Merging debian version 1.65.0+dfsg1-2.

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

28 files changed, 689 insertions, 176 deletions

diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index cc8da7bcc..80b067812 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -30,13 +30,13 @@ extern "Rust" {
     #[rustc_allocator]
     #[rustc_allocator_nounwind]
     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
-    #[cfg_attr(not(bootstrap), rustc_deallocator)]
+    #[rustc_deallocator]
     #[rustc_allocator_nounwind]
     fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
-    #[cfg_attr(not(bootstrap), rustc_reallocator)]
+    #[rustc_reallocator]
     #[rustc_allocator_nounwind]
     fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
-    #[cfg_attr(not(bootstrap), rustc_allocator_zeroed)]
+    #[rustc_allocator_zeroed]
     #[rustc_allocator_nounwind]
     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
 }
diff --git a/library/alloc/src/alloc/tests.rs b/library/alloc/src/alloc/tests.rs
index 7d560964d..b2f019459 100644
--- a/library/alloc/src/alloc/tests.rs
+++ b/library/alloc/src/alloc/tests.rs
@@ -15,7 +15,7 @@ fn allocate_zeroed() {
         let end = i.add(layout.size());
         while i < end {
             assert_eq!(*i, 0);
-            i = i.offset(1);
+            i = i.add(1);
         }
         Global.deallocate(ptr.as_non_null_ptr(), layout);
     }
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index c1ceeb0de..65e323c9e 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -1,4 +1,4 @@
-//! A pointer type for heap allocation.
+//! The `Box<T>` type for heap allocation.
 //!
 //! [`Box<T>`], casually referred to as a 'box', provides the simplest form of
 //! heap allocation in Rust. Boxes provide ownership for this allocation, and
@@ -151,6 +151,8 @@ 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;
 use core::hash::{Hash, Hasher};
@@ -174,6 +176,9 @@ 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))]
 use crate::vec::Vec;
 
@@ -1480,7 +1485,7 @@ impl<T: Copy> From<&[T]> for Box<[T]> {
     /// Converts a `&[T]` into a `Box<[T]>`
     ///
     /// This conversion allocates on the heap
-    /// and performs a copy of `slice`.
+    /// and performs a copy of `slice` and its contents.
     ///
     /// # Examples
     /// ```rust
@@ -2085,3 +2090,304 @@ impl<S: ?Sized + AsyncIterator + Unpin> AsyncIterator for Box<S> {
         (**self).size_hint()
     }
 }
+
+#[cfg(not(bootstrap))]
+impl dyn Error {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[rustc_allow_incoherent_impl]
+    /// 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)
+        }
+    }
+}
+
+#[cfg(not(bootstrap))]
+impl dyn Error + Send {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[rustc_allow_incoherent_impl]
+    /// 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.
+            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send>>(s)
+        })
+    }
+}
+
+#[cfg(not(bootstrap))]
+impl dyn Error + Send + Sync {
+    #[inline]
+    #[stable(feature = "error_downcast", since = "1.3.0")]
+    #[rustc_allow_incoherent_impl]
+    /// 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.
+            mem::transmute::<Box<dyn Error>, Box<dyn Error + Send + Sync>>(s)
+        })
+    }
+}
+
+#[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> {
+    /// 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(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> {
+    /// 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(not(bootstrap))]
+#[cfg(not(no_global_oom_handling))]
+#[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 fmt::Display for StringError {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                fmt::Display::fmt(&self.0, f)
+            }
+        }
+
+        // Purposefully skip printing "StringError(..)"
+        impl fmt::Debug for StringError {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                fmt::Debug::fmt(&self.0, f)
+            }
+        }
+
+        Box::new(StringError(err))
+    }
+}
+
+#[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> {
+    /// 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(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> {
+    /// 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(not(bootstrap))]
+#[cfg(not(no_global_oom_handling))]
+#[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(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> {
+    /// 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(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> {
+    /// 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(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)]
+    fn description(&self) -> &str {
+        core::error::Error::description(&**self)
+    }
+
+    #[allow(deprecated)]
+    fn cause(&self) -> Option<&dyn core::error::Error> {
+        core::error::Error::cause(&**self)
+    }
+
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        core::error::Error::source(&**self)
+    }
+}
diff --git a/library/alloc/src/boxed/thin.rs b/library/alloc/src/boxed/thin.rs
index 649ccfcaa..0a20c74b0 100644
--- a/library/alloc/src/boxed/thin.rs
+++ b/library/alloc/src/boxed/thin.rs
@@ -2,6 +2,8 @@
 // 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;
 #[cfg(not(no_global_oom_handling))]
@@ -271,3 +273,11 @@ impl<H> WithHeader<H> {
         Layout::new::<H>().extend(value_layout)
     }
 }
+
+#[cfg(not(bootstrap))]
+#[unstable(feature = "thin_box", issue = "92791")]
+impl<T: ?Sized + Error> Error for ThinBox<T> {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        self.deref().source()
+    }
+}
diff --git a/library/alloc/src/collections/binary_heap.rs b/library/alloc/src/collections/binary_heap.rs
index 197e7aaac..4583bc9a1 100644
--- a/library/alloc/src/collections/binary_heap.rs
+++ b/library/alloc/src/collections/binary_heap.rs
@@ -1010,7 +1010,8 @@ impl<T> BinaryHeap<T> {
     /// current length. The allocator may reserve more space to speculatively
     /// avoid frequent allocations. 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.
+    /// `Ok(())`. Does nothing if capacity is already sufficient. This method
+    /// preserves the contents even if an error occurs.
     ///
     /// # Errors
     ///
diff --git a/library/alloc/src/collections/btree/dedup_sorted_iter.rs b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
index 60bf83b83..17ee78045 100644
--- a/library/alloc/src/collections/btree/dedup_sorted_iter.rs
+++ b/library/alloc/src/collections/btree/dedup_sorted_iter.rs
@@ -3,7 +3,9 @@ use core::iter::Peekable;
 /// A iterator for deduping the key of a sorted iterator.
 /// When encountering the duplicated key, only the last key-value pair is yielded.
 ///
-/// Used by [`BTreeMap::bulk_build_from_sorted_iter`].
+/// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].
+///
+/// [1]: crate::collections::BTreeMap::bulk_build_from_sorted_iter
 pub struct DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,
diff --git a/library/alloc/src/collections/btree/map/entry.rs b/library/alloc/src/collections/btree/map/entry.rs
index b6eecf9b0..cd7cdc192 100644
--- a/library/alloc/src/collections/btree/map/entry.rs
+++ b/library/alloc/src/collections/btree/map/entry.rs
@@ -133,6 +133,17 @@ 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>
+{
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "key already exists"
+    }
+}
+
 impl<'a, K: Ord, V, A: Allocator + Clone> Entry<'a, K, V, A> {
     /// Ensures a value is in the entry by inserting the default if empty, and returns
     /// a mutable reference to the value in the entry.
diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs
index d831161bc..f1d2d3b30 100644
--- a/library/alloc/src/collections/btree/node.rs
+++ b/library/alloc/src/collections/btree/node.rs
@@ -318,7 +318,7 @@ impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type>
     pub fn ascend(
         self,
     ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
-        assert!(BorrowType::PERMITS_TRAVERSAL);
+        let _ = BorrowType::TRAVERSAL_PERMIT;
         // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut,
         // there might be outstanding mutable references to values that we must not invalidate.
         let leaf_ptr: *const _ = Self::as_leaf_ptr(&self);
@@ -1003,7 +1003,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
     /// both, upon success, do nothing.
     pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
-        assert!(BorrowType::PERMITS_TRAVERSAL);
+        let _ = BorrowType::TRAVERSAL_PERMIT;
         // We need to use raw pointers to nodes because, if BorrowType is
         // marker::ValMut, there might be outstanding mutable references to
         // values that we must not invalidate. There's no worry accessing the
@@ -1666,15 +1666,17 @@ pub mod marker {
     pub struct ValMut<'a>(PhantomData<&'a mut ()>);
 
     pub trait BorrowType {
-        // Whether node references of this borrow type allow traversing
-        // to other nodes in the tree.
-        const PERMITS_TRAVERSAL: bool = true;
+        // If node references of this borrow type allow traversing to other
+        // nodes in the tree, this constant can be evaluated. Thus reading it
+        // serves as a compile-time assertion.
+        const TRAVERSAL_PERMIT: () = ();
     }
     impl BorrowType for Owned {
-        // Traversal isn't needed, it happens using the result of `borrow_mut`.
+        // Reject evaluation, because traversal isn't needed. Instead traversal
+        // happens using the result of `borrow_mut`.
         // By disabling traversal, and only creating new references to roots,
         // we know that every reference of the `Owned` type is to a root node.
-        const PERMITS_TRAVERSAL: bool = false;
+        const TRAVERSAL_PERMIT: () = panic!();
     }
     impl BorrowType for Dying {}
     impl<'a> BorrowType for Immut<'a> {}
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index e21c8aa3b..6480fcaf9 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -1570,7 +1570,7 @@ impl<'a, T> CursorMut<'a, T> {
     /// that the cursor points to is unchanged, even if it is the "ghost" node.
     ///
     /// This operation should compute in *O*(1) time.
-    // `push_front` continues to point to "ghost" when it addes a node to mimic
+    // `push_front` continues to point to "ghost" when it adds a node to mimic
     // the behavior of `insert_before` on an empty list.
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn push_front(&mut self, elt: T) {
diff --git a/library/alloc/src/collections/mod.rs b/library/alloc/src/collections/mod.rs
index 628a5b155..21d0def08 100644
--- a/library/alloc/src/collections/mod.rs
+++ b/library/alloc/src/collections/mod.rs
@@ -152,3 +152,7 @@ trait SpecExtend<I: IntoIterator> {
     /// Extends `self` with the contents of the given iterator.
     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/drain.rs b/library/alloc/src/collections/vec_deque/drain.rs
index 05f94da6d..41baa7102 100644
--- a/library/alloc/src/collections/vec_deque/drain.rs
+++ b/library/alloc/src/collections/vec_deque/drain.rs
@@ -1,10 +1,12 @@
+use core::fmt;
 use core::iter::FusedIterator;
+use core::marker::PhantomData;
+use core::mem::{self, MaybeUninit};
 use core::ptr::{self, NonNull};
-use core::{fmt, mem};
 
 use crate::alloc::{Allocator, Global};
 
-use super::{count, Iter, VecDeque};
+use super::{count, wrap_index, VecDeque};
 
 /// A draining iterator over the elements of a `VecDeque`.
 ///
@@ -20,18 +22,24 @@ pub struct Drain<
 > {
     after_tail: usize,
     after_head: usize,
-    iter: Iter<'a, T>,
+    ring: NonNull<[T]>,
+    tail: usize,
+    head: usize,
     deque: NonNull<VecDeque<T, A>>,
+    _phantom: PhantomData<&'a T>,
 }
 
 impl<'a, T, A: Allocator> Drain<'a, T, A> {
     pub(super) unsafe fn new(
         after_tail: usize,
         after_head: usize,
-        iter: Iter<'a, T>,
+        ring: &'a [MaybeUninit<T>],
+        tail: usize,
+        head: usize,
         deque: NonNull<VecDeque<T, A>>,
     ) -> Self {
-        Drain { after_tail, after_head, iter, deque }
+        let ring = unsafe { NonNull::new_unchecked(ring as *const [MaybeUninit<T>] as *mut _) };
+        Drain { after_tail, after_head, ring, tail, head, deque, _phantom: PhantomData }
     }
 }
 
@@ -41,7 +49,9 @@ impl<T: fmt::Debug, A: Allocator> fmt::Debug for Drain<'_, T, A> {
         f.debug_tuple("Drain")
             .field(&self.after_tail)
             .field(&self.after_head)
-            .field(&self.iter)
+            .field(&self.ring)
+            .field(&self.tail)
+            .field(&self.head)
             .finish()
     }
 }
@@ -118,12 +128,21 @@ impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        self.iter.next().map(|elt| unsafe { ptr::read(elt) })
+        if self.tail == self.head {
+            return None;
+        }
+        let tail = self.tail;
+        self.tail = wrap_index(self.tail.wrapping_add(1), self.ring.len());
+        // Safety:
+        // - `self.tail` in a ring buffer is always a valid index.
+        // - `self.head` and `self.tail` equality is checked above.
+        unsafe { Some(ptr::read(self.ring.as_ptr().get_unchecked_mut(tail))) }
     }
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        self.iter.size_hint()
+        let len = count(self.tail, self.head, self.ring.len());
+        (len, Some(len))
     }
 }
 
@@ -131,7 +150,14 @@ impl<T, A: Allocator> Iterator for Drain<'_, T, A> {
 impl<T, A: Allocator> DoubleEndedIterator for Drain<'_, T, A> {
     #[inline]
     fn next_back(&mut self) -> Option<T> {
-        self.iter.next_back().map(|elt| unsafe { ptr::read(elt) })
+        if self.tail == self.head {
+            return None;
+        }
+        self.head = wrap_index(self.head.wrapping_sub(1), self.ring.len());
+        // Safety:
+        // - `self.head` in a ring buffer is always a valid index.
+        // - `self.head` and `self.tail` equality is checked above.
+        unsafe { Some(ptr::read(self.ring.as_ptr().get_unchecked_mut(self.head))) }
     }
 }
 
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index 4d895d837..e3f4deb08 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -794,7 +794,8 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// in the given deque. The collection may reserve more space to speculatively 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.
+    /// `Ok(())`. Does nothing if capacity is already sufficient. This method
+    /// preserves the contents even if an error occurs.
     ///
     /// # Errors
     ///
@@ -1333,9 +1334,8 @@ impl<T, A: Allocator> VecDeque<T, A> {
             // it.  We do not write to `self` nor reborrow to a mutable reference.
             // Hence the raw pointer we created above, for `deque`, remains valid.
             let ring = self.buffer_as_slice();
-            let iter = Iter::new(ring, drain_tail, drain_head);
 
-            Drain::new(drain_head, head, iter, deque)
+            Drain::new(drain_head, head, ring, drain_tail, drain_head, deque)
         }
     }
 
@@ -2447,8 +2447,8 @@ impl<T, A: Allocator> VecDeque<T, A> {
                     let mut right_offset = 0;
                     for i in left_edge..right_edge {
                         right_offset = (i - left_edge) % (cap - right_edge);
-                        let src: isize = (right_edge + right_offset) as isize;
-                        ptr::swap(buf.add(i), buf.offset(src));
+                        let src = right_edge + right_offset;
+                        ptr::swap(buf.add(i), buf.add(src));
                     }
                     let n_ops = right_edge - left_edge;
                     left_edge += n_ops;
diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index ae61b1f1e..aede6d54c 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -436,9 +436,9 @@ impl CString {
     ///
     /// unsafe {
     ///     assert_eq!(b'f', *ptr as u8);
-    ///     assert_eq!(b'o', *ptr.offset(1) as u8);
-    ///     assert_eq!(b'o', *ptr.offset(2) as u8);
-    ///     assert_eq!(b'\0', *ptr.offset(3) as u8);
+    ///     assert_eq!(b'o', *ptr.add(1) as u8);
+    ///     assert_eq!(b'o', *ptr.add(2) as u8);
+    ///     assert_eq!(b'\0', *ptr.add(3) as u8);
     ///
     ///     // retake pointer to free memory
     ///     let _ = CString::from_raw(ptr);
@@ -1121,3 +1121,29 @@ impl CStr {
         CString::from(self)
     }
 }
+
+#[cfg(not(bootstrap))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl core::error::Error for NulError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "nul byte found in data"
+    }
+}
+
+#[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)]
+    fn description(&self) -> &str {
+        "C string contained non-utf8 bytes"
+    }
+
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        Some(self.__source())
+    }
+}
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 8b6f40548..8619467c2 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -56,10 +56,6 @@
 //! [`Rc`]: rc
 //! [`RefCell`]: core::cell
 
-// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
-// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
-// rustc itself never sets the feature, so this line has no affect there.
-#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 #![allow(unused_attributes)]
 #![stable(feature = "alloc", since = "1.36.0")]
 #![doc(
@@ -77,6 +73,10 @@
 ))]
 #![no_std]
 #![needs_allocator]
+// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no affect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 //
 // Lints:
 #![deny(unsafe_op_in_unsafe_fn)]
@@ -111,6 +111,8 @@
 #![feature(const_pin)]
 #![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(exact_size_is_empty)]
 #![feature(extend_one)]
 #![feature(fmt_internals)]
@@ -127,10 +129,12 @@
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(pattern)]
 #![feature(pointer_byte_offsets)]
+#![cfg_attr(not(bootstrap), 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(slice_from_ptr_range)]
 #![feature(slice_group_by)]
@@ -145,6 +149,7 @@
 #![feature(unchecked_math)]
 #![feature(unicode_internals)]
 #![feature(unsize)]
+#![feature(utf8_chunks)]
 #![feature(std_internals)]
 //
 // Language features:
@@ -164,7 +169,7 @@
 #![cfg_attr(not(test), feature(generator_trait))]
 #![feature(hashmap_internals)]
 #![feature(lang_items)]
-#![feature(let_else)]
+#![cfg_attr(bootstrap, feature(let_else))]
 #![feature(min_specialization)]
 #![feature(negative_impls)]
 #![feature(never_type)]
@@ -178,6 +183,7 @@
 #![feature(unboxed_closures)]
 #![feature(unsized_fn_params)]
 #![feature(c_unwind)]
+#![feature(with_negative_coherence)]
 //
 // Rustdoc features:
 #![feature(doc_cfg)]
diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
index 88eb6aa7a..5198bf297 100644
--- a/library/alloc/src/macros.rs
+++ b/library/alloc/src/macros.rs
@@ -107,6 +107,8 @@ macro_rules! vec {
 /// format!("test");
 /// format!("hello {}", "world!");
 /// format!("x = {}, y = {y}", 10, y = 30);
+/// let (x, y) = (1, 2);
+/// format!("{x} + {y} = 3");
 /// ```
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index b89b03683..6d247681c 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -1142,7 +1142,7 @@ impl<T: Clone> Rc<T> {
     /// be cloned.
     ///
     /// See also [`get_mut`], which will fail rather than cloning the inner value
-    /// or diassociating [`Weak`] pointers.
+    /// or disassociating [`Weak`] pointers.
     ///
     /// [`clone`]: Clone::clone
     /// [`get_mut`]: Rc::get_mut
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index 63d4d9452..bcd3f49e2 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -1,82 +1,12 @@
-//! A dynamically-sized view into a contiguous sequence, `[T]`.
+//! Utilities for the slice primitive type.
 //!
 //! *[See also the slice primitive type](slice).*
 //!
-//! Slices are a view into a block of memory represented as a pointer and a
-//! length.
+//! Most of the structs in this module are iterator types which can only be created
+//! using a certain function. For example, `slice.iter()` yields an [`Iter`].
 //!
-//! ```
-//! // slicing a Vec
-//! let vec = vec![1, 2, 3];
-//! let int_slice = &vec[..];
-//! // coercing an array to a slice
-//! let str_slice: &[&str] = &["one", "two", "three"];
-//! ```
-//!
-//! Slices are either mutable or shared. The shared slice type is `&[T]`,
-//! while the mutable slice type is `&mut [T]`, where `T` represents the element
-//! type. For example, you can mutate the block of memory that a mutable slice
-//! points to:
-//!
-//! ```
-//! let x = &mut [1, 2, 3];
-//! x[1] = 7;
-//! assert_eq!(x, &[1, 7, 3]);
-//! ```
-//!
-//! Here are some of the things this module contains:
-//!
-//! ## Structs
-//!
-//! There are several structs that are useful for slices, such as [`Iter`], which
-//! represents iteration over a slice.
-//!
-//! ## Trait Implementations
-//!
-//! There are several implementations of common traits for slices. Some examples
-//! include:
-//!
-//! * [`Clone`]
-//! * [`Eq`], [`Ord`] - for slices whose element type are [`Eq`] or [`Ord`].
-//! * [`Hash`] - for slices whose element type is [`Hash`].
-//!
-//! ## Iteration
-//!
-//! The slices implement `IntoIterator`. The iterator yields references to the
-//! slice elements.
-//!
-//! ```
-//! let numbers = &[0, 1, 2];
-//! for n in numbers {
-//!     println!("{n} is a number!");
-//! }
-//! ```
-//!
-//! The mutable slice yields mutable references to the elements:
-//!
-//! ```
-//! let mut scores = [7, 8, 9];
-//! for score in &mut scores[..] {
-//!     *score += 1;
-//! }
-//! ```
-//!
-//! This iterator yields mutable references to the slice's elements, so while
-//! the element type of the slice is `i32`, the element type of the iterator is
-//! `&mut i32`.
-//!
-//! * [`.iter`] and [`.iter_mut`] are the explicit methods to return the default
-//!   iterators.
-//! * Further methods that return iterators are [`.split`], [`.splitn`],
-//!   [`.chunks`], [`.windows`] and more.
-//!
-//! [`Hash`]: core::hash::Hash
-//! [`.iter`]: slice::iter
-//! [`.iter_mut`]: slice::iter_mut
-//! [`.split`]: slice::split
-//! [`.splitn`]: slice::splitn
-//! [`.chunks`]: slice::chunks
-//! [`.windows`]: slice::windows
+//! A few functions are provided to create a slice from a value reference
+//! or from a raw pointer.
 #![stable(feature = "rust1", since = "1.0.0")]
 // Many of the usings in this module are only used in the test configuration.
 // It's cleaner to just turn off the unused_imports warning than to fix them.
@@ -1024,7 +954,7 @@ where
             // Consume the greater side.
             // If equal, prefer the right run to maintain stability.
             unsafe {
-                let to_copy = if is_less(&*right.offset(-1), &*left.offset(-1)) {
+                let to_copy = if is_less(&*right.sub(1), &*left.sub(1)) {
                     decrement_and_get(left)
                 } else {
                     decrement_and_get(right)
@@ -1038,12 +968,12 @@ where
 
     unsafe fn get_and_increment<T>(ptr: &mut *mut T) -> *mut T {
         let old = *ptr;
-        *ptr = unsafe { ptr.offset(1) };
+        *ptr = unsafe { ptr.add(1) };
         old
     }
 
     unsafe fn decrement_and_get<T>(ptr: &mut *mut T) -> *mut T {
-        *ptr = unsafe { ptr.offset(-1) };
+        *ptr = unsafe { ptr.sub(1) };
         *ptr
     }
 
diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
index d5ed2c4ad..b28d20cda 100644
--- a/library/alloc/src/str.rs
+++ b/library/alloc/src/str.rs
@@ -1,26 +1,6 @@
-//! Unicode string slices.
+//! Utilities for the `str` primitive type.
 //!
 //! *[See also the `str` primitive type](str).*
-//!
-//! The `&str` type is one of the two main string types, the other being `String`.
-//! Unlike its `String` counterpart, its contents are borrowed.
-//!
-//! # Basic Usage
-//!
-//! A basic string declaration of `&str` type:
-//!
-//! ```
-//! let hello_world = "Hello, World!";
-//! ```
-//!
-//! Here we have declared a string literal, also known as a string slice.
-//! String literals have a static lifetime, which means the string `hello_world`
-//! is guaranteed to be valid for the duration of the entire program.
-//! We can explicitly specify `hello_world`'s lifetime as well:
-//!
-//! ```
-//! let hello_world: &'static str = "Hello, world!";
-//! ```
 
 #![stable(feature = "rust1", since = "1.0.0")]
 // Many of the usings in this module are only used in the test configuration.
@@ -71,6 +51,8 @@ pub use core::str::{RSplit, Split};
 pub use core::str::{RSplitN, SplitN};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplitTerminator, SplitTerminator};
+#[unstable(feature = "utf8_chunks", issue = "99543")]
+pub use core::str::{Utf8Chunk, Utf8Chunks};
 
 /// Note: `str` in `Concat<str>` is not meaningful here.
 /// This type parameter of the trait only exists to enable another impl.
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index a5118e533..f2448396c 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -44,6 +44,8 @@
 
 #[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;
 use core::iter::FusedIterator;
@@ -58,9 +60,9 @@ use core::ops::Bound::{Excluded, Included, Unbounded};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr;
 use core::slice;
-#[cfg(not(no_global_oom_handling))]
-use core::str::lossy;
 use core::str::pattern::Pattern;
+#[cfg(not(no_global_oom_handling))]
+use core::str::Utf8Chunks;
 
 #[cfg(not(no_global_oom_handling))]
 use crate::borrow::{Cow, ToOwned};
@@ -628,11 +630,11 @@ impl String {
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf8_lossy(v: &[u8]) -> Cow<'_, str> {
-        let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
+        let mut iter = Utf8Chunks::new(v);
 
         let first_valid = if let Some(chunk) = iter.next() {
-            let lossy::Utf8LossyChunk { valid, broken } = chunk;
-            if broken.is_empty() {
+            let valid = chunk.valid();
+            if chunk.invalid().is_empty() {
                 debug_assert_eq!(valid.len(), v.len());
                 return Cow::Borrowed(valid);
             }
@@ -647,9 +649,9 @@ impl String {
         res.push_str(first_valid);
         res.push_str(REPLACEMENT);
 
-        for lossy::Utf8LossyChunk { valid, broken } in iter {
-            res.push_str(valid);
-            if !broken.is_empty() {
+        for chunk in iter {
+            res.push_str(chunk.valid());
+            if !chunk.invalid().is_empty() {
                 res.push_str(REPLACEMENT);
             }
         }
@@ -1080,7 +1082,8 @@ impl String {
     /// current length. The allocator may reserve more space to speculatively
     /// avoid frequent allocations. 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.
+    /// `Ok(())`. Does nothing if capacity is already sufficient. This method
+    /// preserves the contents even if an error occurs.
     ///
     /// # Errors
     ///
@@ -1938,6 +1941,24 @@ impl fmt::Display for FromUtf16Error {
     }
 }
 
+#[cfg(not(bootstrap))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for FromUtf8Error {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "invalid utf-8"
+    }
+}
+
+#[cfg(not(bootstrap))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for FromUtf16Error {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "invalid utf-16"
+    }
+}
+
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Clone for String {
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 4c03cc3ed..4377edeee 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -2763,3 +2763,25 @@ fn data_offset_align(align: usize) -> usize {
     let layout = Layout::new::<ArcInner<()>>();
     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)]
+    fn description(&self) -> &str {
+        core::error::Error::description(&**self)
+    }
+
+    #[allow(deprecated)]
+    fn cause(&self) -> Option<&dyn core::error::Error> {
+        core::error::Error::cause(&**self)
+    }
+
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        core::error::Error::source(&**self)
+    }
+
+    fn provide<'a>(&'a self, req: &mut core::any::Demand<'a>) {
+        core::error::Error::provide(&**self, req);
+    }
+}
diff --git a/library/alloc/src/sync/tests.rs b/library/alloc/src/sync/tests.rs
index 202d0e7f0..0fae8953a 100644
--- a/library/alloc/src/sync/tests.rs
+++ b/library/alloc/src/sync/tests.rs
@@ -618,3 +618,22 @@ fn test_arc_cyclic_two_refs() {
     assert_eq!(Arc::strong_count(&two_refs), 3);
     assert_eq!(Arc::weak_count(&two_refs), 2);
 }
+
+/// Test for Arc::drop bug (https://github.com/rust-lang/rust/issues/55005)
+#[test]
+#[cfg(miri)] // relies on Stacked Borrows in Miri
+fn arc_drop_dereferenceable_race() {
+    // The bug seems to take up to 700 iterations to reproduce with most seeds (tested 0-9).
+    for _ in 0..750 {
+        let arc_1 = Arc::new(());
+        let arc_2 = arc_1.clone();
+        let thread = thread::spawn(|| drop(arc_2));
+        // Spin a bit; makes the race more likely to appear
+        let mut i = 0;
+        while i < 256 {
+            i += 1;
+        }
+        drop(arc_1);
+        thread.join().unwrap();
+    }
+}
diff --git a/library/alloc/src/vec/drain.rs b/library/alloc/src/vec/drain.rs
index 5cdee0bd4..5b73906a1 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;
+use core::mem::{self, ManuallyDrop};
 use core::ptr::{self, NonNull};
 use core::slice::{self};
 
@@ -65,6 +65,77 @@ impl<'a, T, A: Allocator> Drain<'a, T, A> {
     pub fn allocator(&self) -> &A {
         unsafe { self.vec.as_ref().allocator() }
     }
+
+    /// Keep unyielded elements in the source `Vec`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(drain_keep_rest)]
+    ///
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// let mut drain = vec.drain(..);
+    ///
+    /// assert_eq!(drain.next().unwrap(), 'a');
+    ///
+    /// // This call keeps 'b' and 'c' in the vec.
+    /// drain.keep_rest();
+    ///
+    /// // If we wouldn't call `keep_rest()`,
+    /// // `vec` would be empty.
+    /// assert_eq!(vec, ['b', 'c']);
+    /// ```
+    #[unstable(feature = "drain_keep_rest", issue = "101122")]
+    pub fn keep_rest(self) {
+        // At this moment layout looks like this:
+        //
+        // [head] [yielded by next] [unyielded] [yielded by next_back] [tail]
+        //        ^-- start         \_________/-- unyielded_len        \____/-- self.tail_len
+        //                          ^-- unyielded_ptr                  ^-- tail
+        //
+        // Normally `Drop` impl would drop [unyielded] and then move [tail] to the `start`.
+        // Here we want to
+        // 1. Move [unyielded] to `start`
+        // 2. Move [tail] to a new start at `start + len(unyielded)`
+        // 3. Update length of the original vec to `len(head) + len(unyielded) + len(tail)`
+        //    a. In case of ZST, this is the only thing we want to do
+        // 4. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do
+        let mut this = ManuallyDrop::new(self);
+
+        unsafe {
+            let source_vec = this.vec.as_mut();
+
+            let start = source_vec.len();
+            let tail = this.tail_start;
+
+            let unyielded_len = this.iter.len();
+            let unyielded_ptr = this.iter.as_slice().as_ptr();
+
+            // ZSTs have no identity, so we don't need to move them around.
+            let needs_move = mem::size_of::<T>() != 0;
+
+            if needs_move {
+                let start_ptr = source_vec.as_mut_ptr().add(start);
+
+                // memmove back unyielded elements
+                if unyielded_ptr != start_ptr {
+                    let src = unyielded_ptr;
+                    let dst = start_ptr;
+
+                    ptr::copy(src, dst, unyielded_len);
+                }
+
+                // memmove back untouched tail
+                if tail != (start + unyielded_len) {
+                    let src = source_vec.as_ptr().add(tail);
+                    let dst = start_ptr.add(unyielded_len);
+                    ptr::copy(src, dst, this.tail_len);
+                }
+            }
+
+            source_vec.set_len(start + unyielded_len + this.tail_len);
+        }
+    }
 }
 
 #[stable(feature = "vec_drain_as_slice", since = "1.46.0")]
diff --git a/library/alloc/src/vec/drain_filter.rs b/library/alloc/src/vec/drain_filter.rs
index 3c37c92ae..8c03f1692 100644
--- a/library/alloc/src/vec/drain_filter.rs
+++ b/library/alloc/src/vec/drain_filter.rs
@@ -1,6 +1,7 @@
 use crate::alloc::{Allocator, Global};
-use core::ptr::{self};
-use core::slice::{self};
+use core::mem::{self, ManuallyDrop};
+use core::ptr;
+use core::slice;
 
 use super::Vec;
 
@@ -54,6 +55,61 @@ where
     pub fn allocator(&self) -> &A {
         self.vec.allocator()
     }
+
+    /// Keep unyielded elements in the source `Vec`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(drain_filter)]
+    /// #![feature(drain_keep_rest)]
+    ///
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// let mut drain = vec.drain_filter(|_| true);
+    ///
+    /// assert_eq!(drain.next().unwrap(), 'a');
+    ///
+    /// // This call keeps 'b' and 'c' in the vec.
+    /// drain.keep_rest();
+    ///
+    /// // If we wouldn't call `keep_rest()`,
+    /// // `vec` would be empty.
+    /// assert_eq!(vec, ['b', 'c']);
+    /// ```
+    #[unstable(feature = "drain_keep_rest", issue = "101122")]
+    pub fn keep_rest(self) {
+        // At this moment layout looks like this:
+        //
+        //  _____________________/-- old_len
+        // /                     \
+        // [kept] [yielded] [tail]
+        //        \_______/ ^-- idx
+        //                \-- del
+        //
+        // Normally `Drop` impl would drop [tail] (via .for_each(drop), ie still calling `pred`)
+        //
+        // 1. Move [tail] after [kept]
+        // 2. Update length of the original vec to `old_len - del`
+        //    a. In case of ZST, this is the only thing we want to do
+        // 3. Do *not* drop self, as everything is put in a consistent state already, there is nothing to do
+        let mut this = ManuallyDrop::new(self);
+
+        unsafe {
+            // ZSTs have no identity, so we don't need to move them around.
+            let needs_move = mem::size_of::<T>() != 0;
+
+            if needs_move && this.idx < this.old_len && this.del > 0 {
+                let ptr = this.vec.as_mut_ptr();
+                let src = ptr.add(this.idx);
+                let dst = src.sub(this.del);
+                let tail_len = this.old_len - this.idx;
+                src.copy_to(dst, tail_len);
+            }
+
+            let new_len = this.old_len - this.del;
+            this.vec.set_len(new_len);
+        }
+    }
 }
 
 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
diff --git a/library/alloc/src/vec/in_place_collect.rs b/library/alloc/src/vec/in_place_collect.rs
index 55dcb84ad..b211421b2 100644
--- a/library/alloc/src/vec/in_place_collect.rs
+++ b/library/alloc/src/vec/in_place_collect.rs
@@ -267,7 +267,7 @@ where
             // one slot in the underlying storage will have been freed up and we can immediately
             // write back the result.
             unsafe {
-                let dst = dst_buf.offset(i as isize);
+                let dst = dst_buf.add(i);
                 debug_assert!(dst as *const _ <= end, "InPlaceIterable contract violation");
                 ptr::write(dst, self.__iterator_get_unchecked(i));
                 // Since this executes user code which can panic we have to bump the pointer
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 1b483e3fc..b4157fd58 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -4,7 +4,6 @@ use crate::alloc::{Allocator, Global};
 use crate::raw_vec::RawVec;
 use core::array;
 use core::fmt;
-use core::intrinsics::arith_offset;
 use core::iter::{
     FusedIterator, InPlaceIterable, SourceIter, TrustedLen, TrustedRandomAccessNoCoerce,
 };
@@ -148,19 +147,19 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
     #[inline]
     fn next(&mut self) -> Option<T> {
-        if self.ptr as *const _ == self.end {
+        if self.ptr == self.end {
             None
         } else if mem::size_of::<T>() == 0 {
             // purposefully don't use 'ptr.offset' because for
             // vectors with 0-size elements this would return the
             // same pointer.
-            self.ptr = unsafe { arith_offset(self.ptr as *const i8, 1) as *mut T };
+            self.ptr = self.ptr.wrapping_byte_add(1);
 
             // Make up a value of this ZST.
             Some(unsafe { mem::zeroed() })
         } else {
             let old = self.ptr;
-            self.ptr = unsafe { self.ptr.offset(1) };
+            self.ptr = unsafe { self.ptr.add(1) };
 
             Some(unsafe { ptr::read(old) })
         }
@@ -184,7 +183,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
             // 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.
-            self.ptr = unsafe { arith_offset(self.ptr as *const i8, step_size as isize) as *mut T }
+            self.ptr = self.ptr.wrapping_byte_add(step_size);
         } else {
             // SAFETY: the min() above ensures that step_size is in bounds
             self.ptr = unsafe { self.ptr.add(step_size) };
@@ -217,7 +216,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
                 return Err(unsafe { array::IntoIter::new_unchecked(raw_ary, 0..len) });
             }
 
-            self.ptr = unsafe { arith_offset(self.ptr as *const i8, N as isize) as *mut T };
+            self.ptr = self.ptr.wrapping_byte_add(N);
             // Safety: ditto
             return Ok(unsafe { MaybeUninit::array_assume_init(raw_ary) });
         }
@@ -267,12 +266,12 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
             None
         } else if mem::size_of::<T>() == 0 {
             // See above for why 'ptr.offset' isn't used
-            self.end = unsafe { arith_offset(self.end as *const i8, -1) as *mut T };
+            self.end = self.end.wrapping_byte_sub(1);
 
             // Make up a value of this ZST.
             Some(unsafe { mem::zeroed() })
         } else {
-            self.end = unsafe { self.end.offset(-1) };
+            self.end = unsafe { self.end.sub(1) };
 
             Some(unsafe { ptr::read(self.end) })
         }
@@ -283,12 +282,10 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
         let step_size = self.len().min(n);
         if mem::size_of::<T>() == 0 {
             // SAFETY: same as for advance_by()
-            self.end = unsafe {
-                arith_offset(self.end as *const i8, step_size.wrapping_neg() as isize) as *mut T
-            }
+            self.end = self.end.wrapping_byte_sub(step_size);
         } else {
             // SAFETY: same as for advance_by()
-            self.end = unsafe { self.end.offset(step_size.wrapping_neg() as isize) };
+            self.end = unsafe { self.end.sub(step_size) };
         }
         let to_drop = ptr::slice_from_raw_parts_mut(self.end as *mut T, step_size);
         // SAFETY: same as for advance_by()
diff --git a/library/alloc/src/vec/is_zero.rs b/library/alloc/src/vec/is_zero.rs
index 92a32779b..2e025c8a4 100644
--- a/library/alloc/src/vec/is_zero.rs
+++ b/library/alloc/src/vec/is_zero.rs
@@ -1,3 +1,5 @@
+use core::num::{Saturating, Wrapping};
+
 use crate::boxed::Box;
 
 #[rustc_specialization_trait]
@@ -144,3 +146,17 @@ impl_is_zero_option_of_nonzero!(
     NonZeroUsize,
     NonZeroIsize,
 );
+
+unsafe impl<T: IsZero> IsZero for Wrapping<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+unsafe impl<T: IsZero> IsZero for Saturating<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index fa9f2131c..60b36af5e 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -59,7 +59,7 @@ use core::cmp::Ordering;
 use core::convert::TryFrom;
 use core::fmt;
 use core::hash::{Hash, Hasher};
-use core::intrinsics::{arith_offset, assume};
+use core::intrinsics::assume;
 use core::iter;
 #[cfg(not(no_global_oom_handling))]
 use core::iter::FromIterator;
@@ -436,7 +436,7 @@ impl<T> Vec<T> {
     /// an explanation of the difference between length and capacity, see
     /// *[Capacity and reallocation]*.
     ///
-    /// If it is imporant to know the exact allocated capacity of a `Vec`,
+    /// If it is important to know the exact allocated capacity of a `Vec`,
     /// always use the [`capacity`] method after construction.
     ///
     /// For `Vec<T>` where `T` is a zero-sized type, there will be no allocation
@@ -542,8 +542,8 @@ impl<T> Vec<T> {
     ///
     /// unsafe {
     ///     // Overwrite memory with 4, 5, 6
-    ///     for i in 0..len as isize {
-    ///         ptr::write(p.offset(i), 4 + i);
+    ///     for i in 0..len {
+    ///         ptr::write(p.add(i), 4 + i);
     ///     }
     ///
     ///     // Put everything back together into a Vec
@@ -591,7 +591,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// an explanation of the difference between length and capacity, see
     /// *[Capacity and reallocation]*.
     ///
-    /// If it is imporant to know the exact allocated capacity of a `Vec`,
+    /// If it is important to know the exact allocated capacity of a `Vec`,
     /// always use the [`capacity`] method after construction.
     ///
     /// For `Vec<T, A>` where `T` is a zero-sized type, there will be no allocation
@@ -702,8 +702,8 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// unsafe {
     ///     // Overwrite memory with 4, 5, 6
-    ///     for i in 0..len as isize {
-    ///         ptr::write(p.offset(i), 4 + i);
+    ///     for i in 0..len {
+    ///         ptr::write(p.add(i), 4 + i);
     ///     }
     ///
     ///     // Put everything back together into a Vec
@@ -875,7 +875,8 @@ impl<T, A: Allocator> Vec<T, A> {
     /// in the given `Vec<T>`. The collection may reserve more space to speculatively 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.
+    /// `Ok(())`. Does nothing if capacity is already sufficient. This method
+    /// preserves the contents even if an error occurs.
     ///
     /// # Errors
     ///
@@ -1393,7 +1394,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 if index < len {
                     // Shift everything over to make space. (Duplicating the
                     // `index`th element into two consecutive places.)
-                    ptr::copy(p, p.offset(1), len - index);
+                    ptr::copy(p, p.add(1), len - index);
                 } else if index == len {
                     // No elements need shifting.
                 } else {
@@ -1455,7 +1456,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 ret = ptr::read(ptr);
 
                 // Shift everything down to fill in that spot.
-                ptr::copy(ptr.offset(1), ptr, len - index - 1);
+                ptr::copy(ptr.add(1), ptr, len - index - 1);
             }
             self.set_len(len - 1);
             ret
@@ -2408,7 +2409,7 @@ impl<T, A: Allocator> Vec<T, A> {
             // Write all elements except the last one
             for _ in 1..n {
                 ptr::write(ptr, value.next());
-                ptr = ptr.offset(1);
+                ptr = ptr.add(1);
                 // Increment the length in every step in case next() panics
                 local_len.increment_len(1);
             }
@@ -2677,7 +2678,7 @@ impl<T, A: Allocator> IntoIterator for Vec<T, A> {
             let alloc = ManuallyDrop::new(ptr::read(me.allocator()));
             let begin = me.as_mut_ptr();
             let end = if mem::size_of::<T>() == 0 {
-                arith_offset(begin as *const i8, me.len() as isize) as *const T
+                begin.wrapping_byte_add(me.len())
             } else {
                 begin.add(me.len()) as *const T
             };
@@ -2927,6 +2928,8 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
 impl<T> const Default for Vec<T> {
     /// Creates an empty `Vec<T>`.
+    ///
+    /// The vector will not allocate until elements are pushed onto it.
     fn default() -> Vec<T> {
         Vec::new()
     }
diff --git a/library/alloc/src/vec/spec_extend.rs b/library/alloc/src/vec/spec_extend.rs
index 506ee0ecf..1ea9c827a 100644
--- a/library/alloc/src/vec/spec_extend.rs
+++ b/library/alloc/src/vec/spec_extend.rs
@@ -39,7 +39,7 @@ where
                 let mut local_len = SetLenOnDrop::new(&mut self.len);
                 iterator.for_each(move |element| {
                     ptr::write(ptr, element);
-                    ptr = ptr.offset(1);
+                    ptr = ptr.add(1);
                     // Since the loop executes user code which can panic we have to bump the pointer
                     // after each step.
                     // NB can't overflow since we would have had to alloc the address space