_birthtime(&self) -> i64 {
+        self.as_inner().as_inner().st_birthtime as i64
+    }
+    fn st_birthtime_nsec(&self) -> i64 {
+        self.as_inner().as_inner().st_birthtime_nsec as i64
+    }
+    fn st_blksize(&self) -> u64 {
+        self.as_inner().as_inner().st_blksize as u64
+    }
+    fn st_blocks(&self) -> u64 {
+        self.as_inner().as_inner().st_blocks as u64
+    }
+    fn st_gen(&self) -> u32 {
+        self.as_inner().as_inner().st_gen as u32
+    }
+    fn st_flags(&self) -> u32 {
+        self.as_inner().as_inner().st_flags as u32
+    }
+    fn st_lspare(&self) -> u32 {
+        self.as_inner().as_inner().st_lspare as u32
+    }
+}
diff --git a/library/std/src/os/watchos/mod.rs b/library/std/src/os/watchos/mod.rs
new file mode 100644
index 000000000..cd6454ebb
--- /dev/null
+++ b/library/std/src/os/watchos/mod.rs
@@ -0,0 +1,6 @@
+//! watchOS-specific definitions
+
+#![stable(feature = "raw_ext", since = "1.1.0")]
+
+pub mod fs;
+pub mod raw;
diff --git a/library/std/src/os/watchos/raw.rs b/library/std/src/os/watchos/raw.rs
new file mode 100644
index 000000000..630a533d9
--- /dev/null
+++ b/library/std/src/os/watchos/raw.rs
@@ -0,0 +1,83 @@
+//! watchOS-specific raw type definitions
+
+#![stable(feature = "raw_ext", since = "1.1.0")]
+#![deprecated(
+    since = "1.8.0",
+    note = "these type aliases are no longer supported by \
+              the standard library, the `libc` crate on \
+              crates.io should be used instead for the correct \
+              definitions"
+)]
+#![allow(deprecated)]
+
+use crate::os::raw::c_long;
+
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type blkcnt_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type blksize_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type dev_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type ino_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type mode_t = u32;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type nlink_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type off_t = u64;
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub type time_t = i64;
+
+#[stable(feature = "pthread_t", since = "1.8.0")]
+pub type pthread_t = usize;
+
+#[repr(C)]
+#[derive(Clone)]
+#[stable(feature = "raw_ext", since = "1.1.0")]
+pub struct stat {
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_dev: i32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_mode: u16,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_nlink: u16,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_ino: u64,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_uid: u32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_gid: u32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_rdev: i32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_atime: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_atime_nsec: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_mtime: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_mtime_nsec: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_ctime: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_ctime_nsec: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_birthtime: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_birthtime_nsec: c_long,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_size: i64,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_blocks: i64,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_blksize: i32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_flags: u32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_gen: u32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_lspare: i32,
+    #[stable(feature = "raw_ext", since = "1.1.0")]
+    pub st_qspare: [i64; 2],
+}
diff --git a/library/std/src/os/windows/io/handle.rs b/library/std/src/os/windows/io/handle.rs
index 16cc8fa27..1dfecc573 100644
--- a/library/std/src/os/windows/io/handle.rs
+++ b/library/std/src/os/windows/io/handle.rs
@@ -384,6 +384,23 @@ impl fmt::Debug for OwnedHandle {
     }
 }
 
+macro_rules! impl_is_terminal {
+    ($($t:ty),*$(,)?) => {$(
+        #[unstable(feature = "sealed", issue = "none")]
+        impl crate::sealed::Sealed for $t {}
+
+        #[unstable(feature = "is_terminal", issue = "98070")]
+        impl crate::io::IsTerminal for $t {
+            #[inline]
+            fn is_terminal(&self) -> bool {
+                crate::sys::io::is_terminal(self)
+            }
+        }
+    )*}
+}
+
+impl_is_terminal!(BorrowedHandle<'_>, OwnedHandle);
+
 /// A trait to borrow the handle from an underlying object.
 #[stable(feature = "io_safety", since = "1.63.0")]
 pub trait AsHandle {
diff --git a/library/std/src/panicking.rs b/library/std/src/panicking.rs
index 25c9201f2..d4976a469 100644
--- a/library/std/src/panicking.rs
+++ b/library/std/src/panicking.rs
@@ -18,9 +18,9 @@ use crate::intrinsics;
 use crate::mem::{self, ManuallyDrop};
 use crate::process;
 use crate::sync::atomic::{AtomicBool, Ordering};
+use crate::sync::{PoisonError, RwLock};
 use crate::sys::stdio::panic_output;
 use crate::sys_common::backtrace;
-use crate::sys_common::rwlock::StaticRwLock;
 use crate::sys_common::thread_info;
 use crate::thread;
 
@@ -71,20 +71,29 @@ extern "C" fn __rust_foreign_exception() -> ! {
     rtabort!("Rust cannot catch foreign exceptions");
 }
 
-#[derive(Copy, Clone)]
 enum Hook {
     Default,
-    Custom(*mut (dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send)),
+    Custom(Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>),
 }
 
 impl Hook {
-    fn custom(f: impl Fn(&PanicInfo<'_>) + 'static + Sync + Send) -> Self {
-        Self::Custom(Box::into_raw(Box::new(f)))
+    #[inline]
+    fn into_box(self) -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
+        match self {
+            Hook::Default => Box::new(default_hook),
+            Hook::Custom(hook) => hook,
+        }
+    }
+}
+
+impl Default for Hook {
+    #[inline]
+    fn default() -> Hook {
+        Hook::Default
     }
 }
 
-static HOOK_LOCK: StaticRwLock = StaticRwLock::new();
-static mut HOOK: Hook = Hook::Default;
+static HOOK: RwLock<Hook> = RwLock::new(Hook::Default);
 
 /// Registers a custom panic hook, replacing any that was previously registered.
 ///
@@ -125,24 +134,13 @@ pub fn set_hook(hook: Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send>) {
         panic!("cannot modify the panic hook from a panicking thread");
     }
 
-    // SAFETY:
-    //
-    // - `HOOK` can only be modified while holding write access to `HOOK_LOCK`.
-    // - The argument of `Box::from_raw` is always a valid pointer that was created using
-    // `Box::into_raw`.
-    unsafe {
-        let guard = HOOK_LOCK.write();
-        let old_hook = HOOK;
-        HOOK = Hook::Custom(Box::into_raw(hook));
-        drop(guard);
-
-        if let Hook::Custom(ptr) = old_hook {
-            #[allow(unused_must_use)]
-            {
-                Box::from_raw(ptr);
-            }
-        }
-    }
+    let new = Hook::Custom(hook);
+    let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
+    let old = mem::replace(&mut *hook, new);
+    drop(hook);
+    // Only drop the old hook after releasing the lock to avoid deadlocking
+    // if its destructor panics.
+    drop(old);
 }
 
 /// Unregisters the current panic hook, returning it.
@@ -179,22 +177,11 @@ pub fn take_hook() -> Box<dyn Fn(&PanicInfo<'_>) + 'static + Sync + Send> {
         panic!("cannot modify the panic hook from a panicking thread");
     }
 
-    // SAFETY:
-    //
-    // - `HOOK` can only be modified while holding write access to `HOOK_LOCK`.
-    // - The argument of `Box::from_raw` is always a valid pointer that was created using
-    // `Box::into_raw`.
-    unsafe {
-        let guard = HOOK_LOCK.write();
-        let hook = HOOK;
-        HOOK = Hook::Default;
-        drop(guard);
+    let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
+    let old_hook = mem::take(&mut *hook);
+    drop(hook);
 
-        match hook {
-            Hook::Default => Box::new(default_hook),
-            Hook::Custom(ptr) => Box::from_raw(ptr),
-        }
-    }
+    old_hook.into_box()
 }
 
 /// Atomic combination of [`take_hook`] and [`set_hook`]. Use this to replace the panic handler with
@@ -240,24 +227,9 @@ where
         panic!("cannot modify the panic hook from a panicking thread");
     }
 
-    // SAFETY:
-    //
-    // - `HOOK` can only be modified while holding write access to `HOOK_LOCK`.
-    // - The argument of `Box::from_raw` is always a valid pointer that was created using
-    // `Box::into_raw`.
-    unsafe {
-        let guard = HOOK_LOCK.write();
-        let old_hook = HOOK;
-        HOOK = Hook::Default;
-
-        let prev = match old_hook {
-            Hook::Default => Box::new(default_hook),
-            Hook::Custom(ptr) => Box::from_raw(ptr),
-        };
-
-        HOOK = Hook::custom(move |info| hook_fn(&prev, info));
-        drop(guard);
-    }
+    let mut hook = HOOK.write().unwrap_or_else(PoisonError::into_inner);
+    let prev = mem::take(&mut *hook).into_box();
+    *hook = Hook::Custom(Box::new(move |info| hook_fn(&prev, info)));
 }
 
 fn default_hook(info: &PanicInfo<'_>) {
@@ -328,7 +300,7 @@ pub mod panic_count {
     thread_local! { static LOCAL_PANIC_COUNT: Cell<usize> = const { Cell::new(0) } }
 
     // Sum of panic counts from all threads. The purpose of this is to have
-    // a fast path in `is_zero` (which is used by `panicking`). In any particular
+    // a fast path in `count_is_zero` (which is used by `panicking`). In any particular
     // thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
     // then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
     // and after increase and decrease, but not necessarily during their execution.
@@ -336,6 +308,14 @@ pub mod panic_count {
     // Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG)
     // records whether panic::always_abort() has been called.  This can only be
     // set, never cleared.
+    // panic::always_abort() is usually called to prevent memory allocations done by
+    // the panic handling in the child created by `libc::fork`.
+    // Memory allocations performed in  a child created with `libc::fork` are undefined
+    // behavior in most operating systems.
+    // Accessing LOCAL_PANIC_COUNT in a child created by `libc::fork` would lead to a memory
+    // allocation. Only GLOBAL_PANIC_COUNT can be accessed in this situation. This is
+    // sufficient because a child process will always have exactly one thread only.
+    // See also #85261 for details.
     //
     // This could be viewed as a struct containing a single bit and an n-1-bit
     // value, but if we wrote it like that it would be more than a single word,
@@ -346,15 +326,26 @@ pub mod panic_count {
     // panicking thread consumes at least 2 bytes of address space.
     static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0);
 
+    // Return the state of the ALWAYS_ABORT_FLAG and number of panics.
+    //
+    // If ALWAYS_ABORT_FLAG is not set, the number is determined on a per-thread
+    // base (stored in LOCAL_PANIC_COUNT), i.e. it is the amount of recursive calls
+    // of the calling thread.
+    // If ALWAYS_ABORT_FLAG is set, the number equals the *global* number of panic
+    // calls. See above why LOCAL_PANIC_COUNT is not used.
     pub fn increase() -> (bool, usize) {
-        (
-            GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed) & ALWAYS_ABORT_FLAG != 0,
+        let global_count = GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed);
+        let must_abort = global_count & ALWAYS_ABORT_FLAG != 0;
+        let panics = if must_abort {
+            global_count & !ALWAYS_ABORT_FLAG
+        } else {
             LOCAL_PANIC_COUNT.with(|c| {
                 let next = c.get() + 1;
                 c.set(next);
                 next
-            }),
-        )
+            })
+        };
+        (must_abort, panics)
     }
 
     pub fn decrease() {
@@ -397,7 +388,7 @@ pub mod panic_count {
     }
 
     // Slow path is in a separate function to reduce the amount of code
-    // inlined from `is_zero`.
+    // inlined from `count_is_zero`.
     #[inline(never)]
     #[cold]
     fn is_zero_slow_path() -> bool {
@@ -682,27 +673,26 @@ fn rust_panic_with_hook(
         crate::sys::abort_internal();
     }
 
-    unsafe {
-        let mut info = PanicInfo::internal_constructor(message, location, can_unwind);
-        let _guard = HOOK_LOCK.read();
-        match HOOK {
-            // Some platforms (like wasm) know that printing to stderr won't ever actually
-            // print anything, and if that's the case we can skip the default
-            // hook. Since string formatting happens lazily when calling `payload`
-            // methods, this means we avoid formatting the string at all!
-            // (The panic runtime might still call `payload.take_box()` though and trigger
-            // formatting.)
-            Hook::Default if panic_output().is_none() => {}
-            Hook::Default => {
-                info.set_payload(payload.get());
-                default_hook(&info);
-            }
-            Hook::Custom(ptr) => {
-                info.set_payload(payload.get());
-                (*ptr)(&info);
-            }
-        };
-    }
+    let mut info = PanicInfo::internal_constructor(message, location, can_unwind);
+    let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner);
+    match *hook {
+        // Some platforms (like wasm) know that printing to stderr won't ever actually
+        // print anything, and if that's the case we can skip the default
+        // hook. Since string formatting happens lazily when calling `payload`
+        // methods, this means we avoid formatting the string at all!
+        // (The panic runtime might still call `payload.take_box()` though and trigger
+        // formatting.)
+        Hook::Default if panic_output().is_none() => {}
+        Hook::Default => {
+            info.set_payload(payload.get());
+            default_hook(&info);
+        }
+        Hook::Custom(ref hook) => {
+            info.set_payload(payload.get());
+            hook(&info);
+        }
+    };
+    drop(hook);
 
     if panics > 1 || !can_unwind {
         // If a thread panics while it's already unwinding then we
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 5dfeb517a..9d6328162 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -2158,6 +2158,7 @@ impl Path {
     /// assert_eq!(grand_parent.parent(), None);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[doc(alias = "dirname")]
     #[must_use]
     pub fn parent(&self) -> Option<&Path> {
         let mut comps = self.components();
@@ -2225,6 +2226,7 @@ impl Path {
     /// assert_eq!(None, Path::new("/").file_name());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[doc(alias = "basename")]
     #[must_use]
     pub fn file_name(&self) -> Option<&OsStr> {
         self.components().next_back().and_then(|p| match p {
@@ -2401,7 +2403,7 @@ impl Path {
         self.file_name().map(split_file_at_dot).and_then(|(before, _after)| Some(before))
     }
 
-    /// Extracts the extension of [`self.file_name`], if possible.
+    /// Extracts the extension (without the leading dot) of [`self.file_name`], if possible.
     ///
     /// The extension is:
     ///
diff --git a/library/std/src/personality/dwarf/eh.rs b/library/std/src/personality/dwarf/eh.rs
index 8799137b7..27b50c13b 100644
--- a/library/std/src/personality/dwarf/eh.rs
+++ b/library/std/src/personality/dwarf/eh.rs
@@ -98,9 +98,8 @@ pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result
                 }
             }
         }
-        // Ip is not present in the table.  This should not happen... but it does: issue #35011.
-        // So rather than returning EHAction::Terminate, we do this.
-        Ok(EHAction::None)
+        // Ip is not present in the table. This indicates a nounwind call.
+        Ok(EHAction::Terminate)
     } else {
         // SjLj version:
         // The "IP" is an index into the call-site table, with two exceptions:
diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs
index 242f44ade..331714a99 100644
--- a/library/std/src/primitive_docs.rs
+++ b/library/std/src/primitive_docs.rs
@@ -611,7 +611,19 @@ mod prim_pointer {}
 ///
 /// Arrays coerce to [slices (`[T]`)][slice], so a slice method may be called on
 /// an array. Indeed, this provides most of the API for working with arrays.
-/// Slices have a dynamic size and do not coerce to arrays.
+///
+/// Slices have a dynamic size and do not coerce to arrays. Instead, use
+/// `slice.try_into().unwrap()` or `<ArrayType>::try_from(slice).unwrap()`.
+///
+/// Array's `try_from(slice)` implementations (and the corresponding `slice.try_into()`
+/// array implementations) succeed if the input slice length is the same as the result
+/// array length. They optimize especially well when the optimizer can easily determine
+/// the slice length, e.g. `<[u8; 4]>::try_from(&slice[4..8]).unwrap()`. Array implements
+/// [TryFrom](crate::convert::TryFrom) returning:
+///
+/// - `[T; N]` copies from the slice's elements
+/// - `&[T; N]` references the original slice's elements
+/// - `&mut [T; N]` references the original slice's elements
 ///
 /// You can move elements out of an array with a [slice pattern]. If you want
 /// one element, see [`mem::replace`].
@@ -640,6 +652,15 @@ mod prim_pointer {}
 /// for x in &array { }
 /// ```
 ///
+/// You can use `<ArrayType>::try_from(slice)` or `slice.try_into()` to get an array from
+/// a slice:
+///
+/// ```
+/// let bytes: [u8; 3] = [1, 0, 2];
+/// assert_eq!(1, u16::from_le_bytes(<[u8; 2]>::try_from(&bytes[0..2]).unwrap()));
+/// assert_eq!(512, u16::from_le_bytes(bytes[1..3].try_into().unwrap()));
+/// ```
+///
 /// You can use a [slice pattern] to move elements out of an array:
 ///
 /// ```
diff --git a/library/std/src/process.rs b/library/std/src/process.rs
index d91d4fa64..400d25beb 100644
--- a/library/std/src/process.rs
+++ b/library/std/src/process.rs
@@ -1629,7 +1629,7 @@ impl ExitStatusError {
     ///
     /// This is exactly like [`code()`](Self::code), except that it returns a `NonZeroI32`.
     ///
-    /// Plain `code`, returning a plain integer, is provided because is is often more convenient.
+    /// Plain `code`, returning a plain integer, is provided because it is often more convenient.
     /// The returned value from `code()` is indeed also nonzero; use `code_nonzero()` when you want
     /// a type-level guarantee of nonzeroness.
     ///
@@ -2154,8 +2154,16 @@ pub fn id() -> u32 {
 #[cfg_attr(not(test), lang = "termination")]
 #[stable(feature = "termination_trait_lib", since = "1.61.0")]
 #[rustc_on_unimplemented(
-    message = "`main` has invalid return type `{Self}`",
-    label = "`main` can only return types that implement `{Termination}`"
+    on(
+        all(not(bootstrap), cause = "MainFunctionType"),
+        message = "`main` has invalid return type `{Self}`",
+        label = "`main` can only return types that implement `{Termination}`"
+    ),
+    on(
+        bootstrap,
+        message = "`main` has invalid return type `{Self}`",
+        label = "`main` can only return types that implement `{Termination}`"
+    )
 )]
 pub trait Termination {
     /// Is called to get the representation of the value as status code.
@@ -2200,9 +2208,7 @@ impl<T: Termination, E: fmt::Debug> Termination for Result<T, E> {
         match self {
             Ok(val) => val.report(),
             Err(err) => {
-                // Ignore error if the write fails, for example because stderr is
-                // already closed. There is not much point panicking at this point.
-                let _ = writeln!(io::stderr(), "Error: {err:?}");
+                io::attempt_print_to_stderr(format_args_nl!("Error: {err:?}"));
                 ExitCode::FAILURE
             }
         }
diff --git a/library/std/src/rt.rs b/library/std/src/rt.rs
index 98f6cc7aa..9c2f0c1dd 100644
--- a/library/std/src/rt.rs
+++ b/library/std/src/rt.rs
@@ -89,7 +89,7 @@ macro_rules! rtunwrap {
 // `src/tools/tidy/src/pal.rs` for more info. On all other platforms, `sigpipe`
 // has a value, but its value is ignored.
 //
-// Even though it is an `u8`, it only ever has 3 values. These are documented in
+// Even though it is an `u8`, it only ever has 4 values. These are documented in
 // `compiler/rustc_session/src/config/sigpipe.rs`.
 #[cfg_attr(test, allow(dead_code))]
 unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
@@ -160,15 +160,12 @@ fn lang_start<T: crate::process::Termination + 'static>(
     main: fn() -> T,
     argc: isize,
     argv: *const *const u8,
-    #[cfg(not(bootstrap))] sigpipe: u8,
+    sigpipe: u8,
 ) -> isize {
     let Ok(v) = lang_start_internal(
         &move || crate::sys_common::backtrace::__rust_begin_short_backtrace(main).report().to_i32(),
         argc,
         argv,
-        #[cfg(bootstrap)]
-        2, // Temporary inlining of sigpipe::DEFAULT until bootstrap stops being special
-        #[cfg(not(bootstrap))]
         sigpipe,
     );
     v
diff --git a/library/std/src/sync/mpsc/stream.rs b/library/std/src/sync/mpsc/stream.rs
index 4c3812c79..4592e9141 100644
--- a/library/std/src/sync/mpsc/stream.rs
+++ b/library/std/src/sync/mpsc/stream.rs
@@ -114,7 +114,7 @@ impl<T> Packet<T> {
         match self.queue.producer_addition().cnt.fetch_add(1, Ordering::SeqCst) {
             // As described in the mod's doc comment, -1 == wakeup
             -1 => UpWoke(self.take_to_wake()),
-            // As as described before, SPSC queues must be >= -2
+            // As described before, SPSC queues must be >= -2
             -2 => UpSuccess,
 
             // Be sure to preserve the disconnected state, and the return value
diff --git a/library/std/src/sync/once.rs b/library/std/src/sync/once.rs
index a7feea588..0f25417d6 100644
--- a/library/std/src/sync/once.rs
+++ b/library/std/src/sync/once.rs
@@ -3,99 +3,12 @@
 //! This primitive is meant to be used to run one-time initialization. An
 //! example use case would be for initializing an FFI library.
 
-// A "once" is a relatively simple primitive, and it's also typically provided
-// by the OS as well (see `pthread_once` or `InitOnceExecuteOnce`). The OS
-// primitives, however, tend to have surprising restrictions, such as the Unix
-// one doesn't allow an argument to be passed to the function.
-//
-// As a result, we end up implementing it ourselves in the standard library.
-// This also gives us the opportunity to optimize the implementation a bit which
-// should help the fast path on call sites. Consequently, let's explain how this
-// primitive works now!
-//
-// So to recap, the guarantees of a Once are that it will call the
-// initialization closure at most once, and it will never return until the one
-// that's running has finished running. This means that we need some form of
-// blocking here while the custom callback is running at the very least.
-// Additionally, we add on the restriction of **poisoning**. Whenever an
-// initialization closure panics, the Once enters a "poisoned" state which means
-// that all future calls will immediately panic as well.
-//
-// So to implement this, one might first reach for a `Mutex`, but those cannot
-// be put into a `static`. It also gets a lot harder with poisoning to figure
-// out when the mutex needs to be deallocated because it's not after the closure
-// finishes, but after the first successful closure finishes.
-//
-// All in all, this is instead implemented with atomics and lock-free
-// operations! Whee! Each `Once` has one word of atomic state, and this state is
-// CAS'd on to determine what to do. There are four possible state of a `Once`:
-//
-// * Incomplete - no initialization has run yet, and no thread is currently
-//                using the Once.
-// * Poisoned - some thread has previously attempted to initialize the Once, but
-//              it panicked, so the Once is now poisoned. There are no other
-//              threads currently accessing this Once.
-// * Running - some thread is currently attempting to run initialization. It may
-//             succeed, so all future threads need to wait for it to finish.
-//             Note that this state is accompanied with a payload, described
-//             below.
-// * Complete - initialization has completed and all future calls should finish
-//              immediately.
-//
-// With 4 states we need 2 bits to encode this, and we use the remaining bits
-// in the word we have allocated as a queue of threads waiting for the thread
-// responsible for entering the RUNNING state. This queue is just a linked list
-// of Waiter nodes which is monotonically increasing in size. Each node is
-// allocated on the stack, and whenever the running closure finishes it will
-// consume the entire queue and notify all waiters they should try again.
-//
-// You'll find a few more details in the implementation, but that's the gist of
-// it!
-//
-// Atomic orderings:
-// When running `Once` we deal with multiple atomics:
-// `Once.state_and_queue` and an unknown number of `Waiter.signaled`.
-// * `state_and_queue` is used (1) as a state flag, (2) for synchronizing the
-//   result of the `Once`, and (3) for synchronizing `Waiter` nodes.
-//     - At the end of the `call_inner` function we have to make sure the result
-//       of the `Once` is acquired. So every load which can be the only one to
-//       load COMPLETED must have at least Acquire ordering, which means all
-//       three of them.
-//     - `WaiterQueue::Drop` is the only place that may store COMPLETED, and
-//       must do so with Release ordering to make the result available.
-//     - `wait` inserts `Waiter` nodes as a pointer in `state_and_queue`, and
-//       needs to make the nodes available with Release ordering. The load in
-//       its `compare_exchange` can be Relaxed because it only has to compare
-//       the atomic, not to read other data.
-//     - `WaiterQueue::Drop` must see the `Waiter` nodes, so it must load
-//       `state_and_queue` with Acquire ordering.
-//     - There is just one store where `state_and_queue` is used only as a
-//       state flag, without having to synchronize data: switching the state
-//       from INCOMPLETE to RUNNING in `call_inner`. This store can be Relaxed,
-//       but the read has to be Acquire because of the requirements mentioned
-//       above.
-// * `Waiter.signaled` is both used as a flag, and to protect a field with
-//   interior mutability in `Waiter`. `Waiter.thread` is changed in
-//   `WaiterQueue::Drop` which then sets `signaled` with Release ordering.
-//   After `wait` loads `signaled` with Acquire and sees it is true, it needs to
-//   see the changes to drop the `Waiter` struct correctly.
-// * There is one place where the two atomics `Once.state_and_queue` and
-//   `Waiter.signaled` come together, and might be reordered by the compiler or
-//   processor. Because both use Acquire ordering such a reordering is not
-//   allowed, so no need for SeqCst.
-
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests;
 
-use crate::cell::Cell;
 use crate::fmt;
-use crate::marker;
 use crate::panic::{RefUnwindSafe, UnwindSafe};
-use crate::ptr;
-use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
-use crate::thread::{self, Thread};
-
-type Masked = ();
+use crate::sys_common::once as sys;
 
 /// A synchronization primitive which can be used to run a one-time global
 /// initialization. Useful for one-time initialization for FFI or related
@@ -114,19 +27,9 @@ type Masked = ();
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Once {
-    // `state_and_queue` is actually a pointer to a `Waiter` with extra state
-    // bits, so we add the `PhantomData` appropriately.
-    state_and_queue: AtomicPtr<Masked>,
-    _marker: marker::PhantomData<*const Waiter>,
+    inner: sys::Once,
 }
 
-// The `PhantomData` of a raw pointer removes these two auto traits, but we
-// enforce both below in the implementation so this should be safe to add.
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl Sync for Once {}
-#[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl Send for Once {}
-
 #[stable(feature = "sync_once_unwind_safe", since = "1.59.0")]
 impl UnwindSafe for Once {}
 
@@ -136,10 +39,8 @@ impl RefUnwindSafe for Once {}
 /// State yielded to [`Once::call_once_force()`]’s closure parameter. The state
 /// can be used to query the poison status of the [`Once`].
 #[stable(feature = "once_poison", since = "1.51.0")]
-#[derive(Debug)]
 pub struct OnceState {
-    poisoned: bool,
-    set_state_on_drop_to: Cell<*mut Masked>,
+    pub(crate) inner: sys::OnceState,
 }
 
 /// Initialization value for static [`Once`] values.
@@ -159,38 +60,6 @@ pub struct OnceState {
 )]
 pub const ONCE_INIT: Once = Once::new();
 
-// Four states that a Once can be in, encoded into the lower bits of
-// `state_and_queue` in the Once structure.
-const INCOMPLETE: usize = 0x0;
-const POISONED: usize = 0x1;
-const RUNNING: usize = 0x2;
-const COMPLETE: usize = 0x3;
-
-// Mask to learn about the state. All other bits are the queue of waiters if
-// this is in the RUNNING state.
-const STATE_MASK: usize = 0x3;
-
-// Representation of a node in the linked list of waiters, used while in the
-// RUNNING state.
-// Note: `Waiter` can't hold a mutable pointer to the next thread, because then
-// `wait` would both hand out a mutable reference to its `Waiter` node, and keep
-// a shared reference to check `signaled`. Instead we hold shared references and
-// use interior mutability.
-#[repr(align(4))] // Ensure the two lower bits are free to use as state bits.
-struct Waiter {
-    thread: Cell<Option<Thread>>,
-    signaled: AtomicBool,
-    next: *const Waiter,
-}
-
-// Head of a linked list of waiters.
-// Every node is a struct on the stack of a waiting thread.
-// Will wake up the waiters when it gets dropped, i.e. also on panic.
-struct WaiterQueue<'a> {
-    state_and_queue: &'a AtomicPtr<Masked>,
-    set_state_on_drop_to: *mut Masked,
-}
-
 impl Once {
     /// Creates a new `Once` value.
     #[inline]
@@ -198,10 +67,7 @@ impl Once {
     #[rustc_const_stable(feature = "const_once_new", since = "1.32.0")]
     #[must_use]
     pub const fn new() -> Once {
-        Once {
-            state_and_queue: AtomicPtr::new(ptr::invalid_mut(INCOMPLETE)),
-            _marker: marker::PhantomData,
-        }
+        Once { inner: sys::Once::new() }
     }
 
     /// Performs an initialization routine once and only once. The given closure
@@ -261,6 +127,7 @@ impl Once {
     /// This is similar to [poisoning with mutexes][poison].
     ///
     /// [poison]: struct.Mutex.html#poisoning
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[track_caller]
     pub fn call_once<F>(&self, f: F)
@@ -268,12 +135,12 @@ impl Once {
         F: FnOnce(),
     {
         // Fast path check
-        if self.is_completed() {
+        if self.inner.is_completed() {
             return;
         }
 
         let mut f = Some(f);
-        self.call_inner(false, &mut |_| f.take().unwrap()());
+        self.inner.call(false, &mut |_| f.take().unwrap()());
     }
 
     /// Performs the same function as [`call_once()`] except ignores poisoning.
@@ -320,18 +187,19 @@ impl Once {
     /// // once any success happens, we stop propagating the poison
     /// INIT.call_once(|| {});
     /// ```
+    #[inline]
     #[stable(feature = "once_poison", since = "1.51.0")]
     pub fn call_once_force<F>(&self, f: F)
     where
         F: FnOnce(&OnceState),
     {
         // Fast path check
-        if self.is_completed() {
+        if self.inner.is_completed() {
             return;
         }
 
         let mut f = Some(f);
-        self.call_inner(true, &mut |p| f.take().unwrap()(p));
+        self.inner.call(true, &mut |p| f.take().unwrap()(p));
     }
 
     /// Returns `true` if some [`call_once()`] call has completed
@@ -378,119 +246,7 @@ impl Once {
     #[stable(feature = "once_is_completed", since = "1.43.0")]
     #[inline]
     pub fn is_completed(&self) -> bool {
-        // An `Acquire` load is enough because that makes all the initialization
-        // operations visible to us, and, this being a fast path, weaker
-        // ordering helps with performance. This `Acquire` synchronizes with
-        // `Release` operations on the slow path.
-        self.state_and_queue.load(Ordering::Acquire).addr() == COMPLETE
-    }
-
-    // This is a non-generic function to reduce the monomorphization cost of
-    // using `call_once` (this isn't exactly a trivial or small implementation).
-    //
-    // Additionally, this is tagged with `#[cold]` as it should indeed be cold
-    // and it helps let LLVM know that calls to this function should be off the
-    // fast path. Essentially, this should help generate more straight line code
-    // in LLVM.
-    //
-    // Finally, this takes an `FnMut` instead of a `FnOnce` because there's
-    // currently no way to take an `FnOnce` and call it via virtual dispatch
-    // without some allocation overhead.
-    #[cold]
-    #[track_caller]
-    fn call_inner(&self, ignore_poisoning: bool, init: &mut dyn FnMut(&OnceState)) {
-        let mut state_and_queue = self.state_and_queue.load(Ordering::Acquire);
-        loop {
-            match state_and_queue.addr() {
-                COMPLETE => break,
-                POISONED if !ignore_poisoning => {
-                    // Panic to propagate the poison.
-                    panic!("Once instance has previously been poisoned");
-                }
-                POISONED | INCOMPLETE => {
-                    // Try to register this thread as the one RUNNING.
-                    let exchange_result = self.state_and_queue.compare_exchange(
-                        state_and_queue,
-                        ptr::invalid_mut(RUNNING),
-                        Ordering::Acquire,
-                        Ordering::Acquire,
-                    );
-                    if let Err(old) = exchange_result {
-                        state_and_queue = old;
-                        continue;
-                    }
-                    // `waiter_queue` will manage other waiting threads, and
-                    // wake them up on drop.
-                    let mut waiter_queue = WaiterQueue {
-                        state_and_queue: &self.state_and_queue,
-                        set_state_on_drop_to: ptr::invalid_mut(POISONED),
-                    };
-                    // Run the initialization function, letting it know if we're
-                    // poisoned or not.
-                    let init_state = OnceState {
-                        poisoned: state_and_queue.addr() == POISONED,
-                        set_state_on_drop_to: Cell::new(ptr::invalid_mut(COMPLETE)),
-                    };
-                    init(&init_state);
-                    waiter_queue.set_state_on_drop_to = init_state.set_state_on_drop_to.get();
-                    break;
-                }
-                _ => {
-                    // All other values must be RUNNING with possibly a
-                    // pointer to the waiter queue in the more significant bits.
-                    assert!(state_and_queue.addr() & STATE_MASK == RUNNING);
-                    wait(&self.state_and_queue, state_and_queue);
-                    state_and_queue = self.state_and_queue.load(Ordering::Acquire);
-                }
-            }
-        }
-    }
-}
-
-fn wait(state_and_queue: &AtomicPtr<Masked>, mut current_state: *mut Masked) {
-    // Note: the following code was carefully written to avoid creating a
-    // mutable reference to `node` that gets aliased.
-    loop {
-        // Don't queue this thread if the status is no longer running,
-        // otherwise we will not be woken up.
-        if current_state.addr() & STATE_MASK != RUNNING {
-            return;
-        }
-
-        // Create the node for our current thread.
-        let node = Waiter {
-            thread: Cell::new(Some(thread::current())),
-            signaled: AtomicBool::new(false),
-            next: current_state.with_addr(current_state.addr() & !STATE_MASK) as *const Waiter,
-        };
-        let me = &node as *const Waiter as *const Masked as *mut Masked;
-
-        // Try to slide in the node at the head of the linked list, making sure
-        // that another thread didn't just replace the head of the linked list.
-        let exchange_result = state_and_queue.compare_exchange(
-            current_state,
-            me.with_addr(me.addr() | RUNNING),
-            Ordering::Release,
-            Ordering::Relaxed,
-        );
-        if let Err(old) = exchange_result {
-            current_state = old;
-            continue;
-        }
-
-        // We have enqueued ourselves, now lets wait.
-        // It is important not to return before being signaled, otherwise we
-        // would drop our `Waiter` node and leave a hole in the linked list
-        // (and a dangling reference). Guard against spurious wakeups by
-        // reparking ourselves until we are signaled.
-        while !node.signaled.load(Ordering::Acquire) {
-            // If the managing thread happens to signal and unpark us before we
-            // can park ourselves, the result could be this thread never gets
-            // unparked. Luckily `park` comes with the guarantee that if it got
-            // an `unpark` just before on an unparked thread it does not park.
-            thread::park();
-        }
-        break;
+        self.inner.is_completed()
     }
 }
 
@@ -501,37 +257,6 @@ impl fmt::Debug for Once {
     }
 }
 
-impl Drop for WaiterQueue<'_> {
-    fn drop(&mut self) {
-        // Swap out our state with however we finished.
-        let state_and_queue =
-            self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel);
-
-        // We should only ever see an old state which was RUNNING.
-        assert_eq!(state_and_queue.addr() & STATE_MASK, RUNNING);
-
-        // Walk the entire linked list of waiters and wake them up (in lifo
-        // order, last to register is first to wake up).
-        unsafe {
-            // Right after setting `node.signaled = true` the other thread may
-            // free `node` if there happens to be has a spurious wakeup.
-            // So we have to take out the `thread` field and copy the pointer to
-            // `next` first.
-            let mut queue =
-                state_and_queue.with_addr(state_and_queue.addr() & !STATE_MASK) as *const Waiter;
-            while !queue.is_null() {
-                let next = (*queue).next;
-                let thread = (*queue).thread.take().unwrap();
-                (*queue).signaled.store(true, Ordering::Release);
-                // ^- FIXME (maybe): This is another case of issue #55005
-                // `store()` has a potentially dangling ref to `signaled`.
-                queue = next;
-                thread.unpark();
-            }
-        }
-    }
-}
-
 impl OnceState {
     /// Returns `true` if the associated [`Once`] was poisoned prior to the
     /// invocation of the closure passed to [`Once::call_once_force()`].
@@ -568,13 +293,22 @@ impl OnceState {
     ///     assert!(!state.is_poisoned());
     /// });
     #[stable(feature = "once_poison", since = "1.51.0")]
+    #[inline]
     pub fn is_poisoned(&self) -> bool {
-        self.poisoned
+        self.inner.is_poisoned()
     }
 
     /// Poison the associated [`Once`] without explicitly panicking.
-    // NOTE: This is currently only exposed for the `lazy` module
+    // NOTE: This is currently only exposed for `OnceLock`.
+    #[inline]
     pub(crate) fn poison(&self) {
-        self.set_state_on_drop_to.set(ptr::invalid_mut(POISONED));
+        self.inner.poison();
+    }
+}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for OnceState {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OnceState").field("poisoned", &self.is_poisoned()).finish()
     }
 }
diff --git a/library/std/src/sync/rwlock.rs b/library/std/src/sync/rwlock.rs
index 9ab781561..8b3877607 100644
--- a/library/std/src/sync/rwlock.rs
+++ b/library/std/src/sync/rwlock.rs
@@ -76,6 +76,7 @@ use crate::sys_common::rwlock as sys;
 ///
 /// [`Mutex`]: super::Mutex
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "RwLock")]
 pub struct RwLock<T: ?Sized> {
     inner: sys::MovableRwLock,
     poison: poison::Flag,
@@ -166,7 +167,7 @@ impl<T> RwLock<T> {
 }
 
 impl<T: ?Sized> RwLock<T> {
-    /// Locks this rwlock with shared read access, blocking the current thread
+    /// Locks this `RwLock` with shared read access, blocking the current thread
     /// until it can be acquired.
     ///
     /// The calling thread will be blocked until there are no more writers which
@@ -180,9 +181,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// The failure will occur immediately after the lock has been acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. The failure will occur immediately after the lock has been
+    /// acquired.
     ///
     /// # Panics
     ///
@@ -214,7 +216,7 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Attempts to acquire this rwlock with shared read access.
+    /// Attempts to acquire this `RwLock` with shared read access.
     ///
     /// If the access could not be granted at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the shared access
@@ -227,13 +229,13 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return the [`Poisoned`] error if the RwLock is poisoned.
-    /// An RwLock is poisoned whenever a writer panics while holding an exclusive
-    /// lock. `Poisoned` will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return the [`Poisoned`] error if the `RwLock` is
+    /// poisoned. An `RwLock` is poisoned whenever a writer panics while holding
+    /// an exclusive lock. `Poisoned` will only be returned if the lock would
+    /// have otherwise been acquired.
     ///
-    /// This function will return the [`WouldBlock`] error if the RwLock could not
-    /// be acquired because it was already locked exclusively.
+    /// This function will return the [`WouldBlock`] error if the `RwLock` could
+    /// not be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
@@ -262,20 +264,20 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Locks this rwlock with exclusive write access, blocking the current
+    /// Locks this `RwLock` with exclusive write access, blocking the current
     /// thread until it can be acquired.
     ///
     /// This function will not return while other writers or other readers
     /// currently have access to the lock.
     ///
-    /// Returns an RAII guard which will drop the write access of this rwlock
+    /// Returns an RAII guard which will drop the write access of this `RwLock`
     /// when dropped.
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock.
-    /// An error will be returned when the lock is acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will be returned when the lock is acquired.
     ///
     /// # Panics
     ///
@@ -302,7 +304,7 @@ impl<T: ?Sized> RwLock<T> {
         }
     }
 
-    /// Attempts to lock this rwlock with exclusive write access.
+    /// Attempts to lock this `RwLock` with exclusive write access.
     ///
     /// If the lock could not be acquired at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the lock when
@@ -315,13 +317,13 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return the [`Poisoned`] error if the RwLock is
-    /// poisoned. An RwLock is poisoned whenever a writer panics while holding
-    /// an exclusive lock. `Poisoned` will only be returned if the lock would have
-    /// otherwise been acquired.
+    /// This function will return the [`Poisoned`] error if the `RwLock` is
+    /// poisoned. An `RwLock` is poisoned whenever a writer panics while holding
+    /// an exclusive lock. `Poisoned` will only be returned if the lock would
+    /// have otherwise been acquired.
     ///
-    /// This function will return the [`WouldBlock`] error if the RwLock could not
-    /// be acquired because it was already locked exclusively.
+    /// This function will return the [`WouldBlock`] error if the `RwLock` could
+    /// not be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
@@ -421,10 +423,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will only be returned if the lock would have otherwise
+    /// been acquired.
     ///
     /// # Examples
     ///
@@ -454,10 +456,10 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// # Errors
     ///
-    /// This function will return an error if the RwLock is poisoned. An RwLock
-    /// is poisoned whenever a writer panics while holding an exclusive lock. An
-    /// error will only be returned if the lock would have otherwise been
-    /// acquired.
+    /// This function will return an error if the `RwLock` is poisoned. An
+    /// `RwLock` is poisoned whenever a writer panics while holding an exclusive
+    /// lock. An error will only be returned if the lock would have otherwise
+    /// been acquired.
     ///
     /// # Examples
     ///
diff --git a/library/std/src/sys/common/mod.rs b/library/std/src/sys/common/mod.rs
index ff64d2aa8..29fc0835d 100644
--- a/library/std/src/sys/common/mod.rs
+++ b/library/std/src/sys/common/mod.rs
@@ -11,3 +11,7 @@
 #![allow(dead_code)]
 
 pub mod alloc;
+pub mod small_c_string;
+
+#[cfg(test)]
+mod tests;
diff --git a/library/std/src/sys/common/small_c_string.rs b/library/std/src/sys/common/small_c_string.rs
new file mode 100644
index 000000000..01acd5191
--- /dev/null
+++ b/library/std/src/sys/common/small_c_string.rs
@@ -0,0 +1,58 @@
+use crate::ffi::{CStr, CString};
+use crate::mem::MaybeUninit;
+use crate::path::Path;
+use crate::slice;
+use crate::{io, ptr};
+
+// Make sure to stay under 4096 so the compiler doesn't insert a probe frame:
+// https://docs.rs/compiler_builtins/latest/compiler_builtins/probestack/index.html
+#[cfg(not(target_os = "espidf"))]
+const MAX_STACK_ALLOCATION: usize = 384;
+#[cfg(target_os = "espidf")]
+const MAX_STACK_ALLOCATION: usize = 32;
+
+const NUL_ERR: io::Error =
+    io::const_io_error!(io::ErrorKind::InvalidInput, "file name contained an unexpected NUL byte");
+
+#[inline]
+pub fn run_path_with_cstr<T, F>(path: &Path, f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    run_with_cstr(path.as_os_str().bytes(), f)
+}
+
+#[inline]
+pub fn run_with_cstr<T, F>(bytes: &[u8], f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    if bytes.len() >= MAX_STACK_ALLOCATION {
+        return run_with_cstr_allocating(bytes, f);
+    }
+
+    let mut buf = MaybeUninit::<[u8; MAX_STACK_ALLOCATION]>::uninit();
+    let buf_ptr = buf.as_mut_ptr() as *mut u8;
+
+    unsafe {
+        ptr::copy_nonoverlapping(bytes.as_ptr(), buf_ptr, bytes.len());
+        buf_ptr.add(bytes.len()).write(0);
+    }
+
+    match CStr::from_bytes_with_nul(unsafe { slice::from_raw_parts(buf_ptr, bytes.len() + 1) }) {
+        Ok(s) => f(s),
+        Err(_) => Err(NUL_ERR),
+    }
+}
+
+#[cold]
+#[inline(never)]
+fn run_with_cstr_allocating<T, F>(bytes: &[u8], f: F) -> io::Result<T>
+where
+    F: FnOnce(&CStr) -> io::Result<T>,
+{
+    match CString::new(bytes) {
+        Ok(s) => f(&s),
+        Err(_) => Err(NUL_ERR),
+    }
+}
diff --git a/library/std/src/sys/common/tests.rs b/library/std/src/sys/common/tests.rs
new file mode 100644
index 000000000..fb6f5d6af
--- /dev/null
+++ b/library/std/src/sys/common/tests.rs
@@ -0,0 +1,66 @@
+use crate::ffi::CString;
+use crate::hint::black_box;
+use crate::path::Path;
+use crate::sys::common::small_c_string::run_path_with_cstr;
+use core::iter::repeat;
+
+#[test]
+fn stack_allocation_works() {
+    let path = Path::new("abc");
+    let result = run_path_with_cstr(path, |p| {
+        assert_eq!(p, &*CString::new(path.as_os_str().bytes()).unwrap());
+        Ok(42)
+    });
+    assert_eq!(result.unwrap(), 42);
+}
+
+#[test]
+fn stack_allocation_fails() {
+    let path = Path::new("ab\0");
+    assert!(run_path_with_cstr::<(), _>(path, |_| unreachable!()).is_err());
+}
+
+#[test]
+fn heap_allocation_works() {
+    let path = repeat("a").take(384).collect::<String>();
+    let path = Path::new(&path);
+    let result = run_path_with_cstr(path, |p| {
+        assert_eq!(p, &*CString::new(path.as_os_str().bytes()).unwrap());
+        Ok(42)
+    });
+    assert_eq!(result.unwrap(), 42);
+}
+
+#[test]
+fn heap_allocation_fails() {
+    let mut path = repeat("a").take(384).collect::<String>();
+    path.push('\0');
+    let path = Path::new(&path);
+    assert!(run_path_with_cstr::<(), _>(path, |_| unreachable!()).is_err());
+}
+
+#[bench]
+fn bench_stack_path_alloc(b: &mut test::Bencher) {
+    let path = repeat("a").take(383).collect::<String>();
+    let p = Path::new(&path);
+    b.iter(|| {
+        run_path_with_cstr(p, |cstr| {
+            black_box(cstr);
+            Ok(())
+        })
+        .unwrap();
+    });
+}
+
+#[bench]
+fn bench_heap_path_alloc(b: &mut test::Bencher) {
+    let path = repeat("a").take(384).collect::<String>();
+    let p = Path::new(&path);
+    b.iter(|| {
+        run_path_with_cstr(p, |cstr| {
+            black_box(cstr);
+            Ok(())
+        })
+        .unwrap();
+    });
+}
diff --git a/library/std/src/sys/hermit/args.rs b/library/std/src/sys/hermit/args.rs
index 1c7e1dd8d..afcae6c90 100644
--- a/library/std/src/sys/hermit/args.rs
+++ b/library/std/src/sys/hermit/args.rs
@@ -1,20 +1,37 @@
-use crate::ffi::OsString;
+use crate::ffi::{c_char, CStr, OsString};
 use crate::fmt;
+use crate::os::unix::ffi::OsStringExt;
+use crate::ptr;
+use crate::sync::atomic::{
+    AtomicIsize, AtomicPtr,
+    Ordering::{Acquire, Relaxed, Release},
+};
 use crate::vec;
 
+static ARGC: AtomicIsize = AtomicIsize::new(0);
+static ARGV: AtomicPtr<*const u8> = AtomicPtr::new(ptr::null_mut());
+
 /// One-time global initialization.
 pub unsafe fn init(argc: isize, argv: *const *const u8) {
-    imp::init(argc, argv)
-}
-
-/// One-time global cleanup.
-pub unsafe fn cleanup() {
-    imp::cleanup()
+    ARGC.store(argc, Relaxed);
+    // Use release ordering here to broadcast writes by the OS.
+    ARGV.store(argv as *mut *const u8, Release);
 }
 
 /// Returns the command line arguments
 pub fn args() -> Args {
-    imp::args()
+    // Synchronize with the store above.
+    let argv = ARGV.load(Acquire);
+    // If argv has not been initialized yet, do not return any arguments.
+    let argc = if argv.is_null() { 0 } else { ARGC.load(Relaxed) };
+    let args: Vec<OsString> = (0..argc)
+        .map(|i| unsafe {
+            let cstr = CStr::from_ptr(*argv.offset(i) as *const c_char);
+            OsStringExt::from_vec(cstr.to_bytes().to_vec())
+        })
+        .collect();
+
+    Args { iter: args.into_iter() }
 }
 
 pub struct Args {
@@ -51,44 +68,3 @@ impl DoubleEndedIterator for Args {
         self.iter.next_back()
     }
 }
-
-mod imp {
-    use super::Args;
-    use crate::ffi::{CStr, OsString};
-    use crate::os::unix::ffi::OsStringExt;
-    use crate::ptr;
-
-    use crate::sys_common::mutex::StaticMutex;
-
-    static mut ARGC: isize = 0;
-    static mut ARGV: *const *const u8 = ptr::null();
-    static LOCK: StaticMutex = StaticMutex::new();
-
-    pub unsafe fn init(argc: isize, argv: *const *const u8) {
-        let _guard = LOCK.lock();
-        ARGC = argc;
-        ARGV = argv;
-    }
-
-    pub unsafe fn cleanup() {
-        let _guard = LOCK.lock();
-        ARGC = 0;
-        ARGV = ptr::null();
-    }
-
-    pub fn args() -> Args {
-        Args { iter: clone().into_iter() }
-    }
-
-    fn clone() -> Vec<OsString> {
-        unsafe {
-            let _guard = LOCK.lock();
-            (0..ARGC)
-                .map(|i| {
-                    let cstr = CStr::from_ptr(*ARGV.offset(i) as *const i8);
-                    OsStringExt::from_vec(cstr.to_bytes().to_vec())
-                })
-                .collect()
-        }
-    }
-}
diff --git a/library/std/src/sys/hermit/fs.rs b/library/std/src/sys/hermit/fs.rs
index f921839cf..af297ff1e 100644
--- a/library/std/src/sys/hermit/fs.rs
+++ b/library/std/src/sys/hermit/fs.rs
@@ -1,3 +1,4 @@
+use crate::convert::TryFrom;
 use crate::ffi::{CStr, CString, OsString};
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
@@ -5,6 +6,7 @@ use crate::io::{self, Error, ErrorKind};
 use crate::io::{BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
 use crate::os::unix::ffi::OsStrExt;
 use crate::path::{Path, PathBuf};
+use crate::sys::common::small_c_string::run_path_with_cstr;
 use crate::sys::cvt;
 use crate::sys::hermit::abi;
 use crate::sys::hermit::abi::{O_APPEND, O_CREAT, O_EXCL, O_RDONLY, O_RDWR, O_TRUNC, O_WRONLY};
@@ -15,10 +17,6 @@ use crate::sys::unsupported;
 pub use crate::sys_common::fs::{copy, try_exists};
 //pub use crate::sys_common::fs::remove_dir_all;
 
-fn cstr(path: &Path) -> io::Result<CString> {
-    Ok(CString::new(path.as_os_str().as_bytes())?)
-}
-
 #[derive(Debug)]
 pub struct File(FileDesc);
 
@@ -272,8 +270,7 @@ impl OpenOptions {
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
-        let path = cstr(path)?;
-        File::open_c(&path, opts)
+        run_path_with_cstr(path, |path| File::open_c(&path, opts))
     }
 
     pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
@@ -373,9 +370,7 @@ pub fn readdir(_p: &Path) -> io::Result<ReadDir> {
 }
 
 pub fn unlink(path: &Path) -> io::Result<()> {
-    let name = cstr(path)?;
-    let _ = unsafe { cvt(abi::unlink(name.as_ptr()))? };
-    Ok(())
+    run_path_with_cstr(path, |path| cvt(unsafe { abi::unlink(path.as_ptr()) }).map(|_| ()))
 }
 
 pub fn rename(_old: &Path, _new: &Path) -> io::Result<()> {
diff --git a/library/std/src/sys/hermit/mod.rs b/library/std/src/sys/hermit/mod.rs
index 827d82900..e6534df89 100644
--- a/library/std/src/sys/hermit/mod.rs
+++ b/library/std/src/sys/hermit/mod.rs
@@ -106,9 +106,7 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, _sigpipe: u8) {
 
 // SAFETY: must be called only once during runtime cleanup.
 // NOTE: this is not guaranteed to run, for example when the program aborts.
-pub unsafe fn cleanup() {
-    args::cleanup();
-}
+pub unsafe fn cleanup() {}
 
 #[cfg(not(test))]
 #[no_mangle]
diff --git a/library/std/src/sys/mod.rs b/library/std/src/sys/mod.rs
index 167c918c9..c080c176a 100644
--- a/library/std/src/sys/mod.rs
+++ b/library/std/src/sys/mod.rs
@@ -22,7 +22,7 @@
 
 #![allow(missing_debug_implementations)]
 
-mod common;
+pub mod common;
 
 cfg_if::cfg_if! {
     if #[cfg(unix)] {
diff --git a/library/std/src/sys/sgx/abi/tls/mod.rs b/library/std/src/sys/sgx/abi/tls/mod.rs
index 13d96e9a6..09c4ab3d3 100644
--- a/library/std/src/sys/sgx/abi/tls/mod.rs
+++ b/library/std/src/sys/sgx/abi/tls/mod.rs
@@ -111,6 +111,7 @@ impl Tls {
             rtabort!("TLS limit exceeded")
         };
         TLS_DESTRUCTOR[index].store(dtor.map_or(0, |f| f as usize), Ordering::Relaxed);
+        unsafe { Self::current() }.data[index].set(ptr::null_mut());
         Key::from_index(index)
     }
 
diff --git a/library/std/src/sys/sgx/abi/usercalls/alloc.rs b/library/std/src/sys/sgx/abi/usercalls/alloc.rs
index 5409bd177..0d934318c 100644
--- a/library/std/src/sys/sgx/abi/usercalls/alloc.rs
+++ b/library/std/src/sys/sgx/abi/usercalls/alloc.rs
@@ -316,9 +316,9 @@ where
 //   | small1 | Chunk smaller than 8 bytes
 //   +--------+
 fn region_as_aligned_chunks(ptr: *const u8, len: usize) -> (usize, usize, usize) {
-    let small0_size = if ptr as usize % 8 == 0 { 0 } else { 8 - ptr as usize % 8 };
-    let small1_size = (len - small0_size as usize) % 8;
-    let big_size = len - small0_size as usize - small1_size as usize;
+    let small0_size = if ptr.is_aligned_to(8) { 0 } else { 8 - ptr.addr() % 8 };
+    let small1_size = (len - small0_size) % 8;
+    let big_size = len - small0_size - small1_size;
 
     (small0_size, big_size, small1_size)
 }
@@ -364,8 +364,8 @@ pub(crate) unsafe fn copy_to_userspace(src: *const u8, dst: *mut u8, len: usize)
                     mfence
                     lfence
                     ",
-                    val = in(reg_byte) *src.offset(off as isize),
-                    dst = in(reg) dst.offset(off as isize),
+                    val = in(reg_byte) *src.add(off),
+                    dst = in(reg) dst.add(off),
                     seg_sel = in(reg) &mut seg_sel,
                     options(nostack, att_syntax)
                 );
@@ -378,8 +378,8 @@ pub(crate) unsafe fn copy_to_userspace(src: *const u8, dst: *mut u8, len: usize)
     assert!(is_enclave_range(src, len));
     assert!(is_user_range(dst, len));
     assert!(len < isize::MAX as usize);
-    assert!(!(src as usize).overflowing_add(len).1);
-    assert!(!(dst as usize).overflowing_add(len).1);
+    assert!(!src.addr().overflowing_add(len).1);
+    assert!(!dst.addr().overflowing_add(len).1);
 
     if len < 8 {
         // Can't align on 8 byte boundary: copy safely byte per byte
@@ -404,17 +404,17 @@ pub(crate) unsafe fn copy_to_userspace(src: *const u8, dst: *mut u8, len: usize)
 
         unsafe {
             // Copy small0
-            copy_bytewise_to_userspace(src, dst, small0_size as _);
+            copy_bytewise_to_userspace(src, dst, small0_size);
 
             // Copy big
-            let big_src = src.offset(small0_size as _);
-            let big_dst = dst.offset(small0_size as _);
-            copy_quadwords(big_src as _, big_dst, big_size);
+            let big_src = src.add(small0_size);
+            let big_dst = dst.add(small0_size);
+            copy_quadwords(big_src, big_dst, big_size);
 
             // Copy small1
-            let small1_src = src.offset(big_size as isize + small0_size as isize);
-            let small1_dst = dst.offset(big_size as isize + small0_size as isize);
-            copy_bytewise_to_userspace(small1_src, small1_dst, small1_size as _);
+            let small1_src = src.add(big_size + small0_size);
+            let small1_dst = dst.add(big_size + small0_size);
+            copy_bytewise_to_userspace(small1_src, small1_dst, small1_size);
         }
     }
 }
diff --git a/library/std/src/sys/sgx/thread_local_key.rs b/library/std/src/sys/sgx/thread_local_key.rs
index b21784475..c7a57d3a3 100644
--- a/library/std/src/sys/sgx/thread_local_key.rs
+++ b/library/std/src/sys/sgx/thread_local_key.rs
@@ -21,8 +21,3 @@ pub unsafe fn get(key: Key) -> *mut u8 {
 pub unsafe fn destroy(key: Key) {
     Tls::destroy(AbiKey::from_usize(key))
 }
-
-#[inline]
-pub fn requires_synchronized_create() -> bool {
-    false
-}
diff --git a/library/std/src/sys/solid/fs.rs b/library/std/src/sys/solid/fs.rs
index 969222253..6c66b93a3 100644
--- a/library/std/src/sys/solid/fs.rs
+++ b/library/std/src/sys/solid/fs.rs
@@ -175,15 +175,19 @@ impl Iterator for ReadDir {
     type Item = io::Result<DirEntry>;
 
     fn next(&mut self) -> Option<io::Result<DirEntry>> {
-        unsafe {
-            let mut out_dirent = MaybeUninit::uninit();
-            error::SolidError::err_if_negative(abi::SOLID_FS_ReadDir(
+        let entry = unsafe {
+            let mut out_entry = MaybeUninit::uninit();
+            match error::SolidError::err_if_negative(abi::SOLID_FS_ReadDir(
                 self.inner.dirp,
-                out_dirent.as_mut_ptr(),
-            ))
-            .ok()?;
-            Some(Ok(DirEntry { entry: out_dirent.assume_init(), inner: Arc::clone(&self.inner) }))
-        }
+                out_entry.as_mut_ptr(),
+            )) {
+                Ok(_) => out_entry.assume_init(),
+                Err(e) if e.as_raw() == abi::SOLID_ERR_NOTFOUND => return None,
+                Err(e) => return Some(Err(e.as_io_error())),
+            }
+        };
+
+        (entry.d_name[0] != 0).then(|| Ok(DirEntry { entry, inner: Arc::clone(&self.inner) }))
     }
 }
 
diff --git a/library/std/src/sys/solid/os.rs b/library/std/src/sys/solid/os.rs
index b5649d6e0..4906c6268 100644
--- a/library/std/src/sys/solid/os.rs
+++ b/library/std/src/sys/solid/os.rs
@@ -1,4 +1,5 @@
 use super::unsupported;
+use crate::convert::TryFrom;
 use crate::error::Error as StdError;
 use crate::ffi::{CStr, CString, OsStr, OsString};
 use crate::fmt;
@@ -8,7 +9,8 @@ use crate::os::{
     solid::ffi::{OsStrExt, OsStringExt},
 };
 use crate::path::{self, PathBuf};
-use crate::sys_common::rwlock::StaticRwLock;
+use crate::sync::RwLock;
+use crate::sys::common::small_c_string::run_with_cstr;
 use crate::vec;
 
 use super::{error, itron, memchr};
@@ -78,7 +80,7 @@ pub fn current_exe() -> io::Result<PathBuf> {
     unsupported()
 }
 
-static ENV_LOCK: StaticRwLock = StaticRwLock::new();
+static ENV_LOCK: RwLock<()> = RwLock::new(());
 
 pub struct Env {
     iter: vec::IntoIter<(OsString, OsString)>,
@@ -139,35 +141,33 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    let k = CString::new(k.as_bytes()).ok()?;
-    unsafe {
+    let s = run_with_cstr(k.as_bytes(), |k| {
         let _guard = ENV_LOCK.read();
-        let s = libc::getenv(k.as_ptr()) as *const libc::c_char;
-        if s.is_null() {
-            None
-        } else {
-            Some(OsStringExt::from_vec(CStr::from_ptr(s).to_bytes().to_vec()))
-        }
+        Ok(unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char)
+    })
+    .ok()?;
+
+    if s.is_null() {
+        None
+    } else {
+        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
     }
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    let k = CString::new(k.as_bytes())?;
-    let v = CString::new(v.as_bytes())?;
-
-    unsafe {
-        let _guard = ENV_LOCK.write();
-        cvt_env(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
-    }
+    run_with_cstr(k.as_bytes(), |k| {
+        run_with_cstr(v.as_bytes(), |v| {
+            let _guard = ENV_LOCK.write();
+            cvt_env(unsafe { libc::setenv(k.as_ptr(), v.as_ptr(), 1) }).map(drop)
+        })
+    })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    let nbuf = CString::new(n.as_bytes())?;
-
-    unsafe {
+    run_with_cstr(n.as_bytes(), |nbuf| {
         let _guard = ENV_LOCK.write();
-        cvt_env(libc::unsetenv(nbuf.as_ptr())).map(drop)
-    }
+        cvt_env(unsafe { libc::unsetenv(nbuf.as_ptr()) }).map(drop)
+    })
 }
 
 /// In kmclib, `setenv` and `unsetenv` don't always set `errno`, so this
diff --git a/library/std/src/sys/solid/thread_local_key.rs b/library/std/src/sys/solid/thread_local_key.rs
index b17521f70..b37bf9996 100644
--- a/library/std/src/sys/solid/thread_local_key.rs
+++ b/library/std/src/sys/solid/thread_local_key.rs
@@ -19,8 +19,3 @@ pub unsafe fn get(_key: Key) -> *mut u8 {
 pub unsafe fn destroy(_key: Key) {
     panic!("should not be used on the solid target");
 }
-
-#[inline]
-pub fn requires_synchronized_create() -> bool {
-    panic!("should not be used on the solid target");
-}
diff --git a/library/std/src/sys/unix/fs.rs b/library/std/src/sys/unix/fs.rs
index cc347e358..37a49f2d7 100644
--- a/library/std/src/sys/unix/fs.rs
+++ b/library/std/src/sys/unix/fs.rs
@@ -1,13 +1,26 @@
+// miri has some special hacks here that make things unused.
+#![cfg_attr(miri, allow(unused))]
+
 use crate::os::unix::prelude::*;
 
-use crate::ffi::{CStr, CString, OsStr, OsString};
+use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
+#[cfg(any(
+    target_os = "android",
+    target_os = "linux",
+    target_os = "solaris",
+    target_os = "fuchsia",
+    target_os = "redox",
+    target_os = "illumos"
+))]
+use crate::mem::MaybeUninit;
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd};
 use crate::path::{Path, PathBuf};
 use crate::ptr;
 use crate::sync::Arc;
+use crate::sys::common::small_c_string::run_path_with_cstr;
 use crate::sys::fd::FileDesc;
 use crate::sys::time::SystemTime;
 use crate::sys::{cvt, cvt_r};
@@ -260,7 +273,7 @@ pub struct DirEntry {
     // We need to store an owned copy of the entry name on platforms that use
     // readdir() (not readdir_r()), because a) struct dirent may use a flexible
     // array to store the name, b) it lives only until the next readdir() call.
-    name: CString,
+    name: crate::ffi::CString,
 }
 
 // Define a minimal subset of fields we need from `dirent64`, especially since
@@ -313,8 +326,11 @@ pub struct FilePermissions {
     mode: mode_t,
 }
 
-#[derive(Copy, Clone)]
-pub struct FileTimes([libc::timespec; 2]);
+#[derive(Copy, Clone, Debug, Default)]
+pub struct FileTimes {
+    accessed: Option<SystemTime>,
+    modified: Option<SystemTime>,
+}
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct FileType {
@@ -512,45 +528,11 @@ impl FilePermissions {
 
 impl FileTimes {
     pub fn set_accessed(&mut self, t: SystemTime) {
-        self.0[0] = t.t.to_timespec().expect("Invalid system time");
+        self.accessed = Some(t);
     }
 
     pub fn set_modified(&mut self, t: SystemTime) {
-        self.0[1] = t.t.to_timespec().expect("Invalid system time");
-    }
-}
-
-struct TimespecDebugAdapter<'a>(&'a libc::timespec);
-
-impl fmt::Debug for TimespecDebugAdapter<'_> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("timespec")
-            .field("tv_sec", &self.0.tv_sec)
-            .field("tv_nsec", &self.0.tv_nsec)
-            .finish()
-    }
-}
-
-impl fmt::Debug for FileTimes {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("FileTimes")
-            .field("accessed", &TimespecDebugAdapter(&self.0[0]))
-            .field("modified", &TimespecDebugAdapter(&self.0[1]))
-            .finish()
-    }
-}
-
-impl Default for FileTimes {
-    fn default() -> Self {
-        // Redox doesn't appear to support `UTIME_OMIT`, so we stub it out here, and always return
-        // an error in `set_times`.
-        // ESP-IDF and HorizonOS do not support `futimens` at all and the behavior for those OS is therefore
-        // the same as for Redox.
-        #[cfg(any(target_os = "redox", target_os = "espidf", target_os = "horizon"))]
-        let omit = libc::timespec { tv_sec: 0, tv_nsec: 0 };
-        #[cfg(not(any(target_os = "redox", target_os = "espidf", target_os = "horizon")))]
-        let omit = libc::timespec { tv_sec: 0, tv_nsec: libc::UTIME_OMIT as _ };
-        Self([omit; 2])
+        self.modified = Some(t);
     }
 }
 
@@ -614,33 +596,69 @@ impl Iterator for ReadDir {
                     };
                 }
 
-                // Only d_reclen bytes of *entry_ptr are valid, so we can't just copy the
-                // whole thing (#93384).  Instead, copy everything except the name.
-                let mut copy: dirent64 = mem::zeroed();
-                // Can't dereference entry_ptr, so use the local entry to get
-                // offsetof(struct dirent, d_name)
-                let copy_bytes = &mut copy as *mut _ as *mut u8;
-                let copy_name = &mut copy.d_name as *mut _ as *mut u8;
-                let name_offset = copy_name.offset_from(copy_bytes) as usize;
-                let entry_bytes = entry_ptr as *const u8;
-                let entry_name = entry_bytes.add(name_offset);
-                ptr::copy_nonoverlapping(entry_bytes, copy_bytes, name_offset);
+                // The dirent64 struct is a weird imaginary thing that isn't ever supposed
+                // to be worked with by value. Its trailing d_name field is declared
+                // variously as [c_char; 256] or [c_char; 1] on different systems but
+                // either way that size is meaningless; only the offset of d_name is
+                // meaningful. The dirent64 pointers that libc returns from readdir64 are
+                // allowed to point to allocations smaller _or_ LARGER than implied by the
+                // definition of the struct.
+                //
+                // As such, we need to be even more careful with dirent64 than if its
+                // contents were "simply" partially initialized data.
+                //
+                // Like for uninitialized contents, converting entry_ptr to `&dirent64`
+                // would not be legal. However, unique to dirent64 is that we don't even
+                // get to use `addr_of!((*entry_ptr).d_name)` because that operation
+                // requires the full extent of *entry_ptr to be in bounds of the same
+                // allocation, which is not necessarily the case here.
+                //
+                // Absent any other way to obtain a pointer to `(*entry_ptr).d_name`
+                // legally in Rust analogously to how it would be done in C, we instead
+                // need to make our own non-libc allocation that conforms to the weird
+                // imaginary definition of dirent64, and use that for a field offset
+                // computation.
+                macro_rules! offset_ptr {
+                    ($entry_ptr:expr, $field:ident) => {{
+                        const OFFSET: isize = {
+                            let delusion = MaybeUninit::<dirent64>::uninit();
+                            let entry_ptr = delusion.as_ptr();
+                            unsafe {
+                                ptr::addr_of!((*entry_ptr).$field)
+                                    .cast::<u8>()
+                                    .offset_from(entry_ptr.cast::<u8>())
+                            }
+                        };
+                        if true {
+                            // Cast to the same type determined by the else branch.
+                            $entry_ptr.byte_offset(OFFSET).cast::<_>()
+                        } else {
+                            #[allow(deref_nullptr)]
+                            {
+                                ptr::addr_of!((*ptr::null::<dirent64>()).$field)
+                            }
+                        }
+                    }};
+                }
+
+                // d_name is guaranteed to be null-terminated.
+                let name = CStr::from_ptr(offset_ptr!(entry_ptr, d_name).cast());
+                let name_bytes = name.to_bytes();
+                if name_bytes == b"." || name_bytes == b".." {
+                    continue;
+                }
 
                 let entry = dirent64_min {
-                    d_ino: copy.d_ino as u64,
+                    d_ino: *offset_ptr!(entry_ptr, d_ino) as u64,
                     #[cfg(not(any(target_os = "solaris", target_os = "illumos")))]
-                    d_type: copy.d_type as u8,
+                    d_type: *offset_ptr!(entry_ptr, d_type) as u8,
                 };
 
-                let ret = DirEntry {
+                return Some(Ok(DirEntry {
                     entry,
-                    // d_name is guaranteed to be null-terminated.
-                    name: CStr::from_ptr(entry_name as *const _).to_owned(),
+                    name: name.to_owned(),
                     dir: Arc::clone(&self.inner),
-                };
-                if ret.name_bytes() != b"." && ret.name_bytes() != b".." {
-                    return Some(Ok(ret));
-                }
+                }));
             }
         }
     }
@@ -704,7 +722,10 @@ impl DirEntry {
         self.file_name_os_str().to_os_string()
     }
 
-    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "android"))]
+    #[cfg(all(
+        any(target_os = "linux", target_os = "emscripten", target_os = "android"),
+        not(miri)
+    ))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
         let fd = cvt(unsafe { dirfd(self.dir.dirp.0) })?;
         let name = self.name_cstr().as_ptr();
@@ -725,7 +746,10 @@ impl DirEntry {
         Ok(FileAttr::from_stat64(stat))
     }
 
-    #[cfg(not(any(target_os = "linux", target_os = "emscripten", target_os = "android")))]
+    #[cfg(any(
+        not(any(target_os = "linux", target_os = "emscripten", target_os = "android")),
+        miri
+    ))]
     pub fn metadata(&self) -> io::Result<FileAttr> {
         lstat(&self.path())
     }
@@ -829,7 +853,6 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox"
     )))]
-    #[cfg_attr(miri, allow(unused))]
     fn name_cstr(&self) -> &CStr {
         unsafe { CStr::from_ptr(self.entry.d_name.as_ptr()) }
     }
@@ -841,7 +864,6 @@ impl DirEntry {
         target_os = "fuchsia",
         target_os = "redox"
     ))]
-    #[cfg_attr(miri, allow(unused))]
     fn name_cstr(&self) -> &CStr {
         &self.name
     }
@@ -931,8 +953,7 @@ impl OpenOptions {
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
-        let path = cstr(path)?;
-        File::open_c(&path, opts)
+        run_path_with_cstr(path, |path| File::open_c(path, opts))
     }
 
     pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
@@ -1084,6 +1105,17 @@ impl File {
     }
 
     pub fn set_times(&self, times: FileTimes) -> io::Result<()> {
+        #[cfg(not(any(target_os = "redox", target_os = "espidf", target_os = "horizon")))]
+        let to_timespec = |time: Option<SystemTime>| {
+            match time {
+                Some(time) if let Some(ts) = time.t.to_timespec() => Ok(ts),
+                Some(time) if time > crate::sys::time::UNIX_EPOCH => Err(io::const_io_error!(io::ErrorKind::InvalidInput, "timestamp is too large to set as a file time")),
+                Some(_) => Err(io::const_io_error!(io::ErrorKind::InvalidInput, "timestamp is too small to set as a file time")),
+                None => Ok(libc::timespec { tv_sec: 0, tv_nsec: libc::UTIME_OMIT as _ }),
+            }
+        };
+        #[cfg(not(any(target_os = "redox", target_os = "espidf", target_os = "horizon")))]
+        let times = [to_timespec(times.accessed)?, to_timespec(times.modified)?];
         cfg_if::cfg_if! {
             if #[cfg(any(target_os = "redox", target_os = "espidf", target_os = "horizon"))] {
                 // Redox doesn't appear to support `UTIME_OMIT`.
@@ -1099,7 +1131,7 @@ impl File {
                 cvt(unsafe {
                     weak!(fn futimens(c_int, *const libc::timespec) -> c_int);
                     match futimens.get() {
-                        Some(futimens) => futimens(self.as_raw_fd(), times.0.as_ptr()),
+                        Some(futimens) => futimens(self.as_raw_fd(), times.as_ptr()),
                         #[cfg(target_os = "macos")]
                         None => {
                             fn ts_to_tv(ts: &libc::timespec) -> libc::timeval {
@@ -1108,7 +1140,7 @@ impl File {
                                     tv_usec: (ts.tv_nsec / 1000) as _
                                 }
                             }
-                            let timevals = [ts_to_tv(&times.0[0]), ts_to_tv(&times.0[1])];
+                            let timevals = [ts_to_tv(&times[0]), ts_to_tv(&times[1])];
                             libc::futimes(self.as_raw_fd(), timevals.as_ptr())
                         }
                         // futimes requires even newer Android.
@@ -1121,7 +1153,7 @@ impl File {
                 })?;
                 Ok(())
             } else {
-                cvt(unsafe { libc::futimens(self.as_raw_fd(), times.0.as_ptr()) })?;
+                cvt(unsafe { libc::futimens(self.as_raw_fd(), times.as_ptr()) })?;
                 Ok(())
             }
         }
@@ -1134,9 +1166,7 @@ impl DirBuilder {
     }
 
     pub fn mkdir(&self, p: &Path) -> io::Result<()> {
-        let p = cstr(p)?;
-        cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) })?;
-        Ok(())
+        run_path_with_cstr(p, |p| cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) }).map(|_| ()))
     }
 
     pub fn set_mode(&mut self, mode: u32) {
@@ -1144,10 +1174,6 @@ impl DirBuilder {
     }
 }
 
-fn cstr(path: &Path) -> io::Result<CString> {
-    Ok(CString::new(path.as_os_str().as_bytes())?)
-}
-
 impl AsInner<FileDesc> for File {
     fn as_inner(&self) -> &FileDesc {
         &self.0
@@ -1198,7 +1224,12 @@ impl FromRawFd for File {
 
 impl fmt::Debug for File {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        #[cfg(any(target_os = "linux", target_os = "netbsd"))]
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "netbsd",
+            target_os = "illumos",
+            target_os = "solaris"
+        ))]
         fn get_path(fd: c_int) -> Option<PathBuf> {
             let mut p = PathBuf::from("/proc/self/fd");
             p.push(&fd.to_string());
@@ -1253,14 +1284,23 @@ impl fmt::Debug for File {
             target_os = "macos",
             target_os = "vxworks",
             all(target_os = "freebsd", target_arch = "x86_64"),
-            target_os = "netbsd"
+            target_os = "netbsd",
+            target_os = "illumos",
+            target_os = "solaris"
         )))]
         fn get_path(_fd: c_int) -> Option<PathBuf> {
             // FIXME(#24570): implement this for other Unix platforms
             None
         }
 
-        #[cfg(any(target_os = "linux", target_os = "macos", target_os = "vxworks"))]
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "macos",
+            target_os = "freebsd",
+            target_os = "netbsd",
+            target_os = "openbsd",
+            target_os = "vxworks"
+        ))]
         fn get_mode(fd: c_int) -> Option<(bool, bool)> {
             let mode = unsafe { libc::fcntl(fd, libc::F_GETFL) };
             if mode == -1 {
@@ -1274,7 +1314,14 @@ impl fmt::Debug for File {
             }
         }
 
-        #[cfg(not(any(target_os = "linux", target_os = "macos", target_os = "vxworks")))]
+        #[cfg(not(any(
+            target_os = "linux",
+            target_os = "macos",
+            target_os = "freebsd",
+            target_os = "netbsd",
+            target_os = "openbsd",
+            target_os = "vxworks"
+        )))]
         fn get_mode(_fd: c_int) -> Option<(bool, bool)> {
             // FIXME(#24570): implement this for other Unix platforms
             None
@@ -1293,173 +1340,170 @@ impl fmt::Debug for File {
     }
 }
 
-pub fn readdir(p: &Path) -> io::Result<ReadDir> {
-    let root = p.to_path_buf();
-    let p = cstr(p)?;
-    unsafe {
-        let ptr = libc::opendir(p.as_ptr());
-        if ptr.is_null() {
-            Err(Error::last_os_error())
-        } else {
-            let inner = InnerReadDir { dirp: Dir(ptr), root };
-            Ok(ReadDir {
-                inner: Arc::new(inner),
-                #[cfg(not(any(
-                    target_os = "android",
-                    target_os = "linux",
-                    target_os = "solaris",
-                    target_os = "illumos",
-                    target_os = "fuchsia",
-                    target_os = "redox",
-                )))]
-                end_of_stream: false,
-            })
-        }
+pub fn readdir(path: &Path) -> io::Result<ReadDir> {
+    let ptr = run_path_with_cstr(path, |p| unsafe { Ok(libc::opendir(p.as_ptr())) })?;
+    if ptr.is_null() {
+        Err(Error::last_os_error())
+    } else {
+        let root = path.to_path_buf();
+        let inner = InnerReadDir { dirp: Dir(ptr), root };
+        Ok(ReadDir {
+            inner: Arc::new(inner),
+            #[cfg(not(any(
+                target_os = "android",
+                target_os = "linux",
+                target_os = "solaris",
+                target_os = "illumos",
+                target_os = "fuchsia",
+                target_os = "redox",
+            )))]
+            end_of_stream: false,
+        })
     }
 }
 
 pub fn unlink(p: &Path) -> io::Result<()> {
-    let p = cstr(p)?;
-    cvt(unsafe { libc::unlink(p.as_ptr()) })?;
-    Ok(())
+    run_path_with_cstr(p, |p| cvt(unsafe { libc::unlink(p.as_ptr()) }).map(|_| ()))
 }
 
 pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
-    let old = cstr(old)?;
-    let new = cstr(new)?;
-    cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) })?;
-    Ok(())
+    run_path_with_cstr(old, |old| {
+        run_path_with_cstr(new, |new| {
+            cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) }).map(|_| ())
+        })
+    })
 }
 
 pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
-    let p = cstr(p)?;
-    cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) })?;
-    Ok(())
+    run_path_with_cstr(p, |p| cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) }).map(|_| ()))
 }
 
 pub fn rmdir(p: &Path) -> io::Result<()> {
-    let p = cstr(p)?;
-    cvt(unsafe { libc::rmdir(p.as_ptr()) })?;
-    Ok(())
+    run_path_with_cstr(p, |p| cvt(unsafe { libc::rmdir(p.as_ptr()) }).map(|_| ()))
 }
 
 pub fn readlink(p: &Path) -> io::Result<PathBuf> {
-    let c_path = cstr(p)?;
-    let p = c_path.as_ptr();
+    run_path_with_cstr(p, |c_path| {
+        let p = c_path.as_ptr();
 
-    let mut buf = Vec::with_capacity(256);
+        let mut buf = Vec::with_capacity(256);
 
-    loop {
-        let buf_read =
-            cvt(unsafe { libc::readlink(p, buf.as_mut_ptr() as *mut _, buf.capacity()) })? as usize;
+        loop {
+            let buf_read =
+                cvt(unsafe { libc::readlink(p, buf.as_mut_ptr() as *mut _, buf.capacity()) })?
+                    as usize;
 
-        unsafe {
-            buf.set_len(buf_read);
-        }
+            unsafe {
+                buf.set_len(buf_read);
+            }
 
-        if buf_read != buf.capacity() {
-            buf.shrink_to_fit();
+            if buf_read != buf.capacity() {
+                buf.shrink_to_fit();
 
-            return Ok(PathBuf::from(OsString::from_vec(buf)));
-        }
+                return Ok(PathBuf::from(OsString::from_vec(buf)));
+            }
 
-        // Trigger the internal buffer resizing logic of `Vec` by requiring
-        // more space than the current capacity. The length is guaranteed to be
-        // the same as the capacity due to the if statement above.
-        buf.reserve(1);
-    }
+            // Trigger the internal buffer resizing logic of `Vec` by requiring
+            // more space than the current capacity. The length is guaranteed to be
+            // the same as the capacity due to the if statement above.
+            buf.reserve(1);
+        }
+    })
 }
 
 pub fn symlink(original: &Path, link: &Path) -> io::Result<()> {
-    let original = cstr(original)?;
-    let link = cstr(link)?;
-    cvt(unsafe { libc::symlink(original.as_ptr(), link.as_ptr()) })?;
-    Ok(())
+    run_path_with_cstr(original, |original| {
+        run_path_with_cstr(link, |link| {
+            cvt(unsafe { libc::symlink(original.as_ptr(), link.as_ptr()) }).map(|_| ())
+        })
+    })
 }
 
 pub fn link(original: &Path, link: &Path) -> io::Result<()> {
-    let original = cstr(original)?;
-    let link = cstr(link)?;
-    cfg_if::cfg_if! {
-        if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon"))] {
-            // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
-            // it implementation-defined whether `link` follows symlinks, so rely on the
-            // `symlink_hard_link` test in library/std/src/fs/tests.rs to check the behavior.
-            // Android has `linkat` on newer versions, but we happen to know `link`
-            // always has the correct behavior, so it's here as well.
-            cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
-        } else if #[cfg(target_os = "macos")] {
-            // On MacOS, older versions (<=10.9) lack support for linkat while newer
-            // versions have it. We want to use linkat if it is available, so we use weak!
-            // to check. `linkat` is preferable to `link` because it gives us a flag to
-            // specify how symlinks should be handled. We pass 0 as the flags argument,
-            // meaning it shouldn't follow symlinks.
-            weak!(fn linkat(c_int, *const c_char, c_int, *const c_char, c_int) -> c_int);
-
-            if let Some(f) = linkat.get() {
-                cvt(unsafe { f(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
-            } else {
-                cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
-            };
-        } else {
-            // Where we can, use `linkat` instead of `link`; see the comment above
-            // this one for details on why.
-            cvt(unsafe { libc::linkat(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
-        }
-    }
-    Ok(())
+    run_path_with_cstr(original, |original| {
+        run_path_with_cstr(link, |link| {
+            cfg_if::cfg_if! {
+                if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon"))] {
+                    // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
+                    // it implementation-defined whether `link` follows symlinks, so rely on the
+                    // `symlink_hard_link` test in library/std/src/fs/tests.rs to check the behavior.
+                    // Android has `linkat` on newer versions, but we happen to know `link`
+                    // always has the correct behavior, so it's here as well.
+                    cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
+                } else if #[cfg(target_os = "macos")] {
+                    // On MacOS, older versions (<=10.9) lack support for linkat while newer
+                    // versions have it. We want to use linkat if it is available, so we use weak!
+                    // to check. `linkat` is preferable to `link` because it gives us a flag to
+                    // specify how symlinks should be handled. We pass 0 as the flags argument,
+                    // meaning it shouldn't follow symlinks.
+                    weak!(fn linkat(c_int, *const c_char, c_int, *const c_char, c_int) -> c_int);
+
+                    if let Some(f) = linkat.get() {
+                        cvt(unsafe { f(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
+                    } else {
+                        cvt(unsafe { libc::link(original.as_ptr(), link.as_ptr()) })?;
+                    };
+                } else {
+                    // Where we can, use `linkat` instead of `link`; see the comment above
+                    // this one for details on why.
+                    cvt(unsafe { libc::linkat(libc::AT_FDCWD, original.as_ptr(), libc::AT_FDCWD, link.as_ptr(), 0) })?;
+                }
+            }
+            Ok(())
+        })
+    })
 }
 
 pub fn stat(p: &Path) -> io::Result<FileAttr> {
-    let p = cstr(p)?;
-
-    cfg_has_statx! {
-        if let Some(ret) = unsafe { try_statx(
-            libc::AT_FDCWD,
-            p.as_ptr(),
-            libc::AT_STATX_SYNC_AS_STAT,
-            libc::STATX_ALL,
-        ) } {
-            return ret;
+    run_path_with_cstr(p, |p| {
+        cfg_has_statx! {
+            if let Some(ret) = unsafe { try_statx(
+                libc::AT_FDCWD,
+                p.as_ptr(),
+                libc::AT_STATX_SYNC_AS_STAT,
+                libc::STATX_ALL,
+            ) } {
+                return ret;
+            }
         }
-    }
 
-    let mut stat: stat64 = unsafe { mem::zeroed() };
-    cvt(unsafe { stat64(p.as_ptr(), &mut stat) })?;
-    Ok(FileAttr::from_stat64(stat))
+        let mut stat: stat64 = unsafe { mem::zeroed() };
+        cvt(unsafe { stat64(p.as_ptr(), &mut stat) })?;
+        Ok(FileAttr::from_stat64(stat))
+    })
 }
 
 pub fn lstat(p: &Path) -> io::Result<FileAttr> {
-    let p = cstr(p)?;
-
-    cfg_has_statx! {
-        if let Some(ret) = unsafe { try_statx(
-            libc::AT_FDCWD,
-            p.as_ptr(),
-            libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
-            libc::STATX_ALL,
-        ) } {
-            return ret;
+    run_path_with_cstr(p, |p| {
+        cfg_has_statx! {
+            if let Some(ret) = unsafe { try_statx(
+                libc::AT_FDCWD,
+                p.as_ptr(),
+                libc::AT_SYMLINK_NOFOLLOW | libc::AT_STATX_SYNC_AS_STAT,
+                libc::STATX_ALL,
+            ) } {
+                return ret;
+            }
         }
-    }
 
-    let mut stat: stat64 = unsafe { mem::zeroed() };
-    cvt(unsafe { lstat64(p.as_ptr(), &mut stat) })?;
-    Ok(FileAttr::from_stat64(stat))
+        let mut stat: stat64 = unsafe { mem::zeroed() };
+        cvt(unsafe { lstat64(p.as_ptr(), &mut stat) })?;
+        Ok(FileAttr::from_stat64(stat))
+    })
 }
 
 pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
-    let path = CString::new(p.as_os_str().as_bytes())?;
-    let buf;
-    unsafe {
-        let r = libc::realpath(path.as_ptr(), ptr::null_mut());
-        if r.is_null() {
-            return Err(io::Error::last_os_error());
-        }
-        buf = CStr::from_ptr(r).to_bytes().to_vec();
-        libc::free(r as *mut _);
+    let r = run_path_with_cstr(p, |path| unsafe {
+        Ok(libc::realpath(path.as_ptr(), ptr::null_mut()))
+    })?;
+    if r.is_null() {
+        return Err(io::Error::last_os_error());
     }
-    Ok(PathBuf::from(OsString::from_vec(buf)))
+    Ok(PathBuf::from(OsString::from_vec(unsafe {
+        let buf = CStr::from_ptr(r).to_bytes().to_vec();
+        libc::free(r as *mut _);
+        buf
+    })))
 }
 
 fn open_from(from: &Path) -> io::Result<(crate::fs::File, crate::fs::Metadata)> {
@@ -1609,9 +1653,9 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     // Opportunistically attempt to create a copy-on-write clone of `from`
     // using `fclonefileat`.
     if HAS_FCLONEFILEAT.load(Ordering::Relaxed) {
-        let to = cstr(to)?;
-        let clonefile_result =
-            cvt(unsafe { fclonefileat(reader.as_raw_fd(), libc::AT_FDCWD, to.as_ptr(), 0) });
+        let clonefile_result = run_path_with_cstr(to, |to| {
+            cvt(unsafe { fclonefileat(reader.as_raw_fd(), libc::AT_FDCWD, to.as_ptr(), 0) })
+        });
         match clonefile_result {
             Ok(_) => return Ok(reader_metadata.len()),
             Err(err) => match err.raw_os_error() {
@@ -1655,9 +1699,10 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
 }
 
 pub fn chown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
-    let path = cstr(path)?;
-    cvt(unsafe { libc::chown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })?;
-    Ok(())
+    run_path_with_cstr(path, |path| {
+        cvt(unsafe { libc::chown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
+            .map(|_| ())
+    })
 }
 
 pub fn fchown(fd: c_int, uid: u32, gid: u32) -> io::Result<()> {
@@ -1666,16 +1711,15 @@ pub fn fchown(fd: c_int, uid: u32, gid: u32) -> io::Result<()> {
 }
 
 pub fn lchown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
-    let path = cstr(path)?;
-    cvt(unsafe { libc::lchown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })?;
-    Ok(())
+    run_path_with_cstr(path, |path| {
+        cvt(unsafe { libc::lchown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
+            .map(|_| ())
+    })
 }
 
 #[cfg(not(any(target_os = "fuchsia", target_os = "vxworks")))]
 pub fn chroot(dir: &Path) -> io::Result<()> {
-    let dir = cstr(dir)?;
-    cvt(unsafe { libc::chroot(dir.as_ptr()) })?;
-    Ok(())
+    run_path_with_cstr(dir, |dir| cvt(unsafe { libc::chroot(dir.as_ptr()) }).map(|_| ()))
 }
 
 pub use remove_dir_impl::remove_dir_all;
@@ -1689,13 +1733,14 @@ mod remove_dir_impl {
 // Modern implementation using openat(), unlinkat() and fdopendir()
 #[cfg(not(any(target_os = "redox", target_os = "espidf", target_os = "horizon", miri)))]
 mod remove_dir_impl {
-    use super::{cstr, lstat, Dir, DirEntry, InnerReadDir, ReadDir};
+    use super::{lstat, Dir, DirEntry, InnerReadDir, ReadDir};
     use crate::ffi::CStr;
     use crate::io;
     use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
     use crate::os::unix::prelude::{OwnedFd, RawFd};
     use crate::path::{Path, PathBuf};
     use crate::sync::Arc;
+    use crate::sys::common::small_c_string::run_path_with_cstr;
     use crate::sys::{cvt, cvt_r};
 
     #[cfg(not(all(target_os = "macos", not(target_arch = "aarch64")),))]
@@ -1862,7 +1907,7 @@ mod remove_dir_impl {
         if attr.file_type().is_symlink() {
             crate::fs::remove_file(p)
         } else {
-            remove_dir_all_recursive(None, &cstr(p)?)
+            run_path_with_cstr(p, |p| remove_dir_all_recursive(None, &p))
         }
     }
 
diff --git a/library/std/src/sys/unix/io.rs b/library/std/src/sys/unix/io.rs
index deb5ee76b..29c340dd3 100644
--- a/library/std/src/sys/unix/io.rs
+++ b/library/std/src/sys/unix/io.rs
@@ -1,4 +1,5 @@
 use crate::marker::PhantomData;
+use crate::os::fd::{AsFd, AsRawFd};
 use crate::slice;
 
 use libc::{c_void, iovec};
@@ -74,3 +75,8 @@ impl<'a> IoSliceMut<'a> {
         unsafe { slice::from_raw_parts_mut(self.vec.iov_base as *mut u8, self.vec.iov_len) }
     }
 }
+
+pub fn is_terminal(fd: &impl AsFd) -> bool {
+    let fd = fd.as_fd();
+    unsafe { libc::isatty(fd.as_raw_fd()) != 0 }
+}
diff --git a/library/std/src/sys/unix/kernel_copy.rs b/library/std/src/sys/unix/kernel_copy.rs
index 8f7abb55e..94546ca09 100644
--- a/library/std/src/sys/unix/kernel_copy.rs
+++ b/library/std/src/sys/unix/kernel_copy.rs
@@ -20,7 +20,7 @@
 //! Since those syscalls have requirements that cannot be fully checked in advance and
 //! gathering additional information about file descriptors would require additional syscalls
 //! anyway it simply attempts to use them one after another (guided by inaccurate hints) to
-//! figure out which one works and and falls back to the generic read-write copy loop if none of them
+//! figure out which one works and falls back to the generic read-write copy loop if none of them
 //! does.
 //! Once a working syscall is found for a pair of file descriptors it will be called in a loop
 //! until the copy operation is completed.
diff --git a/library/std/src/sys/unix/locks/mod.rs b/library/std/src/sys/unix/locks/mod.rs
index f5f92f693..9bb314b70 100644
--- a/library/std/src/sys/unix/locks/mod.rs
+++ b/library/std/src/sys/unix/locks/mod.rs
@@ -11,21 +11,21 @@ cfg_if::cfg_if! {
         mod futex_rwlock;
         mod futex_condvar;
         pub(crate) use futex_mutex::{Mutex, MovableMutex};
-        pub(crate) use futex_rwlock::{RwLock, MovableRwLock};
+        pub(crate) use futex_rwlock::MovableRwLock;
         pub(crate) use futex_condvar::MovableCondvar;
     } else if #[cfg(target_os = "fuchsia")] {
         mod fuchsia_mutex;
         mod futex_rwlock;
         mod futex_condvar;
         pub(crate) use fuchsia_mutex::{Mutex, MovableMutex};
-        pub(crate) use futex_rwlock::{RwLock, MovableRwLock};
+        pub(crate) use futex_rwlock::MovableRwLock;
         pub(crate) use futex_condvar::MovableCondvar;
     } else {
         mod pthread_mutex;
         mod pthread_rwlock;
         mod pthread_condvar;
         pub(crate) use pthread_mutex::{Mutex, MovableMutex};
-        pub(crate) use pthread_rwlock::{RwLock, MovableRwLock};
+        pub(crate) use pthread_rwlock::MovableRwLock;
         pub(crate) use pthread_condvar::MovableCondvar;
     }
 }
diff --git a/library/std/src/sys/unix/mod.rs b/library/std/src/sys/unix/mod.rs
index c84e292ea..9055a011c 100644
--- a/library/std/src/sys/unix/mod.rs
+++ b/library/std/src/sys/unix/mod.rs
@@ -163,17 +163,27 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
             // See the other file for docs. NOTE: Make sure to keep them in
             // sync!
             mod sigpipe {
+                pub const DEFAULT: u8 = 0;
                 pub const INHERIT: u8 = 1;
                 pub const SIG_IGN: u8 = 2;
                 pub const SIG_DFL: u8 = 3;
             }
 
-            let handler = match sigpipe {
-                sigpipe::INHERIT => None,
-                sigpipe::SIG_IGN => Some(libc::SIG_IGN),
-                sigpipe::SIG_DFL => Some(libc::SIG_DFL),
+            let (sigpipe_attr_specified, handler) = match sigpipe {
+                sigpipe::DEFAULT => (false, Some(libc::SIG_IGN)),
+                sigpipe::INHERIT => (true, None),
+                sigpipe::SIG_IGN => (true, Some(libc::SIG_IGN)),
+                sigpipe::SIG_DFL => (true, Some(libc::SIG_DFL)),
                 _ => unreachable!(),
             };
+            // The bootstrap compiler doesn't know about sigpipe::DEFAULT, and always passes in
+            // SIG_IGN. This causes some tests to fail because they expect SIGPIPE to be reset to
+            // default on process spawning (which doesn't happen if #[unix_sigpipe] is specified).
+            // Since we can't differentiate between the cases here, treat SIG_IGN as DEFAULT
+            // unconditionally.
+            if sigpipe_attr_specified && !(cfg!(bootstrap) && sigpipe == sigpipe::SIG_IGN) {
+                UNIX_SIGPIPE_ATTR_SPECIFIED.store(true, crate::sync::atomic::Ordering::Relaxed);
+            }
             if let Some(handler) = handler {
                 rtassert!(signal(libc::SIGPIPE, handler) != libc::SIG_ERR);
             }
@@ -181,6 +191,26 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     }
 }
 
+// This is set (up to once) in reset_sigpipe.
+#[cfg(not(any(
+    target_os = "espidf",
+    target_os = "emscripten",
+    target_os = "fuchsia",
+    target_os = "horizon"
+)))]
+static UNIX_SIGPIPE_ATTR_SPECIFIED: crate::sync::atomic::AtomicBool =
+    crate::sync::atomic::AtomicBool::new(false);
+
+#[cfg(not(any(
+    target_os = "espidf",
+    target_os = "emscripten",
+    target_os = "fuchsia",
+    target_os = "horizon"
+)))]
+pub(crate) fn unix_sigpipe_attr_specified() -> bool {
+    UNIX_SIGPIPE_ATTR_SPECIFIED.load(crate::sync::atomic::Ordering::Relaxed)
+}
+
 // SAFETY: must be called only once during runtime cleanup.
 // NOTE: this is not guaranteed to run, for example when the program aborts.
 pub unsafe fn cleanup() {
@@ -352,16 +382,12 @@ cfg_if::cfg_if! {
         extern "C" {}
     } else if #[cfg(target_os = "macos")] {
         #[link(name = "System")]
-        // res_init and friends require -lresolv on macOS/iOS.
-        // See #41582 and https://blog.achernya.com/2013/03/os-x-has-silly-libsystem.html
-        #[link(name = "resolv")]
         extern "C" {}
     } else if #[cfg(any(target_os = "ios", target_os = "watchos"))] {
         #[link(name = "System")]
         #[link(name = "objc")]
         #[link(name = "Security", kind = "framework")]
         #[link(name = "Foundation", kind = "framework")]
-        #[link(name = "resolv")]
         extern "C" {}
     } else if #[cfg(target_os = "fuchsia")] {
         #[link(name = "zircon")]
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index 46545a083..2f2663db6 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -7,6 +7,7 @@ mod tests;
 
 use crate::os::unix::prelude::*;
 
+use crate::convert::TryFrom;
 use crate::error::Error as StdError;
 use crate::ffi::{CStr, CString, OsStr, OsString};
 use crate::fmt;
@@ -17,10 +18,11 @@ use crate::path::{self, PathBuf};
 use crate::ptr;
 use crate::slice;
 use crate::str;
+use crate::sync::{PoisonError, RwLock};
+use crate::sys::common::small_c_string::{run_path_with_cstr, run_with_cstr};
 use crate::sys::cvt;
 use crate::sys::fd;
 use crate::sys::memchr;
-use crate::sys_common::rwlock::{StaticRwLock, StaticRwLockReadGuard};
 use crate::vec;
 
 #[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
@@ -125,7 +127,9 @@ pub fn error_string(errno: i32) -> String {
         }
 
         let p = p as *const _;
-        str::from_utf8(CStr::from_ptr(p).to_bytes()).unwrap().to_owned()
+        // We can't always expect a UTF-8 environment. When we don't get that luxury,
+        // it's better to give a low-quality error message than none at all.
+        String::from_utf8_lossy(CStr::from_ptr(p).to_bytes()).into()
     }
 }
 
@@ -168,12 +172,8 @@ pub fn chdir(p: &path::Path) -> io::Result<()> {
 
 #[cfg(not(target_os = "espidf"))]
 pub fn chdir(p: &path::Path) -> io::Result<()> {
-    let p: &OsStr = p.as_ref();
-    let p = CString::new(p.as_bytes())?;
-    if unsafe { libc::chdir(p.as_ptr()) } != 0 {
-        return Err(io::Error::last_os_error());
-    }
-    Ok(())
+    let result = run_path_with_cstr(p, |p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
+    if result == 0 { Ok(()) } else { Err(io::Error::last_os_error()) }
 }
 
 pub struct SplitPaths<'a> {
@@ -501,10 +501,10 @@ pub unsafe fn environ() -> *mut *const *const c_char {
     ptr::addr_of_mut!(environ)
 }
 
-static ENV_LOCK: StaticRwLock = StaticRwLock::new();
+static ENV_LOCK: RwLock<()> = RwLock::new(());
 
-pub fn env_read_lock() -> StaticRwLockReadGuard {
-    ENV_LOCK.read()
+pub fn env_read_lock() -> impl Drop {
+    ENV_LOCK.read().unwrap_or_else(PoisonError::into_inner)
 }
 
 /// Returns a vector of (variable, value) byte-vector pairs for all the
@@ -546,35 +546,32 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    let k = CString::new(k.as_bytes()).ok()?;
-    unsafe {
+    let s = run_with_cstr(k.as_bytes(), |k| {
         let _guard = env_read_lock();
-        let s = libc::getenv(k.as_ptr()) as *const libc::c_char;
-        if s.is_null() {
-            None
-        } else {
-            Some(OsStringExt::from_vec(CStr::from_ptr(s).to_bytes().to_vec()))
-        }
+        Ok(unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char)
+    })
+    .ok()?;
+    if s.is_null() {
+        None
+    } else {
+        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
     }
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    let k = CString::new(k.as_bytes())?;
-    let v = CString::new(v.as_bytes())?;
-
-    unsafe {
-        let _guard = ENV_LOCK.write();
-        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
-    }
+    run_with_cstr(k.as_bytes(), |k| {
+        run_with_cstr(v.as_bytes(), |v| {
+            let _guard = ENV_LOCK.write();
+            cvt(unsafe { libc::setenv(k.as_ptr(), v.as_ptr(), 1) }).map(drop)
+        })
+    })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    let nbuf = CString::new(n.as_bytes())?;
-
-    unsafe {
+    run_with_cstr(n.as_bytes(), |nbuf| {
         let _guard = ENV_LOCK.write();
-        cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
-    }
+        cvt(unsafe { libc::unsetenv(nbuf.as_ptr()) }).map(drop)
+    })
 }
 
 #[cfg(not(target_os = "espidf"))]
diff --git a/library/std/src/sys/unix/process/process_common.rs b/library/std/src/sys/unix/process/process_common.rs
index 2834ee0ac..848adca78 100644
--- a/library/std/src/sys/unix/process/process_common.rs
+++ b/library/std/src/sys/unix/process/process_common.rs
@@ -39,10 +39,12 @@ cfg_if::cfg_if! {
 // https://github.com/aosp-mirror/platform_bionic/blob/ad8dcd6023294b646e5a8288c0ed431b0845da49/libc/include/android/legacy_signal_inlines.h
 cfg_if::cfg_if! {
     if #[cfg(target_os = "android")] {
+        #[allow(dead_code)]
         pub unsafe fn sigemptyset(set: *mut libc::sigset_t) -> libc::c_int {
             set.write_bytes(0u8, 1);
             return 0;
         }
+
         #[allow(dead_code)]
         pub unsafe fn sigaddset(set: *mut libc::sigset_t, signum: libc::c_int) -> libc::c_int {
             use crate::{
diff --git a/library/std/src/sys/unix/process/process_common/tests.rs b/library/std/src/sys/unix/process/process_common/tests.rs
index d176b3401..03631e4e3 100644
--- a/library/std/src/sys/unix/process/process_common/tests.rs
+++ b/library/std/src/sys/unix/process/process_common/tests.rs
@@ -31,41 +31,54 @@ macro_rules! t {
     ignore
 )]
 fn test_process_mask() {
-    unsafe {
-        // Test to make sure that a signal mask does not get inherited.
-        let mut cmd = Command::new(OsStr::new("cat"));
-
-        let mut set = mem::MaybeUninit::<libc::sigset_t>::uninit();
-        let mut old_set = mem::MaybeUninit::<libc::sigset_t>::uninit();
-        t!(cvt(sigemptyset(set.as_mut_ptr())));
-        t!(cvt(sigaddset(set.as_mut_ptr(), libc::SIGINT)));
-        t!(cvt_nz(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), old_set.as_mut_ptr())));
-
-        cmd.stdin(Stdio::MakePipe);
-        cmd.stdout(Stdio::MakePipe);
-
-        let (mut cat, mut pipes) = t!(cmd.spawn(Stdio::Null, true));
-        let stdin_write = pipes.stdin.take().unwrap();
-        let stdout_read = pipes.stdout.take().unwrap();
-
-        t!(cvt_nz(libc::pthread_sigmask(libc::SIG_SETMASK, old_set.as_ptr(), ptr::null_mut())));
-
-        t!(cvt(libc::kill(cat.id() as libc::pid_t, libc::SIGINT)));
-        // We need to wait until SIGINT is definitely delivered. The
-        // easiest way is to write something to cat, and try to read it
-        // back: if SIGINT is unmasked, it'll get delivered when cat is
-        // next scheduled.
-        let _ = stdin_write.write(b"Hello");
-        drop(stdin_write);
-
-        // Either EOF or failure (EPIPE) is okay.
-        let mut buf = [0; 5];
-        if let Ok(ret) = stdout_read.read(&mut buf) {
-            assert_eq!(ret, 0);
+    // Test to make sure that a signal mask *does* get inherited.
+    fn test_inner(mut cmd: Command) {
+        unsafe {
+            let mut set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            let mut old_set = mem::MaybeUninit::<libc::sigset_t>::uninit();
+            t!(cvt(sigemptyset(set.as_mut_ptr())));
+            t!(cvt(sigaddset(set.as_mut_ptr(), libc::SIGINT)));
+            t!(cvt_nz(libc::pthread_sigmask(
+                libc::SIG_SETMASK,
+                set.as_ptr(),
+                old_set.as_mut_ptr()
+            )));
+
+            cmd.stdin(Stdio::MakePipe);
+            cmd.stdout(Stdio::MakePipe);
+
+            let (mut cat, mut pipes) = t!(cmd.spawn(Stdio::Null, true));
+            let stdin_write = pipes.stdin.take().unwrap();
+            let stdout_read = pipes.stdout.take().unwrap();
+
+            t!(cvt_nz(libc::pthread_sigmask(libc::SIG_SETMASK, old_set.as_ptr(), ptr::null_mut())));
+
+            t!(cvt(libc::kill(cat.id() as libc::pid_t, libc::SIGINT)));
+            // We need to wait until SIGINT is definitely delivered. The
+            // easiest way is to write something to cat, and try to read it
+            // back: if SIGINT is unmasked, it'll get delivered when cat is
+            // next scheduled.
+            let _ = stdin_write.write(b"Hello");
+            drop(stdin_write);
+
+            // Exactly 5 bytes should be read.
+            let mut buf = [0; 5];
+            let ret = t!(stdout_read.read(&mut buf));
+            assert_eq!(ret, 5);
+            assert_eq!(&buf, b"Hello");
+
+            t!(cat.wait());
         }
-
-        t!(cat.wait());
     }
+
+    // A plain `Command::new` uses the posix_spawn path on many platforms.
+    let cmd = Command::new(OsStr::new("cat"));
+    test_inner(cmd);
+
+    // Specifying `pre_exec` forces the fork/exec path.
+    let mut cmd = Command::new(OsStr::new("cat"));
+    unsafe { cmd.pre_exec(Box::new(|| Ok(()))) };
+    test_inner(cmd);
 }
 
 #[test]
diff --git a/library/std/src/sys/unix/process/process_fuchsia.rs b/library/std/src/sys/unix/process/process_fuchsia.rs
index 73f5d3a61..66ea3db20 100644
--- a/library/std/src/sys/unix/process/process_fuchsia.rs
+++ b/library/std/src/sys/unix/process/process_fuchsia.rs
@@ -287,7 +287,7 @@ impl ExitStatus {
         // SuS and POSIX) say a wait status is, but Fuchsia apparently uses a u64, so it won't
         // necessarily fit.
         //
-        // It seems to me that that the right answer would be to provide std::os::fuchsia with its
+        // It seems to me that the right answer would be to provide std::os::fuchsia with its
         // own ExitStatusExt, rather that trying to provide a not very convincing imitation of
         // Unix.  Ie, std::os::unix::process:ExitStatusExt ought not to exist on Fuchsia.  But
         // fixing this up that is beyond the scope of my efforts now.
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index 26ae62817..56a805cef 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -2,7 +2,6 @@ use crate::fmt;
 use crate::io::{self, Error, ErrorKind};
 use crate::mem;
 use crate::num::NonZeroI32;
-use crate::ptr;
 use crate::sys;
 use crate::sys::cvt;
 use crate::sys::process::process_common::*;
@@ -310,7 +309,7 @@ impl Command {
                 //FIXME: Redox kernel does not support setgroups yet
                 #[cfg(not(target_os = "redox"))]
                 if libc::getuid() == 0 && self.get_groups().is_none() {
-                    cvt(libc::setgroups(0, ptr::null()))?;
+                    cvt(libc::setgroups(0, crate::ptr::null()))?;
                 }
                 cvt(libc::setuid(u as uid_t))?;
             }
@@ -326,30 +325,26 @@ impl Command {
         // emscripten has no signal support.
         #[cfg(not(target_os = "emscripten"))]
         {
-            use crate::mem::MaybeUninit;
-            use crate::sys::cvt_nz;
-            // Reset signal handling so the child process starts in a
-            // standardized state. libstd ignores SIGPIPE, and signal-handling
-            // libraries often set a mask. Child processes inherit ignored
-            // signals and the signal mask from their parent, but most
-            // UNIX programs do not reset these things on their own, so we
-            // need to clean things up now to avoid confusing the program
-            // we're about to run.
-            let mut set = MaybeUninit::<libc::sigset_t>::uninit();
-            cvt(sigemptyset(set.as_mut_ptr()))?;
-            cvt_nz(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?;
-
-            #[cfg(target_os = "android")] // see issue #88585
-            {
-                let mut action: libc::sigaction = mem::zeroed();
-                action.sa_sigaction = libc::SIG_DFL;
-                cvt(libc::sigaction(libc::SIGPIPE, &action, ptr::null_mut()))?;
-            }
-            #[cfg(not(target_os = "android"))]
-            {
-                let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
-                if ret == libc::SIG_ERR {
-                    return Err(io::Error::last_os_error());
+            // Inherit the signal mask from the parent rather than resetting it (i.e. do not call
+            // pthread_sigmask).
+
+            // If #[unix_sigpipe] is specified, don't reset SIGPIPE to SIG_DFL.
+            // If #[unix_sigpipe] is not specified, reset SIGPIPE to SIG_DFL for backward compatibility.
+            //
+            // #[unix_sigpipe] is an opportunity to change the default here.
+            if !crate::sys::unix_sigpipe_attr_specified() {
+                #[cfg(target_os = "android")] // see issue #88585
+                {
+                    let mut action: libc::sigaction = mem::zeroed();
+                    action.sa_sigaction = libc::SIG_DFL;
+                    cvt(libc::sigaction(libc::SIGPIPE, &action, crate::ptr::null_mut()))?;
+                }
+                #[cfg(not(target_os = "android"))]
+                {
+                    let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
+                    if ret == libc::SIG_ERR {
+                        return Err(io::Error::last_os_error());
+                    }
                 }
             }
         }
@@ -411,7 +406,7 @@ impl Command {
         envp: Option<&CStringArray>,
     ) -> io::Result<Option<Process>> {
         use crate::mem::MaybeUninit;
-        use crate::sys::{self, cvt_nz};
+        use crate::sys::{self, cvt_nz, unix_sigpipe_attr_specified};
 
         if self.get_gid().is_some()
             || self.get_uid().is_some()
@@ -531,13 +526,24 @@ impl Command {
                 cvt_nz(libc::posix_spawnattr_setpgroup(attrs.0.as_mut_ptr(), pgroup))?;
             }
 
-            let mut set = MaybeUninit::<libc::sigset_t>::uninit();
-            cvt(sigemptyset(set.as_mut_ptr()))?;
-            cvt_nz(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?;
-            cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
-            cvt_nz(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?;
+            // Inherit the signal mask from this process rather than resetting it (i.e. do not call
+            // posix_spawnattr_setsigmask).
+
+            // If #[unix_sigpipe] is specified, don't reset SIGPIPE to SIG_DFL.
+            // If #[unix_sigpipe] is not specified, reset SIGPIPE to SIG_DFL for backward compatibility.
+            //
+            // #[unix_sigpipe] is an opportunity to change the default here.
+            if !unix_sigpipe_attr_specified() {
+                let mut default_set = MaybeUninit::<libc::sigset_t>::uninit();
+                cvt(sigemptyset(default_set.as_mut_ptr()))?;
+                cvt(sigaddset(default_set.as_mut_ptr(), libc::SIGPIPE))?;
+                cvt_nz(libc::posix_spawnattr_setsigdefault(
+                    attrs.0.as_mut_ptr(),
+                    default_set.as_ptr(),
+                ))?;
+                flags |= libc::POSIX_SPAWN_SETSIGDEF;
+            }
 
-            flags |= libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK;
             cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
 
             // Make sure we synchronize access to the global `environ` resource
@@ -822,14 +828,14 @@ impl crate::os::linux::process::ChildExt for crate::process::Child {
         self.handle
             .pidfd
             .as_ref()
-            .ok_or_else(|| Error::new(ErrorKind::Other, "No pidfd was created."))
+            .ok_or_else(|| Error::new(ErrorKind::Uncategorized, "No pidfd was created."))
     }
 
     fn take_pidfd(&mut self) -> io::Result<PidFd> {
         self.handle
             .pidfd
             .take()
-            .ok_or_else(|| Error::new(ErrorKind::Other, "No pidfd was created."))
+            .ok_or_else(|| Error::new(ErrorKind::Uncategorized, "No pidfd was created."))
     }
 }
 
diff --git a/library/std/src/sys/unix/stdio.rs b/library/std/src/sys/unix/stdio.rs
index 329f9433d..b3626c564 100644
--- a/library/std/src/sys/unix/stdio.rs
+++ b/library/std/src/sys/unix/stdio.rs
@@ -1,6 +1,6 @@
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
-use crate::os::unix::io::{AsFd, BorrowedFd, FromRawFd};
+use crate::os::unix::io::FromRawFd;
 use crate::sys::fd::FileDesc;
 
 pub struct Stdin(());
@@ -91,51 +91,3 @@ pub const STDIN_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
 pub fn panic_output() -> Option<impl io::Write> {
     Some(Stderr::new())
 }
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl AsFd for io::Stdin {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDIN_FILENO) }
-    }
-}
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl<'a> AsFd for io::StdinLock<'a> {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDIN_FILENO) }
-    }
-}
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl AsFd for io::Stdout {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDOUT_FILENO) }
-    }
-}
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl<'a> AsFd for io::StdoutLock<'a> {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDOUT_FILENO) }
-    }
-}
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl AsFd for io::Stderr {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDERR_FILENO) }
-    }
-}
-
-#[stable(feature = "io_safety", since = "1.63.0")]
-impl<'a> AsFd for io::StderrLock<'a> {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(libc::STDERR_FILENO) }
-    }
-}
diff --git a/library/std/src/sys/unix/thread.rs b/library/std/src/sys/unix/thread.rs
index f6b627afc..c1d30dd9d 100644
--- a/library/std/src/sys/unix/thread.rs
+++ b/library/std/src/sys/unix/thread.rs
@@ -137,7 +137,9 @@ impl Thread {
         unsafe {
             // Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20.
             let name = truncate_cstr(name, TASK_COMM_LEN);
-            libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
+            let res = libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
+            // We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
+            debug_assert_eq!(res, 0);
         }
     }
 
@@ -152,20 +154,22 @@ impl Thread {
     pub fn set_name(name: &CStr) {
         unsafe {
             let name = truncate_cstr(name, libc::MAXTHREADNAMESIZE);
-            libc::pthread_setname_np(name.as_ptr());
+            let res = libc::pthread_setname_np(name.as_ptr());
+            // We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
+            debug_assert_eq!(res, 0);
         }
     }
 
     #[cfg(target_os = "netbsd")]
     pub fn set_name(name: &CStr) {
-        use crate::ffi::CString;
-        let cname = CString::new(&b"%s"[..]).unwrap();
         unsafe {
-            libc::pthread_setname_np(
+            let cname = CStr::from_bytes_with_nul_unchecked(b"%s\0".as_slice());
+            let res = libc::pthread_setname_np(
                 libc::pthread_self(),
                 cname.as_ptr(),
                 name.as_ptr() as *mut libc::c_void,
             );
+            debug_assert_eq!(res, 0);
         }
     }
 
@@ -178,9 +182,8 @@ impl Thread {
         }
 
         if let Some(f) = pthread_setname_np.get() {
-            unsafe {
-                f(libc::pthread_self(), name.as_ptr());
-            }
+            let res = unsafe { f(libc::pthread_self(), name.as_ptr()) };
+            debug_assert_eq!(res, 0);
         }
     }
 
@@ -785,6 +788,16 @@ pub mod guard {
             const GUARD_PAGES: usize = 1;
             let guard = guardaddr..guardaddr + GUARD_PAGES * page_size;
             Some(guard)
+        } else if cfg!(target_os = "openbsd") {
+            // OpenBSD stack already includes a guard page, and stack is
+            // immutable.
+            //
+            // We'll just note where we expect rlimit to start
+            // faulting, so our handler can report "stack overflow", and
+            // trust that the kernel's own stack guard will work.
+            let stackptr = get_stack_start_aligned()?;
+            let stackaddr = stackptr.addr();
+            Some(stackaddr - page_size..stackaddr)
         } else {
             // Reallocate the last page of the stack.
             // This ensures SIGBUS will be raised on
diff --git a/library/std/src/sys/unix/thread_local_dtor.rs b/library/std/src/sys/unix/thread_local_dtor.rs
index 6e8be2a91..d7fd2130f 100644
--- a/library/std/src/sys/unix/thread_local_dtor.rs
+++ b/library/std/src/sys/unix/thread_local_dtor.rs
@@ -17,6 +17,7 @@
     target_os = "redox",
     target_os = "emscripten"
 ))]
+#[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::mem;
     use crate::sys_common::thread_local_dtor::register_dtor_fallback;
diff --git a/library/std/src/sys/unix/thread_local_key.rs b/library/std/src/sys/unix/thread_local_key.rs
index 2c5b94b1e..2b2d079ee 100644
--- a/library/std/src/sys/unix/thread_local_key.rs
+++ b/library/std/src/sys/unix/thread_local_key.rs
@@ -27,8 +27,3 @@ pub unsafe fn destroy(key: Key) {
     let r = libc::pthread_key_delete(key);
     debug_assert_eq!(r, 0);
 }
-
-#[inline]
-pub fn requires_synchronized_create() -> bool {
-    false
-}
diff --git a/library/std/src/sys/unix/thread_parker/darwin.rs b/library/std/src/sys/unix/thread_parker/darwin.rs
new file mode 100644
index 000000000..2f5356fe2
--- /dev/null
+++ b/library/std/src/sys/unix/thread_parker/darwin.rs
@@ -0,0 +1,131 @@
+//! Thread parking for Darwin-based systems.
+//!
+//! Darwin actually has futex syscalls (`__ulock_wait`/`__ulock_wake`), but they
+//! cannot be used in `std` because they are non-public (their use will lead to
+//! rejection from the App Store) and because they are only available starting
+//! with macOS version 10.12, even though the minimum target version is 10.7.
+//!
+//! Therefore, we need to look for other synchronization primitives. Luckily, Darwin
+//! supports semaphores, which allow us to implement the behaviour we need with
+//! only one primitive (as opposed to a mutex-condvar pair). We use the semaphore
+//! provided by libdispatch, as the underlying Mach semaphore is only dubiously
+//! public.
+
+use crate::pin::Pin;
+use crate::sync::atomic::{
+    AtomicI8,
+    Ordering::{Acquire, Release},
+};
+use crate::time::Duration;
+
+type dispatch_semaphore_t = *mut crate::ffi::c_void;
+type dispatch_time_t = u64;
+
+const DISPATCH_TIME_NOW: dispatch_time_t = 0;
+const DISPATCH_TIME_FOREVER: dispatch_time_t = !0;
+
+// Contained in libSystem.dylib, which is linked by default.
+extern "C" {
+    fn dispatch_time(when: dispatch_time_t, delta: i64) -> dispatch_time_t;
+    fn dispatch_semaphore_create(val: isize) -> dispatch_semaphore_t;
+    fn dispatch_semaphore_wait(dsema: dispatch_semaphore_t, timeout: dispatch_time_t) -> isize;
+    fn dispatch_semaphore_signal(dsema: dispatch_semaphore_t) -> isize;
+    fn dispatch_release(object: *mut crate::ffi::c_void);
+}
+
+const EMPTY: i8 = 0;
+const NOTIFIED: i8 = 1;
+const PARKED: i8 = -1;
+
+pub struct Parker {
+    semaphore: dispatch_semaphore_t,
+    state: AtomicI8,
+}
+
+unsafe impl Sync for Parker {}
+unsafe impl Send for Parker {}
+
+impl Parker {
+    pub unsafe fn new(parker: *mut Parker) {
+        let semaphore = dispatch_semaphore_create(0);
+        assert!(
+            !semaphore.is_null(),
+            "failed to create dispatch semaphore for thread synchronization"
+        );
+        parker.write(Parker { semaphore, state: AtomicI8::new(EMPTY) })
+    }
+
+    // Does not need `Pin`, but other implementation do.
+    pub unsafe fn park(self: Pin<&Self>) {
+        // The semaphore counter must be zero at this point, because unparking
+        // threads will not actually increase it until we signalled that we
+        // are waiting.
+
+        // Change NOTIFIED to EMPTY and EMPTY to PARKED.
+        if self.state.fetch_sub(1, Acquire) == NOTIFIED {
+            return;
+        }
+
+        // Another thread may increase the semaphore counter from this point on.
+        // If it is faster than us, we will decrement it again immediately below.
+        // If we are faster, we wait.
+
+        // Ensure that the semaphore counter has actually been decremented, even
+        // if the call timed out for some reason.
+        while dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER) != 0 {}
+
+        // At this point, the semaphore counter is zero again.
+
+        // We were definitely woken up, so we don't need to check the state.
+        // Still, we need to reset the state using a swap to observe the state
+        // change with acquire ordering.
+        self.state.swap(EMPTY, Acquire);
+    }
+
+    // Does not need `Pin`, but other implementation do.
+    pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) {
+        if self.state.fetch_sub(1, Acquire) == NOTIFIED {
+            return;
+        }
+
+        let nanos = dur.as_nanos().try_into().unwrap_or(i64::MAX);
+        let timeout = dispatch_time(DISPATCH_TIME_NOW, nanos);
+
+        let timeout = dispatch_semaphore_wait(self.semaphore, timeout) != 0;
+
+        let state = self.state.swap(EMPTY, Acquire);
+        if state == NOTIFIED && timeout {
+            // If the state was NOTIFIED but semaphore_wait returned without
+            // decrementing the count because of a timeout, it means another
+            // thread is about to call semaphore_signal. We must wait for that
+            // to happen to ensure the semaphore count is reset.
+            while dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER) != 0 {}
+        } else {
+            // Either a timeout occurred and we reset the state before any thread
+            // tried to wake us up, or we were woken up and reset the state,
+            // making sure to observe the state change with acquire ordering.
+            // Either way, the semaphore counter is now zero again.
+        }
+    }
+
+    // Does not need `Pin`, but other implementation do.
+    pub fn unpark(self: Pin<&Self>) {
+        let state = self.state.swap(NOTIFIED, Release);
+        if state == PARKED {
+            unsafe {
+                dispatch_semaphore_signal(self.semaphore);
+            }
+        }
+    }
+}
+
+impl Drop for Parker {
+    fn drop(&mut self) {
+        // SAFETY:
+        // We always ensure that the semaphore count is reset, so this will
+        // never cause an exception.
+        unsafe {
+            dispatch_release(self.semaphore);
+        }
+    }
+}
diff --git a/library/std/src/sys/unix/thread_parker/mod.rs b/library/std/src/sys/unix/thread_parker/mod.rs
index e2453580d..35f1e68a8 100644
--- a/library/std/src/sys/unix/thread_parker/mod.rs
+++ b/library/std/src/sys/unix/thread_parker/mod.rs
@@ -11,7 +11,18 @@
 )))]
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "netbsd")] {
+    if #[cfg(all(
+        any(
+            target_os = "macos",
+            target_os = "ios",
+            target_os = "watchos",
+            target_os = "tvos",
+        ),
+        not(miri),
+    ))] {
+        mod darwin;
+        pub use darwin::Parker;
+    } else if #[cfg(target_os = "netbsd")] {
         mod netbsd;
         pub use netbsd::Parker;
     } else {
diff --git a/library/std/src/sys/unix/time.rs b/library/std/src/sys/unix/time.rs
index dff973f59..cca9c6767 100644
--- a/library/std/src/sys/unix/time.rs
+++ b/library/std/src/sys/unix/time.rs
@@ -7,6 +7,12 @@ const NSEC_PER_SEC: u64 = 1_000_000_000;
 pub const UNIX_EPOCH: SystemTime = SystemTime { t: Timespec::zero() };
 
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[repr(transparent)]
+#[rustc_layout_scalar_valid_range_start(0)]
+#[rustc_layout_scalar_valid_range_end(999_999_999)]
+struct Nanoseconds(u32);
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SystemTime {
     pub(in crate::sys::unix) t: Timespec,
 }
@@ -14,7 +20,7 @@ pub struct SystemTime {
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub(in crate::sys::unix) struct Timespec {
     tv_sec: i64,
-    tv_nsec: i64,
+    tv_nsec: Nanoseconds,
 }
 
 impl SystemTime {
@@ -46,18 +52,20 @@ impl fmt::Debug for SystemTime {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("SystemTime")
             .field("tv_sec", &self.t.tv_sec)
-            .field("tv_nsec", &self.t.tv_nsec)
+            .field("tv_nsec", &self.t.tv_nsec.0)
             .finish()
     }
 }
 
 impl Timespec {
     pub const fn zero() -> Timespec {
-        Timespec { tv_sec: 0, tv_nsec: 0 }
+        Timespec::new(0, 0)
     }
 
-    fn new(tv_sec: i64, tv_nsec: i64) -> Timespec {
-        Timespec { tv_sec, tv_nsec }
+    const fn new(tv_sec: i64, tv_nsec: i64) -> Timespec {
+        assert!(tv_nsec >= 0 && tv_nsec < NSEC_PER_SEC as i64);
+        // SAFETY: The assert above checks tv_nsec is within the valid range
+        Timespec { tv_sec, tv_nsec: unsafe { Nanoseconds(tv_nsec as u32) } }
     }
 
     pub fn sub_timespec(&self, other: &Timespec) -> Result<Duration, Duration> {
@@ -75,12 +83,12 @@ impl Timespec {
             //
             // Ideally this code could be rearranged such that it more
             // directly expresses the lower-cost behavior we want from it.
-            let (secs, nsec) = if self.tv_nsec >= other.tv_nsec {
-                ((self.tv_sec - other.tv_sec) as u64, (self.tv_nsec - other.tv_nsec) as u32)
+            let (secs, nsec) = if self.tv_nsec.0 >= other.tv_nsec.0 {
+                ((self.tv_sec - other.tv_sec) as u64, self.tv_nsec.0 - other.tv_nsec.0)
             } else {
                 (
                     (self.tv_sec - other.tv_sec - 1) as u64,
-                    self.tv_nsec as u32 + (NSEC_PER_SEC as u32) - other.tv_nsec as u32,
+                    self.tv_nsec.0 + (NSEC_PER_SEC as u32) - other.tv_nsec.0,
                 )
             };
 
@@ -102,7 +110,7 @@ impl Timespec {
 
         // Nano calculations can't overflow because nanos are <1B which fit
         // in a u32.
-        let mut nsec = other.subsec_nanos() + self.tv_nsec as u32;
+        let mut nsec = other.subsec_nanos() + self.tv_nsec.0;
         if nsec >= NSEC_PER_SEC as u32 {
             nsec -= NSEC_PER_SEC as u32;
             secs = secs.checked_add(1)?;
@@ -118,7 +126,7 @@ impl Timespec {
             .and_then(|secs| self.tv_sec.checked_sub(secs))?;
 
         // Similar to above, nanos can't overflow.
-        let mut nsec = self.tv_nsec as i32 - other.subsec_nanos() as i32;
+        let mut nsec = self.tv_nsec.0 as i32 - other.subsec_nanos() as i32;
         if nsec < 0 {
             nsec += NSEC_PER_SEC as i32;
             secs = secs.checked_sub(1)?;
@@ -130,7 +138,7 @@ impl Timespec {
     pub fn to_timespec(&self) -> Option<libc::timespec> {
         Some(libc::timespec {
             tv_sec: self.tv_sec.try_into().ok()?,
-            tv_nsec: self.tv_nsec.try_into().ok()?,
+            tv_nsec: self.tv_nsec.0.try_into().ok()?,
         })
     }
 }
@@ -293,7 +301,7 @@ mod inner {
         fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             f.debug_struct("Instant")
                 .field("tv_sec", &self.t.tv_sec)
-                .field("tv_nsec", &self.t.tv_nsec)
+                .field("tv_nsec", &self.t.tv_nsec.0)
                 .finish()
         }
     }
@@ -334,7 +342,7 @@ mod inner {
                     let mut t = MaybeUninit::uninit();
                     cvt(unsafe { clock_gettime64(clock, t.as_mut_ptr()) }).unwrap();
                     let t = unsafe { t.assume_init() };
-                    return Timespec { tv_sec: t.tv_sec, tv_nsec: t.tv_nsec as i64 };
+                    return Timespec::new(t.tv_sec, t.tv_nsec as i64);
                 }
             }
 
diff --git a/library/std/src/sys/unsupported/io.rs b/library/std/src/sys/unsupported/io.rs
index d5f475b43..82610ffab 100644
--- a/library/std/src/sys/unsupported/io.rs
+++ b/library/std/src/sys/unsupported/io.rs
@@ -45,3 +45,7 @@ impl<'a> IoSliceMut<'a> {
         self.0
     }
 }
+
+pub fn is_terminal<T>(_: &T) -> bool {
+    false
+}
diff --git a/library/std/src/sys/unsupported/locks/condvar.rs b/library/std/src/sys/unsupported/locks/condvar.rs
index e703fd0d2..527a26a12 100644
--- a/library/std/src/sys/unsupported/locks/condvar.rs
+++ b/library/std/src/sys/unsupported/locks/condvar.rs
@@ -7,6 +7,7 @@ pub type MovableCondvar = Condvar;
 
 impl Condvar {
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Condvar {
         Condvar {}
     }
diff --git a/library/std/src/sys/unsupported/locks/mod.rs b/library/std/src/sys/unsupported/locks/mod.rs
index d412ff152..602a2d623 100644
--- a/library/std/src/sys/unsupported/locks/mod.rs
+++ b/library/std/src/sys/unsupported/locks/mod.rs
@@ -3,4 +3,4 @@ mod mutex;
 mod rwlock;
 pub use condvar::{Condvar, MovableCondvar};
 pub use mutex::{MovableMutex, Mutex};
-pub use rwlock::{MovableRwLock, RwLock};
+pub use rwlock::MovableRwLock;
diff --git a/library/std/src/sys/unsupported/locks/mutex.rs b/library/std/src/sys/unsupported/locks/mutex.rs
index 2be0b34b9..87ea475c6 100644
--- a/library/std/src/sys/unsupported/locks/mutex.rs
+++ b/library/std/src/sys/unsupported/locks/mutex.rs
@@ -12,6 +12,7 @@ unsafe impl Sync for Mutex {} // no threads on this platform
 
 impl Mutex {
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Mutex {
         Mutex { locked: Cell::new(false) }
     }
diff --git a/library/std/src/sys/unsupported/locks/rwlock.rs b/library/std/src/sys/unsupported/locks/rwlock.rs
index aca5fb715..5292691b9 100644
--- a/library/std/src/sys/unsupported/locks/rwlock.rs
+++ b/library/std/src/sys/unsupported/locks/rwlock.rs
@@ -12,6 +12,7 @@ unsafe impl Sync for RwLock {} // no threads on this platform
 
 impl RwLock {
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> RwLock {
         RwLock { mode: Cell::new(0) }
     }
diff --git a/library/std/src/sys/unsupported/thread_local_dtor.rs b/library/std/src/sys/unsupported/thread_local_dtor.rs
index 85d660983..84660ea58 100644
--- a/library/std/src/sys/unsupported/thread_local_dtor.rs
+++ b/library/std/src/sys/unsupported/thread_local_dtor.rs
@@ -1,5 +1,6 @@
 #![unstable(feature = "thread_local_internals", issue = "none")]
 
+#[cfg_attr(target_family = "wasm", allow(unused))] // unused on wasm32-unknown-unknown
 pub unsafe fn register_dtor(_t: *mut u8, _dtor: unsafe extern "C" fn(*mut u8)) {
     // FIXME: right now there is no concept of "thread exit", but this is likely
     // going to show up at some point in the form of an exported symbol that the
diff --git a/library/std/src/sys/unsupported/thread_local_key.rs b/library/std/src/sys/unsupported/thread_local_key.rs
index c31b61cbf..b6e5e4cd2 100644
--- a/library/std/src/sys/unsupported/thread_local_key.rs
+++ b/library/std/src/sys/unsupported/thread_local_key.rs
@@ -19,8 +19,3 @@ pub unsafe fn get(_key: Key) -> *mut u8 {
 pub unsafe fn destroy(_key: Key) {
     panic!("should not be used on this target");
 }
-
-#[inline]
-pub fn requires_synchronized_create() -> bool {
-    panic!("should not be used on this target");
-}
diff --git a/library/std/src/sys/wasi/fs.rs b/library/std/src/sys/wasi/fs.rs
index 510cf36b1..d4866bbc3 100644
--- a/library/std/src/sys/wasi/fs.rs
+++ b/library/std/src/sys/wasi/fs.rs
@@ -1,7 +1,7 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 
 use super::fd::WasiFd;
-use crate::ffi::{CStr, CString, OsStr, OsString};
+use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
 use crate::iter;
@@ -12,6 +12,7 @@ use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd
 use crate::path::{Path, PathBuf};
 use crate::ptr;
 use crate::sync::Arc;
+use crate::sys::common::small_c_string::run_path_with_cstr;
 use crate::sys::time::SystemTime;
 use crate::sys::unsupported;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
@@ -65,8 +66,8 @@ pub struct FilePermissions {
 
 #[derive(Copy, Clone, Debug, Default)]
 pub struct FileTimes {
-    accessed: Option<wasi::Timestamp>,
-    modified: Option<wasi::Timestamp>,
+    accessed: Option<SystemTime>,
+    modified: Option<SystemTime>,
 }
 
 #[derive(PartialEq, Eq, Hash, Debug, Copy, Clone)]
@@ -120,11 +121,11 @@ impl FilePermissions {
 
 impl FileTimes {
     pub fn set_accessed(&mut self, t: SystemTime) {
-        self.accessed = Some(t.to_wasi_timestamp_or_panic());
+        self.accessed = Some(t);
     }
 
     pub fn set_modified(&mut self, t: SystemTime) {
-        self.modified = Some(t.to_wasi_timestamp_or_panic());
+        self.modified = Some(t);
     }
 }
 
@@ -476,9 +477,16 @@ impl File {
     }
 
     pub fn set_times(&self, times: FileTimes) -> io::Result<()> {
+        let to_timestamp = |time: Option<SystemTime>| {
+            match time {
+                Some(time) if let Some(ts) = time.to_wasi_timestamp() => Ok(ts),
+                Some(_) => Err(io::const_io_error!(io::ErrorKind::InvalidInput, "timestamp is too large to set as a file time")),
+                None => Ok(0),
+            }
+        };
         self.fd.filestat_set_times(
-            times.accessed.unwrap_or(0),
-            times.modified.unwrap_or(0),
+            to_timestamp(times.accessed)?,
+            to_timestamp(times.modified)?,
             times.accessed.map_or(0, |_| wasi::FSTFLAGS_ATIM)
                 | times.modified.map_or(0, |_| wasi::FSTFLAGS_MTIM),
         )
@@ -687,51 +695,52 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 /// Note that this can fail if `p` doesn't look like it can be opened relative
 /// to any pre-opened file descriptor.
 fn open_parent(p: &Path) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
-    let p = CString::new(p.as_os_str().as_bytes())?;
-    let mut buf = Vec::<u8>::with_capacity(512);
-    loop {
-        unsafe {
-            let mut relative_path = buf.as_ptr().cast();
-            let mut abs_prefix = ptr::null();
-            let fd = __wasilibc_find_relpath(
-                p.as_ptr(),
-                &mut abs_prefix,
-                &mut relative_path,
-                buf.capacity(),
-            );
-            if fd == -1 {
-                if io::Error::last_os_error().raw_os_error() == Some(libc::ENOMEM) {
-                    // Trigger the internal buffer resizing logic of `Vec` by requiring
-                    // more space than the current capacity.
-                    let cap = buf.capacity();
-                    buf.set_len(cap);
-                    buf.reserve(1);
-                    continue;
-                }
-                let msg = format!(
-                    "failed to find a pre-opened file descriptor \
-                     through which {:?} could be opened",
-                    p
+    run_path_with_cstr(p, |p| {
+        let mut buf = Vec::<u8>::with_capacity(512);
+        loop {
+            unsafe {
+                let mut relative_path = buf.as_ptr().cast();
+                let mut abs_prefix = ptr::null();
+                let fd = __wasilibc_find_relpath(
+                    p.as_ptr(),
+                    &mut abs_prefix,
+                    &mut relative_path,
+                    buf.capacity(),
                 );
-                return Err(io::Error::new(io::ErrorKind::Uncategorized, msg));
-            }
-            let relative = CStr::from_ptr(relative_path).to_bytes().to_vec();
+                if fd == -1 {
+                    if io::Error::last_os_error().raw_os_error() == Some(libc::ENOMEM) {
+                        // Trigger the internal buffer resizing logic of `Vec` by requiring
+                        // more space than the current capacity.
+                        let cap = buf.capacity();
+                        buf.set_len(cap);
+                        buf.reserve(1);
+                        continue;
+                    }
+                    let msg = format!(
+                        "failed to find a pre-opened file descriptor \
+                     through which {:?} could be opened",
+                        p
+                    );
+                    return Err(io::Error::new(io::ErrorKind::Uncategorized, msg));
+                }
+                let relative = CStr::from_ptr(relative_path).to_bytes().to_vec();
 
-            return Ok((
-                ManuallyDrop::new(WasiFd::from_raw_fd(fd as c_int)),
-                PathBuf::from(OsString::from_vec(relative)),
-            ));
+                return Ok((
+                    ManuallyDrop::new(WasiFd::from_raw_fd(fd as c_int)),
+                    PathBuf::from(OsString::from_vec(relative)),
+                ));
+            }
         }
-    }
 
-    extern "C" {
-        pub fn __wasilibc_find_relpath(
-            path: *const libc::c_char,
-            abs_prefix: *mut *const libc::c_char,
-            relative_path: *mut *const libc::c_char,
-            relative_path_len: libc::size_t,
-        ) -> libc::c_int;
-    }
+        extern "C" {
+            pub fn __wasilibc_find_relpath(
+                path: *const libc::c_char,
+                abs_prefix: *mut *const libc::c_char,
+                relative_path: *mut *const libc::c_char,
+                relative_path_len: libc::size_t,
+            ) -> libc::c_int;
+        }
+    })
 }
 
 pub fn osstr2str(f: &OsStr) -> io::Result<&str> {
diff --git a/library/std/src/sys/wasi/io.rs b/library/std/src/sys/wasi/io.rs
index ee017d13a..2cd45df88 100644
--- a/library/std/src/sys/wasi/io.rs
+++ b/library/std/src/sys/wasi/io.rs
@@ -1,6 +1,7 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 
 use crate::marker::PhantomData;
+use crate::os::fd::{AsFd, AsRawFd};
 use crate::slice;
 
 #[derive(Copy, Clone)]
@@ -71,3 +72,8 @@ impl<'a> IoSliceMut<'a> {
         unsafe { slice::from_raw_parts_mut(self.vec.buf as *mut u8, self.vec.buf_len) }
     }
 }
+
+pub fn is_terminal(fd: &impl AsFd) -> bool {
+    let fd = fd.as_fd();
+    unsafe { libc::isatty(fd.as_raw_fd()) != 0 }
+}
diff --git a/library/std/src/sys/wasi/mod.rs b/library/std/src/sys/wasi/mod.rs
index 683a07a34..c8c47763a 100644
--- a/library/std/src/sys/wasi/mod.rs
+++ b/library/std/src/sys/wasi/mod.rs
@@ -25,6 +25,9 @@ pub mod cmath;
 pub mod env;
 pub mod fd;
 pub mod fs;
+#[allow(unused)]
+#[path = "../wasm/atomics/futex.rs"]
+pub mod futex;
 pub mod io;
 #[path = "../unsupported/locks/mod.rs"]
 pub mod locks;
diff --git a/library/std/src/sys/wasi/os.rs b/library/std/src/sys/wasi/os.rs
index c5229a188..f5513e999 100644
--- a/library/std/src/sys/wasi/os.rs
+++ b/library/std/src/sys/wasi/os.rs
@@ -1,14 +1,15 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 
-use crate::any::Any;
 use crate::error::Error as StdError;
-use crate::ffi::{CStr, CString, OsStr, OsString};
+use crate::ffi::{CStr, OsStr, OsString};
 use crate::fmt;
 use crate::io;
 use crate::marker::PhantomData;
+use crate::ops::Drop;
 use crate::os::wasi::prelude::*;
 use crate::path::{self, PathBuf};
 use crate::str;
+use crate::sys::common::small_c_string::{run_path_with_cstr, run_with_cstr};
 use crate::sys::memchr;
 use crate::sys::unsupported;
 use crate::vec;
@@ -23,10 +24,26 @@ mod libc {
     }
 }
 
-#[cfg(not(target_feature = "atomics"))]
-pub unsafe fn env_lock() -> impl Any {
-    // No need for a lock if we're single-threaded, but this function will need
-    // to get implemented for multi-threaded scenarios
+cfg_if::cfg_if! {
+    if #[cfg(target_feature = "atomics")] {
+        // Access to the environment must be protected by a lock in multi-threaded scenarios.
+        use crate::sync::{PoisonError, RwLock};
+        static ENV_LOCK: RwLock<()> = RwLock::new(());
+        pub fn env_read_lock() -> impl Drop {
+            ENV_LOCK.read().unwrap_or_else(PoisonError::into_inner)
+        }
+        pub fn env_write_lock() -> impl Drop {
+            ENV_LOCK.write().unwrap_or_else(PoisonError::into_inner)
+        }
+    } else {
+        // No need for a lock if we are single-threaded.
+        pub fn env_read_lock() -> impl Drop {
+            Box::new(())
+        }
+        pub fn env_write_lock() -> impl Drop {
+            Box::new(())
+        }
+    }
 }
 
 pub fn errno() -> i32 {
@@ -77,13 +94,10 @@ pub fn getcwd() -> io::Result<PathBuf> {
 }
 
 pub fn chdir(p: &path::Path) -> io::Result<()> {
-    let p: &OsStr = p.as_ref();
-    let p = CString::new(p.as_bytes())?;
-    unsafe {
-        match libc::chdir(p.as_ptr()) == (0 as libc::c_int) {
-            true => Ok(()),
-            false => Err(io::Error::last_os_error()),
-        }
+    let result = run_path_with_cstr(p, |p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
+    match result == (0 as libc::c_int) {
+        true => Ok(()),
+        false => Err(io::Error::last_os_error()),
     }
 }
 
@@ -146,7 +160,7 @@ impl Iterator for Env {
 
 pub fn env() -> Env {
     unsafe {
-        let _guard = env_lock();
+        let _guard = env_read_lock();
         let mut environ = libc::environ;
         let mut result = Vec::new();
         if !environ.is_null() {
@@ -176,35 +190,32 @@ pub fn env() -> Env {
 }
 
 pub fn getenv(k: &OsStr) -> Option<OsString> {
-    let k = CString::new(k.as_bytes()).ok()?;
-    unsafe {
-        let _guard = env_lock();
-        let s = libc::getenv(k.as_ptr()) as *const libc::c_char;
-        if s.is_null() {
-            None
-        } else {
-            Some(OsStringExt::from_vec(CStr::from_ptr(s).to_bytes().to_vec()))
-        }
+    let s = run_with_cstr(k.as_bytes(), |k| unsafe {
+        let _guard = env_read_lock();
+        Ok(libc::getenv(k.as_ptr()) as *const libc::c_char)
+    })
+    .ok()?;
+    if s.is_null() {
+        None
+    } else {
+        Some(OsStringExt::from_vec(unsafe { CStr::from_ptr(s) }.to_bytes().to_vec()))
     }
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    let k = CString::new(k.as_bytes())?;
-    let v = CString::new(v.as_bytes())?;
-
-    unsafe {
-        let _guard = env_lock();
-        cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
-    }
+    run_with_cstr(k.as_bytes(), |k| {
+        run_with_cstr(v.as_bytes(), |v| unsafe {
+            let _guard = env_write_lock();
+            cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
+        })
+    })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    let nbuf = CString::new(n.as_bytes())?;
-
-    unsafe {
-        let _guard = env_lock();
+    run_with_cstr(n.as_bytes(), |nbuf| unsafe {
+        let _guard = env_write_lock();
         cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
-    }
+    })
 }
 
 pub fn temp_dir() -> PathBuf {
diff --git a/library/std/src/sys/wasi/stdio.rs b/library/std/src/sys/wasi/stdio.rs
index d2081771b..4cc0e4ed5 100644
--- a/library/std/src/sys/wasi/stdio.rs
+++ b/library/std/src/sys/wasi/stdio.rs
@@ -4,7 +4,7 @@ use super::fd::WasiFd;
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
 use crate::os::raw;
-use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd};
+use crate::os::wasi::io::{AsRawFd, FromRawFd};
 
 pub struct Stdin;
 pub struct Stdout;
@@ -23,13 +23,6 @@ impl AsRawFd for Stdin {
     }
 }
 
-impl AsFd for Stdin {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(0) }
-    }
-}
-
 impl io::Read for Stdin {
     fn read(&mut self, data: &mut [u8]) -> io::Result<usize> {
         self.read_vectored(&mut [IoSliceMut::new(data)])
@@ -58,13 +51,6 @@ impl AsRawFd for Stdout {
     }
 }
 
-impl AsFd for Stdout {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(1) }
-    }
-}
-
 impl io::Write for Stdout {
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         self.write_vectored(&[IoSlice::new(data)])
@@ -96,13 +82,6 @@ impl AsRawFd for Stderr {
     }
 }
 
-impl AsFd for Stderr {
-    #[inline]
-    fn as_fd(&self) -> BorrowedFd<'_> {
-        unsafe { BorrowedFd::borrow_raw(2) }
-    }
-}
-
 impl io::Write for Stderr {
     fn write(&mut self, data: &[u8]) -> io::Result<usize> {
         self.write_vectored(&[IoSlice::new(data)])
diff --git a/library/std/src/sys/wasi/time.rs b/library/std/src/sys/wasi/time.rs
index 3d326e491..016b06efb 100644
--- a/library/std/src/sys/wasi/time.rs
+++ b/library/std/src/sys/wasi/time.rs
@@ -47,8 +47,8 @@ impl SystemTime {
         SystemTime(Duration::from_nanos(ts))
     }
 
-    pub fn to_wasi_timestamp_or_panic(&self) -> wasi::Timestamp {
-        self.0.as_nanos().try_into().expect("time does not fit in WASI timestamp")
+    pub fn to_wasi_timestamp(&self) -> Option<wasi::Timestamp> {
+        self.0.as_nanos().try_into().ok()
     }
 
     pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
diff --git a/library/std/src/sys/wasm/mod.rs b/library/std/src/sys/wasm/mod.rs
index 4159efe2a..93838390b 100644
--- a/library/std/src/sys/wasm/mod.rs
+++ b/library/std/src/sys/wasm/mod.rs
@@ -57,7 +57,7 @@ cfg_if::cfg_if! {
             mod futex_rwlock;
             pub(crate) use futex_condvar::{Condvar, MovableCondvar};
             pub(crate) use futex_mutex::{Mutex, MovableMutex};
-            pub(crate) use futex_rwlock::{RwLock, MovableRwLock};
+            pub(crate) use futex_rwlock::MovableRwLock;
         }
         #[path = "atomics/futex.rs"]
         pub mod futex;
diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 89d0ab59b..be6fc2ebb 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -71,6 +71,7 @@ pub type BCRYPT_ALG_HANDLE = LPVOID;
 pub type PCONDITION_VARIABLE = *mut CONDITION_VARIABLE;
 pub type PLARGE_INTEGER = *mut c_longlong;
 pub type PSRWLOCK = *mut SRWLOCK;
+pub type LPINIT_ONCE = *mut INIT_ONCE;
 
 pub type SOCKET = crate::os::windows::raw::SOCKET;
 pub type socklen_t = c_int;
@@ -126,6 +127,10 @@ pub const SECURITY_SQOS_PRESENT: DWORD = 0x00100000;
 
 pub const FIONBIO: c_ulong = 0x8004667e;
 
+pub const MAX_PATH: usize = 260;
+
+pub const FILE_TYPE_PIPE: u32 = 3;
+
 #[repr(C)]
 #[derive(Copy)]
 pub struct WIN32_FIND_DATAW {
@@ -194,6 +199,9 @@ pub const DUPLICATE_SAME_ACCESS: DWORD = 0x00000002;
 
 pub const CONDITION_VARIABLE_INIT: CONDITION_VARIABLE = CONDITION_VARIABLE { ptr: ptr::null_mut() };
 pub const SRWLOCK_INIT: SRWLOCK = SRWLOCK { ptr: ptr::null_mut() };
+pub const INIT_ONCE_STATIC_INIT: INIT_ONCE = INIT_ONCE { ptr: ptr::null_mut() };
+
+pub const INIT_ONCE_INIT_FAILED: DWORD = 0x00000004;
 
 pub const DETACHED_PROCESS: DWORD = 0x00000008;
 pub const CREATE_NEW_PROCESS_GROUP: DWORD = 0x00000200;
@@ -279,7 +287,6 @@ pub const STATUS_INVALID_PARAMETER: NTSTATUS = 0xc000000d_u32 as _;
 pub const STATUS_PENDING: NTSTATUS = 0x103 as _;
 pub const STATUS_END_OF_FILE: NTSTATUS = 0xC0000011_u32 as _;
 pub const STATUS_NOT_IMPLEMENTED: NTSTATUS = 0xC0000002_u32 as _;
-pub const STATUS_NOT_SUPPORTED: NTSTATUS = 0xC00000BB_u32 as _;
 
 // Equivalent to the `NT_SUCCESS` C preprocessor macro.
 // See: https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/using-ntstatus-values
@@ -289,6 +296,7 @@ pub fn nt_success(status: NTSTATUS) -> bool {
 
 // "RNG\0"
 pub const BCRYPT_RNG_ALGORITHM: &[u16] = &[b'R' as u16, b'N' as u16, b'G' as u16, 0];
+pub const BCRYPT_USE_SYSTEM_PREFERRED_RNG: DWORD = 0x00000002;
 
 #[repr(C)]
 pub struct UNICODE_STRING {
@@ -535,6 +543,12 @@ pub struct SYMBOLIC_LINK_REPARSE_BUFFER {
 /// NB: Use carefully! In general using this as a reference is likely to get the
 /// provenance wrong for the `PathBuffer` field!
 #[repr(C)]
+pub struct FILE_NAME_INFO {
+    pub FileNameLength: DWORD,
+    pub FileName: [WCHAR; 1],
+}
+
+#[repr(C)]
 pub struct MOUNT_POINT_REPARSE_BUFFER {
     pub SubstituteNameOffset: c_ushort,
     pub SubstituteNameLength: c_ushort,
@@ -565,6 +579,10 @@ pub struct CONDITION_VARIABLE {
 pub struct SRWLOCK {
     pub ptr: LPVOID,
 }
+#[repr(C)]
+pub struct INIT_ONCE {
+    pub ptr: LPVOID,
+}
 
 #[repr(C)]
 pub struct REPARSE_MOUNTPOINT_DATA_BUFFER {
@@ -817,10 +835,6 @@ if #[cfg(not(target_vendor = "uwp"))] {
 
     #[link(name = "advapi32")]
     extern "system" {
-        // Forbidden when targeting UWP
-        #[link_name = "SystemFunction036"]
-        pub fn RtlGenRandom(RandomBuffer: *mut u8, RandomBufferLength: ULONG) -> BOOLEAN;
-
         // Allowed but unused by UWP
         pub fn OpenProcessToken(
             ProcessHandle: HANDLE,
@@ -959,6 +973,7 @@ extern "system" {
     pub fn TlsAlloc() -> DWORD;
     pub fn TlsGetValue(dwTlsIndex: DWORD) -> LPVOID;
     pub fn TlsSetValue(dwTlsIndex: DWORD, lpTlsvalue: LPVOID) -> BOOL;
+    pub fn TlsFree(dwTlsIndex: DWORD) -> BOOL;
     pub fn GetLastError() -> DWORD;
     pub fn QueryPerformanceFrequency(lpFrequency: *mut LARGE_INTEGER) -> BOOL;
     pub fn QueryPerformanceCounter(lpPerformanceCount: *mut LARGE_INTEGER) -> BOOL;
@@ -1101,6 +1116,7 @@ extern "system" {
         lpFileInformation: LPVOID,
         dwBufferSize: DWORD,
     ) -> BOOL;
+    pub fn GetFileType(hfile: HANDLE) -> DWORD;
     pub fn SleepConditionVariableSRW(
         ConditionVariable: PCONDITION_VARIABLE,
         SRWLock: PSRWLOCK,
@@ -1118,6 +1134,14 @@ extern "system" {
     pub fn TryAcquireSRWLockExclusive(SRWLock: PSRWLOCK) -> BOOLEAN;
     pub fn TryAcquireSRWLockShared(SRWLock: PSRWLOCK) -> BOOLEAN;
 
+    pub fn InitOnceBeginInitialize(
+        lpInitOnce: LPINIT_ONCE,
+        dwFlags: DWORD,
+        fPending: LPBOOL,
+        lpContext: *mut LPVOID,
+    ) -> BOOL;
+    pub fn InitOnceComplete(lpInitOnce: LPINIT_ONCE, dwFlags: DWORD, lpContext: LPVOID) -> BOOL;
+
     pub fn CompareStringOrdinal(
         lpString1: LPCWSTR,
         cchCount1: c_int,
diff --git a/library/std/src/sys/windows/fs.rs b/library/std/src/sys/windows/fs.rs
index 155d0297e..378098038 100644
--- a/library/std/src/sys/windows/fs.rs
+++ b/library/std/src/sys/windows/fs.rs
@@ -1,5 +1,6 @@
 use crate::os::windows::prelude::*;
 
+use crate::borrow::Cow;
 use crate::ffi::OsString;
 use crate::fmt;
 use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
@@ -572,6 +573,14 @@ impl File {
                 "Cannot set file timestamp to 0",
             ));
         }
+        let is_max =
+            |t: c::FILETIME| t.dwLowDateTime == c::DWORD::MAX && t.dwHighDateTime == c::DWORD::MAX;
+        if times.accessed.map_or(false, is_max) || times.modified.map_or(false, is_max) {
+            return Err(io::const_io_error!(
+                io::ErrorKind::InvalidInput,
+                "Cannot set file timestamp to 0xFFFF_FFFF_FFFF_FFFF",
+            ));
+        }
         cvt(unsafe {
             c::SetFileTime(self.as_handle(), None, times.accessed.as_ref(), times.modified.as_ref())
         })?;
@@ -711,7 +720,7 @@ impl<'a> DirBuffIter<'a> {
     }
 }
 impl<'a> Iterator for DirBuffIter<'a> {
-    type Item = (&'a [u16], bool);
+    type Item = (Cow<'a, [u16]>, bool);
     fn next(&mut self) -> Option<Self::Item> {
         use crate::mem::size_of;
         let buffer = &self.buffer?[self.cursor..];
@@ -726,15 +735,19 @@ impl<'a> Iterator for DirBuffIter<'a> {
         //   `FileNameLength` bytes)
         let (name, is_directory, next_entry) = unsafe {
             let info = buffer.as_ptr().cast::<c::FILE_ID_BOTH_DIR_INFO>();
-            // Guaranteed to be aligned in documentation for
+            // While this is guaranteed to be aligned in documentation for
             // https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-file_id_both_dir_info
-            assert!(info.is_aligned());
-            let next_entry = (*info).NextEntryOffset as usize;
-            let name = crate::slice::from_raw_parts(
+            // it does not seem that reality is so kind, and assuming this
+            // caused crashes in some cases (https://github.com/rust-lang/rust/issues/104530)
+            // presumably, this can be blamed on buggy filesystem drivers, but who knows.
+            let next_entry = ptr::addr_of!((*info).NextEntryOffset).read_unaligned() as usize;
+            let length = ptr::addr_of!((*info).FileNameLength).read_unaligned() as usize;
+            let attrs = ptr::addr_of!((*info).FileAttributes).read_unaligned();
+            let name = from_maybe_unaligned(
                 ptr::addr_of!((*info).FileName).cast::<u16>(),
-                (*info).FileNameLength as usize / size_of::<u16>(),
+                length / size_of::<u16>(),
             );
-            let is_directory = ((*info).FileAttributes & c::FILE_ATTRIBUTE_DIRECTORY) != 0;
+            let is_directory = (attrs & c::FILE_ATTRIBUTE_DIRECTORY) != 0;
 
             (name, is_directory, next_entry)
         };
@@ -747,13 +760,21 @@ impl<'a> Iterator for DirBuffIter<'a> {
 
         // Skip `.` and `..` pseudo entries.
         const DOT: u16 = b'.' as u16;
-        match name {
+        match &name[..] {
             [DOT] | [DOT, DOT] => self.next(),
             _ => Some((name, is_directory)),
         }
     }
 }
 
+unsafe fn from_maybe_unaligned<'a>(p: *const u16, len: usize) -> Cow<'a, [u16]> {
+    if p.is_aligned() {
+        Cow::Borrowed(crate::slice::from_raw_parts(p, len))
+    } else {
+        Cow::Owned((0..len).map(|i| p.add(i).read_unaligned()).collect())
+    }
+}
+
 /// Open a link relative to the parent directory, ensure no symlinks are followed.
 fn open_link_no_reparse(parent: &File, name: &[u16], access: u32) -> io::Result<File> {
     // This is implemented using the lower level `NtCreateFile` function as
@@ -1109,13 +1130,13 @@ fn remove_dir_all_iterative(f: &File, delete: fn(&File) -> io::Result<()>) -> io
             if is_directory {
                 let child_dir = open_link_no_reparse(
                     &dir,
-                    name,
+                    &name,
                     c::SYNCHRONIZE | c::DELETE | c::FILE_LIST_DIRECTORY,
                 )?;
                 dirlist.push(child_dir);
             } else {
                 for i in 1..=MAX_RETRIES {
-                    let result = open_link_no_reparse(&dir, name, c::SYNCHRONIZE | c::DELETE);
+                    let result = open_link_no_reparse(&dir, &name, c::SYNCHRONIZE | c::DELETE);
                     match result {
                         Ok(f) => delete(&f)?,
                         // Already deleted, so skip.
diff --git a/library/std/src/sys/windows/io.rs b/library/std/src/sys/windows/io.rs
index fb06df1f8..2cc34c986 100644
--- a/library/std/src/sys/windows/io.rs
+++ b/library/std/src/sys/windows/io.rs
@@ -1,6 +1,10 @@
 use crate::marker::PhantomData;
+use crate::mem::size_of;
+use crate::os::windows::io::{AsHandle, AsRawHandle, BorrowedHandle};
 use crate::slice;
-use crate::sys::c;
+use crate::sys::{c, Align8};
+use core;
+use libc;
 
 #[derive(Copy, Clone)]
 #[repr(transparent)]
@@ -78,3 +82,73 @@ impl<'a> IoSliceMut<'a> {
         unsafe { slice::from_raw_parts_mut(self.vec.buf as *mut u8, self.vec.len as usize) }
     }
 }
+
+pub fn is_terminal(h: &impl AsHandle) -> bool {
+    unsafe { handle_is_console(h.as_handle()) }
+}
+
+unsafe fn handle_is_console(handle: BorrowedHandle<'_>) -> bool {
+    let handle = handle.as_raw_handle();
+
+    // A null handle means the process has no console.
+    if handle.is_null() {
+        return false;
+    }
+
+    let mut out = 0;
+    if c::GetConsoleMode(handle, &mut out) != 0 {
+        // False positives aren't possible. If we got a console then we definitely have a console.
+        return true;
+    }
+
+    // At this point, we *could* have a false negative. We can determine that this is a true
+    // negative if we can detect the presence of a console on any of the standard I/O streams. If
+    // another stream has a console, then we know we're in a Windows console and can therefore
+    // trust the negative.
+    for std_handle in [c::STD_INPUT_HANDLE, c::STD_OUTPUT_HANDLE, c::STD_ERROR_HANDLE] {
+        let std_handle = c::GetStdHandle(std_handle);
+        if !std_handle.is_null()
+            && std_handle != handle
+            && c::GetConsoleMode(std_handle, &mut out) != 0
+        {
+            return false;
+        }
+    }
+
+    // Otherwise, we fall back to an msys hack to see if we can detect the presence of a pty.
+    msys_tty_on(handle)
+}
+
+unsafe fn msys_tty_on(handle: c::HANDLE) -> bool {
+    // Early return if the handle is not a pipe.
+    if c::GetFileType(handle) != c::FILE_TYPE_PIPE {
+        return false;
+    }
+
+    const SIZE: usize = size_of::<c::FILE_NAME_INFO>() + c::MAX_PATH * size_of::<c::WCHAR>();
+    let mut name_info_bytes = Align8([0u8; SIZE]);
+    let res = c::GetFileInformationByHandleEx(
+        handle,
+        c::FileNameInfo,
+        name_info_bytes.0.as_mut_ptr() as *mut libc::c_void,
+        SIZE as u32,
+    );
+    if res == 0 {
+        return false;
+    }
+    let name_info: &c::FILE_NAME_INFO = &*(name_info_bytes.0.as_ptr() as *const c::FILE_NAME_INFO);
+    let name_len = name_info.FileNameLength as usize / 2;
+    // Offset to get the `FileName` field.
+    let name_ptr = name_info_bytes.0.as_ptr().offset(size_of::<c::DWORD>() as isize).cast::<u16>();
+    let s = core::slice::from_raw_parts(name_ptr, name_len);
+    let name = String::from_utf16_lossy(s);
+    // Get the file name only.
+    let name = name.rsplit('\\').next().unwrap_or(&name);
+    // This checks whether 'pty' exists in the file name, which indicates that
+    // a pseudo-terminal is attached. To mitigate against false positives
+    // (e.g., an actual file name that contains 'pty'), we also require that
+    // the file name begins with either the strings 'msys-' or 'cygwin-'.)
+    let is_msys = name.starts_with("msys-") || name.starts_with("cygwin-");
+    let is_pty = name.contains("-pty");
+    is_msys && is_pty
+}
diff --git a/library/std/src/sys/windows/locks/mod.rs b/library/std/src/sys/windows/locks/mod.rs
index d412ff152..602a2d623 100644
--- a/library/std/src/sys/windows/locks/mod.rs
+++ b/library/std/src/sys/windows/locks/mod.rs
@@ -3,4 +3,4 @@ mod mutex;
 mod rwlock;
 pub use condvar::{Condvar, MovableCondvar};
 pub use mutex::{MovableMutex, Mutex};
-pub use rwlock::{MovableRwLock, RwLock};
+pub use rwlock::MovableRwLock;
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index 02d5af471..9cbb4ef19 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -16,6 +16,7 @@ use crate::os::windows::ffi::{OsStrExt, OsStringExt};
 use crate::os::windows::io::{AsHandle, AsRawHandle, BorrowedHandle, FromRawHandle, IntoRawHandle};
 use crate::path::{Path, PathBuf};
 use crate::ptr;
+use crate::sync::Mutex;
 use crate::sys::args::{self, Arg};
 use crate::sys::c;
 use crate::sys::c::NonZeroDWORD;
@@ -25,7 +26,6 @@ use crate::sys::handle::Handle;
 use crate::sys::path;
 use crate::sys::pipe::{self, AnonPipe};
 use crate::sys::stdio;
-use crate::sys_common::mutex::StaticMutex;
 use crate::sys_common::process::{CommandEnv, CommandEnvs};
 use crate::sys_common::IntoInner;
 
@@ -301,9 +301,9 @@ impl Command {
         //
         // For more information, msdn also has an article about this race:
         // https://support.microsoft.com/kb/315939
-        static CREATE_PROCESS_LOCK: StaticMutex = StaticMutex::new();
+        static CREATE_PROCESS_LOCK: Mutex<()> = Mutex::new(());
 
-        let _guard = unsafe { CREATE_PROCESS_LOCK.lock() };
+        let _guard = CREATE_PROCESS_LOCK.lock();
 
         let mut pipes = StdioPipes { stdin: None, stdout: None, stderr: None };
         let null = Stdio::Null;
diff --git a/library/std/src/sys/windows/rand.rs b/library/std/src/sys/windows/rand.rs
index d6cd8f802..b5a49489d 100644
--- a/library/std/src/sys/windows/rand.rs
+++ b/library/std/src/sys/windows/rand.rs
@@ -13,15 +13,12 @@
 //! but significant number of users to experience panics caused by a failure of
 //! this function. See [#94098].
 //!
-//! The current version changes this to use the `BCRYPT_RNG_ALG_HANDLE`
-//! [Pseudo-handle], which gets the default RNG algorithm without querying the
-//! system preference thus hopefully avoiding the previous issue.
-//! This is only supported on Windows 10+ so a fallback is used for older versions.
+//! The current version falls back to using `BCryptOpenAlgorithmProvider` if
+//! `BCRYPT_USE_SYSTEM_PREFERRED_RNG` fails for any reason.
 //!
 //! [#94098]: https://github.com/rust-lang/rust/issues/94098
 //! [`RtlGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
 //! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
-//! [Pseudo-handle]: https://docs.microsoft.com/en-us/windows/win32/seccng/cng-algorithm-pseudo-handles
 use crate::mem;
 use crate::ptr;
 use crate::sys::c;
@@ -33,37 +30,35 @@ use crate::sys::c;
 /// [`HashMap`]: crate::collections::HashMap
 /// [`RandomState`]: crate::collections::hash_map::RandomState
 pub fn hashmap_random_keys() -> (u64, u64) {
-    Rng::open().and_then(|rng| rng.gen_random_keys()).unwrap_or_else(fallback_rng)
+    Rng::SYSTEM.gen_random_keys().unwrap_or_else(fallback_rng)
 }
 
-struct Rng(c::BCRYPT_ALG_HANDLE);
+struct Rng {
+    algorithm: c::BCRYPT_ALG_HANDLE,
+    flags: u32,
+}
 impl Rng {
-    #[cfg(miri)]
-    fn open() -> Result<Self, c::NTSTATUS> {
-        const BCRYPT_RNG_ALG_HANDLE: c::BCRYPT_ALG_HANDLE = ptr::invalid_mut(0x81);
-        let _ = (
-            c::BCryptOpenAlgorithmProvider,
-            c::BCryptCloseAlgorithmProvider,
-            c::BCRYPT_RNG_ALGORITHM,
-            c::STATUS_NOT_SUPPORTED,
-        );
-        Ok(Self(BCRYPT_RNG_ALG_HANDLE))
+    const SYSTEM: Self = unsafe { Self::new(ptr::null_mut(), c::BCRYPT_USE_SYSTEM_PREFERRED_RNG) };
+
+    /// Create the RNG from an existing algorithm handle.
+    ///
+    /// # Safety
+    ///
+    /// The handle must either be null or a valid algorithm handle.
+    const unsafe fn new(algorithm: c::BCRYPT_ALG_HANDLE, flags: u32) -> Self {
+        Self { algorithm, flags }
     }
-    #[cfg(not(miri))]
-    // Open a handle to the RNG algorithm.
+
+    /// Open a handle to the RNG algorithm.
     fn open() -> Result<Self, c::NTSTATUS> {
         use crate::sync::atomic::AtomicPtr;
         use crate::sync::atomic::Ordering::{Acquire, Release};
-        const ERROR_VALUE: c::LPVOID = ptr::invalid_mut(usize::MAX);
 
         // An atomic is used so we don't need to reopen the handle every time.
         static HANDLE: AtomicPtr<crate::ffi::c_void> = AtomicPtr::new(ptr::null_mut());
 
         let mut handle = HANDLE.load(Acquire);
-        // We use a sentinel value to designate an error occurred last time.
-        if handle == ERROR_VALUE {
-            Err(c::STATUS_NOT_SUPPORTED)
-        } else if handle.is_null() {
+        if handle.is_null() {
             let status = unsafe {
                 c::BCryptOpenAlgorithmProvider(
                     &mut handle,
@@ -80,13 +75,12 @@ impl Rng {
                     unsafe { c::BCryptCloseAlgorithmProvider(handle, 0) };
                     handle = previous_handle;
                 }
-                Ok(Self(handle))
+                Ok(unsafe { Self::new(handle, 0) })
             } else {
-                HANDLE.store(ERROR_VALUE, Release);
                 Err(status)
             }
         } else {
-            Ok(Self(handle))
+            Ok(unsafe { Self::new(handle, 0) })
         }
     }
 
@@ -94,33 +88,19 @@ impl Rng {
         let mut v = (0, 0);
         let status = unsafe {
             let size = mem::size_of_val(&v).try_into().unwrap();
-            c::BCryptGenRandom(self.0, ptr::addr_of_mut!(v).cast(), size, 0)
+            c::BCryptGenRandom(self.algorithm, ptr::addr_of_mut!(v).cast(), size, self.flags)
         };
         if c::nt_success(status) { Ok(v) } else { Err(status) }
     }
 }
 
-/// Generate random numbers using the fallback RNG function (RtlGenRandom)
-#[cfg(not(target_vendor = "uwp"))]
+/// Generate random numbers using the fallback RNG function
 #[inline(never)]
 fn fallback_rng(rng_status: c::NTSTATUS) -> (u64, u64) {
-    let mut v = (0, 0);
-    let ret =
-        unsafe { c::RtlGenRandom(&mut v as *mut _ as *mut u8, mem::size_of_val(&v) as c::ULONG) };
-
-    if ret != 0 {
-        v
-    } else {
-        panic!(
-            "RNG broken: {rng_status:#x}, fallback RNG broken: {}",
-            crate::io::Error::last_os_error()
-        )
+    match Rng::open().and_then(|rng| rng.gen_random_keys()) {
+        Ok(keys) => keys,
+        Err(status) => {
+            panic!("RNG broken: {rng_status:#x}, fallback RNG broken: {status:#x}")
+        }
     }
 }
-
-/// We can't use RtlGenRandom with UWP, so there is no fallback
-#[cfg(target_vendor = "uwp")]
-#[inline(never)]
-fn fallback_rng(rng_status: c::NTSTATUS) -> (u64, u64) {
-    panic!("RNG broken: {rng_status:#x} fallback RNG broken: RtlGenRandom() not supported on UWP");
-}
diff --git a/library/std/src/sys/windows/thread_local_key.rs b/library/std/src/sys/windows/thread_local_key.rs
index ec670238e..17628b757 100644
--- a/library/std/src/sys/windows/thread_local_key.rs
+++ b/library/std/src/sys/windows/thread_local_key.rs
@@ -1,11 +1,16 @@
-use crate::mem::ManuallyDrop;
+use crate::cell::UnsafeCell;
 use crate::ptr;
-use crate::sync::atomic::AtomicPtr;
-use crate::sync::atomic::Ordering::SeqCst;
+use crate::sync::atomic::{
+    AtomicPtr, AtomicU32,
+    Ordering::{AcqRel, Acquire, Relaxed, Release},
+};
 use crate::sys::c;
 
-pub type Key = c::DWORD;
-pub type Dtor = unsafe extern "C" fn(*mut u8);
+#[cfg(test)]
+mod tests;
+
+type Key = c::DWORD;
+type Dtor = unsafe extern "C" fn(*mut u8);
 
 // Turns out, like pretty much everything, Windows is pretty close the
 // functionality that Unix provides, but slightly different! In the case of
@@ -22,60 +27,109 @@ pub type Dtor = unsafe extern "C" fn(*mut u8);
 // To accomplish this feat, we perform a number of threads, all contained
 // within this module:
 //
-// * All TLS destructors are tracked by *us*, not the windows runtime. This
+// * All TLS destructors are tracked by *us*, not the Windows runtime. This
 //   means that we have a global list of destructors for each TLS key that
 //   we know about.
 // * When a thread exits, we run over the entire list and run dtors for all
 //   non-null keys. This attempts to match Unix semantics in this regard.
 //
-// This ends up having the overhead of using a global list, having some
-// locks here and there, and in general just adding some more code bloat. We
-// attempt to optimize runtime by forgetting keys that don't have
-// destructors, but this only gets us so far.
-//
 // For more details and nitty-gritty, see the code sections below!
 //
 // [1]: https://www.codeproject.com/Articles/8113/Thread-Local-Storage-The-C-Way
-// [2]: https://github.com/ChromiumWebApps/chromium/blob/master/base
-//                        /threading/thread_local_storage_win.cc#L42
+// [2]: https://github.com/ChromiumWebApps/chromium/blob/master/base/threading/thread_local_storage_win.cc#L42
 
-// -------------------------------------------------------------------------
-// Native bindings
-//
-// This section is just raw bindings to the native functions that Windows
-// provides, There's a few extra calls to deal with destructors.
+pub struct StaticKey {
+    /// The key value shifted up by one. Since TLS_OUT_OF_INDEXES == DWORD::MAX
+    /// is not a valid key value, this allows us to use zero as sentinel value
+    /// without risking overflow.
+    key: AtomicU32,
+    dtor: Option<Dtor>,
+    next: AtomicPtr<StaticKey>,
+    /// Currently, destructors cannot be unregistered, so we cannot use racy
+    /// initialization for keys. Instead, we need synchronize initialization.
+    /// Use the Windows-provided `Once` since it does not require TLS.
+    once: UnsafeCell<c::INIT_ONCE>,
+}
 
-#[inline]
-pub unsafe fn create(dtor: Option<Dtor>) -> Key {
-    let key = c::TlsAlloc();
-    assert!(key != c::TLS_OUT_OF_INDEXES);
-    if let Some(f) = dtor {
-        register_dtor(key, f);
+impl StaticKey {
+    #[inline]
+    pub const fn new(dtor: Option<Dtor>) -> StaticKey {
+        StaticKey {
+            key: AtomicU32::new(0),
+            dtor,
+            next: AtomicPtr::new(ptr::null_mut()),
+            once: UnsafeCell::new(c::INIT_ONCE_STATIC_INIT),
+        }
     }
-    key
-}
 
-#[inline]
-pub unsafe fn set(key: Key, value: *mut u8) {
-    let r = c::TlsSetValue(key, value as c::LPVOID);
-    debug_assert!(r != 0);
-}
+    #[inline]
+    pub unsafe fn set(&'static self, val: *mut u8) {
+        let r = c::TlsSetValue(self.key(), val.cast());
+        debug_assert_eq!(r, c::TRUE);
+    }
 
-#[inline]
-pub unsafe fn get(key: Key) -> *mut u8 {
-    c::TlsGetValue(key) as *mut u8
-}
+    #[inline]
+    pub unsafe fn get(&'static self) -> *mut u8 {
+        c::TlsGetValue(self.key()).cast()
+    }
 
-#[inline]
-pub unsafe fn destroy(_key: Key) {
-    rtabort!("can't destroy tls keys on windows")
-}
+    #[inline]
+    unsafe fn key(&'static self) -> Key {
+        match self.key.load(Acquire) {
+            0 => self.init(),
+            key => key - 1,
+        }
+    }
+
+    #[cold]
+    unsafe fn init(&'static self) -> Key {
+        if self.dtor.is_some() {
+            let mut pending = c::FALSE;
+            let r = c::InitOnceBeginInitialize(self.once.get(), 0, &mut pending, ptr::null_mut());
+            assert_eq!(r, c::TRUE);
 
-#[inline]
-pub fn requires_synchronized_create() -> bool {
-    true
+            if pending == c::FALSE {
+                // Some other thread initialized the key, load it.
+                self.key.load(Relaxed) - 1
+            } else {
+                let key = c::TlsAlloc();
+                if key == c::TLS_OUT_OF_INDEXES {
+                    // Wakeup the waiting threads before panicking to avoid deadlock.
+                    c::InitOnceComplete(self.once.get(), c::INIT_ONCE_INIT_FAILED, ptr::null_mut());
+                    panic!("out of TLS indexes");
+                }
+
+                self.key.store(key + 1, Release);
+                register_dtor(self);
+
+                let r = c::InitOnceComplete(self.once.get(), 0, ptr::null_mut());
+                debug_assert_eq!(r, c::TRUE);
+
+                key
+            }
+        } else {
+            // If there is no destructor to clean up, we can use racy initialization.
+
+            let key = c::TlsAlloc();
+            assert_ne!(key, c::TLS_OUT_OF_INDEXES, "out of TLS indexes");
+
+            match self.key.compare_exchange(0, key + 1, AcqRel, Acquire) {
+                Ok(_) => key,
+                Err(new) => {
+                    // Some other thread completed initialization first, so destroy
+                    // our key and use theirs.
+                    let r = c::TlsFree(key);
+                    debug_assert_eq!(r, c::TRUE);
+                    new - 1
+                }
+            }
+        }
+    }
 }
 
+unsafe impl Send for StaticKey {}
+unsafe impl Sync for StaticKey {}
+
 // -------------------------------------------------------------------------
 // Dtor registration
 //
@@ -96,29 +150,21 @@ pub fn requires_synchronized_create() -> bool {
 // Typically processes have a statically known set of TLS keys which is pretty
 // small, and we'd want to keep this memory alive for the whole process anyway
 // really.
-//
-// Perhaps one day we can fold the `Box` here into a static allocation,
-// expanding the `StaticKey` structure to contain not only a slot for the TLS
-// key but also a slot for the destructor queue on windows. An optimization for
-// another day!
-
-static DTORS: AtomicPtr<Node> = AtomicPtr::new(ptr::null_mut());
-
-struct Node {
-    dtor: Dtor,
-    key: Key,
-    next: *mut Node,
-}
 
-unsafe fn register_dtor(key: Key, dtor: Dtor) {
-    let mut node = ManuallyDrop::new(Box::new(Node { key, dtor, next: ptr::null_mut() }));
+static DTORS: AtomicPtr<StaticKey> = AtomicPtr::new(ptr::null_mut());
 
-    let mut head = DTORS.load(SeqCst);
+/// Should only be called once per key, otherwise loops or breaks may occur in
+/// the linked list.
+unsafe fn register_dtor(key: &'static StaticKey) {
+    let this = <*const StaticKey>::cast_mut(key);
+    // Use acquire ordering to pass along the changes done by the previously
+    // registered keys when we store the new head with release ordering.
+    let mut head = DTORS.load(Acquire);
     loop {
-        node.next = head;
-        match DTORS.compare_exchange(head, &mut **node, SeqCst, SeqCst) {
-            Ok(_) => return, // nothing to drop, we successfully added the node to the list
-            Err(cur) => head = cur,
+        key.next.store(head, Relaxed);
+        match DTORS.compare_exchange_weak(head, this, Release, Acquire) {
+            Ok(_) => break,
+            Err(new) => head = new,
         }
     }
 }
@@ -214,25 +260,29 @@ unsafe extern "system" fn on_tls_callback(h: c::LPVOID, dwReason: c::DWORD, pv:
     unsafe fn reference_tls_used() {}
 }
 
-#[allow(dead_code)] // actually called above
+#[allow(dead_code)] // actually called below
 unsafe fn run_dtors() {
-    let mut any_run = true;
     for _ in 0..5 {
-        if !any_run {
-            break;
-        }
-        any_run = false;
-        let mut cur = DTORS.load(SeqCst);
+        let mut any_run = false;
+
+        // Use acquire ordering to observe key initialization.
+        let mut cur = DTORS.load(Acquire);
         while !cur.is_null() {
-            let ptr = c::TlsGetValue((*cur).key);
+            let key = (*cur).key.load(Relaxed) - 1;
+            let dtor = (*cur).dtor.unwrap();
 
+            let ptr = c::TlsGetValue(key);
             if !ptr.is_null() {
-                c::TlsSetValue((*cur).key, ptr::null_mut());
-                ((*cur).dtor)(ptr as *mut _);
+                c::TlsSetValue(key, ptr::null_mut());
+                dtor(ptr as *mut _);
                 any_run = true;
             }
 
-            cur = (*cur).next;
+            cur = (*cur).next.load(Relaxed);
+        }
+
+        if !any_run {
+            break;
         }
     }
 }
diff --git a/library/std/src/sys/windows/thread_local_key/tests.rs b/library/std/src/sys/windows/thread_local_key/tests.rs
new file mode 100644
index 000000000..c95f383fb
--- /dev/null
+++ b/library/std/src/sys/windows/thread_local_key/tests.rs
@@ -0,0 +1,53 @@
+use super::StaticKey;
+use crate::ptr;
+
+#[test]
+fn smoke() {
+    static K1: StaticKey = StaticKey::new(None);
+    static K2: StaticKey = StaticKey::new(None);
+
+    unsafe {
+        assert!(K1.get().is_null());
+        assert!(K2.get().is_null());
+        K1.set(ptr::invalid_mut(1));
+        K2.set(ptr::invalid_mut(2));
+        assert_eq!(K1.get() as usize, 1);
+        assert_eq!(K2.get() as usize, 2);
+    }
+}
+
+#[test]
+fn destructors() {
+    use crate::mem::ManuallyDrop;
+    use crate::sync::Arc;
+    use crate::thread;
+
+    unsafe extern "C" fn destruct(ptr: *mut u8) {
+        drop(Arc::from_raw(ptr as *const ()));
+    }
+
+    static KEY: StaticKey = StaticKey::new(Some(destruct));
+
+    let shared1 = Arc::new(());
+    let shared2 = Arc::clone(&shared1);
+
+    unsafe {
+        assert!(KEY.get().is_null());
+        KEY.set(Arc::into_raw(shared1) as *mut u8);
+    }
+
+    thread::spawn(move || unsafe {
+        assert!(KEY.get().is_null());
+        KEY.set(Arc::into_raw(shared2) as *mut u8);
+    })
+    .join()
+    .unwrap();
+
+    // Leak the Arc, let the TLS destructor clean it up.
+    let shared1 = unsafe { ManuallyDrop::new(Arc::from_raw(KEY.get() as *const ())) };
+    assert_eq!(
+        Arc::strong_count(&shared1),
+        1,
+        "destructor should have dropped the other reference on thread exit"
+    );
+}
diff --git a/library/std/src/sys_common/backtrace.rs b/library/std/src/sys_common/backtrace.rs
index 31164afdc..8807077cb 100644
--- a/library/std/src/sys_common/backtrace.rs
+++ b/library/std/src/sys_common/backtrace.rs
@@ -7,15 +7,14 @@ use crate::fmt;
 use crate::io;
 use crate::io::prelude::*;
 use crate::path::{self, Path, PathBuf};
-use crate::sys_common::mutex::StaticMutex;
+use crate::sync::{Mutex, PoisonError};
 
 /// Max number of frames to print.
 const MAX_NB_FRAMES: usize = 100;
 
-// SAFETY: Don't attempt to lock this reentrantly.
-pub unsafe fn lock() -> impl Drop {
-    static LOCK: StaticMutex = StaticMutex::new();
-    LOCK.lock()
+pub fn lock() -> impl Drop {
+    static LOCK: Mutex<()> = Mutex::new(());
+    LOCK.lock().unwrap_or_else(PoisonError::into_inner)
 }
 
 /// Prints the current backtrace.
diff --git a/library/std/src/sys_common/condvar.rs b/library/std/src/sys_common/condvar.rs
index f3ac1061b..8bc5b2411 100644
--- a/library/std/src/sys_common/condvar.rs
+++ b/library/std/src/sys_common/condvar.rs
@@ -15,6 +15,7 @@ pub struct Condvar {
 impl Condvar {
     /// Creates a new condition variable for use.
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Self {
         Self { inner: imp::MovableCondvar::new(), check: CondvarCheck::new() }
     }
diff --git a/library/std/src/sys_common/condvar/check.rs b/library/std/src/sys_common/condvar/check.rs
index ce8f36704..4ac9e62bf 100644
--- a/library/std/src/sys_common/condvar/check.rs
+++ b/library/std/src/sys_common/condvar/check.rs
@@ -50,6 +50,7 @@ pub struct NoCheck;
 
 #[allow(dead_code)]
 impl NoCheck {
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Self {
         Self
     }
diff --git a/library/std/src/sys_common/mod.rs b/library/std/src/sys_common/mod.rs
index 80f56bf75..8c19f9332 100644
--- a/library/std/src/sys_common/mod.rs
+++ b/library/std/src/sys_common/mod.rs
@@ -27,17 +27,25 @@ pub mod io;
 pub mod lazy_box;
 pub mod memchr;
 pub mod mutex;
+pub mod once;
 pub mod process;
 pub mod remutex;
 pub mod rwlock;
 pub mod thread;
 pub mod thread_info;
 pub mod thread_local_dtor;
-pub mod thread_local_key;
 pub mod thread_parker;
 pub mod wtf8;
 
 cfg_if::cfg_if! {
+    if #[cfg(target_os = "windows")] {
+        pub use crate::sys::thread_local_key;
+    } else {
+        pub mod thread_local_key;
+    }
+}
+
+cfg_if::cfg_if! {
     if #[cfg(any(target_os = "l4re",
                  target_os = "hermit",
                  feature = "restricted-std",
diff --git a/library/std/src/sys_common/mutex.rs b/library/std/src/sys_common/mutex.rs
index 48479f5bd..98046f20f 100644
--- a/library/std/src/sys_common/mutex.rs
+++ b/library/std/src/sys_common/mutex.rs
@@ -1,49 +1,5 @@
 use crate::sys::locks as imp;
 
-/// An OS-based mutual exclusion lock, meant for use in static variables.
-///
-/// This mutex has a const constructor ([`StaticMutex::new`]), does not
-/// implement `Drop` to cleanup resources, and causes UB when used reentrantly.
-///
-/// This mutex does not implement poisoning.
-///
-/// This is a wrapper around `imp::Mutex` that does *not* call `init()` and
-/// `destroy()`.
-pub struct StaticMutex(imp::Mutex);
-
-unsafe impl Sync for StaticMutex {}
-
-impl StaticMutex {
-    /// Creates a new mutex for use.
-    #[inline]
-    pub const fn new() -> Self {
-        Self(imp::Mutex::new())
-    }
-
-    /// Calls raw_lock() and then returns an RAII guard to guarantee the mutex
-    /// will be unlocked.
-    ///
-    /// It is undefined behaviour to call this function while locked by the
-    /// same thread.
-    #[inline]
-    pub unsafe fn lock(&'static self) -> StaticMutexGuard {
-        self.0.lock();
-        StaticMutexGuard(&self.0)
-    }
-}
-
-#[must_use]
-pub struct StaticMutexGuard(&'static imp::Mutex);
-
-impl Drop for StaticMutexGuard {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe {
-            self.0.unlock();
-        }
-    }
-}
-
 /// An OS-based mutual exclusion lock.
 ///
 /// This mutex cleans up its resources in its `Drop` implementation, may safely
@@ -61,6 +17,7 @@ unsafe impl Sync for MovableMutex {}
 impl MovableMutex {
     /// Creates a new mutex.
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Self {
         Self(imp::MovableMutex::new())
     }
diff --git a/library/std/src/sys_common/net.rs b/library/std/src/sys_common/net.rs
index 3ad802afa..fad4a6333 100644
--- a/library/std/src/sys_common/net.rs
+++ b/library/std/src/sys_common/net.rs
@@ -2,12 +2,13 @@
 mod tests;
 
 use crate::cmp;
-use crate::ffi::CString;
+use crate::convert::{TryFrom, TryInto};
 use crate::fmt;
 use crate::io::{self, ErrorKind, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr};
 use crate::ptr;
+use crate::sys::common::small_c_string::run_with_cstr;
 use crate::sys::net::netc as c;
 use crate::sys::net::{cvt, cvt_gai, cvt_r, init, wrlen_t, Socket};
 use crate::sys_common::{AsInner, FromInner, IntoInner};
@@ -197,14 +198,15 @@ impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
     fn try_from((host, port): (&'a str, u16)) -> io::Result<LookupHost> {
         init();
 
-        let c_host = CString::new(host)?;
-        let mut hints: c::addrinfo = unsafe { mem::zeroed() };
-        hints.ai_socktype = c::SOCK_STREAM;
-        let mut res = ptr::null_mut();
-        unsafe {
-            cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res))
-                .map(|_| LookupHost { original: res, cur: res, port })
-        }
+        run_with_cstr(host.as_bytes(), |c_host| {
+            let mut hints: c::addrinfo = unsafe { mem::zeroed() };
+            hints.ai_socktype = c::SOCK_STREAM;
+            let mut res = ptr::null_mut();
+            unsafe {
+                cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res))
+                    .map(|_| LookupHost { original: res, cur: res, port })
+            }
+        })
     }
 }
 
diff --git a/library/std/src/sys_common/once/futex.rs b/library/std/src/sys_common/once/futex.rs
new file mode 100644
index 000000000..5c7e6c013
--- /dev/null
+++ b/library/std/src/sys_common/once/futex.rs
@@ -0,0 +1,134 @@
+use crate::cell::Cell;
+use crate::sync as public;
+use crate::sync::atomic::{
+    AtomicU32,
+    Ordering::{Acquire, Relaxed, Release},
+};
+use crate::sys::futex::{futex_wait, futex_wake_all};
+
+// On some platforms, the OS is very nice and handles the waiter queue for us.
+// This means we only need one atomic value with 5 states:
+
+/// No initialization has run yet, and no thread is currently using the Once.
+const INCOMPLETE: u32 = 0;
+/// Some thread has previously attempted to initialize the Once, but it panicked,
+/// so the Once is now poisoned. There are no other threads currently accessing
+/// this Once.
+const POISONED: u32 = 1;
+/// Some thread is currently attempting to run initialization. It may succeed,
+/// so all future threads need to wait for it to finish.
+const RUNNING: u32 = 2;
+/// Some thread is currently attempting to run initialization and there are threads
+/// waiting for it to finish.
+const QUEUED: u32 = 3;
+/// Initialization has completed and all future calls should finish immediately.
+const COMPLETE: u32 = 4;
+
+// Threads wait by setting the state to QUEUED and calling `futex_wait` on the state
+// variable. When the running thread finishes, it will wake all waiting threads using
+// `futex_wake_all`.
+
+pub struct OnceState {
+    poisoned: bool,
+    set_state_to: Cell<u32>,
+}
+
+impl OnceState {
+    #[inline]
+    pub fn is_poisoned(&self) -> bool {
+        self.poisoned
+    }
+
+    #[inline]
+    pub fn poison(&self) {
+        self.set_state_to.set(POISONED);
+    }
+}
+
+struct CompletionGuard<'a> {
+    state: &'a AtomicU32,
+    set_state_on_drop_to: u32,
+}
+
+impl<'a> Drop for CompletionGuard<'a> {
+    fn drop(&mut self) {
+        // Use release ordering to propagate changes to all threads checking
+        // up on the Once. `futex_wake_all` does its own synchronization, hence
+        // we do not need `AcqRel`.
+        if self.state.swap(self.set_state_on_drop_to, Release) == QUEUED {
+            futex_wake_all(&self.state);
+        }
+    }
+}
+
+pub struct Once {
+    state: AtomicU32,
+}
+
+impl Once {
+    #[inline]
+    pub const fn new() -> Once {
+        Once { state: AtomicU32::new(INCOMPLETE) }
+    }
+
+    #[inline]
+    pub fn is_completed(&self) -> bool {
+        // Use acquire ordering to make all initialization changes visible to the
+        // current thread.
+        self.state.load(Acquire) == COMPLETE
+    }
+
+    // This uses FnMut to match the API of the generic implementation. As this
+    // implementation is quite light-weight, it is generic over the closure and
+    // so avoids the cost of dynamic dispatch.
+    #[cold]
+    #[track_caller]
+    pub fn call(&self, ignore_poisoning: bool, f: &mut impl FnMut(&public::OnceState)) {
+        let mut state = self.state.load(Acquire);
+        loop {
+            match state {
+                POISONED if !ignore_poisoning => {
+                    // Panic to propagate the poison.
+                    panic!("Once instance has previously been poisoned");
+                }
+                INCOMPLETE | POISONED => {
+                    // Try to register the current thread as the one running.
+                    if let Err(new) =
+                        self.state.compare_exchange_weak(state, RUNNING, Acquire, Acquire)
+                    {
+                        state = new;
+                        continue;
+                    }
+                    // `waiter_queue` will manage other waiting threads, and
+                    // wake them up on drop.
+                    let mut waiter_queue =
+                        CompletionGuard { state: &self.state, set_state_on_drop_to: POISONED };
+                    // Run the function, letting it know if we're poisoned or not.
+                    let f_state = public::OnceState {
+                        inner: OnceState {
+                            poisoned: state == POISONED,
+                            set_state_to: Cell::new(COMPLETE),
+                        },
+                    };
+                    f(&f_state);
+                    waiter_queue.set_state_on_drop_to = f_state.inner.set_state_to.get();
+                    return;
+                }
+                RUNNING | QUEUED => {
+                    // Set the state to QUEUED if it is not already.
+                    if state == RUNNING
+                        && let Err(new) = self.state.compare_exchange_weak(RUNNING, QUEUED, Relaxed, Acquire)
+                    {
+                        state = new;
+                        continue;
+                    }
+
+                    futex_wait(&self.state, QUEUED, None);
+                    state = self.state.load(Acquire);
+                }
+                COMPLETE => return,
+                _ => unreachable!("state is never set to invalid values"),
+            }
+        }
+    }
+}
diff --git a/library/std/src/sys_common/once/generic.rs b/library/std/src/sys_common/once/generic.rs
new file mode 100644
index 000000000..acf5f2471
--- /dev/null
+++ b/library/std/src/sys_common/once/generic.rs
@@ -0,0 +1,282 @@
+// Each `Once` has one word of atomic state, and this state is CAS'd on to
+// determine what to do. There are four possible state of a `Once`:
+//
+// * Incomplete - no initialization has run yet, and no thread is currently
+//                using the Once.
+// * Poisoned - some thread has previously attempted to initialize the Once, but
+//              it panicked, so the Once is now poisoned. There are no other
+//              threads currently accessing this Once.
+// * Running - some thread is currently attempting to run initialization. It may
+//             succeed, so all future threads need to wait for it to finish.
+//             Note that this state is accompanied with a payload, described
+//             below.
+// * Complete - initialization has completed and all future calls should finish
+//              immediately.
+//
+// With 4 states we need 2 bits to encode this, and we use the remaining bits
+// in the word we have allocated as a queue of threads waiting for the thread
+// responsible for entering the RUNNING state. This queue is just a linked list
+// of Waiter nodes which is monotonically increasing in size. Each node is
+// allocated on the stack, and whenever the running closure finishes it will
+// consume the entire queue and notify all waiters they should try again.
+//
+// You'll find a few more details in the implementation, but that's the gist of
+// it!
+//
+// Atomic orderings:
+// When running `Once` we deal with multiple atomics:
+// `Once.state_and_queue` and an unknown number of `Waiter.signaled`.
+// * `state_and_queue` is used (1) as a state flag, (2) for synchronizing the
+//   result of the `Once`, and (3) for synchronizing `Waiter` nodes.
+//     - At the end of the `call` function we have to make sure the result
+//       of the `Once` is acquired. So every load which can be the only one to
+//       load COMPLETED must have at least acquire ordering, which means all
+//       three of them.
+//     - `WaiterQueue::drop` is the only place that may store COMPLETED, and
+//       must do so with release ordering to make the result available.
+//     - `wait` inserts `Waiter` nodes as a pointer in `state_and_queue`, and
+//       needs to make the nodes available with release ordering. The load in
+//       its `compare_exchange` can be relaxed because it only has to compare
+//       the atomic, not to read other data.
+//     - `WaiterQueue::drop` must see the `Waiter` nodes, so it must load
+//       `state_and_queue` with acquire ordering.
+//     - There is just one store where `state_and_queue` is used only as a
+//       state flag, without having to synchronize data: switching the state
+//       from INCOMPLETE to RUNNING in `call`. This store can be Relaxed,
+//       but the read has to be Acquire because of the requirements mentioned
+//       above.
+// * `Waiter.signaled` is both used as a flag, and to protect a field with
+//   interior mutability in `Waiter`. `Waiter.thread` is changed in
+//   `WaiterQueue::drop` which then sets `signaled` with release ordering.
+//   After `wait` loads `signaled` with acquire ordering and sees it is true,
+//   it needs to see the changes to drop the `Waiter` struct correctly.
+// * There is one place where the two atomics `Once.state_and_queue` and
+//   `Waiter.signaled` come together, and might be reordered by the compiler or
+//   processor. Because both use acquire ordering such a reordering is not
+//   allowed, so no need for `SeqCst`.
+
+use crate::cell::Cell;
+use crate::fmt;
+use crate::ptr;
+use crate::sync as public;
+use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
+use crate::thread::{self, Thread};
+
+type Masked = ();
+
+pub struct Once {
+    state_and_queue: AtomicPtr<Masked>,
+}
+
+pub struct OnceState {
+    poisoned: bool,
+    set_state_on_drop_to: Cell<*mut Masked>,
+}
+
+// Four states that a Once can be in, encoded into the lower bits of
+// `state_and_queue` in the Once structure.
+const INCOMPLETE: usize = 0x0;
+const POISONED: usize = 0x1;
+const RUNNING: usize = 0x2;
+const COMPLETE: usize = 0x3;
+
+// Mask to learn about the state. All other bits are the queue of waiters if
+// this is in the RUNNING state.
+const STATE_MASK: usize = 0x3;
+
+// Representation of a node in the linked list of waiters, used while in the
+// RUNNING state.
+// Note: `Waiter` can't hold a mutable pointer to the next thread, because then
+// `wait` would both hand out a mutable reference to its `Waiter` node, and keep
+// a shared reference to check `signaled`. Instead we hold shared references and
+// use interior mutability.
+#[repr(align(4))] // Ensure the two lower bits are free to use as state bits.
+struct Waiter {
+    thread: Cell<Option<Thread>>,
+    signaled: AtomicBool,
+    next: *const Waiter,
+}
+
+// Head of a linked list of waiters.
+// Every node is a struct on the stack of a waiting thread.
+// Will wake up the waiters when it gets dropped, i.e. also on panic.
+struct WaiterQueue<'a> {
+    state_and_queue: &'a AtomicPtr<Masked>,
+    set_state_on_drop_to: *mut Masked,
+}
+
+impl Once {
+    #[inline]
+    pub const fn new() -> Once {
+        Once { state_and_queue: AtomicPtr::new(ptr::invalid_mut(INCOMPLETE)) }
+    }
+
+    #[inline]
+    pub fn is_completed(&self) -> bool {
+        // An `Acquire` load is enough because that makes all the initialization
+        // operations visible to us, and, this being a fast path, weaker
+        // ordering helps with performance. This `Acquire` synchronizes with
+        // `Release` operations on the slow path.
+        self.state_and_queue.load(Ordering::Acquire).addr() == COMPLETE
+    }
+
+    // This is a non-generic function to reduce the monomorphization cost of
+    // using `call_once` (this isn't exactly a trivial or small implementation).
+    //
+    // Additionally, this is tagged with `#[cold]` as it should indeed be cold
+    // and it helps let LLVM know that calls to this function should be off the
+    // fast path. Essentially, this should help generate more straight line code
+    // in LLVM.
+    //
+    // Finally, this takes an `FnMut` instead of a `FnOnce` because there's
+    // currently no way to take an `FnOnce` and call it via virtual dispatch
+    // without some allocation overhead.
+    #[cold]
+    #[track_caller]
+    pub fn call(&self, ignore_poisoning: bool, init: &mut dyn FnMut(&public::OnceState)) {
+        let mut state_and_queue = self.state_and_queue.load(Ordering::Acquire);
+        loop {
+            match state_and_queue.addr() {
+                COMPLETE => break,
+                POISONED if !ignore_poisoning => {
+                    // Panic to propagate the poison.
+                    panic!("Once instance has previously been poisoned");
+                }
+                POISONED | INCOMPLETE => {
+                    // Try to register this thread as the one RUNNING.
+                    let exchange_result = self.state_and_queue.compare_exchange(
+                        state_and_queue,
+                        ptr::invalid_mut(RUNNING),
+                        Ordering::Acquire,
+                        Ordering::Acquire,
+                    );
+                    if let Err(old) = exchange_result {
+                        state_and_queue = old;
+                        continue;
+                    }
+                    // `waiter_queue` will manage other waiting threads, and
+                    // wake them up on drop.
+                    let mut waiter_queue = WaiterQueue {
+                        state_and_queue: &self.state_and_queue,
+                        set_state_on_drop_to: ptr::invalid_mut(POISONED),
+                    };
+                    // Run the initialization function, letting it know if we're
+                    // poisoned or not.
+                    let init_state = public::OnceState {
+                        inner: OnceState {
+                            poisoned: state_and_queue.addr() == POISONED,
+                            set_state_on_drop_to: Cell::new(ptr::invalid_mut(COMPLETE)),
+                        },
+                    };
+                    init(&init_state);
+                    waiter_queue.set_state_on_drop_to = init_state.inner.set_state_on_drop_to.get();
+                    break;
+                }
+                _ => {
+                    // All other values must be RUNNING with possibly a
+                    // pointer to the waiter queue in the more significant bits.
+                    assert!(state_and_queue.addr() & STATE_MASK == RUNNING);
+                    wait(&self.state_and_queue, state_and_queue);
+                    state_and_queue = self.state_and_queue.load(Ordering::Acquire);
+                }
+            }
+        }
+    }
+}
+
+fn wait(state_and_queue: &AtomicPtr<Masked>, mut current_state: *mut Masked) {
+    // Note: the following code was carefully written to avoid creating a
+    // mutable reference to `node` that gets aliased.
+    loop {
+        // Don't queue this thread if the status is no longer running,
+        // otherwise we will not be woken up.
+        if current_state.addr() & STATE_MASK != RUNNING {
+            return;
+        }
+
+        // Create the node for our current thread.
+        let node = Waiter {
+            thread: Cell::new(Some(thread::current())),
+            signaled: AtomicBool::new(false),
+            next: current_state.with_addr(current_state.addr() & !STATE_MASK) as *const Waiter,
+        };
+        let me = &node as *const Waiter as *const Masked as *mut Masked;
+
+        // Try to slide in the node at the head of the linked list, making sure
+        // that another thread didn't just replace the head of the linked list.
+        let exchange_result = state_and_queue.compare_exchange(
+            current_state,
+            me.with_addr(me.addr() | RUNNING),
+            Ordering::Release,
+            Ordering::Relaxed,
+        );
+        if let Err(old) = exchange_result {
+            current_state = old;
+            continue;
+        }
+
+        // We have enqueued ourselves, now lets wait.
+        // It is important not to return before being signaled, otherwise we
+        // would drop our `Waiter` node and leave a hole in the linked list
+        // (and a dangling reference). Guard against spurious wakeups by
+        // reparking ourselves until we are signaled.
+        while !node.signaled.load(Ordering::Acquire) {
+            // If the managing thread happens to signal and unpark us before we
+            // can park ourselves, the result could be this thread never gets
+            // unparked. Luckily `park` comes with the guarantee that if it got
+            // an `unpark` just before on an unparked thread it does not park.
+            thread::park();
+        }
+        break;
+    }
+}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for Once {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Once").finish_non_exhaustive()
+    }
+}
+
+impl Drop for WaiterQueue<'_> {
+    fn drop(&mut self) {
+        // Swap out our state with however we finished.
+        let state_and_queue =
+            self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel);
+
+        // We should only ever see an old state which was RUNNING.
+        assert_eq!(state_and_queue.addr() & STATE_MASK, RUNNING);
+
+        // Walk the entire linked list of waiters and wake them up (in lifo
+        // order, last to register is first to wake up).
+        unsafe {
+            // Right after setting `node.signaled = true` the other thread may
+            // free `node` if there happens to be has a spurious wakeup.
+            // So we have to take out the `thread` field and copy the pointer to
+            // `next` first.
+            let mut queue =
+                state_and_queue.with_addr(state_and_queue.addr() & !STATE_MASK) as *const Waiter;
+            while !queue.is_null() {
+                let next = (*queue).next;
+                let thread = (*queue).thread.take().unwrap();
+                (*queue).signaled.store(true, Ordering::Release);
+                // ^- FIXME (maybe): This is another case of issue #55005
+                // `store()` has a potentially dangling ref to `signaled`.
+                queue = next;
+                thread.unpark();
+            }
+        }
+    }
+}
+
+impl OnceState {
+    #[inline]
+    pub fn is_poisoned(&self) -> bool {
+        self.poisoned
+    }
+
+    #[inline]
+    pub fn poison(&self) {
+        self.set_state_on_drop_to.set(ptr::invalid_mut(POISONED));
+    }
+}
diff --git a/library/std/src/sys_common/once/mod.rs b/library/std/src/sys_common/once/mod.rs
new file mode 100644
index 000000000..8742e68cc
--- /dev/null
+++ b/library/std/src/sys_common/once/mod.rs
@@ -0,0 +1,43 @@
+// A "once" is a relatively simple primitive, and it's also typically provided
+// by the OS as well (see `pthread_once` or `InitOnceExecuteOnce`). The OS
+// primitives, however, tend to have surprising restrictions, such as the Unix
+// one doesn't allow an argument to be passed to the function.
+//
+// As a result, we end up implementing it ourselves in the standard library.
+// This also gives us the opportunity to optimize the implementation a bit which
+// should help the fast path on call sites.
+//
+// So to recap, the guarantees of a Once are that it will call the
+// initialization closure at most once, and it will never return until the one
+// that's running has finished running. This means that we need some form of
+// blocking here while the custom callback is running at the very least.
+// Additionally, we add on the restriction of **poisoning**. Whenever an
+// initialization closure panics, the Once enters a "poisoned" state which means
+// that all future calls will immediately panic as well.
+//
+// So to implement this, one might first reach for a `Mutex`, but those cannot
+// be put into a `static`. It also gets a lot harder with poisoning to figure
+// out when the mutex needs to be deallocated because it's not after the closure
+// finishes, but after the first successful closure finishes.
+//
+// All in all, this is instead implemented with atomics and lock-free
+// operations! Whee!
+
+cfg_if::cfg_if! {
+    if #[cfg(any(
+        target_os = "linux",
+        target_os = "android",
+        all(target_arch = "wasm32", target_feature = "atomics"),
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "dragonfly",
+        target_os = "fuchsia",
+        target_os = "hermit",
+    ))] {
+        mod futex;
+        pub use futex::{Once, OnceState};
+    } else {
+        mod generic;
+        pub use generic::{Once, OnceState};
+    }
+}
diff --git a/library/std/src/sys_common/rwlock.rs b/library/std/src/sys_common/rwlock.rs
index ba56f3a8f..042981dac 100644
--- a/library/std/src/sys_common/rwlock.rs
+++ b/library/std/src/sys_common/rwlock.rs
@@ -1,65 +1,5 @@
 use crate::sys::locks as imp;
 
-/// An OS-based reader-writer lock, meant for use in static variables.
-///
-/// This rwlock does not implement poisoning.
-///
-/// This rwlock has a const constructor ([`StaticRwLock::new`]), does not
-/// implement `Drop` to cleanup resources.
-pub struct StaticRwLock(imp::RwLock);
-
-impl StaticRwLock {
-    /// Creates a new rwlock for use.
-    #[inline]
-    pub const fn new() -> Self {
-        Self(imp::RwLock::new())
-    }
-
-    /// Acquires shared access to the underlying lock, blocking the current
-    /// thread to do so.
-    ///
-    /// The lock is automatically unlocked when the returned guard is dropped.
-    #[inline]
-    pub fn read(&'static self) -> StaticRwLockReadGuard {
-        unsafe { self.0.read() };
-        StaticRwLockReadGuard(&self.0)
-    }
-
-    /// Acquires write access to the underlying lock, blocking the current thread
-    /// to do so.
-    ///
-    /// The lock is automatically unlocked when the returned guard is dropped.
-    #[inline]
-    pub fn write(&'static self) -> StaticRwLockWriteGuard {
-        unsafe { self.0.write() };
-        StaticRwLockWriteGuard(&self.0)
-    }
-}
-
-#[must_use]
-pub struct StaticRwLockReadGuard(&'static imp::RwLock);
-
-impl Drop for StaticRwLockReadGuard {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe {
-            self.0.read_unlock();
-        }
-    }
-}
-
-#[must_use]
-pub struct StaticRwLockWriteGuard(&'static imp::RwLock);
-
-impl Drop for StaticRwLockWriteGuard {
-    #[inline]
-    fn drop(&mut self) {
-        unsafe {
-            self.0.write_unlock();
-        }
-    }
-}
-
 /// An OS-based reader-writer lock.
 ///
 /// This rwlock cleans up its resources in its `Drop` implementation and may
@@ -75,6 +15,7 @@ pub struct MovableRwLock(imp::MovableRwLock);
 impl MovableRwLock {
     /// Creates a new reader-writer lock for use.
     #[inline]
+    #[rustc_const_stable(feature = "const_locks", since = "1.63.0")]
     pub const fn new() -> Self {
         Self(imp::MovableRwLock::new())
     }
diff --git a/library/std/src/sys_common/thread_local_key.rs b/library/std/src/sys_common/thread_local_key.rs
index 032bf604d..747579f17 100644
--- a/library/std/src/sys_common/thread_local_key.rs
+++ b/library/std/src/sys_common/thread_local_key.rs
@@ -53,7 +53,6 @@ mod tests;
 
 use crate::sync::atomic::{self, AtomicUsize, Ordering};
 use crate::sys::thread_local_key as imp;
-use crate::sys_common::mutex::StaticMutex;
 
 /// A type for TLS keys that are statically allocated.
 ///
@@ -151,25 +150,6 @@ impl StaticKey {
     }
 
     unsafe fn lazy_init(&self) -> usize {
-        // Currently the Windows implementation of TLS is pretty hairy, and
-        // it greatly simplifies creation if we just synchronize everything.
-        //
-        // Additionally a 0-index of a tls key hasn't been seen on windows, so
-        // we just simplify the whole branch.
-        if imp::requires_synchronized_create() {
-            // We never call `INIT_LOCK.init()`, so it is UB to attempt to
-            // acquire this mutex reentrantly!
-            static INIT_LOCK: StaticMutex = StaticMutex::new();
-            let _guard = INIT_LOCK.lock();
-            let mut key = self.key.load(Ordering::SeqCst);
-            if key == 0 {
-                key = imp::create(self.dtor) as usize;
-                self.key.store(key, Ordering::SeqCst);
-            }
-            rtassert!(key != 0);
-            return key;
-        }
-
         // POSIX allows the key created here to be 0, but the compare_exchange
         // below relies on using 0 as a sentinel value to check who won the
         // race to set the shared TLS key. As far as I know, there is no
@@ -232,8 +212,6 @@ impl Key {
 
 impl Drop for Key {
     fn drop(&mut self) {
-        // Right now Windows doesn't support TLS key destruction, but this also
-        // isn't used anywhere other than tests, so just leak the TLS key.
-        // unsafe { imp::destroy(self.key) }
+        unsafe { imp::destroy(self.key) }
     }
 }
diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs
index 8aedfc4a6..5d267891b 100644
--- a/library/std/src/thread/local.rs
+++ b/library/std/src/thread/local.rs
@@ -95,6 +95,7 @@ use crate::fmt;
 /// [loader lock]: https://docs.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-best-practices
 /// [`JoinHandle::join`]: crate::thread::JoinHandle::join
 /// [`with`]: LocalKey::with
+#[cfg_attr(not(test), rustc_diagnostic_item = "LocalKey")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct LocalKey<T: 'static> {
     // This outer `LocalKey<T>` type is what's going to be stored in statics,
@@ -900,7 +901,7 @@ pub mod statik {
 }
 
 #[doc(hidden)]
-#[cfg(target_thread_local)]
+#[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics"))),))]
 pub mod fast {
     use super::lazy::LazyKeyInner;
     use crate::cell::Cell;
@@ -1036,7 +1037,10 @@ pub mod fast {
 }
 
 #[doc(hidden)]
-#[cfg(not(target_thread_local))]
+#[cfg(all(
+    not(target_thread_local),
+    not(all(target_family = "wasm", not(target_feature = "atomics"))),
+))]
 pub mod os {
     use super::lazy::LazyKeyInner;
     use crate::cell::Cell;
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index ceea6986e..05023df1b 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -150,6 +150,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 #![deny(unsafe_op_in_unsafe_fn)]
+// Under `test`, `__FastLocalKeyInner` seems unused.
+#![cfg_attr(test, allow(dead_code))]
 
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests;
@@ -160,7 +162,7 @@ use crate::ffi::{CStr, CString};
 use crate::fmt;
 use crate::io;
 use crate::marker::PhantomData;
-use crate::mem;
+use crate::mem::{self, forget};
 use crate::num::NonZeroU64;
 use crate::num::NonZeroUsize;
 use crate::panic;
@@ -192,32 +194,40 @@ pub use scoped::{scope, Scope, ScopedJoinHandle};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::local::{AccessError, LocalKey};
 
-// Select the type used by the thread_local! macro to access TLS keys. There
-// are three types: "static", "fast", "OS". The "OS" thread local key
+// Provide the type used by the thread_local! macro to access TLS keys. This
+// needs to be kept in sync with the macro itself (in `local.rs`).
+// There are three types: "static", "fast", "OS". The "OS" thread local key
 // type is accessed via platform-specific API calls and is slow, while the "fast"
 // key type is accessed via code generated via LLVM, where TLS keys are set up
 // by the elf linker. "static" is for single-threaded platforms where a global
 // static is sufficient.
 
 #[unstable(feature = "libstd_thread_internals", issue = "none")]
-#[cfg(target_thread_local)]
 #[cfg(not(test))]
+#[cfg(all(
+    target_thread_local,
+    not(all(target_family = "wasm", not(target_feature = "atomics"))),
+))]
 #[doc(hidden)]
 pub use self::local::fast::Key as __FastLocalKeyInner;
-#[unstable(feature = "libstd_thread_internals", issue = "none")]
-#[cfg(target_thread_local)]
-#[cfg(test)] // when building for tests, use real std's key
-pub use realstd::thread::__FastLocalKeyInner;
 
+// when building for tests, use real std's type
 #[unstable(feature = "libstd_thread_internals", issue = "none")]
-#[cfg(target_thread_local)]
 #[cfg(test)]
-pub use self::local::fast::Key as __FastLocalKeyInnerUnused; // we import this anyway to silence 'unused' warnings
+#[cfg(all(
+    target_thread_local,
+    not(all(target_family = "wasm", not(target_feature = "atomics"))),
+))]
+pub use realstd::thread::__FastLocalKeyInner;
 
 #[unstable(feature = "libstd_thread_internals", issue = "none")]
+#[cfg(all(
+    not(target_thread_local),
+    not(all(target_family = "wasm", not(target_feature = "atomics"))),
+))]
 #[doc(hidden)]
-#[cfg(not(target_thread_local))]
 pub use self::local::os::Key as __OsLocalKeyInner;
+
 #[unstable(feature = "libstd_thread_internals", issue = "none")]
 #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))]
 #[doc(hidden)]
@@ -499,6 +509,31 @@ impl Builder {
         let output_capture = crate::io::set_output_capture(None);
         crate::io::set_output_capture(output_capture.clone());
 
+        // Pass `f` in `MaybeUninit` because actually that closure might *run longer than the lifetime of `F`*.
+        // See <https://github.com/rust-lang/rust/issues/101983> for more details.
+        // To prevent leaks we use a wrapper that drops its contents.
+        #[repr(transparent)]
+        struct MaybeDangling<T>(mem::MaybeUninit<T>);
+        impl<T> MaybeDangling<T> {
+            fn new(x: T) -> Self {
+                MaybeDangling(mem::MaybeUninit::new(x))
+            }
+            fn into_inner(self) -> T {
+                // SAFETY: we are always initiailized.
+                let ret = unsafe { self.0.assume_init_read() };
+                // Make sure we don't drop.
+                mem::forget(self);
+                ret
+            }
+        }
+        impl<T> Drop for MaybeDangling<T> {
+            fn drop(&mut self) {
+                // SAFETY: we are always initiailized.
+                unsafe { self.0.assume_init_drop() };
+            }
+        }
+
+        let f = MaybeDangling::new(f);
         let main = move || {
             if let Some(name) = their_thread.cname() {
                 imp::Thread::set_name(name);
@@ -506,6 +541,8 @@ impl Builder {
 
             crate::io::set_output_capture(output_capture);
 
+            // SAFETY: we constructed `f` initialized.
+            let f = f.into_inner();
             // SAFETY: the stack guard passed is the one for the current thread.
             // This means the current thread's stack and the new thread's stack
             // are properly set and protected from each other.
@@ -518,6 +555,12 @@ impl Builder {
             // same `JoinInner` as this closure meaning the mutation will be
             // safe (not modify it and affect a value far away).
             unsafe { *their_packet.result.get() = Some(try_result) };
+            // Here `their_packet` gets dropped, and if this is the last `Arc` for that packet that
+            // will call `decrement_num_running_threads` and therefore signal that this thread is
+            // done.
+            drop(their_packet);
+            // Here, the lifetime `'a` and even `'scope` can end. `main` keeps running for a bit
+            // after that before returning itself.
         };
 
         if let Some(scope_data) = &my_packet.scope {
@@ -779,6 +822,8 @@ pub fn panicking() -> bool {
     panicking::panicking()
 }
 
+/// Use [`sleep`].
+///
 /// Puts the current thread to sleep for at least the specified amount of time.
 ///
 /// The thread may sleep longer than the duration specified due to scheduling
@@ -849,10 +894,22 @@ pub fn sleep(dur: Duration) {
     imp::Thread::sleep(dur)
 }
 
+/// Used to ensure that `park` and `park_timeout` do not unwind, as that can
+/// cause undefined behaviour if not handled correctly (see #102398 for context).
+struct PanicGuard;
+
+impl Drop for PanicGuard {
+    fn drop(&mut self) {
+        rtabort!("an irrecoverable error occurred while synchronizing threads")
+    }
+}
+
 /// Blocks unless or until the current thread's token is made available.
 ///
 /// A call to `park` does not guarantee that the thread will remain parked
-/// forever, and callers should be prepared for this possibility.
+/// forever, and callers should be prepared for this possibility. However,
+/// it is guaranteed that this function will not panic (it may abort the
+/// process if the implementation encounters some rare errors).
 ///
 /// # park and unpark
 ///
@@ -937,10 +994,13 @@ pub fn sleep(dur: Duration) {
 /// [`thread::park_timeout`]: park_timeout
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn park() {
+    let guard = PanicGuard;
     // SAFETY: park_timeout is called on the parker owned by this thread.
     unsafe {
         current().inner.as_ref().parker().park();
     }
+    // No panic occurred, do not abort.
+    forget(guard);
 }
 
 /// Use [`park_timeout`].
@@ -1001,10 +1061,13 @@ pub fn park_timeout_ms(ms: u32) {
 /// ```
 #[stable(feature = "park_timeout", since = "1.4.0")]
 pub fn park_timeout(dur: Duration) {
+    let guard = PanicGuard;
     // SAFETY: park_timeout is called on the parker owned by this thread.
     unsafe {
         current().inner.as_ref().parker().park_timeout(dur);
     }
+    // No panic occurred, do not abort.
+    forget(guard);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -1065,24 +1128,21 @@ impl ThreadId {
                     }
                 }
             } else {
-                use crate::sys_common::mutex::StaticMutex;
+                use crate::sync::{Mutex, PoisonError};
 
-                // It is UB to attempt to acquire this mutex reentrantly!
-                static GUARD: StaticMutex = StaticMutex::new();
-                static mut COUNTER: u64 = 0;
+                static COUNTER: Mutex<u64> = Mutex::new(0);
 
-                unsafe {
-                    let guard = GUARD.lock();
+                let mut counter = COUNTER.lock().unwrap_or_else(PoisonError::into_inner);
+                let Some(id) = counter.checked_add(1) else {
+                    // in case the panic handler ends up calling `ThreadId::new()`,
+                    // avoid reentrant lock acquire.
+                    drop(counter);
+                    exhausted();
+                };
 
-                    let Some(id) = COUNTER.checked_add(1) else {
-                        drop(guard); // in case the panic handler ends up calling `ThreadId::new()`, avoid reentrant lock acquire.
-                        exhausted();
-                    };
-
-                    COUNTER = id;
-                    drop(guard);
-                    ThreadId(NonZeroU64::new(id).unwrap())
-                }
+                *counter = id;
+                drop(counter);
+                ThreadId(NonZeroU64::new(id).unwrap())
             }
         }
     }
diff --git a/library/std/src/thread/tests.rs b/library/std/src/thread/tests.rs
index 777964f04..6c9ce6fa0 100644
--- a/library/std/src/thread/tests.rs
+++ b/library/std/src/thread/tests.rs
@@ -276,6 +276,28 @@ fn test_try_panic_any_message_unit_struct() {
 }
 
 #[test]
+fn test_park_unpark_before() {
+    for _ in 0..10 {
+        thread::current().unpark();
+        thread::park();
+    }
+}
+
+#[test]
+fn test_park_unpark_called_other_thread() {
+    for _ in 0..10 {
+        let th = thread::current();
+
+        let _guard = thread::spawn(move || {
+            super::sleep(Duration::from_millis(50));
+            th.unpark();
+        });
+
+        thread::park();
+    }
+}
+
+#[test]
 fn test_park_timeout_unpark_before() {
     for _ in 0..10 {
         thread::current().unpark();
diff --git a/library/std/src/time.rs b/library/std/src/time.rs
index 759a59e1f..ecd06ebf7 100644
--- a/library/std/src/time.rs
+++ b/library/std/src/time.rs
@@ -43,8 +43,8 @@ use crate::sys_common::{FromInner, IntoInner};
 #[stable(feature = "time", since = "1.3.0")]
 pub use core::time::Duration;
 
-#[unstable(feature = "duration_checked_float", issue = "83400")]
-pub use core::time::FromFloatSecsError;
+#[stable(feature = "duration_checked_float", since = "1.66.0")]
+pub use core::time::TryFromFloatSecsError;
 
 /// A measurement of a monotonically nondecreasing clock.
 /// Opaque and useful only with [`Duration`].
@@ -356,7 +356,7 @@ impl Instant {
     ///
     /// # Panics
     ///
-    /// Previous rust versions panicked when self was earlier than the current time. Currently this
+    /// Previous rust versions panicked when the current time was earlier than self. Currently this
     /// method returns a Duration of zero in that case. Future versions may reintroduce the panic.
     /// See [Monotonicity].
     ///
diff --git a/library/std/tests/run-time-detect.rs b/library/std/tests/run-time-detect.rs
index a57a52d9b..02c076f1b 100644
--- a/library/std/tests/run-time-detect.rs
+++ b/library/std/tests/run-time-detect.rs
@@ -14,77 +14,85 @@
 #[cfg(all(target_arch = "arm", any(target_os = "linux", target_os = "android")))]
 fn arm_linux() {
     use std::arch::is_arm_feature_detected;
+    // tidy-alphabetical-start
+    println!("aes: {}", is_arm_feature_detected!("aes"));
+    println!("crc: {}", is_arm_feature_detected!("crc"));
+    println!("crypto: {}", is_arm_feature_detected!("crypto"));
     println!("neon: {}", is_arm_feature_detected!("neon"));
     println!("pmull: {}", is_arm_feature_detected!("pmull"));
-    println!("crypto: {}", is_arm_feature_detected!("crypto"));
-    println!("crc: {}", is_arm_feature_detected!("crc"));
-    println!("aes: {}", is_arm_feature_detected!("aes"));
     println!("sha2: {}", is_arm_feature_detected!("sha2"));
+    // tidy-alphabetical-end
 }
 
 #[test]
 #[cfg(all(target_arch = "aarch64", any(target_os = "linux", target_os = "android")))]
 fn aarch64_linux() {
     use std::arch::is_aarch64_feature_detected;
-    println!("neon: {}", is_aarch64_feature_detected!("neon"));
+    // tidy-alphabetical-start
+    println!("aes: {}", is_aarch64_feature_detected!("aes"));
     println!("asimd: {}", is_aarch64_feature_detected!("asimd"));
-    println!("pmull: {}", is_aarch64_feature_detected!("pmull"));
-    println!("fp16: {}", is_aarch64_feature_detected!("fp16"));
-    println!("sve: {}", is_aarch64_feature_detected!("sve"));
+    println!("bf16: {}", is_aarch64_feature_detected!("bf16"));
+    println!("bti: {}", is_aarch64_feature_detected!("bti"));
     println!("crc: {}", is_aarch64_feature_detected!("crc"));
-    println!("lse: {}", is_aarch64_feature_detected!("lse"));
-    println!("lse2: {}", is_aarch64_feature_detected!("lse2"));
-    println!("rdm: {}", is_aarch64_feature_detected!("rdm"));
-    println!("rcpc: {}", is_aarch64_feature_detected!("rcpc"));
-    println!("rcpc2: {}", is_aarch64_feature_detected!("rcpc2"));
+    println!("dit: {}", is_aarch64_feature_detected!("dit"));
     println!("dotprod: {}", is_aarch64_feature_detected!("dotprod"));
-    println!("tme: {}", is_aarch64_feature_detected!("tme"));
+    println!("dpb2: {}", is_aarch64_feature_detected!("dpb2"));
+    println!("dpb: {}", is_aarch64_feature_detected!("dpb"));
+    println!("f32mm: {}", is_aarch64_feature_detected!("f32mm"));
+    println!("f64mm: {}", is_aarch64_feature_detected!("f64mm"));
+    println!("fcma: {}", is_aarch64_feature_detected!("fcma"));
     println!("fhm: {}", is_aarch64_feature_detected!("fhm"));
-    println!("dit: {}", is_aarch64_feature_detected!("dit"));
     println!("flagm: {}", is_aarch64_feature_detected!("flagm"));
-    println!("ssbs: {}", is_aarch64_feature_detected!("ssbs"));
-    println!("sb: {}", is_aarch64_feature_detected!("sb"));
-    println!("paca: {}", is_aarch64_feature_detected!("paca"));
-    println!("pacg: {}", is_aarch64_feature_detected!("pacg"));
-    println!("dpb: {}", is_aarch64_feature_detected!("dpb"));
-    println!("dpb2: {}", is_aarch64_feature_detected!("dpb2"));
-    println!("sve2: {}", is_aarch64_feature_detected!("sve2"));
-    println!("sve2-aes: {}", is_aarch64_feature_detected!("sve2-aes"));
-    println!("sve2-sm4: {}", is_aarch64_feature_detected!("sve2-sm4"));
-    println!("sve2-sha3: {}", is_aarch64_feature_detected!("sve2-sha3"));
-    println!("sve2-bitperm: {}", is_aarch64_feature_detected!("sve2-bitperm"));
+    println!("fp16: {}", is_aarch64_feature_detected!("fp16"));
     println!("frintts: {}", is_aarch64_feature_detected!("frintts"));
     println!("i8mm: {}", is_aarch64_feature_detected!("i8mm"));
-    println!("f32mm: {}", is_aarch64_feature_detected!("f32mm"));
-    println!("f64mm: {}", is_aarch64_feature_detected!("f64mm"));
-    println!("bf16: {}", is_aarch64_feature_detected!("bf16"));
-    println!("rand: {}", is_aarch64_feature_detected!("rand"));
-    println!("bti: {}", is_aarch64_feature_detected!("bti"));
-    println!("mte: {}", is_aarch64_feature_detected!("mte"));
     println!("jsconv: {}", is_aarch64_feature_detected!("jsconv"));
-    println!("fcma: {}", is_aarch64_feature_detected!("fcma"));
-    println!("aes: {}", is_aarch64_feature_detected!("aes"));
+    println!("lse2: {}", is_aarch64_feature_detected!("lse2"));
+    println!("lse: {}", is_aarch64_feature_detected!("lse"));
+    println!("mte: {}", is_aarch64_feature_detected!("mte"));
+    println!("neon: {}", is_aarch64_feature_detected!("neon"));
+    println!("paca: {}", is_aarch64_feature_detected!("paca"));
+    println!("pacg: {}", is_aarch64_feature_detected!("pacg"));
+    println!("pmull: {}", is_aarch64_feature_detected!("pmull"));
+    println!("rand: {}", is_aarch64_feature_detected!("rand"));
+    println!("rcpc2: {}", is_aarch64_feature_detected!("rcpc2"));
+    println!("rcpc: {}", is_aarch64_feature_detected!("rcpc"));
+    println!("rdm: {}", is_aarch64_feature_detected!("rdm"));
+    println!("sb: {}", is_aarch64_feature_detected!("sb"));
     println!("sha2: {}", is_aarch64_feature_detected!("sha2"));
     println!("sha3: {}", is_aarch64_feature_detected!("sha3"));
     println!("sm4: {}", is_aarch64_feature_detected!("sm4"));
+    println!("ssbs: {}", is_aarch64_feature_detected!("ssbs"));
+    println!("sve2-aes: {}", is_aarch64_feature_detected!("sve2-aes"));
+    println!("sve2-bitperm: {}", is_aarch64_feature_detected!("sve2-bitperm"));
+    println!("sve2-sha3: {}", is_aarch64_feature_detected!("sve2-sha3"));
+    println!("sve2-sm4: {}", is_aarch64_feature_detected!("sve2-sm4"));
+    println!("sve2: {}", is_aarch64_feature_detected!("sve2"));
+    println!("sve: {}", is_aarch64_feature_detected!("sve"));
+    println!("tme: {}", is_aarch64_feature_detected!("tme"));
+    // tidy-alphabetical-end
 }
 
 #[test]
 #[cfg(all(target_arch = "powerpc", target_os = "linux"))]
 fn powerpc_linux() {
     use std::arch::is_powerpc_feature_detected;
+    // tidy-alphabetical-start
     println!("altivec: {}", is_powerpc_feature_detected!("altivec"));
-    println!("vsx: {}", is_powerpc_feature_detected!("vsx"));
     println!("power8: {}", is_powerpc_feature_detected!("power8"));
+    println!("vsx: {}", is_powerpc_feature_detected!("vsx"));
+    // tidy-alphabetical-end
 }
 
 #[test]
 #[cfg(all(target_arch = "powerpc64", target_os = "linux"))]
 fn powerpc64_linux() {
     use std::arch::is_powerpc64_feature_detected;
+    // tidy-alphabetical-start
     println!("altivec: {}", is_powerpc64_feature_detected!("altivec"));
-    println!("vsx: {}", is_powerpc64_feature_detected!("vsx"));
     println!("power8: {}", is_powerpc64_feature_detected!("power8"));
+    println!("vsx: {}", is_powerpc64_feature_detected!("vsx"));
+    // tidy-alphabetical-end
 }
 
 #[test]
@@ -102,9 +110,9 @@ fn x86_all() {
     // the below is in alphabetical order and matches
     // the order of X86_ALLOWED_FEATURES in rustc_codegen_ssa's target_features.rs
 
+    // tidy-alphabetical-start
     println!("adx: {:?}", is_x86_feature_detected!("adx"));
     println!("aes: {:?}", is_x86_feature_detected!("aes"));
-    println!("avx: {:?}", is_x86_feature_detected!("avx"));
     println!("avx2: {:?}", is_x86_feature_detected!("avx2"));
     println!("avx512bf16: {:?}", is_x86_feature_detected!("avx512bf16"));
     println!("avx512bitalg: {:?}", is_x86_feature_detected!("avx512bitalg"));
@@ -117,13 +125,14 @@ fn x86_all() {
     println!("avx512ifma: {:?}", is_x86_feature_detected!("avx512ifma"));
     println!("avx512pf: {:?}", is_x86_feature_detected!("avx512pf"));
     println!("avx512vaes: {:?}", is_x86_feature_detected!("avx512vaes"));
-    println!("avx512vbmi: {:?}", is_x86_feature_detected!("avx512vbmi"));
     println!("avx512vbmi2: {:?}", is_x86_feature_detected!("avx512vbmi2"));
+    println!("avx512vbmi: {:?}", is_x86_feature_detected!("avx512vbmi"));
     println!("avx512vl: {:?}", is_x86_feature_detected!("avx512vl"));
     println!("avx512vnni: {:?}", is_x86_feature_detected!("avx512vnni"));
     println!("avx512vp2intersect: {:?}", is_x86_feature_detected!("avx512vp2intersect"));
     println!("avx512vpclmulqdq: {:?}", is_x86_feature_detected!("avx512vpclmulqdq"));
     println!("avx512vpopcntdq: {:?}", is_x86_feature_detected!("avx512vpopcntdq"));
+    println!("avx: {:?}", is_x86_feature_detected!("avx"));
     println!("bmi1: {:?}", is_x86_feature_detected!("bmi1"));
     println!("bmi2: {:?}", is_x86_feature_detected!("bmi2"));
     println!("cmpxchg16b: {:?}", is_x86_feature_detected!("cmpxchg16b"));
@@ -138,16 +147,17 @@ fn x86_all() {
     println!("rdseed: {:?}", is_x86_feature_detected!("rdseed"));
     println!("rtm: {:?}", is_x86_feature_detected!("rtm"));
     println!("sha: {:?}", is_x86_feature_detected!("sha"));
-    println!("sse: {:?}", is_x86_feature_detected!("sse"));
     println!("sse2: {:?}", is_x86_feature_detected!("sse2"));
     println!("sse3: {:?}", is_x86_feature_detected!("sse3"));
     println!("sse4.1: {:?}", is_x86_feature_detected!("sse4.1"));
     println!("sse4.2: {:?}", is_x86_feature_detected!("sse4.2"));
     println!("sse4a: {:?}", is_x86_feature_detected!("sse4a"));
+    println!("sse: {:?}", is_x86_feature_detected!("sse"));
     println!("ssse3: {:?}", is_x86_feature_detected!("ssse3"));
     println!("tbm: {:?}", is_x86_feature_detected!("tbm"));
     println!("xsave: {:?}", is_x86_feature_detected!("xsave"));
     println!("xsavec: {:?}", is_x86_feature_detected!("xsavec"));
     println!("xsaveopt: {:?}", is_x86_feature_detected!("xsaveopt"));
     println!("xsaves: {:?}", is_x86_feature_detected!("xsaves"));
+    // tidy-alphabetical-end
 }
diff --git a/library/stdarch/ci/android-install-sdk.sh b/library/stdarch/ci/android-install-sdk.sh
index 1beeb312a..3383dcb7f 100644
--- a/library/stdarch/ci/android-install-sdk.sh
+++ b/library/stdarch/ci/android-install-sdk.sh
@@ -19,8 +19,8 @@ set -ex
 # which apparently magically accepts the licenses.
 
 mkdir sdk
-curl --retry 5 https://dl.google.com/android/repository/sdk-tools-linux-3859397.zip -O
-unzip -d sdk sdk-tools-linux-3859397.zip
+curl --retry 5 https://dl.google.com/android/repository/sdk-tools-linux-4333796.zip -O
+unzip -d sdk sdk-tools-linux-4333796.zip
 
 case "$1" in
   arm | armv7)
diff --git a/library/stdarch/ci/docker/aarch64-linux-android/Dockerfile b/library/stdarch/ci/docker/aarch64-linux-android/Dockerfile
index 27bde89c5..6cf9b5061 100644
--- a/library/stdarch/ci/docker/aarch64-linux-android/Dockerfile
+++ b/library/stdarch/ci/docker/aarch64-linux-android/Dockerfile
@@ -1,17 +1,16 @@
-FROM ubuntu:16.04
+FROM ubuntu:22.04
 
-RUN dpkg --add-architecture i386 && \
-    apt-get update && \
+RUN apt-get update && \
     apt-get install -y --no-install-recommends \
   file \
   make \
   curl \
   ca-certificates \
-  python \
+  python-is-python3 \
   unzip \
   expect \
-  openjdk-9-jre \
-  libstdc++6:i386 \
+  openjdk-8-jre \
+  libstdc++6-i386-cross \
   libpulse0 \
   gcc \
   libc6-dev
diff --git a/library/stdarch/ci/docker/arm-linux-androideabi/Dockerfile b/library/stdarch/ci/docker/arm-linux-androideabi/Dockerfile
index 995a9e30e..fb1a0cecf 100644
--- a/library/stdarch/ci/docker/arm-linux-androideabi/Dockerfile
+++ b/library/stdarch/ci/docker/arm-linux-androideabi/Dockerfile
@@ -1,17 +1,16 @@
-FROM ubuntu:16.04
+FROM ubuntu:22.04
 
-RUN dpkg --add-architecture i386 && \
-    apt-get update && \
+RUN apt-get update && \
     apt-get install -y --no-install-recommends \
   file \
   make \
   curl \
   ca-certificates \
-  python \
+  python-is-python3 \
   unzip \
   expect \
-  openjdk-9-jre \
-  libstdc++6:i386 \
+  openjdk-8-jre \
+  libstdc++6-i386-cross \
   libpulse0 \
   gcc \
   libc6-dev
diff --git a/library/stdarch/ci/docker/x86_64-linux-android/Dockerfile b/library/stdarch/ci/docker/x86_64-linux-android/Dockerfile
index c2830b15f..82119be74 100644
--- a/library/stdarch/ci/docker/x86_64-linux-android/Dockerfile
+++ b/library/stdarch/ci/docker/x86_64-linux-android/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:16.04
+FROM ubuntu:22.04
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
@@ -6,7 +6,7 @@ RUN apt-get update && \
   curl \
   gcc \
   libc-dev \
-  python \
+  python-is-python3 \
   unzip \
   file \
   make
diff --git a/library/stdarch/crates/core_arch/src/arm_shared/neon/mod.rs b/library/stdarch/crates/core_arch/src/arm_shared/neon/mod.rs
index 043f7ed51..0559aea83 100644
--- a/library/stdarch/crates/core_arch/src/arm_shared/neon/mod.rs
+++ b/library/stdarch/crates/core_arch/src/arm_shared/neon/mod.rs
@@ -12461,30 +12461,30 @@ mod tests {
     }
     #[simd_test(enable = "neon,i8mm")]
     unsafe fn test_vmmlaq_s32() {
-        let a: i32x4 = i32x4::new(1, 3, 4, 9);
-        let b: i8x16 = i8x16::new(1, 21, 31, 14, 5, 6, 17, 8, 9, 13, 15, 12, 13, 19, 20, 16);
-        let c: i8x16 = i8x16::new(12, 22, 3, 4, 5, 56, 7, 8, 91, 10, 11, 15, 13, 14, 17, 16);
-        let e: i32x4 = i32x4::new(1, 2, 3, 4);
+        let a = i32x4::new(1, 3, 4, -0x10000);
+        let b = i8x16::new(1, 21, 31, 14, 5, 6, -128, 8, 9, 13, 15, 12, 13, -1, 20, 16);
+        let c = i8x16::new(12, 22, 3, 4, -1, 56, 7, 8, 91, 10, -128, 15, 13, 14, 17, 16);
+        let e = i32x4::new(123, -5353, 690, -65576);
         let r: i32x4 = transmute(vmmlaq_s32(transmute(a), transmute(b), transmute(c)));
         assert_eq!(r, e);
     }
 
     #[simd_test(enable = "neon,i8mm")]
     unsafe fn test_vmmlaq_u32() {
-        let a: u32x4 = u32x4::new(1, 3, 4, 9);
-        let b: i8x16 = i8x16::new(1, 21, 31, 14, 5, 6, 17, 8, 9, 13, 15, 12, 13, 19, 20, 16);
-        let c: i8x16 = i8x16::new(12, 22, 3, 4, 5, 56, 7, 8, 91, 10, 11, 15, 13, 14, 17, 16);
-        let e: u32x4 = u32x4::new(1, 2, 3, 4);
+        let a = u32x4::new(1, 3, 4, 0xffff0000);
+        let b = u8x16::new(1, 21, 31, 14, 5, 6, 128, 8, 9, 13, 15, 12, 13, 255, 20, 16);
+        let c = u8x16::new(12, 22, 3, 4, 255, 56, 7, 8, 91, 10, 128, 15, 13, 14, 17, 16);
+        let e = u32x4::new(3195, 6935, 18354, 4294909144);
         let r: u32x4 = transmute(vmmlaq_u32(transmute(a), transmute(b), transmute(c)));
         assert_eq!(r, e);
     }
 
     #[simd_test(enable = "neon,i8mm")]
     unsafe fn test_vusmmlaq_s32() {
-        let a: i32x4 = i32x4::new(1, 3, 4, 9);
-        let b: i8x16 = i8x16::new(1, 21, 31, 14, 5, 6, 17, 8, 9, 13, 15, 12, 13, 19, 20, 16);
-        let c: i8x16 = i8x16::new(12, 22, 3, 4, 5, 56, 7, 8, 91, 10, 11, 15, 13, 14, 17, 16);
-        let e: i32x4 = i32x4::new(1, 2, 3, 4);
+        let a = i32x4::new(1, 3, 4, -0x10000);
+        let b = u8x16::new(1, 21, 31, 14, 5, 6, 128, 8, 9, 13, 15, 12, 13, 255, 20, 16);
+        let c = i8x16::new(12, 22, 3, 4, -1, 56, 7, 8, 91, 10, -128, 15, 13, 14, 17, 16);
+        let e = i32x4::new(1915, -1001, 15026, -61992);
         let r: i32x4 = transmute(vusmmlaq_s32(transmute(a), transmute(b), transmute(c)));
         assert_eq!(r, e);
     }
diff --git a/library/stdarch/crates/core_arch/src/lib.rs b/library/stdarch/crates/core_arch/src/lib.rs
index 9240d0e84..5a9727a0a 100644
--- a/library/stdarch/crates/core_arch/src/lib.rs
+++ b/library/stdarch/crates/core_arch/src/lib.rs
@@ -19,6 +19,7 @@
     doc_cfg,
     tbm_target_feature,
     sse4a_target_feature,
+    riscv_target_feature,
     arm_target_feature,
     cmpxchg16b_target_feature,
     avx512_target_feature,
@@ -30,8 +31,8 @@
     f16c_target_feature,
     allow_internal_unstable,
     decl_macro,
-    bench_black_box,
-    asm_const
+    asm_const,
+    target_feature_11
 )]
 #![cfg_attr(test, feature(test, abi_vectorcall))]
 #![deny(clippy::missing_inline_in_public_items)]
diff --git a/library/stdarch/crates/core_arch/src/macros.rs b/library/stdarch/crates/core_arch/src/macros.rs
index 1e6a3f405..1c917c52b 100644
--- a/library/stdarch/crates/core_arch/src/macros.rs
+++ b/library/stdarch/crates/core_arch/src/macros.rs
@@ -101,11 +101,11 @@ macro_rules! simd_shuffle2 {
             const IDX: [u32; 2] = $idx;
         }
 
-        simd_shuffle2($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 2] = $idx;
-        simd_shuffle2($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
 
@@ -117,11 +117,11 @@ macro_rules! simd_shuffle4 {
             const IDX: [u32; 4] = $idx;
         }
 
-        simd_shuffle4($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 4] = $idx;
-        simd_shuffle4($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
 
@@ -133,11 +133,11 @@ macro_rules! simd_shuffle8 {
             const IDX: [u32; 8] = $idx;
         }
 
-        simd_shuffle8($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 8] = $idx;
-        simd_shuffle8($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
 
@@ -149,11 +149,11 @@ macro_rules! simd_shuffle16 {
             const IDX: [u32; 16] = $idx;
         }
 
-        simd_shuffle16($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 16] = $idx;
-        simd_shuffle16($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
 
@@ -165,11 +165,11 @@ macro_rules! simd_shuffle32 {
             const IDX: [u32; 32] = $idx;
         }
 
-        simd_shuffle32($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 32] = $idx;
-        simd_shuffle32($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
 
@@ -181,10 +181,10 @@ macro_rules! simd_shuffle64 {
             const IDX: [u32; 64] = $idx;
         }
 
-        simd_shuffle64($x, $y, ConstParam::<$($imm),+>::IDX)
+        simd_shuffle($x, $y, ConstParam::<$($imm),+>::IDX)
     }};
     ($x:expr, $y:expr, $idx:expr $(,)?) => {{
         const IDX: [u32; 64] = $idx;
-        simd_shuffle64($x, $y, IDX)
+        simd_shuffle($x, $y, IDX)
     }};
 }
diff --git a/library/stdarch/crates/core_arch/src/mod.rs b/library/stdarch/crates/core_arch/src/mod.rs
index 20751eeec..2f7af22cb 100644
--- a/library/stdarch/crates/core_arch/src/mod.rs
+++ b/library/stdarch/crates/core_arch/src/mod.rs
@@ -3,6 +3,9 @@
 #[macro_use]
 mod macros;
 
+#[cfg(any(target_arch = "riscv32", target_arch = "riscv64", doc))]
+mod riscv_shared;
+
 #[cfg(any(target_arch = "arm", target_arch = "aarch64", doc))]
 mod arm_shared;
 
@@ -276,10 +279,6 @@ mod aarch64;
 #[doc(cfg(any(target_arch = "arm")))]
 mod arm;
 
-#[cfg(any(target_arch = "riscv32", target_arch = "riscv64", doc))]
-#[doc(cfg(any(target_arch = "riscv32", target_arch = "riscv64")))]
-mod riscv_shared;
-
 #[cfg(any(target_arch = "riscv64", doc))]
 #[doc(cfg(any(target_arch = "riscv64")))]
 mod riscv64;
diff --git a/library/stdarch/crates/core_arch/src/riscv_shared/mod.rs b/library/stdarch/crates/core_arch/src/riscv_shared/mod.rs
index 347735df1..0e35fe1f1 100644
--- a/library/stdarch/crates/core_arch/src/riscv_shared/mod.rs
+++ b/library/stdarch/crates/core_arch/src/riscv_shared/mod.rs
@@ -1,4 +1,7 @@
 //! Shared RISC-V intrinsics
+mod p;
+
+pub use p::*;
 
 use crate::arch::asm;
 
@@ -469,6 +472,17 @@ pub unsafe fn hinval_gvma_vmid(vmid: usize) {
     asm!(".insn r 0x73, 0, 0x33, x0, x0, {}", in(reg) vmid, options(nostack))
 }
 
+/// Invalidate hypervisor translation cache for all virtual machines and guest physical addresses
+///
+/// This instruction invalidates any address-translation cache entries that an
+/// `HFENCE.GVMA` instruction with the same values of `gaddr` and `vmid` would invalidate.
+///
+/// This fence specifies all guest physical addresses and all virtual machines.
+#[inline]
+pub unsafe fn hinval_gvma_all() {
+    asm!(".insn r 0x73, 0, 0x33, x0, x0, x0", options(nostack))
+}
+
 /// Reads the floating-point control and status register `fcsr`
 ///
 /// Register `fcsr` is a 32-bit read/write register that selects the dynamic rounding mode
@@ -574,17 +588,6 @@ pub fn fsflags(value: u32) -> u32 {
     original
 }
 
-/// Invalidate hypervisor translation cache for all virtual machines and guest physical addresses
-///
-/// This instruction invalidates any address-translation cache entries that an
-/// `HFENCE.GVMA` instruction with the same values of `gaddr` and `vmid` would invalidate.
-///
-/// This fence specifies all guest physical addresses and all virtual machines.
-#[inline]
-pub unsafe fn hinval_gvma_all() {
-    asm!(".insn r 0x73, 0, 0x33, x0, x0, x0", options(nostack))
-}
-
 /// `P0` transformation function as is used in the SM3 hash algorithm
 ///
 /// This function is included in `Zksh` extension. It's defined as:
@@ -602,12 +605,10 @@ pub unsafe fn hinval_gvma_all() {
 /// According to RISC-V Cryptography Extensions, Volume I, the execution latency of
 /// this instruction must always be independent from the data it operates on.
 #[inline]
+#[target_feature(enable = "zksh")]
 pub fn sm3p0(x: u32) -> u32 {
     let ans: u32;
-    unsafe {
-        // asm!("sm3p0 {}, {}", out(reg) ans, in(reg) x, options(nomem, nostack))
-        asm!(".insn i 0x13, 0x1, {}, {}, 0x108", out(reg) ans, in(reg) x, options(nomem, nostack))
-    };
+    unsafe { asm!("sm3p0 {}, {}", lateout(reg) ans, in(reg) x, options(pure, nomem, nostack)) };
     ans
 }
 
@@ -634,12 +635,10 @@ pub fn sm3p0(x: u32) -> u32 {
 /// According to RISC-V Cryptography Extensions, Volume I, the execution latency of
 /// this instruction must always be independent from the data it operates on.
 #[inline]
+#[target_feature(enable = "zksh")]
 pub fn sm3p1(x: u32) -> u32 {
     let ans: u32;
-    unsafe {
-        // asm!("sm3p1 {}, {}", out(reg) ans, in(reg) x, options(nomem, nostack))
-        asm!(".insn i 0x13, 0x1, {}, {}, 0x109", out(reg) ans, in(reg) x, options(nomem, nostack))
-    };
+    unsafe { asm!("sm3p1 {}, {}", lateout(reg) ans, in(reg) x, options(pure, nomem, nostack)) };
     ans
 }
 
@@ -674,33 +673,28 @@ pub fn sm3p1(x: u32) -> u32 {
 /// It can be implemented by `sm4ed` instruction like:
 ///
 /// ```no_run
+/// # #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+/// # fn round_function(x0: u32, x1: u32, x2: u32, x3: u32, rk: u32) -> u32 {
+/// # #[cfg(target_arch = "riscv32")] use core::arch::riscv32::sm4ed;
+/// # #[cfg(target_arch = "riscv64")] use core::arch::riscv64::sm4ed;
 /// let a = x1 ^ x2 ^ x3 ^ rk;
 /// let c0 = sm4ed::<0>(x0, a);
 /// let c1 = sm4ed::<1>(c0, a); // c1 represents c[0..=1], etc.
 /// let c2 = sm4ed::<2>(c1, a);
 /// let c3 = sm4ed::<3>(c2, a);
 /// return c3; // c3 represents c[0..=3]
+/// # }
 /// ```
 ///
 /// According to RISC-V Cryptography Extensions, Volume I, the execution latency of
 /// this instruction must always be independent from the data it operates on.
+#[inline]
+#[target_feature(enable = "zksed")]
 pub fn sm4ed<const BS: u8>(x: u32, a: u32) -> u32 {
     static_assert!(BS: u8 where BS <= 3);
     let ans: u32;
-    match BS {
-        0 => unsafe {
-            asm!(".insn r 0x33, 0, 0x18, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) a, options(nomem, nostack))
-        },
-        1 => unsafe {
-            asm!(".insn r 0x33, 0, 0x38, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) a, options(nomem, nostack))
-        },
-        2 => unsafe {
-            asm!(".insn r 0x33, 0, 0x58, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) a, options(nomem, nostack))
-        },
-        3 => unsafe {
-            asm!(".insn r 0x33, 0, 0x78, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) a, options(nomem, nostack))
-        },
-        _ => unreachable!(),
+    unsafe {
+        asm!("sm4ed {}, {}, {}, {}", lateout(reg) ans, in(reg) x, in(reg) a, const BS, options(pure, nomem, nostack))
     };
     ans
 }
@@ -739,33 +733,28 @@ pub fn sm4ed<const BS: u8>(x: u32, a: u32) -> u32 {
 /// Hence, the key schedule operation can be implemented by `sm4ks` instruction like:
 ///
 /// ```no_run
+/// # #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
+/// # fn key_schedule(k0: u32, k1: u32, k2: u32, k3: u32, ck_i: u32) -> u32 {
+/// # #[cfg(target_arch = "riscv32")] use core::arch::riscv32::sm4ks;
+/// # #[cfg(target_arch = "riscv64")] use core::arch::riscv64::sm4ks;
 /// let k = k1 ^ k2 ^ k3 ^ ck_i;
 /// let c0 = sm4ks::<0>(k0, k);
 /// let c1 = sm4ks::<1>(c0, k); // c1 represents c[0..=1], etc.
 /// let c2 = sm4ks::<2>(c1, k);
 /// let c3 = sm4ks::<3>(c2, k);
 /// return c3; // c3 represents c[0..=3]
+/// # }
 /// ```
 ///
 /// According to RISC-V Cryptography Extensions, Volume I, the execution latency of
 /// this instruction must always be independent from the data it operates on.
+#[inline]
+#[target_feature(enable = "zksed")]
 pub fn sm4ks<const BS: u8>(x: u32, k: u32) -> u32 {
     static_assert!(BS: u8 where BS <= 3);
     let ans: u32;
-    match BS {
-        0 => unsafe {
-            asm!(".insn r 0x33, 0, 0x1A, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) k, options(nomem, nostack))
-        },
-        1 => unsafe {
-            asm!(".insn r 0x33, 0, 0x3A, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) k, options(nomem, nostack))
-        },
-        2 => unsafe {
-            asm!(".insn r 0x33, 0, 0x5A, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) k, options(nomem, nostack))
-        },
-        3 => unsafe {
-            asm!(".insn r 0x33, 0, 0x7A, {}, {}, {}", out(reg) ans, in(reg) x, in(reg) k, options(nomem, nostack))
-        },
-        _ => unreachable!(),
+    unsafe {
+        asm!("sm4ks {}, {}, {}, {}", lateout(reg) ans, in(reg) x, in(reg) k, const BS, options(pure, nomem, nostack))
     };
     ans
 }
diff --git a/library/stdarch/crates/core_arch/src/riscv_shared/p.rs b/library/stdarch/crates/core_arch/src/riscv_shared/p.rs
new file mode 100644
index 000000000..a26044aee
--- /dev/null
+++ b/library/stdarch/crates/core_arch/src/riscv_shared/p.rs
@@ -0,0 +1,1061 @@
+//! RISC-V Packed SIMD intrinsics; shared part.
+//!
+//! RV64 only part is placed in riscv64 folder.
+use crate::arch::asm;
+
+/// Adds packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn add16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x20, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the sum of packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn radd16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x00, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the sum of packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn uradd16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x10, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kadd16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x08, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukadd16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x18, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn sub16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x21, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the subtraction result of packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn rsub16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x01, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the subtraction result of packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn ursub16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x11, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn ksub16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x09, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn uksub16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x19, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross adds and subtracts packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn cras16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x22, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross halves of adds and subtracts packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn rcras16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x02, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross halves of adds and subtracts packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn urcras16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x12, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross adds and subtracts packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kcras16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross adds and subtracts packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukcras16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross subtracts and adds packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn crsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x23, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross halves of subtracts and adds packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn rcrsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x03, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross halves of subtracts and adds packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn urcrsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x13, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross subtracts and adds packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kcrsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Cross subtracts and adds packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukcrsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight adds and subtracts packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn stas16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x7A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight halves of adds and subtracts packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn rstas16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x5A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight halves of adds and subtracts packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn urstas16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x6A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight adds and subtracts packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kstas16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x62, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight adds and subtracts packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukstas16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x72, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight subtracts and adds packed 16-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn stsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x7B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight halves of subtracts and adds packed 16-bit signed numbers, dropping least bits
+#[inline]
+pub fn rstsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x5B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight halves of subtracts and adds packed 16-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn urstsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x6B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight subtracts and adds packed 16-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kstsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x63, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Straight subtracts and adds packed 16-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukstsa16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x73, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds packed 8-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn add8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x24, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the sum of packed 8-bit signed numbers, dropping least bits
+#[inline]
+pub fn radd8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x04, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the sum of packed 8-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn uradd8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x14, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds packed 8-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn kadd8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0C, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds packed 8-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn ukadd8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1C, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 8-bit signed numbers, discarding overflow bits
+#[inline]
+pub fn sub8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x25, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the subtraction result of packed 8-bit signed numbers, dropping least bits
+#[inline]
+pub fn rsub8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x05, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Halves the subtraction result of packed 8-bit unsigned numbers, dropping least bits
+#[inline]
+pub fn ursub8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x15, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 8-bit signed numbers, saturating at the numeric bounds
+#[inline]
+pub fn ksub8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0D, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts packed 8-bit unsigned numbers, saturating at the numeric bounds
+#[inline]
+pub fn uksub8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1D, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Arithmetic right shift packed 16-bit elements without rounding up
+#[inline]
+pub fn sra16(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x28, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Arithmetic right shift packed 16-bit elements with rounding up
+#[inline]
+pub fn sra16u(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x30, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical right shift packed 16-bit elements without rounding up
+#[inline]
+pub fn srl16(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x29, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical right shift packed 16-bit elements with rounding up
+#[inline]
+pub fn srl16u(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x31, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical left shift packed 16-bit elements, discarding overflow bits
+#[inline]
+pub fn sll16(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical left shift packed 16-bit elements, saturating at the numeric bounds
+#[inline]
+pub fn ksll16(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x32, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical saturating left then arithmetic right shift packed 16-bit elements
+#[inline]
+pub fn kslra16(a: usize, b: i32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical saturating left then arithmetic right shift packed 16-bit elements
+#[inline]
+pub fn kslra16u(a: usize, b: i32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x33, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Arithmetic right shift packed 8-bit elements without rounding up
+#[inline]
+pub fn sra8(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2C, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Arithmetic right shift packed 8-bit elements with rounding up
+#[inline]
+pub fn sra8u(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x34, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical right shift packed 8-bit elements without rounding up
+#[inline]
+pub fn srl8(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2D, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical right shift packed 8-bit elements with rounding up
+#[inline]
+pub fn srl8u(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x35, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical left shift packed 8-bit elements, discarding overflow bits
+#[inline]
+pub fn sll8(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2E, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical left shift packed 8-bit elements, saturating at the numeric bounds
+#[inline]
+pub fn ksll8(a: usize, b: u32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x36, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical saturating left then arithmetic right shift packed 8-bit elements
+#[inline]
+pub fn kslra8(a: usize, b: i32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x2F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Logical saturating left then arithmetic right shift packed 8-bit elements
+#[inline]
+pub fn kslra8u(a: usize, b: i32) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x37, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare equality for packed 16-bit elements
+#[inline]
+pub fn cmpeq16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x26, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 16-bit packed signed integers are less than the others
+#[inline]
+pub fn scmplt16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x06, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 16-bit packed signed integers are less than or equal to the others
+#[inline]
+pub fn scmple16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0E, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 16-bit packed unsigned integers are less than the others
+#[inline]
+pub fn ucmplt16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x16, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 16-bit packed unsigned integers are less than or equal to the others
+#[inline]
+pub fn ucmple16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1E, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare equality for packed 8-bit elements
+#[inline]
+pub fn cmpeq8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x27, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 8-bit packed signed integers are less than the others
+#[inline]
+pub fn scmplt8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x07, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 8-bit packed signed integers are less than or equal to the others
+#[inline]
+pub fn scmple8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 8-bit packed unsigned integers are less than the others
+#[inline]
+pub fn ucmplt8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x17, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Compare whether 8-bit packed unsigned integers are less than or equal to the others
+#[inline]
+pub fn ucmple8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x1F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get minimum values from 16-bit packed signed integers
+#[inline]
+pub fn smin16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x40, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get minimum values from 16-bit packed unsigned integers
+#[inline]
+pub fn umin16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x48, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get maximum values from 16-bit packed signed integers
+#[inline]
+pub fn smax16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x41, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get maximum values from 16-bit packed unsigned integers
+#[inline]
+pub fn umax16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x49, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/* todo: sclip16, uclip16 */
+
+/// Compute the absolute value of packed 16-bit signed integers
+#[inline]
+pub fn kabs16(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAD1", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of redundant sign bits of the packed 16-bit elements
+#[inline]
+pub fn clrs16(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAE8", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of leading zero bits of the packed 16-bit elements
+#[inline]
+pub fn clz16(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAE9", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Swap the 16-bit halfwords within each 32-bit word of a register
+#[inline]
+pub fn swap16(a: usize) -> usize {
+    let value: usize;
+    // this instruction is an alias for `pkbt rd, rs1, rs1`.
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x0F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get minimum values from 8-bit packed signed integers
+#[inline]
+pub fn smin8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x44, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get minimum values from 8-bit packed unsigned integers
+#[inline]
+pub fn umin8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x4C, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get maximum values from 8-bit packed signed integers
+#[inline]
+pub fn smax8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x45, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Get maximum values from 8-bit packed unsigned integers
+#[inline]
+pub fn umax8(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x4D, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/* todo: sclip8, uclip8 */
+
+/// Compute the absolute value of packed 8-bit signed integers
+#[inline]
+pub fn kabs8(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAD0", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of redundant sign bits of the packed 8-bit elements
+#[inline]
+pub fn clrs8(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAE0", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of leading zero bits of the packed 8-bit elements
+#[inline]
+pub fn clz8(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAE1", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Swap the 8-bit bytes within each 16-bit halfword of a register.
+#[inline]
+pub fn swap8(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAD8", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack first and zeroth into two 16-bit signed halfwords in each 32-bit chunk
+#[inline]
+pub fn sunpkd810(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAC8", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack second and zeroth into two 16-bit signed halfwords in each 32-bit chunk
+#[inline]
+pub fn sunpkd820(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAC9", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and zeroth into two 16-bit signed halfwords in each 32-bit chunk
+#[inline]
+pub fn sunpkd830(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACA", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and first into two 16-bit signed halfwords in each 32-bit chunk
+#[inline]
+pub fn sunpkd831(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACB", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and second into two 16-bit signed halfwords in each 32-bit chunk
+#[inline]
+pub fn sunpkd832(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAD3", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack first and zeroth into two 16-bit unsigned halfwords in each 32-bit chunk
+#[inline]
+pub fn zunpkd810(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACC", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack second and zeroth into two 16-bit unsigned halfwords in each 32-bit chunk
+#[inline]
+pub fn zunpkd820(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACD", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and zeroth into two 16-bit unsigned halfwords in each 32-bit chunk
+#[inline]
+pub fn zunpkd830(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACE", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and first into two 16-bit unsigned halfwords in each 32-bit chunk
+#[inline]
+pub fn zunpkd831(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xACF", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Unpack third and second into two 16-bit unsigned halfwords in each 32-bit chunk
+#[inline]
+pub fn zunpkd832(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAD7", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+// todo: pkbb16, pktt16
+
+/// Pack two 16-bit data from bottom and top half from 32-bit chunks
+#[inline]
+pub fn pkbt16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x0F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Pack two 16-bit data from top and bottom half from 32-bit chunks
+#[inline]
+pub fn pktb16(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x1F, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of redundant sign bits of the packed 32-bit elements
+#[inline]
+pub fn clrs32(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAF8", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Count the number of leading zero bits of the packed 32-bit elements
+#[inline]
+pub fn clz32(a: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn i 0x77, 0x0, {}, {}, 0xAF9", lateout(reg) value, in(reg) a, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Calculate the sum of absolute difference of unsigned 8-bit data elements
+#[inline]
+pub fn pbsad(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x7E, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Calculate and accumulate the sum of absolute difference of unsigned 8-bit data elements
+#[inline]
+pub fn pbsada(t: usize, a: usize, b: usize) -> usize {
+    let mut value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x7F, {}, {}, {}", inlateout(reg) t => value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Multiply signed 8-bit elements and add 16-bit elements on results for packed 32-bit chunks
+#[inline]
+pub fn smaqa(t: usize, a: usize, b: usize) -> usize {
+    let mut value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x64, {}, {}, {}", inlateout(reg) t => value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Multiply unsigned 8-bit elements and add 16-bit elements on results for packed 32-bit chunks
+#[inline]
+pub fn umaqa(t: usize, a: usize, b: usize) -> usize {
+    let mut value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x66, {}, {}, {}", inlateout(reg) t => value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Multiply signed to unsigned 8-bit and add 16-bit elements on results for packed 32-bit chunks
+#[inline]
+pub fn smaqasu(t: usize, a: usize, b: usize) -> usize {
+    let mut value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x0, 0x65, {}, {}, {}", inlateout(reg) t => value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds signed lower 16-bit content of two registers with Q15 saturation
+#[inline]
+pub fn kaddh(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x02, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts signed lower 16-bit content of two registers with Q15 saturation
+#[inline]
+pub fn ksubh(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x03, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Adds signed lower 16-bit content of two registers with U16 saturation
+#[inline]
+pub fn ukaddh(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x0A, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
+
+/// Subtracts signed lower 16-bit content of two registers with U16 saturation
+#[inline]
+pub fn uksubh(a: usize, b: usize) -> usize {
+    let value: usize;
+    unsafe {
+        asm!(".insn r 0x77, 0x1, 0x0B, {}, {}, {}", lateout(reg) value, in(reg) a, in(reg) b, options(pure, nomem, nostack))
+    }
+    value
+}
diff --git a/library/stdarch/crates/core_arch/src/simd_llvm.rs b/library/stdarch/crates/core_arch/src/simd_llvm.rs
index 1970e5c69..decdecaaf 100644
--- a/library/stdarch/crates/core_arch/src/simd_llvm.rs
+++ b/library/stdarch/crates/core_arch/src/simd_llvm.rs
@@ -9,13 +9,7 @@ extern "platform-intrinsic" {
     pub fn simd_gt<T, U>(x: T, y: T) -> U;
     pub fn simd_ge<T, U>(x: T, y: T) -> U;
 
-    pub fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
-    pub fn simd_shuffle4<T, U>(x: T, y: T, idx: [u32; 4]) -> U;
-    pub fn simd_shuffle8<T, U>(x: T, y: T, idx: [u32; 8]) -> U;
-    pub fn simd_shuffle16<T, U>(x: T, y: T, idx: [u32; 16]) -> U;
-    pub fn simd_shuffle32<T, U>(x: T, y: T, idx: [u32; 32]) -> U;
-    pub fn simd_shuffle64<T, U>(x: T, y: T, idx: [u32; 64]) -> U;
-    pub fn simd_shuffle128<T, U>(x: T, y: T, idx: [u32; 128]) -> U;
+    pub fn simd_shuffle<T, U, V>(x: T, y: T, idx: U) -> V;
 
     #[rustc_const_unstable(feature = "const_simd_insert", issue = "none")]
     pub fn simd_insert<T, U>(x: T, idx: u32, val: U) -> T;
diff --git a/library/stdarch/crates/core_arch/src/x86/avx2.rs b/library/stdarch/crates/core_arch/src/x86/avx2.rs
index 24f9c0301..16add3dbb 100644
--- a/library/stdarch/crates/core_arch/src/x86/avx2.rs
+++ b/library/stdarch/crates/core_arch/src/x86/avx2.rs
@@ -2001,7 +2001,7 @@ pub unsafe fn _mm256_min_epu8(a: __m256i, b: __m256i) -> __m256i {
 #[cfg_attr(test, assert_instr(vpmovmskb))]
 #[stable(feature = "simd_x86", since = "1.27.0")]
 pub unsafe fn _mm256_movemask_epi8(a: __m256i) -> i32 {
-    pmovmskb(a.as_i8x32())
+    simd_bitmask::<_, u32>(a.as_i8x32()) as i32
 }
 
 /// Computes the sum of absolute differences (SADs) of quadruplets of unsigned
@@ -3642,8 +3642,6 @@ extern "C" {
     fn pminud(a: u32x8, b: u32x8) -> u32x8;
     #[link_name = "llvm.x86.avx2.pminu.b"]
     fn pminub(a: u8x32, b: u8x32) -> u8x32;
-    #[link_name = "llvm.x86.avx2.pmovmskb"]
-    fn pmovmskb(a: i8x32) -> i32;
     #[link_name = "llvm.x86.avx2.mpsadbw"]
     fn mpsadbw(a: u8x32, b: u8x32, imm8: i32) -> u16x16;
     #[link_name = "llvm.x86.avx2.pmulhu.w"]
diff --git a/library/stdarch/crates/core_arch/src/x86/cpuid.rs b/library/stdarch/crates/core_arch/src/x86/cpuid.rs
index 6b90295ef..2624e8bdf 100644
--- a/library/stdarch/crates/core_arch/src/x86/cpuid.rs
+++ b/library/stdarch/crates/core_arch/src/x86/cpuid.rs
@@ -62,27 +62,27 @@ pub unsafe fn __cpuid_count(leaf: u32, sub_leaf: u32) -> CpuidResult {
     #[cfg(target_arch = "x86")]
     {
         asm!(
-            "movl %ebx, {0}",
+            "mov {0}, ebx",
             "cpuid",
-            "xchgl %ebx, {0}",
-            lateout(reg) ebx,
-            inlateout("eax") leaf => eax,
-            inlateout("ecx") sub_leaf => ecx,
-            lateout("edx") edx,
-            options(nostack, preserves_flags, att_syntax),
+            "xchg {0}, ebx",
+            out(reg) ebx,
+            inout("eax") leaf => eax,
+            inout("ecx") sub_leaf => ecx,
+            out("edx") edx,
+            options(nostack, preserves_flags),
         );
     }
     #[cfg(target_arch = "x86_64")]
     {
         asm!(
-            "movq %rbx, {0:r}",
+            "mov {0:r}, rbx",
             "cpuid",
-            "xchgq %rbx, {0:r}",
-            lateout(reg) ebx,
-            inlateout("eax") leaf => eax,
-            inlateout("ecx") sub_leaf => ecx,
-            lateout("edx") edx,
-            options(nostack, preserves_flags, att_syntax),
+            "xchg {0:r}, rbx",
+            out(reg) ebx,
+            inout("eax") leaf => eax,
+            inout("ecx") sub_leaf => ecx,
+            out("edx") edx,
+            options(nostack, preserves_flags),
         );
     }
     CpuidResult { eax, ebx, ecx, edx }
diff --git a/library/stdarch/crates/core_arch/src/x86/mod.rs b/library/stdarch/crates/core_arch/src/x86/mod.rs
index 547bfe67d..6b50e95b2 100644
--- a/library/stdarch/crates/core_arch/src/x86/mod.rs
+++ b/library/stdarch/crates/core_arch/src/x86/mod.rs
@@ -306,7 +306,7 @@ types! {
 
     /// 256-bit wide set of 16 'u16' types, x86-specific
     ///
-    /// This type is the same as the `__m128bh` type defined by Intel,
+    /// This type is the same as the `__m256bh` type defined by Intel,
     /// representing a 256-bit SIMD register which internally is consisted of
     /// 16 packed `u16` instances. Its purpose is for bf16 related intrinsic
     /// implementations.
@@ -317,7 +317,7 @@ types! {
 
     /// 512-bit wide set of 32 'u16' types, x86-specific
     ///
-    /// This type is the same as the `__m128bh` type defined by Intel,
+    /// This type is the same as the `__m512bh` type defined by Intel,
     /// representing a 512-bit SIMD register which internally is consisted of
     /// 32 packed `u16` instances. Its purpose is for bf16 related intrinsic
     /// implementations.
diff --git a/library/stdarch/crates/core_arch/src/x86/sse2.rs b/library/stdarch/crates/core_arch/src/x86/sse2.rs
index d82b8641f..3e79b3539 100644
--- a/library/stdarch/crates/core_arch/src/x86/sse2.rs
+++ b/library/stdarch/crates/core_arch/src/x86/sse2.rs
@@ -1378,7 +1378,7 @@ pub unsafe fn _mm_insert_epi16<const IMM8: i32>(a: __m128i, i: i32) -> __m128i {
 #[cfg_attr(test, assert_instr(pmovmskb))]
 #[stable(feature = "simd_x86", since = "1.27.0")]
 pub unsafe fn _mm_movemask_epi8(a: __m128i) -> i32 {
-    pmovmskb(a.as_i8x16())
+    simd_bitmask::<_, u16>(a.as_i8x16()) as u32 as i32
 }
 
 /// Shuffles 32-bit integers in `a` using the control in `IMM8`.
@@ -2856,8 +2856,6 @@ extern "C" {
     fn packssdw(a: i32x4, b: i32x4) -> i16x8;
     #[link_name = "llvm.x86.sse2.packuswb.128"]
     fn packuswb(a: i16x8, b: i16x8) -> u8x16;
-    #[link_name = "llvm.x86.sse2.pmovmskb.128"]
-    fn pmovmskb(a: i8x16) -> i32;
     #[link_name = "llvm.x86.sse2.max.sd"]
     fn maxsd(a: __m128d, b: __m128d) -> __m128d;
     #[link_name = "llvm.x86.sse2.max.pd"]
diff --git a/library/stdarch/crates/core_arch/src/x86/sse3.rs b/library/stdarch/crates/core_arch/src/x86/sse3.rs
index ab0dd38fe..61f8a4e78 100644
--- a/library/stdarch/crates/core_arch/src/x86/sse3.rs
+++ b/library/stdarch/crates/core_arch/src/x86/sse3.rs
@@ -1,11 +1,7 @@
 //! Streaming SIMD Extensions 3 (SSE3)
 
 use crate::{
-    core_arch::{
-        simd::*,
-        simd_llvm::{simd_shuffle2, simd_shuffle4},
-        x86::*,
-    },
+    core_arch::{simd::*, simd_llvm::simd_shuffle, x86::*},
     mem::transmute,
 };
 
diff --git a/library/stdarch/crates/std_detect/Cargo.toml b/library/stdarch/crates/std_detect/Cargo.toml
index 1ca0d9c5d..3a482564e 100644
--- a/library/stdarch/crates/std_detect/Cargo.toml
+++ b/library/stdarch/crates/std_detect/Cargo.toml
@@ -22,7 +22,7 @@ maintenance = { status = "experimental" }
 
 [dependencies]
 libc = { version = "0.2", optional = true, default-features = false }
-cfg-if = "0.1.10"
+cfg-if = "1.0.0"
 
 # When built as part of libstd
 core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
diff --git a/library/stdarch/crates/std_detect/src/detect/os/linux/aarch64.rs b/library/stdarch/crates/std_detect/src/detect/os/linux/aarch64.rs
index b6a2e5218..6c79ba86d 100644
--- a/library/stdarch/crates/std_detect/src/detect/os/linux/aarch64.rs
+++ b/library/stdarch/crates/std_detect/src/detect/os/linux/aarch64.rs
@@ -23,58 +23,62 @@ pub(crate) fn detect_features() -> cache::Initializer {
 /// The names match those used for cpuinfo.
 ///
 /// [hwcap]: https://github.com/torvalds/linux/blob/master/arch/arm64/include/uapi/asm/hwcap.h
+#[derive(Debug, Default, PartialEq)]
 struct AtHwcap {
-    fp: bool,    // 0
-    asimd: bool, // 1
-    // evtstrm: bool, // 2 No LLVM support
-    aes: bool,     // 3
-    pmull: bool,   // 4
-    sha1: bool,    // 5
-    sha2: bool,    // 6
-    crc32: bool,   // 7
-    atomics: bool, // 8
-    fphp: bool,    // 9
-    asimdhp: bool, // 10
-    // cpuid: bool, // 11 No LLVM support
-    asimdrdm: bool, // 12
-    jscvt: bool,    // 13
-    fcma: bool,     // 14
-    lrcpc: bool,    // 15
-    dcpop: bool,    // 16
-    sha3: bool,     // 17
-    sm3: bool,      // 18
-    sm4: bool,      // 19
-    asimddp: bool,  // 20
-    sha512: bool,   // 21
-    sve: bool,      // 22
-    fhm: bool,      // 23
-    dit: bool,      // 24
-    uscat: bool,    // 25
-    ilrcpc: bool,   // 26
-    flagm: bool,    // 27
-    ssbs: bool,     // 28
-    sb: bool,       // 29
-    paca: bool,     // 30
-    pacg: bool,     // 31
-    dcpodp: bool,   // 32
-    sve2: bool,     // 33
-    sveaes: bool,   // 34
-    // svepmull: bool, // 35 No LLVM support
-    svebitperm: bool, // 36
-    svesha3: bool,    // 37
-    svesm4: bool,     // 38
-    // flagm2: bool, // 39 No LLVM support
-    frint: bool, // 40
-    // svei8mm: bool, // 41 See i8mm feature
-    svef32mm: bool, // 42
-    svef64mm: bool, // 43
-    // svebf16: bool, // 44 See bf16 feature
-    i8mm: bool, // 45
-    bf16: bool, // 46
-    // dgh: bool, // 47 No LLVM support
-    rng: bool, // 48
-    bti: bool, // 49
-    mte: bool, // 50
+    // AT_HWCAP
+    fp: bool,
+    asimd: bool,
+    // evtstrm: No LLVM support.
+    aes: bool,
+    pmull: bool,
+    sha1: bool,
+    sha2: bool,
+    crc32: bool,
+    atomics: bool,
+    fphp: bool,
+    asimdhp: bool,
+    // cpuid: No LLVM support.
+    asimdrdm: bool,
+    jscvt: bool,
+    fcma: bool,
+    lrcpc: bool,
+    dcpop: bool,
+    sha3: bool,
+    sm3: bool,
+    sm4: bool,
+    asimddp: bool,
+    sha512: bool,
+    sve: bool,
+    fhm: bool,
+    dit: bool,
+    uscat: bool,
+    ilrcpc: bool,
+    flagm: bool,
+    ssbs: bool,
+    sb: bool,
+    paca: bool,
+    pacg: bool,
+
+    // AT_HWCAP2
+    dcpodp: bool,
+    sve2: bool,
+    sveaes: bool,
+    // svepmull: No LLVM support.
+    svebitperm: bool,
+    svesha3: bool,
+    svesm4: bool,
+    // flagm2: No LLVM support.
+    frint: bool,
+    // svei8mm: See i8mm feature.
+    svef32mm: bool,
+    svef64mm: bool,
+    // svebf16: See bf16 feature.
+    i8mm: bool,
+    bf16: bool,
+    // dgh: No LLVM support.
+    rng: bool,
+    bti: bool,
+    mte: bool,
 }
 
 impl From<auxvec::AuxVec> for AtHwcap {
@@ -113,25 +117,25 @@ impl From<auxvec::AuxVec> for AtHwcap {
             sb: bit::test(auxv.hwcap, 29),
             paca: bit::test(auxv.hwcap, 30),
             pacg: bit::test(auxv.hwcap, 31),
-            dcpodp: bit::test(auxv.hwcap, 32),
-            sve2: bit::test(auxv.hwcap, 33),
-            sveaes: bit::test(auxv.hwcap, 34),
-            // svepmull: bit::test(auxv.hwcap, 35),
-            svebitperm: bit::test(auxv.hwcap, 36),
-            svesha3: bit::test(auxv.hwcap, 37),
-            svesm4: bit::test(auxv.hwcap, 38),
-            // flagm2: bit::test(auxv.hwcap, 39),
-            frint: bit::test(auxv.hwcap, 40),
-            // svei8mm: bit::test(auxv.hwcap, 41),
-            svef32mm: bit::test(auxv.hwcap, 42),
-            svef64mm: bit::test(auxv.hwcap, 43),
-            // svebf16: bit::test(auxv.hwcap, 44),
-            i8mm: bit::test(auxv.hwcap, 45),
-            bf16: bit::test(auxv.hwcap, 46),
-            // dgh: bit::test(auxv.hwcap, 47),
-            rng: bit::test(auxv.hwcap, 48),
-            bti: bit::test(auxv.hwcap, 49),
-            mte: bit::test(auxv.hwcap, 50),
+            dcpodp: bit::test(auxv.hwcap2, 0),
+            sve2: bit::test(auxv.hwcap2, 1),
+            sveaes: bit::test(auxv.hwcap2, 2),
+            // svepmull: bit::test(auxv.hwcap2, 3),
+            svebitperm: bit::test(auxv.hwcap2, 4),
+            svesha3: bit::test(auxv.hwcap2, 5),
+            svesm4: bit::test(auxv.hwcap2, 6),
+            // flagm2: bit::test(auxv.hwcap2, 7),
+            frint: bit::test(auxv.hwcap2, 8),
+            // svei8mm: bit::test(auxv.hwcap2, 9),
+            svef32mm: bit::test(auxv.hwcap2, 10),
+            svef64mm: bit::test(auxv.hwcap2, 11),
+            // svebf16: bit::test(auxv.hwcap2, 12),
+            i8mm: bit::test(auxv.hwcap2, 13),
+            bf16: bit::test(auxv.hwcap2, 14),
+            // dgh: bit::test(auxv.hwcap2, 15),
+            rng: bit::test(auxv.hwcap2, 16),
+            bti: bit::test(auxv.hwcap2, 17),
+            mte: bit::test(auxv.hwcap2, 18),
         }
     }
 }
@@ -288,3 +292,86 @@ impl AtHwcap {
         value
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[cfg(feature = "std_detect_file_io")]
+    mod auxv_from_file {
+        use super::auxvec::auxv_from_file;
+        use super::*;
+        // The baseline hwcaps used in the (artificial) auxv test files.
+        fn baseline_hwcaps() -> AtHwcap {
+            AtHwcap {
+                fp: true,
+                asimd: true,
+                aes: true,
+                pmull: true,
+                sha1: true,
+                sha2: true,
+                crc32: true,
+                atomics: true,
+                fphp: true,
+                asimdhp: true,
+                asimdrdm: true,
+                lrcpc: true,
+                dcpop: true,
+                asimddp: true,
+                ssbs: true,
+                ..AtHwcap::default()
+            }
+        }
+
+        #[test]
+        fn linux_empty_hwcap2_aarch64() {
+            let file = concat!(
+                env!("CARGO_MANIFEST_DIR"),
+                "/src/detect/test_data/linux-empty-hwcap2-aarch64.auxv"
+            );
+            println!("file: {}", file);
+            let v = auxv_from_file(file).unwrap();
+            println!("HWCAP : 0x{:0x}", v.hwcap);
+            println!("HWCAP2: 0x{:0x}", v.hwcap2);
+            assert_eq!(AtHwcap::from(v), baseline_hwcaps());
+        }
+        #[test]
+        fn linux_no_hwcap2_aarch64() {
+            let file = concat!(
+                env!("CARGO_MANIFEST_DIR"),
+                "/src/detect/test_data/linux-no-hwcap2-aarch64.auxv"
+            );
+            println!("file: {}", file);
+            let v = auxv_from_file(file).unwrap();
+            println!("HWCAP : 0x{:0x}", v.hwcap);
+            println!("HWCAP2: 0x{:0x}", v.hwcap2);
+            assert_eq!(AtHwcap::from(v), baseline_hwcaps());
+        }
+        #[test]
+        fn linux_hwcap2_aarch64() {
+            let file = concat!(
+                env!("CARGO_MANIFEST_DIR"),
+                "/src/detect/test_data/linux-hwcap2-aarch64.auxv"
+            );
+            println!("file: {}", file);
+            let v = auxv_from_file(file).unwrap();
+            println!("HWCAP : 0x{:0x}", v.hwcap);
+            println!("HWCAP2: 0x{:0x}", v.hwcap2);
+            assert_eq!(
+                AtHwcap::from(v),
+                AtHwcap {
+                    // Some other HWCAP bits.
+                    paca: true,
+                    pacg: true,
+                    // HWCAP2-only bits.
+                    dcpodp: true,
+                    frint: true,
+                    rng: true,
+                    bti: true,
+                    mte: true,
+                    ..baseline_hwcaps()
+                }
+            );
+        }
+    }
+}
diff --git a/library/stdarch/crates/std_detect/src/detect/os/linux/auxvec.rs b/library/stdarch/crates/std_detect/src/detect/os/linux/auxvec.rs
index e6447d0cd..c903903bd 100644
--- a/library/stdarch/crates/std_detect/src/detect/os/linux/auxvec.rs
+++ b/library/stdarch/crates/std_detect/src/detect/os/linux/auxvec.rs
@@ -7,6 +7,7 @@ pub(crate) const AT_NULL: usize = 0;
 pub(crate) const AT_HWCAP: usize = 16;
 /// Key to access the CPU Hardware capabilities 2 bitfield.
 #[cfg(any(
+    target_arch = "aarch64",
     target_arch = "arm",
     target_arch = "powerpc",
     target_arch = "powerpc64"
@@ -21,6 +22,7 @@ pub(crate) const AT_HWCAP2: usize = 26;
 pub(crate) struct AuxVec {
     pub hwcap: usize,
     #[cfg(any(
+        target_arch = "aarch64",
         target_arch = "arm",
         target_arch = "powerpc",
         target_arch = "powerpc64"
@@ -64,13 +66,14 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
         if let Ok(hwcap) = getauxval(AT_HWCAP) {
             // Targets with only AT_HWCAP:
             #[cfg(any(
-                target_arch = "aarch64",
                 target_arch = "riscv32",
                 target_arch = "riscv64",
                 target_arch = "mips",
                 target_arch = "mips64"
             ))]
             {
+                // Zero could indicate that no features were detected, but it's also used to
+                // indicate an error. In either case, try the fallback.
                 if hwcap != 0 {
                     return Ok(AuxVec { hwcap });
                 }
@@ -78,13 +81,18 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
 
             // Targets with AT_HWCAP and AT_HWCAP2:
             #[cfg(any(
+                target_arch = "aarch64",
                 target_arch = "arm",
                 target_arch = "powerpc",
                 target_arch = "powerpc64"
             ))]
             {
                 if let Ok(hwcap2) = getauxval(AT_HWCAP2) {
-                    if hwcap != 0 && hwcap2 != 0 {
+                    // Zero could indicate that no features were detected, but it's also used to
+                    // indicate an error. In particular, on many platforms AT_HWCAP2 will be
+                    // legitimately zero, since it contains the most recent feature flags. Use the
+                    // fallback only if no features were detected at all.
+                    if hwcap != 0 || hwcap2 != 0 {
                         return Ok(AuxVec { hwcap, hwcap2 });
                     }
                 }
@@ -97,7 +105,6 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
     {
         // Targets with only AT_HWCAP:
         #[cfg(any(
-            target_arch = "aarch64",
             target_arch = "riscv32",
             target_arch = "riscv64",
             target_arch = "mips",
@@ -105,6 +112,8 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
         ))]
         {
             let hwcap = unsafe { libc::getauxval(AT_HWCAP as libc::c_ulong) as usize };
+            // Zero could indicate that no features were detected, but it's also used to indicate
+            // an error. In either case, try the fallback.
             if hwcap != 0 {
                 return Ok(AuxVec { hwcap });
             }
@@ -112,6 +121,7 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
 
         // Targets with AT_HWCAP and AT_HWCAP2:
         #[cfg(any(
+            target_arch = "aarch64",
             target_arch = "arm",
             target_arch = "powerpc",
             target_arch = "powerpc64"
@@ -119,7 +129,11 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
         {
             let hwcap = unsafe { libc::getauxval(AT_HWCAP as libc::c_ulong) as usize };
             let hwcap2 = unsafe { libc::getauxval(AT_HWCAP2 as libc::c_ulong) as usize };
-            if hwcap != 0 && hwcap2 != 0 {
+            // Zero could indicate that no features were detected, but it's also used to indicate
+            // an error. In particular, on many platforms AT_HWCAP2 will be legitimately zero,
+            // since it contains the most recent feature flags. Use the fallback only if no
+            // features were detected at all.
+            if hwcap != 0 || hwcap2 != 0 {
                 return Ok(AuxVec { hwcap, hwcap2 });
             }
         }
@@ -158,7 +172,7 @@ fn getauxval(key: usize) -> Result<usize, ()> {
 /// Tries to read the auxiliary vector from the `file`. If this fails, this
 /// function returns `Err`.
 #[cfg(feature = "std_detect_file_io")]
-fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
+pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
     let file = super::read_file(file)?;
 
     // See <https://github.com/torvalds/linux/blob/v3.19/include/uapi/linux/auxvec.h>.
@@ -181,7 +195,6 @@ fn auxv_from_file(file: &str) -> Result<AuxVec, ()> {
 fn auxv_from_buf(buf: &[usize; 64]) -> Result<AuxVec, ()> {
     // Targets with only AT_HWCAP:
     #[cfg(any(
-        target_arch = "aarch64",
         target_arch = "riscv32",
         target_arch = "riscv64",
         target_arch = "mips",
@@ -198,23 +211,25 @@ fn auxv_from_buf(buf: &[usize; 64]) -> Result<AuxVec, ()> {
     }
     // Targets with AT_HWCAP and AT_HWCAP2:
     #[cfg(any(
+        target_arch = "aarch64",
         target_arch = "arm",
         target_arch = "powerpc",
         target_arch = "powerpc64"
     ))]
     {
         let mut hwcap = None;
-        let mut hwcap2 = None;
+        // For some platforms, AT_HWCAP2 was added recently, so let it default to zero.
+        let mut hwcap2 = 0;
         for el in buf.chunks(2) {
             match el[0] {
                 AT_NULL => break,
                 AT_HWCAP => hwcap = Some(el[1]),
-                AT_HWCAP2 => hwcap2 = Some(el[1]),
+                AT_HWCAP2 => hwcap2 = el[1],
                 _ => (),
             }
         }
 
-        if let (Some(hwcap), Some(hwcap2)) = (hwcap, hwcap2) {
+        if let Some(hwcap) = hwcap {
             return Ok(AuxVec { hwcap, hwcap2 });
         }
     }
@@ -256,7 +271,6 @@ mod tests {
     // FIXME: on mips/mips64 getauxval returns 0, and /proc/self/auxv
     // does not always contain the AT_HWCAP key under qemu.
     #[cfg(any(
-        target_arch = "aarch64",
         target_arch = "arm",
         target_arch = "powerpc",
         target_arch = "powerpc64"
@@ -271,6 +285,7 @@ mod tests {
 
         // Targets with AT_HWCAP and AT_HWCAP2:
         #[cfg(any(
+            target_arch = "aarch64",
             target_arch = "arm",
             target_arch = "powerpc",
             target_arch = "powerpc64"
@@ -305,24 +320,31 @@ mod tests {
             }
 
             #[test]
-            #[should_panic]
             fn linux_macos_vb() {
                 let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/macos-virtualbox-linux-x86-4850HQ.auxv");
                 println!("file: {}", file);
+                // The file contains HWCAP but not HWCAP2. In that case, we treat HWCAP2 as zero.
                 let v = auxv_from_file(file).unwrap();
-                // this file is incomplete (contains hwcap but not hwcap2), we
-                // want to fall back to /proc/cpuinfo in this case, so
-                // reading should fail. assert_eq!(v.hwcap, 126614527);
-                // assert_eq!(v.hwcap2, 0);
-                let _ = v;
+                assert_eq!(v.hwcap, 126614527);
+                assert_eq!(v.hwcap2, 0);
             }
         } else if #[cfg(target_arch = "aarch64")] {
             #[test]
-            fn linux_x64() {
-                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-x64-i7-6850k.auxv");
+            fn linux_artificial_aarch64() {
+                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-artificial-aarch64.auxv");
                 println!("file: {}", file);
                 let v = auxv_from_file(file).unwrap();
-                assert_eq!(v.hwcap, 3219913727);
+                assert_eq!(v.hwcap, 0x0123456789abcdef);
+                assert_eq!(v.hwcap2, 0x02468ace13579bdf);
+            }
+            #[test]
+            fn linux_no_hwcap2_aarch64() {
+                let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-no-hwcap2-aarch64.auxv");
+                println!("file: {}", file);
+                let v = auxv_from_file(file).unwrap();
+                // An absent HWCAP2 is treated as zero, and does not prevent acceptance of HWCAP.
+                assert_ne!(v.hwcap, 0);
+                assert_eq!(v.hwcap2, 0);
             }
         }
     }
@@ -353,6 +375,7 @@ mod tests {
 
         // Targets with AT_HWCAP and AT_HWCAP2:
         #[cfg(any(
+            target_arch = "aarch64",
             target_arch = "arm",
             target_arch = "powerpc",
             target_arch = "powerpc64"
diff --git a/library/stdarch/crates/std_detect/src/detect/test_data/linux-artificial-aarch64.auxv b/library/stdarch/crates/std_detect/src/detect/test_data/linux-artificial-aarch64.auxv
new file mode 100644
index 000000000..ec826afcf
--- /dev/null
+++ b/library/stdarch/crates/std_detect/src/detect/test_data/linux-artificial-aarch64.auxv
diff --git a/library/stdarch/crates/std_detect/src/detect/test_data/linux-empty-hwcap2-aarch64.auxv b/library/stdarch/crates/std_detect/src/detect/test_data/linux-empty-hwcap2-aarch64.auxv
new file mode 100644
index 000000000..95537b73f
--- /dev/null
+++ b/library/stdarch/crates/std_detect/src/detect/test_data/linux-empty-hwcap2-aarch64.auxv
diff --git a/library/stdarch/crates/std_detect/src/detect/test_data/linux-hwcap2-aarch64.auxv b/library/stdarch/crates/std_detect/src/detect/test_data/linux-hwcap2-aarch64.auxv
new file mode 100644
index 000000000..1d87264b2
--- /dev/null
+++ b/library/stdarch/crates/std_detect/src/detect/test_data/linux-hwcap2-aarch64.auxv
diff --git a/library/stdarch/crates/std_detect/src/detect/test_data/linux-no-hwcap2-aarch64.auxv b/library/stdarch/crates/std_detect/src/detect/test_data/linux-no-hwcap2-aarch64.auxv
new file mode 100644
index 000000000..35f01cc76
--- /dev/null
+++ b/library/stdarch/crates/std_detect/src/detect/test_data/linux-no-hwcap2-aarch64.auxv
diff --git a/library/stdarch/crates/std_detect/src/detect/test_data/linux-x64-i7-6850k.auxv b/library/stdarch/crates/std_detect/src/detect/test_data/linux-x64-i7-6850k.auxv
deleted file mode 100644
index 6afe1b3b4..000000000
--- a/library/stdarch/crates/std_detect/src/detect/test_data/linux-x64-i7-6850k.auxv
+++ /dev/null
diff --git a/library/stdarch/crates/stdarch-test/Cargo.toml b/library/stdarch/crates/stdarch-test/Cargo.toml
index 9ac1057be..012b4e959 100644
--- a/library/stdarch/crates/stdarch-test/Cargo.toml
+++ b/library/stdarch/crates/stdarch-test/Cargo.toml
@@ -10,7 +10,7 @@ simd-test-macro = { path = "../simd-test-macro" }
 cc = "1.0"
 lazy_static = "1.0"
 rustc-demangle = "0.1.8"
-cfg-if = "0.1"
+cfg-if = "1.0"
 
 # We use a crates.io dependency to disassemble wasm binaries to look for
 # instructions for `#[assert_instr]`. Note that we use an `=` dependency here
diff --git a/library/stdarch/crates/stdarch-test/src/lib.rs b/library/stdarch/crates/stdarch-test/src/lib.rs
index 078736c66..eba17771c 100644
--- a/library/stdarch/crates/stdarch-test/src/lib.rs
+++ b/library/stdarch/crates/stdarch-test/src/lib.rs
@@ -3,7 +3,6 @@
 //! This basically just disassembles the current executable and then parses the
 //! output once globally and then provides the `assert` function which makes
 //! assertions about the disassembly of a function.
-#![feature(bench_black_box)] // For black_box
 #![deny(rust_2018_idioms)]
 #![allow(clippy::missing_docs_in_private_items, clippy::print_stdout)]
 
diff --git a/library/test/src/bench.rs b/library/test/src/bench.rs
index 7869ba2c0..23925e6ea 100644
--- a/library/test/src/bench.rs
+++ b/library/test/src/bench.rs
@@ -49,12 +49,12 @@ impl Bencher {
         self.summary = Some(iter(&mut inner));
     }
 
-    pub fn bench<F>(&mut self, mut f: F) -> Option<stats::Summary>
+    pub fn bench<F>(&mut self, mut f: F) -> Result<Option<stats::Summary>, String>
     where
-        F: FnMut(&mut Bencher),
+        F: FnMut(&mut Bencher) -> Result<(), String>,
     {
-        f(self);
-        self.summary
+        let result = f(self);
+        result.map(|_| self.summary)
     }
 }
 
@@ -195,7 +195,7 @@ pub fn benchmark<F>(
     nocapture: bool,
     f: F,
 ) where
-    F: FnMut(&mut Bencher),
+    F: FnMut(&mut Bencher) -> Result<(), String>,
 {
     let mut bs = Bencher { mode: BenchMode::Auto, summary: None, bytes: 0 };
 
@@ -211,14 +211,14 @@ pub fn benchmark<F>(
 
     let test_result = match result {
         //bs.bench(f) {
-        Ok(Some(ns_iter_summ)) => {
+        Ok(Ok(Some(ns_iter_summ))) => {
             let ns_iter = cmp::max(ns_iter_summ.median as u64, 1);
             let mb_s = bs.bytes * 1000 / ns_iter;
 
             let bs = BenchSamples { ns_iter_summ, mb_s: mb_s as usize };
             TestResult::TrBench(bs)
         }
-        Ok(None) => {
+        Ok(Ok(None)) => {
             // iter not called, so no data.
             // FIXME: error in this case?
             let samples: &mut [f64] = &mut [0.0_f64; 1];
@@ -226,6 +226,7 @@ pub fn benchmark<F>(
             TestResult::TrBench(bs)
         }
         Err(_) => TestResult::TrFailed,
+        Ok(Err(_)) => TestResult::TrFailed,
     };
 
     let stdout = data.lock().unwrap().to_vec();
@@ -233,10 +234,10 @@ pub fn benchmark<F>(
     monitor_ch.send(message).unwrap();
 }
 
-pub fn run_once<F>(f: F)
+pub fn run_once<F>(f: F) -> Result<(), String>
 where
-    F: FnMut(&mut Bencher),
+    F: FnMut(&mut Bencher) -> Result<(), String>,
 {
     let mut bs = Bencher { mode: BenchMode::Single, summary: None, bytes: 0 };
-    bs.bench(f);
+    bs.bench(f).map(|_| ())
 }
diff --git a/library/test/src/cli.rs b/library/test/src/cli.rs
index f981b9c49..8be32183f 100644
--- a/library/test/src/cli.rs
+++ b/library/test/src/cli.rs
@@ -3,9 +3,9 @@
 use std::env;
 use std::path::PathBuf;
 
-use super::helpers::isatty;
 use super::options::{ColorConfig, Options, OutputFormat, RunIgnored};
 use super::time::TestTimeOptions;
+use std::io::{self, IsTerminal};
 
 #[derive(Debug)]
 pub struct TestOpts {
@@ -32,7 +32,7 @@ pub struct TestOpts {
 impl TestOpts {
     pub fn use_color(&self) -> bool {
         match self.color {
-            ColorConfig::AutoColor => !self.nocapture && isatty::stdout_isatty(),
+            ColorConfig::AutoColor => !self.nocapture && io::stdout().is_terminal(),
             ColorConfig::AlwaysColor => true,
             ColorConfig::NeverColor => false,
         }
diff --git a/library/test/src/console.rs b/library/test/src/console.rs
index e9dda9896..b1270c272 100644
--- a/library/test/src/console.rs
+++ b/library/test/src/console.rs
@@ -147,7 +147,7 @@ pub fn list_tests_console(opts: &TestOpts, tests: Vec<TestDescAndFn>) -> io::Res
     let mut ntest = 0;
     let mut nbench = 0;
 
-    for test in filter_tests(&opts, tests) {
+    for test in filter_tests(&opts, tests).into_iter() {
         use crate::TestFn::*;
 
         let TestDescAndFn { desc: TestDesc { name, .. }, testfn } = test;
diff --git a/library/test/src/helpers/isatty.rs b/library/test/src/helpers/isatty.rs
deleted file mode 100644
index 874ecc376..000000000
--- a/library/test/src/helpers/isatty.rs
+++ /dev/null
@@ -1,32 +0,0 @@
-//! Helper module which provides a function to test
-//! if stdout is a tty.
-
-cfg_if::cfg_if! {
-    if #[cfg(unix)] {
-        pub fn stdout_isatty() -> bool {
-            unsafe { libc::isatty(libc::STDOUT_FILENO) != 0 }
-        }
-    } else if #[cfg(windows)] {
-        pub fn stdout_isatty() -> bool {
-            type DWORD = u32;
-            type BOOL = i32;
-            type HANDLE = *mut u8;
-            type LPDWORD = *mut u32;
-            const STD_OUTPUT_HANDLE: DWORD = -11i32 as DWORD;
-            extern "system" {
-                fn GetStdHandle(which: DWORD) -> HANDLE;
-                fn GetConsoleMode(hConsoleHandle: HANDLE, lpMode: LPDWORD) -> BOOL;
-            }
-            unsafe {
-                let handle = GetStdHandle(STD_OUTPUT_HANDLE);
-                let mut out = 0;
-                GetConsoleMode(handle, &mut out) != 0
-            }
-        }
-    } else {
-        // FIXME: Implement isatty on SGX
-        pub fn stdout_isatty() -> bool {
-            false
-        }
-    }
-}
diff --git a/library/test/src/helpers/mod.rs b/library/test/src/helpers/mod.rs
index 049cadf86..6f366a911 100644
--- a/library/test/src/helpers/mod.rs
+++ b/library/test/src/helpers/mod.rs
@@ -3,6 +3,5 @@
 
 pub mod concurrency;
 pub mod exit_code;
-pub mod isatty;
 pub mod metrics;
 pub mod shuffle;
diff --git a/library/test/src/lib.rs b/library/test/src/lib.rs
index 3b7193adc..141f16d17 100644
--- a/library/test/src/lib.rs
+++ b/library/test/src/lib.rs
@@ -6,7 +6,8 @@
 //! benchmarks themselves) should be done via the `#[test]` and
 //! `#[bench]` attributes.
 //!
-//! See the [Testing Chapter](../book/ch11-00-testing.html) of the book for more details.
+//! See the [Testing Chapter](../book/ch11-00-testing.html) of the book for more
+//! details.
 
 // Currently, not much of this is meant for users. It is intended to
 // support the simplest interface possible for representing and
@@ -15,10 +16,11 @@
 
 #![unstable(feature = "test", issue = "50297")]
 #![doc(test(attr(deny(warnings))))]
-#![feature(bench_black_box)]
 #![feature(internal_output_capture)]
+#![feature(is_terminal)]
 #![feature(staged_api)]
 #![feature(process_exitcode_internals)]
+#![feature(panic_can_unwind)]
 #![feature(test)]
 
 // Public reexports
@@ -53,6 +55,7 @@ use std::{
     collections::VecDeque,
     env, io,
     io::prelude::Write,
+    mem::ManuallyDrop,
     panic::{self, catch_unwind, AssertUnwindSafe, PanicInfo},
     process::{self, Command, Termination},
     sync::mpsc::{channel, Sender},
@@ -77,6 +80,7 @@ mod types;
 #[cfg(test)]
 mod tests;
 
+use core::any::Any;
 use event::{CompletedTest, TestEvent};
 use helpers::concurrency::get_concurrency;
 use helpers::exit_code::get_exit_code;
@@ -110,6 +114,29 @@ pub fn test_main(args: &[String], tests: Vec<TestDescAndFn>, options: Option<Opt
             process::exit(ERROR_EXIT_CODE);
         }
     } else {
+        if !opts.nocapture {
+            // If we encounter a non-unwinding panic, flush any captured output from the current test,
+            // and stop  capturing output to ensure that the non-unwinding panic message is visible.
+            // We also acquire the locks for both output streams to prevent output from other threads
+            // from interleaving with the panic message or appearing after it.
+            let builtin_panic_hook = panic::take_hook();
+            let hook = Box::new({
+                move |info: &'_ PanicInfo<'_>| {
+                    if !info.can_unwind() {
+                        std::mem::forget(std::io::stderr().lock());
+                        let mut stdout = ManuallyDrop::new(std::io::stdout().lock());
+                        if let Some(captured) = io::set_output_capture(None) {
+                            if let Ok(data) = captured.lock() {
+                                let _ = stdout.write_all(&data);
+                                let _ = stdout.flush();
+                            }
+                        }
+                    }
+                    builtin_panic_hook(info);
+                }
+            });
+            panic::set_hook(hook);
+        }
         match console::run_tests_console(&opts, tests) {
             Ok(true) => {}
             Ok(false) => process::exit(ERROR_EXIT_CODE),
@@ -176,17 +203,20 @@ fn make_owned_test(test: &&TestDescAndFn) -> TestDescAndFn {
     }
 }
 
-/// Invoked when unit tests terminate. Should panic if the unit
-/// Tests is considered a failure. By default, invokes `report()`
-/// and checks for a `0` result.
-pub fn assert_test_result<T: Termination>(result: T) {
+/// Invoked when unit tests terminate. Returns `Result::Err` if the test is
+/// considered a failure. By default, invokes `report() and checks for a `0`
+/// result.
+pub fn assert_test_result<T: Termination>(result: T) -> Result<(), String> {
     let code = result.report().to_i32();
-    assert_eq!(
-        code, 0,
-        "the test returned a termination value with a non-zero status code ({}) \
-         which indicates a failure",
-        code
-    );
+    if code == 0 {
+        Ok(())
+    } else {
+        Err(format!(
+            "the test returned a termination value with a non-zero status code \
+             ({}) which indicates a failure",
+            code
+        ))
+    }
 }
 
 pub fn run_tests<F>(
@@ -242,7 +272,7 @@ where
     let event = TestEvent::TeFiltered(filtered_descs, shuffle_seed);
     notify_about_test_event(event)?;
 
-    let (filtered_tests, filtered_benchs): (Vec<_>, _) = filtered_tests
+    let (mut filtered_tests, filtered_benchs): (Vec<_>, _) = filtered_tests
         .into_iter()
         .enumerate()
         .map(|(i, e)| (TestId(i), e))
@@ -250,12 +280,12 @@ where
 
     let concurrency = opts.test_threads.unwrap_or_else(get_concurrency);
 
-    let mut remaining = filtered_tests;
     if let Some(shuffle_seed) = shuffle_seed {
-        shuffle_tests(shuffle_seed, &mut remaining);
-    } else {
-        remaining.reverse();
+        shuffle_tests(shuffle_seed, &mut filtered_tests);
     }
+    // Store the tests in a VecDeque so we can efficiently remove the first element to run the
+    // tests in the order they were passed (unless shuffled).
+    let mut remaining = VecDeque::from(filtered_tests);
     let mut pending = 0;
 
     let (tx, rx) = channel::<CompletedTest>();
@@ -295,7 +325,7 @@ where
 
     if concurrency == 1 {
         while !remaining.is_empty() {
-            let (id, test) = remaining.pop().unwrap();
+            let (id, test) = remaining.pop_front().unwrap();
             let event = TestEvent::TeWait(test.desc.clone());
             notify_about_test_event(event)?;
             let join_handle =
@@ -309,7 +339,7 @@ where
     } else {
         while pending > 0 || !remaining.is_empty() {
             while pending < concurrency && !remaining.is_empty() {
-                let (id, test) = remaining.pop().unwrap();
+                let (id, test) = remaining.pop_front().unwrap();
                 let timeout = time::get_default_test_timeout();
                 let desc = test.desc.clone();
 
@@ -421,9 +451,6 @@ pub fn filter_tests(opts: &TestOpts, tests: Vec<TestDescAndFn>) -> Vec<TestDescA
         RunIgnored::No => {}
     }
 
-    // Sort the tests alphabetically
-    filtered.sort_by(|t1, t2| t1.desc.name.as_slice().cmp(t2.desc.name.as_slice()));
-
     filtered
 }
 
@@ -479,7 +506,7 @@ pub fn run_test(
         id: TestId,
         desc: TestDesc,
         monitor_ch: Sender<CompletedTest>,
-        testfn: Box<dyn FnOnce() + Send>,
+        testfn: Box<dyn FnOnce() -> Result<(), String> + Send>,
         opts: TestRunOpts,
     ) -> Option<thread::JoinHandle<()>> {
         let concurrency = opts.concurrency;
@@ -568,11 +595,11 @@ pub fn run_test(
 
 /// Fixed frame used to clean the backtrace with `RUST_BACKTRACE=1`.
 #[inline(never)]
-fn __rust_begin_short_backtrace<F: FnOnce()>(f: F) {
-    f();
+fn __rust_begin_short_backtrace<T, F: FnOnce() -> T>(f: F) -> T {
+    let result = f();
 
     // prevent this frame from being tail-call optimised away
-    black_box(());
+    black_box(result)
 }
 
 fn run_test_in_process(
@@ -580,7 +607,7 @@ fn run_test_in_process(
     desc: TestDesc,
     nocapture: bool,
     report_time: bool,
-    testfn: Box<dyn FnOnce() + Send>,
+    testfn: Box<dyn FnOnce() -> Result<(), String> + Send>,
     monitor_ch: Sender<CompletedTest>,
     time_opts: Option<time::TestTimeOptions>,
 ) {
@@ -592,7 +619,7 @@ fn run_test_in_process(
     }
 
     let start = report_time.then(Instant::now);
-    let result = catch_unwind(AssertUnwindSafe(testfn));
+    let result = fold_err(catch_unwind(AssertUnwindSafe(testfn)));
     let exec_time = start.map(|start| {
         let duration = start.elapsed();
         TestExecTime(duration)
@@ -609,6 +636,19 @@ fn run_test_in_process(
     monitor_ch.send(message).unwrap();
 }
 
+fn fold_err<T, E>(
+    result: Result<Result<T, E>, Box<dyn Any + Send>>,
+) -> Result<T, Box<dyn Any + Send>>
+where
+    E: Send + 'static,
+{
+    match result {
+        Ok(Err(e)) => Err(Box::new(e)),
+        Ok(Ok(v)) => Ok(v),
+        Err(e) => Err(e),
+    }
+}
+
 fn spawn_test_subprocess(
     id: TestId,
     desc: TestDesc,
@@ -664,7 +704,10 @@ fn spawn_test_subprocess(
     monitor_ch.send(message).unwrap();
 }
 
-fn run_test_in_spawned_subprocess(desc: TestDesc, testfn: Box<dyn FnOnce() + Send>) -> ! {
+fn run_test_in_spawned_subprocess(
+    desc: TestDesc,
+    testfn: Box<dyn FnOnce() -> Result<(), String> + Send>,
+) -> ! {
     let builtin_panic_hook = panic::take_hook();
     let record_result = Arc::new(move |panic_info: Option<&'_ PanicInfo<'_>>| {
         let test_result = match panic_info {
@@ -690,7 +733,9 @@ fn run_test_in_spawned_subprocess(desc: TestDesc, testfn: Box<dyn FnOnce() + Sen
     });
     let record_result2 = record_result.clone();
     panic::set_hook(Box::new(move |info| record_result2(Some(&info))));
-    testfn();
+    if let Err(message) = testfn() {
+        panic!("{}", message);
+    }
     record_result(None);
     unreachable!("panic=abort callback should have exited the process")
 }
diff --git a/library/test/src/term.rs b/library/test/src/term.rs
index b256ab7b8..a14b0d4f5 100644
--- a/library/test/src/term.rs
+++ b/library/test/src/term.rs
@@ -39,7 +39,7 @@ pub(crate) fn stdout() -> Option<Box<StdoutTerminal>> {
 pub(crate) fn stdout() -> Option<Box<StdoutTerminal>> {
     TerminfoTerminal::new(io::stdout())
         .map(|t| Box::new(t) as Box<StdoutTerminal>)
-        .or_else(|| WinConsole::new(io::stdout()).ok().map(|t| Box::new(t) as Box<StdoutTerminal>))
+        .or_else(|| Some(Box::new(WinConsole::new(io::stdout())) as Box<StdoutTerminal>))
 }
 
 /// Terminal color definitions
diff --git a/library/test/src/term/win.rs b/library/test/src/term/win.rs
index 4bdbd6ee7..55020141a 100644
--- a/library/test/src/term/win.rs
+++ b/library/test/src/term/win.rs
@@ -113,8 +113,7 @@ impl<T: Write + Send + 'static> WinConsole<T> {
         }
     }
 
-    /// Returns `None` whenever the terminal cannot be created for some reason.
-    pub(crate) fn new(out: T) -> io::Result<WinConsole<T>> {
+    pub(crate) fn new(out: T) -> WinConsole<T> {
         use std::mem::MaybeUninit;
 
         let fg;
@@ -132,13 +131,13 @@ impl<T: Write + Send + 'static> WinConsole<T> {
                 bg = color::BLACK;
             }
         }
-        Ok(WinConsole {
+        WinConsole {
             buf: out,
             def_foreground: fg,
             def_background: bg,
             foreground: fg,
             background: bg,
-        })
+        }
     }
 }
 
diff --git a/library/test/src/tests.rs b/library/test/src/tests.rs
index 0b81aff59..b54be64ef 100644
--- a/library/test/src/tests.rs
+++ b/library/test/src/tests.rs
@@ -67,7 +67,7 @@ fn one_ignored_one_unignored_test() -> Vec<TestDescAndFn> {
                 no_run: false,
                 test_type: TestType::Unknown,
             },
-            testfn: DynTestFn(Box::new(move || {})),
+            testfn: DynTestFn(Box::new(move || Ok(()))),
         },
         TestDescAndFn {
             desc: TestDesc {
@@ -79,14 +79,14 @@ fn one_ignored_one_unignored_test() -> Vec<TestDescAndFn> {
                 no_run: false,
                 test_type: TestType::Unknown,
             },
-            testfn: DynTestFn(Box::new(move || {})),
+            testfn: DynTestFn(Box::new(move || Ok(()))),
         },
     ]
 }
 
 #[test]
 pub fn do_not_run_ignored_tests() {
-    fn f() {
+    fn f() -> Result<(), String> {
         panic!();
     }
     let desc = TestDescAndFn {
@@ -109,7 +109,9 @@ pub fn do_not_run_ignored_tests() {
 
 #[test]
 pub fn ignored_tests_result_in_ignored() {
-    fn f() {}
+    fn f() -> Result<(), String> {
+        Ok(())
+    }
     let desc = TestDescAndFn {
         desc: TestDesc {
             name: StaticTestName("whatever"),
@@ -132,7 +134,7 @@ pub fn ignored_tests_result_in_ignored() {
 #[test]
 #[cfg(not(target_os = "emscripten"))]
 fn test_should_panic() {
-    fn f() {
+    fn f() -> Result<(), String> {
         panic!();
     }
     let desc = TestDescAndFn {
@@ -157,7 +159,7 @@ fn test_should_panic() {
 #[test]
 #[cfg(not(target_os = "emscripten"))]
 fn test_should_panic_good_message() {
-    fn f() {
+    fn f() -> Result<(), String> {
         panic!("an error message");
     }
     let desc = TestDescAndFn {
@@ -183,7 +185,7 @@ fn test_should_panic_good_message() {
 #[cfg(not(target_os = "emscripten"))]
 fn test_should_panic_bad_message() {
     use crate::tests::TrFailedMsg;
-    fn f() {
+    fn f() -> Result<(), String> {
         panic!("an error message");
     }
     let expected = "foobar";
@@ -214,7 +216,7 @@ fn test_should_panic_bad_message() {
 fn test_should_panic_non_string_message_type() {
     use crate::tests::TrFailedMsg;
     use std::any::TypeId;
-    fn f() {
+    fn f() -> Result<(), String> {
         std::panic::panic_any(1i32);
     }
     let expected = "foobar";
@@ -249,7 +251,9 @@ fn test_should_panic_but_succeeds() {
     let should_panic_variants = [ShouldPanic::Yes, ShouldPanic::YesWithMessage("error message")];
 
     for &should_panic in should_panic_variants.iter() {
-        fn f() {}
+        fn f() -> Result<(), String> {
+            Ok(())
+        }
         let desc = TestDescAndFn {
             desc: TestDesc {
                 name: StaticTestName("whatever"),
@@ -283,7 +287,9 @@ fn test_should_panic_but_succeeds() {
 }
 
 fn report_time_test_template(report_time: bool) -> Option<TestExecTime> {
-    fn f() {}
+    fn f() -> Result<(), String> {
+        Ok(())
+    }
     let desc = TestDescAndFn {
         desc: TestDesc {
             name: StaticTestName("whatever"),
@@ -318,7 +324,9 @@ fn test_should_report_time() {
 }
 
 fn time_test_failure_template(test_type: TestType) -> TestResult {
-    fn f() {}
+    fn f() -> Result<(), String> {
+        Ok(())
+    }
     let desc = TestDescAndFn {
         desc: TestDesc {
             name: StaticTestName("whatever"),
@@ -480,7 +488,7 @@ pub fn exclude_should_panic_option() {
             no_run: false,
             test_type: TestType::Unknown,
         },
-        testfn: DynTestFn(Box::new(move || {})),
+        testfn: DynTestFn(Box::new(move || Ok(()))),
     });
 
     let filtered = filter_tests(&opts, tests);
@@ -504,7 +512,7 @@ pub fn exact_filter_match() {
                     no_run: false,
                     test_type: TestType::Unknown,
                 },
-                testfn: DynTestFn(Box::new(move || {})),
+                testfn: DynTestFn(Box::new(move || Ok(()))),
             })
             .collect()
     }
@@ -580,7 +588,9 @@ fn sample_tests() -> Vec<TestDescAndFn> {
         "test::run_include_ignored_option".to_string(),
         "test::sort_tests".to_string(),
     ];
-    fn testfn() {}
+    fn testfn() -> Result<(), String> {
+        Ok(())
+    }
     let mut tests = Vec::new();
     for name in &names {
         let test = TestDescAndFn {
@@ -601,33 +611,6 @@ fn sample_tests() -> Vec<TestDescAndFn> {
 }
 
 #[test]
-pub fn sort_tests() {
-    let mut opts = TestOpts::new();
-    opts.run_tests = true;
-
-    let tests = sample_tests();
-    let filtered = filter_tests(&opts, tests);
-
-    let expected = vec![
-        "isize::test_pow".to_string(),
-        "isize::test_to_str".to_string(),
-        "sha1::test".to_string(),
-        "test::do_not_run_ignored_tests".to_string(),
-        "test::filter_for_ignored_option".to_string(),
-        "test::first_free_arg_should_be_a_filter".to_string(),
-        "test::ignored_tests_result_in_ignored".to_string(),
-        "test::parse_ignored_flag".to_string(),
-        "test::parse_include_ignored_flag".to_string(),
-        "test::run_include_ignored_option".to_string(),
-        "test::sort_tests".to_string(),
-    ];
-
-    for (a, b) in expected.iter().zip(filtered) {
-        assert_eq!(*a, b.desc.name.to_string());
-    }
-}
-
-#[test]
 pub fn shuffle_tests() {
     let mut opts = TestOpts::new();
     opts.shuffle = true;
@@ -717,21 +700,26 @@ pub fn test_metricmap_compare() {
 
 #[test]
 pub fn test_bench_once_no_iter() {
-    fn f(_: &mut Bencher) {}
-    bench::run_once(f);
+    fn f(_: &mut Bencher) -> Result<(), String> {
+        Ok(())
+    }
+    bench::run_once(f).unwrap();
 }
 
 #[test]
 pub fn test_bench_once_iter() {
-    fn f(b: &mut Bencher) {
-        b.iter(|| {})
+    fn f(b: &mut Bencher) -> Result<(), String> {
+        b.iter(|| {});
+        Ok(())
     }
-    bench::run_once(f);
+    bench::run_once(f).unwrap();
 }
 
 #[test]
 pub fn test_bench_no_iter() {
-    fn f(_: &mut Bencher) {}
+    fn f(_: &mut Bencher) -> Result<(), String> {
+        Ok(())
+    }
 
     let (tx, rx) = channel();
 
@@ -751,8 +739,9 @@ pub fn test_bench_no_iter() {
 
 #[test]
 pub fn test_bench_iter() {
-    fn f(b: &mut Bencher) {
-        b.iter(|| {})
+    fn f(b: &mut Bencher) -> Result<(), String> {
+        b.iter(|| {});
+        Ok(())
     }
 
     let (tx, rx) = channel();
@@ -821,3 +810,33 @@ fn should_sort_failures_before_printing_them() {
     let bpos = s.find("b").unwrap();
     assert!(apos < bpos);
 }
+
+#[test]
+#[cfg(not(target_os = "emscripten"))]
+fn test_dyn_bench_returning_err_fails_when_run_as_test() {
+    fn f(_: &mut Bencher) -> Result<(), String> {
+        Result::Err("An error".into())
+    }
+    let desc = TestDescAndFn {
+        desc: TestDesc {
+            name: StaticTestName("whatever"),
+            ignore: false,
+            ignore_message: None,
+            should_panic: ShouldPanic::No,
+            compile_fail: false,
+            no_run: false,
+            test_type: TestType::Unknown,
+        },
+        testfn: DynBenchFn(Box::new(f)),
+    };
+    let (tx, rx) = channel();
+    let notify = move |event: TestEvent| {
+        if let TestEvent::TeResult(result) = event {
+            tx.send(result).unwrap();
+        }
+        Ok(())
+    };
+    run_tests(&TestOpts { run_tests: true, ..TestOpts::new() }, vec![desc], notify).unwrap();
+    let result = rx.recv().unwrap().result;
+    assert_eq!(result, TrFailed);
+}
diff --git a/library/test/src/types.rs b/library/test/src/types.rs
index ffb1efe18..888afff79 100644
--- a/library/test/src/types.rs
+++ b/library/test/src/types.rs
@@ -75,14 +75,15 @@ impl fmt::Display for TestName {
 }
 
 // A function that runs a test. If the function returns successfully,
-// the test succeeds; if the function panics then the test fails. We
-// may need to come up with a more clever definition of test in order
-// to support isolation of tests into threads.
+// the test succeeds; if the function panics or returns Result::Err
+// then the test fails. We may need to come up with a more clever
+// definition of test in order to support isolation of tests into
+// threads.
 pub enum TestFn {
-    StaticTestFn(fn()),
-    StaticBenchFn(fn(&mut Bencher)),
-    DynTestFn(Box<dyn FnOnce() + Send>),
-    DynBenchFn(Box<dyn Fn(&mut Bencher) + Send>),
+    StaticTestFn(fn() -> Result<(), String>),
+    StaticBenchFn(fn(&mut Bencher) -> Result<(), String>),
+    DynTestFn(Box<dyn FnOnce() -> Result<(), String> + Send>),
+    DynBenchFn(Box<dyn Fn(&mut Bencher) -> Result<(), String> + Send>),
 }
 
 impl TestFn {