Merging upstream version 1.69.0+dfsg1.

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

103 files changed, 6864 insertions, 1342 deletions

diff --git a/library/core/benches/array.rs b/library/core/benches/array.rs
new file mode 100644
index 000000000..d8cc44d05
--- /dev/null
+++ b/library/core/benches/array.rs
@@ -0,0 +1,19 @@
+use test::black_box;
+use test::Bencher;
+
+macro_rules! map_array {
+    ($func_name:ident, $start_item: expr, $map_item: expr, $arr_size: expr) => {
+        #[bench]
+        fn $func_name(b: &mut Bencher) {
+            let arr = [$start_item; $arr_size];
+            b.iter(|| black_box(arr).map(|_| black_box($map_item)));
+        }
+    };
+}
+
+map_array!(map_8byte_8byte_8, 0u64, 1u64, 80);
+map_array!(map_8byte_8byte_64, 0u64, 1u64, 640);
+map_array!(map_8byte_8byte_256, 0u64, 1u64, 2560);
+
+map_array!(map_8byte_256byte_256, 0u64, [0u64; 4], 2560);
+map_array!(map_256byte_8byte_256, [0u64; 4], 0u64, 2560);
diff --git a/library/core/benches/char/methods.rs b/library/core/benches/char/methods.rs
index 9408f83c3..5d4df1ac8 100644
--- a/library/core/benches/char/methods.rs
+++ b/library/core/benches/char/methods.rs
@@ -1,26 +1,26 @@
-use test::Bencher;
+use test::{black_box, Bencher};
 
 const CHARS: [char; 9] = ['0', 'x', '2', '5', 'A', 'f', '7', '8', '9'];
 const RADIX: [u32; 5] = [2, 8, 10, 16, 32];
 
 #[bench]
 fn bench_to_digit_radix_2(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(2)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(2)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_10(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(10)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(10)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_16(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(16)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(16)).min())
 }
 
 #[bench]
 fn bench_to_digit_radix_36(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_digit(36)).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_digit(36)).min())
 }
 
 #[bench]
@@ -31,47 +31,59 @@ fn bench_to_digit_radix_var(b: &mut Bencher) {
             .cycle()
             .zip(RADIX.iter().cycle())
             .take(10_000)
-            .map(|(c, radix)| c.to_digit(*radix))
+            .map(|(c, radix)| black_box(c).to_digit(*radix))
             .min()
     })
 }
 
 #[bench]
 fn bench_to_ascii_uppercase(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_uppercase()).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_ascii_uppercase()).min())
 }
 
 #[bench]
 fn bench_to_ascii_lowercase(b: &mut Bencher) {
-    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_lowercase()).min())
+    b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| black_box(c).to_ascii_lowercase()).min())
 }
 
 #[bench]
 fn bench_ascii_mix_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (0..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_mix_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (0..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_char_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (0..=127).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_ascii_char_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (0..=127).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
 
 #[bench]
 fn bench_non_ascii_char_to_uppercase(b: &mut Bencher) {
-    b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
+    b.iter(|| {
+        (128..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_uppercase()).count()
+    })
 }
 
 #[bench]
 fn bench_non_ascii_char_to_lowercase(b: &mut Bencher) {
-    b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
+    b.iter(|| {
+        (128..=255).cycle().take(10_000).map(|b| black_box(char::from(b)).to_lowercase()).count()
+    })
 }
diff --git a/library/core/benches/lib.rs b/library/core/benches/lib.rs
index f1244d932..e4100120d 100644
--- a/library/core/benches/lib.rs
+++ b/library/core/benches/lib.rs
@@ -9,6 +9,7 @@
 extern crate test;
 
 mod any;
+mod array;
 mod ascii;
 mod char;
 mod fmt;
diff --git a/library/core/benches/num/flt2dec/strategy/dragon.rs b/library/core/benches/num/flt2dec/strategy/dragon.rs
index 319b9773e..377c99eff 100644
--- a/library/core/benches/num/flt2dec/strategy/dragon.rs
+++ b/library/core/benches/num/flt2dec/strategy/dragon.rs
@@ -1,14 +1,14 @@
 use super::super::*;
 use core::num::flt2dec::strategy::dragon::*;
 use std::mem::MaybeUninit;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 #[bench]
 fn bench_small_shortest(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -17,7 +17,7 @@ fn bench_big_shortest(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -26,7 +26,7 @@ fn bench_small_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -35,7 +35,7 @@ fn bench_big_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -44,7 +44,7 @@ fn bench_small_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -53,7 +53,7 @@ fn bench_big_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -62,7 +62,7 @@ fn bench_small_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -71,6 +71,6 @@ fn bench_big_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
diff --git a/library/core/benches/num/flt2dec/strategy/grisu.rs b/library/core/benches/num/flt2dec/strategy/grisu.rs
index 8e47a046c..6bea5e55d 100644
--- a/library/core/benches/num/flt2dec/strategy/grisu.rs
+++ b/library/core/benches/num/flt2dec/strategy/grisu.rs
@@ -1,7 +1,7 @@
 use super::super::*;
 use core::num::flt2dec::strategy::grisu::*;
 use std::mem::MaybeUninit;
-use test::Bencher;
+use test::{black_box, Bencher};
 
 pub fn decode_finite<T: DecodableFloat>(v: T) -> Decoded {
     match decode(v).1 {
@@ -15,7 +15,7 @@ fn bench_small_shortest(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -24,7 +24,7 @@ fn bench_big_shortest(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); MAX_SIG_DIGITS];
     b.iter(|| {
-        format_shortest(&decoded, &mut buf);
+        format_shortest(black_box(&decoded), &mut buf);
     });
 }
 
@@ -33,7 +33,7 @@ fn bench_small_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -42,7 +42,7 @@ fn bench_big_exact_3(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 3];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -51,7 +51,7 @@ fn bench_small_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -60,7 +60,7 @@ fn bench_big_exact_12(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 12];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -69,7 +69,7 @@ fn bench_small_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(3.141592f64);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
 
@@ -78,6 +78,6 @@ fn bench_big_exact_inf(b: &mut Bencher) {
     let decoded = decode_finite(f64::MAX);
     let mut buf = [MaybeUninit::new(0); 1024];
     b.iter(|| {
-        format_exact(&decoded, &mut buf, i16::MIN);
+        format_exact(black_box(&decoded), &mut buf, i16::MIN);
     });
 }
diff --git a/library/core/src/alloc/global.rs b/library/core/src/alloc/global.rs
index 1d80b8bf9..18da70451 100644
--- a/library/core/src/alloc/global.rs
+++ b/library/core/src/alloc/global.rs
@@ -203,7 +203,7 @@ pub unsafe trait GlobalAlloc {
         ptr
     }
 
-    /// Shrink or grow a block of memory to the given `new_size`.
+    /// Shrink or grow a block of memory to the given `new_size` in bytes.
     /// The block is described by the given `ptr` pointer and `layout`.
     ///
     /// If this returns a non-null pointer, then ownership of the memory block
@@ -211,10 +211,11 @@ pub unsafe trait GlobalAlloc {
     /// Any access to the old `ptr` is Undefined Behavior, even if the
     /// allocation remained in-place. The newly returned pointer is the only valid pointer
     /// for accessing this memory now.
+    ///
     /// The new memory block is allocated with `layout`,
-    /// but with the `size` updated to `new_size`. This new layout must be
-    /// used when deallocating the new memory block with `dealloc`. The range
-    /// `0..min(layout.size(), new_size)` of the new memory block is
+    /// but with the `size` updated to `new_size` in bytes.
+    /// This new layout must be used when deallocating the new memory block with `dealloc`.
+    /// The range `0..min(layout.size(), new_size)` of the new memory block is
     /// guaranteed to have the same values as the original block.
     ///
     /// If this method returns null, then ownership of the memory
diff --git a/library/core/src/any.rs b/library/core/src/any.rs
index c0fb0d993..c27646b8f 100644
--- a/library/core/src/any.rs
+++ b/library/core/src/any.rs
@@ -56,7 +56,7 @@
 //!     let value_any = value as &dyn Any;
 //!
 //!     // Try to convert our value to a `String`. If successful, we want to
-//!     // output the String`'s length as well as its value. If not, it's a
+//!     // output the `String`'s length as well as its value. If not, it's a
 //!     // different type: just print it out unadorned.
 //!     match value_any.downcast_ref::<String>() {
 //!         Some(as_string) => {
diff --git a/library/core/src/array/drain.rs b/library/core/src/array/drain.rs
new file mode 100644
index 000000000..5fadf907b
--- /dev/null
+++ b/library/core/src/array/drain.rs
@@ -0,0 +1,76 @@
+use crate::iter::{TrustedLen, UncheckedIterator};
+use crate::mem::ManuallyDrop;
+use crate::ptr::drop_in_place;
+use crate::slice;
+
+/// A situationally-optimized version of `array.into_iter().for_each(func)`.
+///
+/// [`crate::array::IntoIter`]s are great when you need an owned iterator, but
+/// storing the entire array *inside* the iterator like that can sometimes
+/// pessimize code.  Notable, it can be more bytes than you really want to move
+/// around, and because the array accesses index into it SRoA has a harder time
+/// optimizing away the type than it does iterators that just hold a couple pointers.
+///
+/// Thus this function exists, which gives a way to get *moved* access to the
+/// elements of an array using a small iterator -- no bigger than a slice iterator.
+///
+/// The function-taking-a-closure structure makes it safe, as it keeps callers
+/// from looking at already-dropped elements.
+pub(crate) fn drain_array_with<T, R, const N: usize>(
+    array: [T; N],
+    func: impl for<'a> FnOnce(Drain<'a, T>) -> R,
+) -> R {
+    let mut array = ManuallyDrop::new(array);
+    // SAFETY: Now that the local won't drop it, it's ok to construct the `Drain` which will.
+    let drain = Drain(array.iter_mut());
+    func(drain)
+}
+
+/// See [`drain_array_with`] -- this is `pub(crate)` only so it's allowed to be
+/// mentioned in the signature of that method.  (Otherwise it hits `E0446`.)
+// INVARIANT: It's ok to drop the remainder of the inner iterator.
+pub(crate) struct Drain<'a, T>(slice::IterMut<'a, T>);
+
+impl<T> Drop for Drain<'_, T> {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariant, we're allowed to drop all these.
+        unsafe { drop_in_place(self.0.as_mut_slice()) }
+    }
+}
+
+impl<T> Iterator for Drain<'_, T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        let p: *const T = self.0.next()?;
+        // SAFETY: The iterator was already advanced, so we won't drop this later.
+        Some(unsafe { p.read() })
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let n = self.len();
+        (n, Some(n))
+    }
+}
+
+impl<T> ExactSizeIterator for Drain<'_, T> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.0.len()
+    }
+}
+
+// SAFETY: This is a 1:1 wrapper for a slice iterator, which is also `TrustedLen`.
+unsafe impl<T> TrustedLen for Drain<'_, T> {}
+
+impl<T> UncheckedIterator for Drain<'_, T> {
+    unsafe fn next_unchecked(&mut self) -> T {
+        // SAFETY: `Drain` is 1:1 with the inner iterator, so if the caller promised
+        // that there's an element left, the inner iterator has one too.
+        let p: *const T = unsafe { self.0.next_unchecked() };
+        // SAFETY: The iterator was already advanced, so we won't drop this later.
+        unsafe { p.read() }
+    }
+}
diff --git a/library/core/src/array/equality.rs b/library/core/src/array/equality.rs
index b2c895f88..d749865f7 100644
--- a/library/core/src/array/equality.rs
+++ b/library/core/src/array/equality.rs
@@ -1,6 +1,5 @@
+use crate::cmp::BytewiseEq;
 use crate::convert::TryInto;
-use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
-use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<A, B, const N: usize> PartialEq<[B; N]> for [A; N]
@@ -144,74 +143,14 @@ impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
     }
 }
 
-impl<T: IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
+impl<T: BytewiseEq<U>, U, const N: usize> SpecArrayEq<U, N> for T {
     fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
-        // SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`.
-        unsafe {
-            let b = &*b.as_ptr().cast::<[T; N]>();
-            crate::intrinsics::raw_eq(a, b)
-        }
+        // SAFETY: Arrays are compared element-wise, and don't add any padding
+        // between elements, so when the elements are `BytewiseEq`, we can
+        // compare the entire array at once.
+        unsafe { crate::intrinsics::raw_eq(a, crate::mem::transmute(b)) }
     }
     fn spec_ne(a: &[T; N], b: &[U; N]) -> bool {
         !Self::spec_eq(a, b)
     }
 }
-
-/// `U` exists on here mostly because `min_specialization` didn't let me
-/// repeat the `T` type parameter in the above specialization, so instead
-/// the `T == U` constraint comes from the impls on this.
-/// # Safety
-/// - Neither `Self` nor `U` has any padding.
-/// - `Self` and `U` have the same layout.
-/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things)
-#[rustc_specialization_trait]
-unsafe trait IsRawEqComparable<U>: PartialEq<U> {}
-
-macro_rules! is_raw_eq_comparable {
-    ($($t:ty),+ $(,)?) => {$(
-        unsafe impl IsRawEqComparable<$t> for $t {}
-    )+};
-}
-
-// SAFETY: All the ordinary integer types have no padding, and are not pointers.
-is_raw_eq_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
-
-// SAFETY: bool and char have *niches*, but no *padding* (and these are not pointer types), so this
-// is sound
-is_raw_eq_comparable!(bool, char);
-
-// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers,
-// and they compare like their underlying numeric type.
-is_raw_eq_comparable!(
-    NonZeroU8,
-    NonZeroU16,
-    NonZeroU32,
-    NonZeroU64,
-    NonZeroU128,
-    NonZeroUsize,
-    NonZeroI8,
-    NonZeroI16,
-    NonZeroI32,
-    NonZeroI64,
-    NonZeroI128,
-    NonZeroIsize,
-);
-
-// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
-// are also safe to equality-compare bitwise inside an `Option`.
-// The way `PartialOrd` is defined for `Option` means that this wouldn't work
-// for `<` or `>` on the signed types, but since we only do `==` it's fine.
-is_raw_eq_comparable!(
-    Option<NonZeroU8>,
-    Option<NonZeroU16>,
-    Option<NonZeroU32>,
-    Option<NonZeroU64>,
-    Option<NonZeroU128>,
-    Option<NonZeroUsize>,
-    Option<NonZeroI8>,
-    Option<NonZeroI16>,
-    Option<NonZeroI32>,
-    Option<NonZeroI64>,
-    Option<NonZeroI128>,
-    Option<NonZeroIsize>,
-);
diff --git a/library/core/src/array/mod.rs b/library/core/src/array/mod.rs
index 2825e0bbb..1643842d6 100644
--- a/library/core/src/array/mod.rs
+++ b/library/core/src/array/mod.rs
@@ -10,16 +10,19 @@ use crate::convert::{Infallible, TryFrom};
 use crate::error::Error;
 use crate::fmt;
 use crate::hash::{self, Hash};
-use crate::iter::TrustedLen;
+use crate::iter::UncheckedIterator;
 use crate::mem::{self, MaybeUninit};
 use crate::ops::{
     ChangeOutputType, ControlFlow, FromResidual, Index, IndexMut, NeverShortCircuit, Residual, Try,
 };
 use crate::slice::{Iter, IterMut};
 
+mod drain;
 mod equality;
 mod iter;
 
+pub(crate) use drain::drain_array_with;
+
 #[stable(feature = "array_value_iter", since = "1.51.0")]
 pub use iter::IntoIter;
 
@@ -52,16 +55,11 @@ pub use iter::IntoIter;
 /// ```
 #[inline]
 #[stable(feature = "array_from_fn", since = "1.63.0")]
-pub fn from_fn<T, const N: usize, F>(mut cb: F) -> [T; N]
+pub fn from_fn<T, const N: usize, F>(cb: F) -> [T; N]
 where
     F: FnMut(usize) -> T,
 {
-    let mut idx = 0;
-    [(); N].map(|_| {
-        let res = cb(idx);
-        idx += 1;
-        res
-    })
+    try_from_fn(NeverShortCircuit::wrap_mut_1(cb)).0
 }
 
 /// Creates an array `[T; N]` where each fallible array element `T` is returned by the `cb` call.
@@ -101,9 +99,14 @@ where
     R: Try,
     R::Residual: Residual<[R::Output; N]>,
 {
-    // SAFETY: we know for certain that this iterator will yield exactly `N`
-    // items.
-    unsafe { try_collect_into_array_unchecked(&mut (0..N).map(cb)) }
+    let mut array = MaybeUninit::uninit_array::<N>();
+    match try_from_fn_erased(&mut array, cb) {
+        ControlFlow::Break(r) => FromResidual::from_residual(r),
+        ControlFlow::Continue(()) => {
+            // SAFETY: All elements of the array were populated.
+            try { unsafe { MaybeUninit::array_assume_init(array) } }
+        }
+    }
 }
 
 /// Converts a reference to `T` into a reference to an array of length 1 (without copying).
@@ -131,7 +134,8 @@ pub struct TryFromSliceError(());
 impl fmt::Display for TryFromSliceError {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Display::fmt(self.__description(), f)
+        #[allow(deprecated)]
+        self.description().fmt(f)
     }
 }
 
@@ -139,20 +143,6 @@ impl fmt::Display for TryFromSliceError {
 impl Error for TryFromSliceError {
     #[allow(deprecated)]
     fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-impl TryFromSliceError {
-    #[unstable(
-        feature = "array_error_internals",
-        reason = "available through Error trait and this method should not \
-                     be exposed publicly",
-        issue = "none"
-    )]
-    #[inline]
-    #[doc(hidden)]
-    pub fn __description(&self) -> &str {
         "could not convert slice to array"
     }
 }
@@ -427,9 +417,7 @@ trait SpecArrayClone: Clone {
 impl<T: Clone> SpecArrayClone for T {
     #[inline]
     default fn clone<const N: usize>(array: &[T; N]) -> [T; N] {
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { collect_into_array_unchecked(&mut array.iter().cloned()) }
+        from_trusted_iterator(array.iter().cloned())
     }
 }
 
@@ -513,9 +501,7 @@ impl<T, const N: usize> [T; N] {
     where
         F: FnMut(T) -> U,
     {
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) }
+        self.try_map(NeverShortCircuit::wrap_mut_1(f)).0
     }
 
     /// A fallible function `f` applied to each element on array `self` in order to
@@ -552,9 +538,7 @@ impl<T, const N: usize> [T; N] {
         R: Try,
         R::Residual: Residual<[R::Output; N]>,
     {
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { try_collect_into_array_unchecked(&mut IntoIterator::into_iter(self).map(f)) }
+        drain_array_with(self, |iter| try_from_trusted_iterator(iter.map(f)))
     }
 
     /// 'Zips up' two arrays into a single array of pairs.
@@ -575,11 +559,9 @@ impl<T, const N: usize> [T; N] {
     /// ```
     #[unstable(feature = "array_zip", issue = "80094")]
     pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N] {
-        let mut iter = IntoIterator::into_iter(self).zip(rhs);
-
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { collect_into_array_unchecked(&mut iter) }
+        drain_array_with(self, |lhs| {
+            drain_array_with(rhs, |rhs| from_trusted_iterator(crate::iter::zip(lhs, rhs)))
+        })
     }
 
     /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
@@ -626,9 +608,7 @@ impl<T, const N: usize> [T; N] {
     /// ```
     #[unstable(feature = "array_methods", issue = "76118")]
     pub fn each_ref(&self) -> [&T; N] {
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { collect_into_array_unchecked(&mut self.iter()) }
+        from_trusted_iterator(self.iter())
     }
 
     /// Borrows each element mutably and returns an array of mutable references
@@ -648,9 +628,7 @@ impl<T, const N: usize> [T; N] {
     /// ```
     #[unstable(feature = "array_methods", issue = "76118")]
     pub fn each_mut(&mut self) -> [&mut T; N] {
-        // SAFETY: we know for certain that this iterator will yield exactly `N`
-        // items.
-        unsafe { collect_into_array_unchecked(&mut self.iter_mut()) }
+        from_trusted_iterator(self.iter_mut())
     }
 
     /// Divides one array reference into two at an index.
@@ -810,105 +788,71 @@ impl<T, const N: usize> [T; N] {
     }
 }
 
-/// Pulls `N` items from `iter` and returns them as an array. If the iterator
-/// yields fewer than `N` items, this function exhibits undefined behavior.
+/// Populate an array from the first `N` elements of `iter`
 ///
-/// See [`try_collect_into_array`] for more information.
+/// # Panics
 ///
+/// If the iterator doesn't actually have enough items.
 ///
-/// # Safety
-///
-/// It is up to the caller to guarantee that `iter` yields at least `N` items.
-/// Violating this condition causes undefined behavior.
-unsafe fn try_collect_into_array_unchecked<I, T, R, const N: usize>(iter: &mut I) -> R::TryType
-where
-    // Note: `TrustedLen` here is somewhat of an experiment. This is just an
-    // internal function, so feel free to remove if this bound turns out to be a
-    // bad idea. In that case, remember to also remove the lower bound
-    // `debug_assert!` below!
-    I: Iterator + TrustedLen,
-    I::Item: Try<Output = T, Residual = R>,
-    R: Residual<[T; N]>,
-{
-    debug_assert!(N <= iter.size_hint().1.unwrap_or(usize::MAX));
-    debug_assert!(N <= iter.size_hint().0);
-
-    // SAFETY: covered by the function contract.
-    unsafe { try_collect_into_array(iter).unwrap_unchecked() }
+/// By depending on `TrustedLen`, however, we can do that check up-front (where
+/// it easily optimizes away) so it doesn't impact the loop that fills the array.
+#[inline]
+fn from_trusted_iterator<T, const N: usize>(iter: impl UncheckedIterator<Item = T>) -> [T; N] {
+    try_from_trusted_iterator(iter.map(NeverShortCircuit)).0
 }
 
-// Infallible version of `try_collect_into_array_unchecked`.
-unsafe fn collect_into_array_unchecked<I, const N: usize>(iter: &mut I) -> [I::Item; N]
+#[inline]
+fn try_from_trusted_iterator<T, R, const N: usize>(
+    iter: impl UncheckedIterator<Item = R>,
+) -> ChangeOutputType<R, [T; N]>
 where
-    I: Iterator + TrustedLen,
+    R: Try<Output = T>,
+    R::Residual: Residual<[T; N]>,
 {
-    let mut map = iter.map(NeverShortCircuit);
-
-    // SAFETY: The same safety considerations w.r.t. the iterator length
-    // apply for `try_collect_into_array_unchecked` as for
-    // `collect_into_array_unchecked`
-    match unsafe { try_collect_into_array_unchecked(&mut map) } {
-        NeverShortCircuit(array) => array,
+    assert!(iter.size_hint().0 >= N);
+    fn next<T>(mut iter: impl UncheckedIterator<Item = T>) -> impl FnMut(usize) -> T {
+        move |_| {
+            // SAFETY: We know that `from_fn` will call this at most N times,
+            // and we checked to ensure that we have at least that many items.
+            unsafe { iter.next_unchecked() }
+        }
     }
+
+    try_from_fn(next(iter))
 }
 
-/// Pulls `N` items from `iter` and returns them as an array. If the iterator
-/// yields fewer than `N` items, `Err` is returned containing an iterator over
-/// the already yielded items.
+/// Version of [`try_from_fn`] using a passed-in slice in order to avoid
+/// needing to monomorphize for every array length.
 ///
-/// Since the iterator is passed as a mutable reference and this function calls
-/// `next` at most `N` times, the iterator can still be used afterwards to
-/// retrieve the remaining items.
+/// This takes a generator rather than an iterator so that *at the type level*
+/// it never needs to worry about running out of items.  When combined with
+/// an infallible `Try` type, that means the loop canonicalizes easily, allowing
+/// it to optimize well.
 ///
-/// If `iter.next()` panicks, all items already yielded by the iterator are
-/// dropped.
+/// It would be *possible* to unify this and [`iter_next_chunk_erased`] into one
+/// function that does the union of both things, but last time it was that way
+/// it resulted in poor codegen from the "are there enough source items?" checks
+/// not optimizing away.  So if you give it a shot, make sure to watch what
+/// happens in the codegen tests.
 #[inline]
-fn try_collect_into_array<I, T, R, const N: usize>(
-    iter: &mut I,
-) -> Result<R::TryType, IntoIter<T, N>>
+fn try_from_fn_erased<T, R>(
+    buffer: &mut [MaybeUninit<T>],
+    mut generator: impl FnMut(usize) -> R,
+) -> ControlFlow<R::Residual>
 where
-    I: Iterator,
-    I::Item: Try<Output = T, Residual = R>,
-    R: Residual<[T; N]>,
+    R: Try<Output = T>,
 {
-    if N == 0 {
-        // SAFETY: An empty array is always inhabited and has no validity invariants.
-        return Ok(Try::from_output(unsafe { mem::zeroed() }));
-    }
+    let mut guard = Guard { array_mut: buffer, initialized: 0 };
 
-    let mut array = MaybeUninit::uninit_array::<N>();
-    let mut guard = Guard { array_mut: &mut array, initialized: 0 };
-
-    for _ in 0..N {
-        match iter.next() {
-            Some(item_rslt) => {
-                let item = match item_rslt.branch() {
-                    ControlFlow::Break(r) => {
-                        return Ok(FromResidual::from_residual(r));
-                    }
-                    ControlFlow::Continue(elem) => elem,
-                };
-
-                // SAFETY: `guard.initialized` starts at 0, which means push can be called
-                // at most N times, which this loop does.
-                unsafe {
-                    guard.push_unchecked(item);
-                }
-            }
-            None => {
-                let alive = 0..guard.initialized;
-                mem::forget(guard);
-                // SAFETY: `array` was initialized with exactly `initialized`
-                // number of elements.
-                return Err(unsafe { IntoIter::new_unchecked(array, alive) });
-            }
-        }
+    while guard.initialized < guard.array_mut.len() {
+        let item = generator(guard.initialized).branch()?;
+
+        // SAFETY: The loop condition ensures we have space to push the item
+        unsafe { guard.push_unchecked(item) };
     }
 
     mem::forget(guard);
-    // SAFETY: All elements of the array were populated in the loop above.
-    let output = unsafe { array.transpose().assume_init() };
-    Ok(Try::from_output(output))
+    ControlFlow::Continue(())
 }
 
 /// Panic guard for incremental initialization of arrays.
@@ -922,14 +866,14 @@ where
 ///
 /// To minimize indirection fields are still pub but callers should at least use
 /// `push_unchecked` to signal that something unsafe is going on.
-pub(crate) struct Guard<'a, T, const N: usize> {
+struct Guard<'a, T> {
     /// The array to be initialized.
-    pub array_mut: &'a mut [MaybeUninit<T>; N],
+    pub array_mut: &'a mut [MaybeUninit<T>],
     /// The number of items that have been initialized so far.
     pub initialized: usize,
 }
 
-impl<T, const N: usize> Guard<'_, T, N> {
+impl<T> Guard<'_, T> {
     /// Adds an item to the array and updates the initialized item counter.
     ///
     /// # Safety
@@ -947,28 +891,73 @@ impl<T, const N: usize> Guard<'_, T, N> {
     }
 }
 
-impl<T, const N: usize> Drop for Guard<'_, T, N> {
+impl<T> Drop for Guard<'_, T> {
     fn drop(&mut self) {
-        debug_assert!(self.initialized <= N);
+        debug_assert!(self.initialized <= self.array_mut.len());
 
         // SAFETY: this slice will contain only initialized objects.
         unsafe {
             crate::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
-                &mut self.array_mut.get_unchecked_mut(..self.initialized),
+                self.array_mut.get_unchecked_mut(..self.initialized),
             ));
         }
     }
 }
 
-/// Returns the next chunk of `N` items from the iterator or errors with an
-/// iterator over the remainder. Used for `Iterator::next_chunk`.
+/// Pulls `N` items from `iter` and returns them as an array. If the iterator
+/// yields fewer than `N` items, `Err` is returned containing an iterator over
+/// the already yielded items.
+///
+/// Since the iterator is passed as a mutable reference and this function calls
+/// `next` at most `N` times, the iterator can still be used afterwards to
+/// retrieve the remaining items.
+///
+/// If `iter.next()` panicks, all items already yielded by the iterator are
+/// dropped.
+///
+/// Used for [`Iterator::next_chunk`].
+#[inline]
+pub(crate) fn iter_next_chunk<T, const N: usize>(
+    iter: &mut impl Iterator<Item = T>,
+) -> Result<[T; N], IntoIter<T, N>> {
+    let mut array = MaybeUninit::uninit_array::<N>();
+    let r = iter_next_chunk_erased(&mut array, iter);
+    match r {
+        Ok(()) => {
+            // SAFETY: All elements of `array` were populated.
+            Ok(unsafe { MaybeUninit::array_assume_init(array) })
+        }
+        Err(initialized) => {
+            // SAFETY: Only the first `initialized` elements were populated
+            Err(unsafe { IntoIter::new_unchecked(array, 0..initialized) })
+        }
+    }
+}
+
+/// Version of [`iter_next_chunk`] using a passed-in slice in order to avoid
+/// needing to monomorphize for every array length.
+///
+/// Unfortunately this loop has two exit conditions, the buffer filling up
+/// or the iterator running out of items, making it tend to optimize poorly.
 #[inline]
-pub(crate) fn iter_next_chunk<I, const N: usize>(
-    iter: &mut I,
-) -> Result<[I::Item; N], IntoIter<I::Item, N>>
-where
-    I: Iterator,
-{
-    let mut map = iter.map(NeverShortCircuit);
-    try_collect_into_array(&mut map).map(|NeverShortCircuit(arr)| arr)
+fn iter_next_chunk_erased<T>(
+    buffer: &mut [MaybeUninit<T>],
+    iter: &mut impl Iterator<Item = T>,
+) -> Result<(), usize> {
+    let mut guard = Guard { array_mut: buffer, initialized: 0 };
+    while guard.initialized < guard.array_mut.len() {
+        let Some(item) = iter.next() else {
+            // Unlike `try_from_fn_erased`, we want to keep the partial results,
+            // so we need to defuse the guard instead of using `?`.
+            let initialized = guard.initialized;
+            mem::forget(guard);
+            return Err(initialized)
+        };
+
+        // SAFETY: The loop condition ensures we have space to push the item
+        unsafe { guard.push_unchecked(item) };
+    }
+
+    mem::forget(guard);
+    Ok(())
 }
diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index 129213fde..897d03595 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -196,7 +196,7 @@ use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
 use crate::marker::{PhantomData, Unsize};
 use crate::mem;
-use crate::ops::{CoerceUnsized, Deref, DerefMut};
+use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
 use crate::ptr::{self, NonNull};
 
 mod lazy;
@@ -571,6 +571,16 @@ impl<T: Default> Cell<T> {
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
 
+// Allow types that wrap `Cell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `Cell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: Cell<&Self>` won't work
+// `self: CellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
+
 impl<T> Cell<[T]> {
     /// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
     ///
@@ -622,7 +632,7 @@ pub struct RefCell<T: ?Sized> {
     // Stores the location of the earliest currently active borrow.
     // This gets updated whenever we go from having zero borrows
     // to having a single borrow. When a borrow occurs, this gets included
-    // in the generated `BorrowError/`BorrowMutError`
+    // in the generated `BorrowError`/`BorrowMutError`
     #[cfg(feature = "debug_refcell")]
     borrowed_at: Cell<Option<&'static crate::panic::Location<'static>>>,
     value: UnsafeCell<T>,
@@ -2078,6 +2088,16 @@ impl<T> const From<T> for UnsafeCell<T> {
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 
+// Allow types that wrap `UnsafeCell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `UnsafeCell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: UnsafeCell<&Self>` won't work
+// `self: UnsafeCellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
+
 /// [`UnsafeCell`], but [`Sync`].
 ///
 /// This is just an `UnsafeCell`, except it implements `Sync`
@@ -2169,6 +2189,17 @@ impl<T> const From<T> for SyncUnsafeCell<T> {
 //#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
 impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
 
+// Allow types that wrap `SyncUnsafeCell` to also implement `DispatchFromDyn`
+// and become object safe method receivers.
+// Note that currently `SyncUnsafeCell` itself cannot be a method receiver
+// because it does not implement Deref.
+// In other words:
+// `self: SyncUnsafeCell<&Self>` won't work
+// `self: SyncUnsafeCellWrapper<Self>` becomes possible
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+//#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
+impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
+
 #[allow(unused)]
 fn assert_coerce_unsized(
     a: UnsafeCell<&i32>,
diff --git a/library/core/src/cell/once.rs b/library/core/src/cell/once.rs
index 7757068a4..f74e563f1 100644
--- a/library/core/src/cell/once.rs
+++ b/library/core/src/cell/once.rs
@@ -298,3 +298,7 @@ impl<T> const From<T> for OnceCell<T> {
         OnceCell { inner: UnsafeCell::new(Some(value)) }
     }
 }
+
+// Just like for `Cell<T>` this isn't needed, but results in nicer error messages.
+#[unstable(feature = "once_cell", issue = "74465")]
+impl<T> !Sync for OnceCell<T> {}
diff --git a/library/core/src/char/convert.rs b/library/core/src/char/convert.rs
index f1a51a550..136bbcb8b 100644
--- a/library/core/src/char/convert.rs
+++ b/library/core/src/char/convert.rs
@@ -2,6 +2,7 @@
 
 use crate::char::TryFromCharError;
 use crate::convert::TryFrom;
+use crate::error::Error;
 use crate::fmt;
 use crate::mem::transmute;
 use crate::str::FromStr;
@@ -150,14 +151,16 @@ pub struct ParseCharError {
     kind: CharErrorKind,
 }
 
-impl ParseCharError {
-    #[unstable(
-        feature = "char_error_internals",
-        reason = "this method should not be available publicly",
-        issue = "none"
-    )]
-    #[doc(hidden)]
-    pub fn __description(&self) -> &str {
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+enum CharErrorKind {
+    EmptyString,
+    TooManyChars,
+}
+
+#[stable(feature = "char_from_str", since = "1.20.0")]
+impl Error for ParseCharError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
         match self.kind {
             CharErrorKind::EmptyString => "cannot parse char from empty string",
             CharErrorKind::TooManyChars => "too many characters in string",
@@ -165,16 +168,11 @@ impl ParseCharError {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-enum CharErrorKind {
-    EmptyString,
-    TooManyChars,
-}
-
 #[stable(feature = "char_from_str", since = "1.20.0")]
 impl fmt::Display for ParseCharError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.__description().fmt(f)
+        #[allow(deprecated)]
+        self.description().fmt(f)
     }
 }
 
diff --git a/library/core/src/char/decode.rs b/library/core/src/char/decode.rs
index eeb088030..dbfe251f2 100644
--- a/library/core/src/char/decode.rs
+++ b/library/core/src/char/decode.rs
@@ -3,8 +3,6 @@
 use crate::error::Error;
 use crate::fmt;
 
-use super::from_u32_unchecked;
-
 /// An iterator that decodes UTF-16 encoded code points from an iterator of `u16`s.
 ///
 /// This `struct` is created by the [`decode_utf16`] method on [`char`]. See its
@@ -49,7 +47,7 @@ impl<I: Iterator<Item = u16>> Iterator for DecodeUtf16<I> {
 
         if !u.is_utf16_surrogate() {
             // SAFETY: not a surrogate
-            Some(Ok(unsafe { from_u32_unchecked(u as u32) }))
+            Some(Ok(unsafe { char::from_u32_unchecked(u as u32) }))
         } else if u >= 0xDC00 {
             // a trailing surrogate
             Some(Err(DecodeUtf16Error { code: u }))
@@ -69,7 +67,7 @@ impl<I: Iterator<Item = u16>> Iterator for DecodeUtf16<I> {
             // all ok, so lets decode it.
             let c = (((u & 0x3ff) as u32) << 10 | (u2 & 0x3ff) as u32) + 0x1_0000;
             // SAFETY: we checked that it's a legal unicode value
-            Some(Ok(unsafe { from_u32_unchecked(c) }))
+            Some(Ok(unsafe { char::from_u32_unchecked(c) }))
         }
     }
 
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index 3e7383b4c..9bc97ea0b 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -53,15 +53,13 @@ impl char {
     /// Basic usage:
     ///
     /// ```
-    /// use std::char::decode_utf16;
-    ///
     /// // 𝄞mus<invalid>ic<invalid>
     /// let v = [
     ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
     /// ];
     ///
     /// assert_eq!(
-    ///     decode_utf16(v)
+    ///     char::decode_utf16(v)
     ///         .map(|r| r.map_err(|e| e.unpaired_surrogate()))
     ///         .collect::<Vec<_>>(),
     ///     vec![
@@ -77,16 +75,14 @@ impl char {
     /// A lossy decoder can be obtained by replacing `Err` results with the replacement character:
     ///
     /// ```
-    /// use std::char::{decode_utf16, REPLACEMENT_CHARACTER};
-    ///
     /// // 𝄞mus<invalid>ic<invalid>
     /// let v = [
     ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
     /// ];
     ///
     /// assert_eq!(
-    ///     decode_utf16(v)
-    ///        .map(|r| r.unwrap_or(REPLACEMENT_CHARACTER))
+    ///     char::decode_utf16(v)
+    ///        .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
     ///        .collect::<String>(),
     ///     "𝄞mus�ic�"
     /// );
@@ -123,8 +119,6 @@ impl char {
     /// Basic usage:
     ///
     /// ```
-    /// use std::char;
-    ///
     /// let c = char::from_u32(0x2764);
     ///
     /// assert_eq!(Some('❤'), c);
@@ -133,8 +127,6 @@ impl char {
     /// Returning `None` when the input is not a valid `char`:
     ///
     /// ```
-    /// use std::char;
-    ///
     /// let c = char::from_u32(0x110000);
     ///
     /// assert_eq!(None, c);
@@ -176,8 +168,6 @@ impl char {
     /// Basic usage:
     ///
     /// ```
-    /// use std::char;
-    ///
     /// let c = unsafe { char::from_u32_unchecked(0x2764) };
     ///
     /// assert_eq!('❤', c);
@@ -210,8 +200,6 @@ impl char {
     /// Basic usage:
     ///
     /// ```
-    /// use std::char;
-    ///
     /// let c = char::from_digit(4, 10);
     ///
     /// assert_eq!(Some('4'), c);
@@ -225,8 +213,6 @@ impl char {
     /// Returning `None` when the input is not a digit:
     ///
     /// ```
-    /// use std::char;
-    ///
     /// let c = char::from_digit(20, 10);
     ///
     /// assert_eq!(None, c);
@@ -235,8 +221,6 @@ impl char {
     /// Passing a large radix, causing a panic:
     ///
     /// ```should_panic
-    /// use std::char;
-    ///
     /// // this panics
     /// let _c = char::from_digit(1, 37);
     /// ```
@@ -1786,7 +1770,7 @@ pub fn encode_utf16_raw(mut code: u32, dst: &mut [u16]) -> &mut [u16] {
         } else {
             panic!(
                 "encode_utf16: need {} units to encode U+{:X}, but the buffer has {}",
-                from_u32_unchecked(code).len_utf16(),
+                char::from_u32_unchecked(code).len_utf16(),
                 code,
                 dst.len(),
             )
diff --git a/library/core/src/char/mod.rs b/library/core/src/char/mod.rs
index af98059cf..8ec78e887 100644
--- a/library/core/src/char/mod.rs
+++ b/library/core/src/char/mod.rs
@@ -189,7 +189,7 @@ impl Iterator for EscapeUnicode {
             }
             EscapeUnicodeState::Value => {
                 let hex_digit = ((self.c as u32) >> (self.hex_digit_idx * 4)) & 0xf;
-                let c = from_digit(hex_digit, 16).unwrap();
+                let c = char::from_digit(hex_digit, 16).unwrap();
                 if self.hex_digit_idx == 0 {
                     self.state = EscapeUnicodeState::RightBrace;
                 } else {
diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
index a7d6fec7d..068637d1a 100644
--- a/library/core/src/cmp.rs
+++ b/library/core/src/cmp.rs
@@ -22,7 +22,9 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use crate::const_closure::ConstFnMutClosure;
+mod bytewise;
+pub(crate) use bytewise::BytewiseEq;
+
 use crate::marker::Destruct;
 
 use self::Ordering::*;
@@ -798,12 +800,6 @@ pub trait Ord: Eq + PartialOrd<Self> {
         Self: Sized,
         Self: ~const Destruct,
     {
-        #[cfg(not(bootstrap))]
-        {
-            max_by(self, other, Ord::cmp)
-        }
-
-        #[cfg(bootstrap)]
         match self.cmp(&other) {
             Ordering::Less | Ordering::Equal => other,
             Ordering::Greater => self,
@@ -828,12 +824,6 @@ pub trait Ord: Eq + PartialOrd<Self> {
         Self: Sized,
         Self: ~const Destruct,
     {
-        #[cfg(not(bootstrap))]
-        {
-            min_by(self, other, Ord::cmp)
-        }
-
-        #[cfg(bootstrap)]
         match self.cmp(&other) {
             Ordering::Less | Ordering::Equal => self,
             Ordering::Greater => other,
@@ -1200,12 +1190,7 @@ 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")]
-#[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,
-{
+pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
     match compare(&v1, &v2) {
         Ordering::Less | Ordering::Equal => v1,
         Ordering::Greater => v2,
@@ -1227,30 +1212,8 @@ where
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-#[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,
-{
-    cfg_if! {
-        if #[cfg(bootstrap)] {
-            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))
-        } else {
-            min_by(v1, v2, const |v1, v2| f(v1).cmp(&f(v2)))
-        }
-    }
+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)))
 }
 
 /// Compares and returns the maximum of two values.
@@ -1291,12 +1254,7 @@ 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")]
-#[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,
-{
+pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
     match compare(&v1, &v2) {
         Ordering::Less | Ordering::Equal => v2,
         Ordering::Greater => v1,
@@ -1318,24 +1276,8 @@ where
 #[inline]
 #[must_use]
 #[stable(feature = "cmp_min_max_by", since = "1.53.0")]
-#[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))
+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)))
 }
 
 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
@@ -1536,9 +1478,10 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
+    #[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+    impl<A: ?Sized, B: ?Sized> const PartialOrd<&B> for &A
     where
-        A: PartialOrd<B>,
+        A: ~const PartialOrd<B>,
     {
         #[inline]
         fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
diff --git a/library/core/src/cmp/bytewise.rs b/library/core/src/cmp/bytewise.rs
new file mode 100644
index 000000000..2548d9e24
--- /dev/null
+++ b/library/core/src/cmp/bytewise.rs
@@ -0,0 +1,83 @@
+use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
+use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};
+
+/// Types where `==` & `!=` are equivalent to comparing their underlying bytes.
+///
+/// Importantly, this means no floating-point types, as those have different
+/// byte representations (like `-0` and `+0`) which compare as the same.
+/// Since byte arrays are `Eq`, that implies that these types are probably also
+/// `Eq`, but that's not technically required to use this trait.
+///
+/// `Rhs` is *de facto* always `Self`, but the separate parameter is important
+/// to avoid the `specializing impl repeats parameter` error when consuming this.
+///
+/// # Safety
+///
+/// - `Self` and `Rhs` have no padding.
+/// - `Self` and `Rhs` have the same layout (size and alignment).
+/// - Neither `Self` nor `Rhs` have provenance, so integer comparisons are correct.
+/// - `<Self as PartialEq<Rhs>>::{eq,ne}` are equivalent to comparing the bytes.
+#[rustc_specialization_trait]
+pub(crate) unsafe trait BytewiseEq<Rhs = Self>: PartialEq<Rhs> + Sized {}
+
+macro_rules! is_bytewise_comparable {
+    ($($t:ty),+ $(,)?) => {$(
+        unsafe impl BytewiseEq for $t {}
+    )+};
+}
+
+// SAFETY: All the ordinary integer types have no padding, and are not pointers.
+is_bytewise_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);
+
+// SAFETY: These have *niches*, but no *padding* and no *provenance*,
+// so we can compare them directly.
+is_bytewise_comparable!(bool, char, super::Ordering);
+
+// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers,
+// and they compare like their underlying numeric type.
+is_bytewise_comparable!(
+    NonZeroU8,
+    NonZeroU16,
+    NonZeroU32,
+    NonZeroU64,
+    NonZeroU128,
+    NonZeroUsize,
+    NonZeroI8,
+    NonZeroI16,
+    NonZeroI32,
+    NonZeroI64,
+    NonZeroI128,
+    NonZeroIsize,
+);
+
+// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
+// are also safe to equality-compare bitwise inside an `Option`.
+// The way `PartialOrd` is defined for `Option` means that this wouldn't work
+// for `<` or `>` on the signed types, but since we only do `==` it's fine.
+is_bytewise_comparable!(
+    Option<NonZeroU8>,
+    Option<NonZeroU16>,
+    Option<NonZeroU32>,
+    Option<NonZeroU64>,
+    Option<NonZeroU128>,
+    Option<NonZeroUsize>,
+    Option<NonZeroI8>,
+    Option<NonZeroI16>,
+    Option<NonZeroI32>,
+    Option<NonZeroI64>,
+    Option<NonZeroI128>,
+    Option<NonZeroIsize>,
+);
+
+macro_rules! is_bytewise_comparable_array_length {
+    ($($n:literal),+ $(,)?) => {$(
+        // SAFETY: Arrays have no padding between elements, so if the elements are
+        // `BytewiseEq`, then the whole array can be too.
+        unsafe impl<T: BytewiseEq<U>, U> BytewiseEq<[U; $n]> for [T; $n] {}
+    )+};
+}
+
+// Frustratingly, this can't be made const-generic as it gets
+//    error: specializing impl repeats parameter `N`
+// so just do it for a couple of plausibly-common ones.
+is_bytewise_comparable_array_length!(0, 1, 2, 3, 4, 6, 8, 12, 16, 24, 32, 48, 64);
diff --git a/library/core/src/const_closure.rs b/library/core/src/const_closure.rs
deleted file mode 100644
index 97900a486..000000000
--- a/library/core/src/const_closure.rs
+++ /dev/null
@@ -1,78 +0,0 @@
-use crate::marker::Destruct;
-use crate::marker::Tuple;
-
-/// 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: Tuple, 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: Tuple, 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 f95b880df..805354be0 100644
--- a/library/core/src/convert/mod.rs
+++ b/library/core/src/convert/mod.rs
@@ -542,7 +542,7 @@ pub trait Into<T>: Sized {
 #[const_trait]
 pub trait From<T>: Sized {
     /// Converts to this type from the input type.
-    #[lang = "from"]
+    #[rustc_diagnostic_item = "from_fn"]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn from(value: T) -> Self;
diff --git a/library/core/src/error.rs b/library/core/src/error.rs
index 7152300ab..d4103183c 100644
--- a/library/core/src/error.rs
+++ b/library/core/src/error.rs
@@ -28,6 +28,7 @@ use crate::fmt::{Debug, Display};
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "Error")]
 #[rustc_has_incoherent_inherent_impls]
+#[cfg_attr(not(bootstrap), allow(multiple_supertrait_upcastable))]
 pub trait Error: Debug + Display {
     /// The lower-level source of this error, if any.
     ///
@@ -485,26 +486,10 @@ impl Error for crate::char::CharTryFromError {
     }
 }
 
-#[stable(feature = "char_from_str", since = "1.20.0")]
-impl Error for crate::char::ParseCharError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
 #[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 {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
+#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
 impl Error for crate::ffi::FromBytesUntilNulError {}
 
 #[unstable(feature = "get_many_mut", issue = "104642")]
diff --git a/library/core/src/ffi/c_str.rs b/library/core/src/ffi/c_str.rs
index 15dd9ea7e..fe8abdf7f 100644
--- a/library/core/src/ffi/c_str.rs
+++ b/library/core/src/ffi/c_str.rs
@@ -1,4 +1,5 @@
 use crate::cmp::Ordering;
+use crate::error::Error;
 use crate::ffi::c_char;
 use crate::fmt;
 use crate::intrinsics;
@@ -129,10 +130,12 @@ impl FromBytesWithNulError {
     const fn not_nul_terminated() -> FromBytesWithNulError {
         FromBytesWithNulError { kind: FromBytesWithNulErrorKind::NotNulTerminated }
     }
+}
 
-    #[doc(hidden)]
-    #[unstable(feature = "cstr_internals", issue = "none")]
-    pub fn __description(&self) -> &str {
+#[stable(feature = "frombyteswithnulerror_impls", since = "1.17.0")]
+impl Error for FromBytesWithNulError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
         match self.kind {
             FromBytesWithNulErrorKind::InteriorNul(..) => {
                 "data provided contains an interior nul byte"
@@ -150,10 +153,10 @@ impl FromBytesWithNulError {
 /// This error is created by the [`CStr::from_bytes_until_nul`] method.
 ///
 #[derive(Clone, PartialEq, Eq, Debug)]
-#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
+#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
 pub struct FromBytesUntilNulError(());
 
-#[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
+#[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
 impl fmt::Display for FromBytesUntilNulError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "data provided does not contain a nul")
@@ -180,7 +183,7 @@ impl Default for &CStr {
 impl fmt::Display for FromBytesWithNulError {
     #[allow(deprecated, deprecated_in_future)]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str(self.__description())?;
+        f.write_str(self.description())?;
         if let FromBytesWithNulErrorKind::InteriorNul(pos) = self.kind {
             write!(f, " at byte pos {pos}")?;
         }
@@ -306,8 +309,6 @@ impl CStr {
     ///
     /// # Examples
     /// ```
-    /// #![feature(cstr_from_bytes_until_nul)]
-    ///
     /// use std::ffi::CStr;
     ///
     /// let mut buffer = [0u8; 16];
@@ -322,8 +323,9 @@ impl CStr {
     /// assert_eq!(c_str.to_str().unwrap(), "AAAAAAAA");
     /// ```
     ///
-    #[unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
-    #[rustc_const_unstable(feature = "cstr_from_bytes_until_nul", issue = "95027")]
+    #[rustc_allow_const_fn_unstable(const_slice_index)]
+    #[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
+    #[rustc_const_stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
     pub const fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError> {
         let nul_pos = memchr::memchr(0, bytes);
         match nul_pos {
@@ -455,6 +457,10 @@ impl CStr {
     /// to a contiguous region of memory terminated with a 0 byte to represent
     /// the end of the string.
     ///
+    /// The type of the returned pointer is
+    /// [`*const c_char`][crate::ffi::c_char], and whether it's
+    /// an alias for `*const i8` or `*const u8` is platform-specific.
+    ///
     /// **WARNING**
     ///
     /// The returned pointer is read-only; writing to it (including passing it
@@ -468,6 +474,7 @@ impl CStr {
     /// # #![allow(unused_must_use)] #![allow(temporary_cstring_as_ptr)]
     /// use std::ffi::CString;
     ///
+    /// // Do not do this:
     /// let ptr = CString::new("Hello").expect("CString::new failed").as_ptr();
     /// unsafe {
     ///     // `ptr` is dangling
diff --git a/library/core/src/ffi/mod.rs b/library/core/src/ffi/mod.rs
index 76daceecd..27f665904 100644
--- a/library/core/src/ffi/mod.rs
+++ b/library/core/src/ffi/mod.rs
@@ -144,6 +144,7 @@ mod c_char_definition {
                 )
             ),
             all(target_os = "fuchsia", target_arch = "aarch64"),
+            all(target_os = "nto", target_arch = "aarch64"),
             target_os = "horizon"
         ))] {
             pub type c_char = u8;
diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
index fa5073e33..c9821bf81 100644
--- a/library/core/src/fmt/mod.rs
+++ b/library/core/src/fmt/mod.rs
@@ -267,6 +267,7 @@ extern "C" {
 /// family of functions. It contains a function to format the given value. At
 /// compile time it is ensured that the function and the value have the correct
 /// types, and then this struct is used to canonicalize arguments to one type.
+#[cfg_attr(not(bootstrap), lang = "format_argument")]
 #[derive(Copy, Clone)]
 #[allow(missing_debug_implementations)]
 #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
@@ -279,6 +280,7 @@ pub struct ArgumentV1<'a> {
 /// This struct represents the unsafety of constructing an `Arguments`.
 /// It exists, rather than an unsafe function, in order to simplify the expansion
 /// of `format_args!(..)` and reduce the scope of the `unsafe` block.
+#[cfg_attr(not(bootstrap), lang = "format_unsafe_arg")]
 #[allow(missing_debug_implementations)]
 #[doc(hidden)]
 #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
@@ -473,8 +475,8 @@ impl<'a> Arguments<'a> {
 /// ```
 ///
 /// [`format()`]: ../../std/fmt/fn.format.html
+#[cfg_attr(not(bootstrap), lang = "format_arguments")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(test), rustc_diagnostic_item = "Arguments")]
 #[derive(Copy, Clone)]
 pub struct Arguments<'a> {
     // Format string pieces to print.
@@ -489,9 +491,26 @@ pub struct Arguments<'a> {
 }
 
 impl<'a> Arguments<'a> {
-    /// Get the formatted string, if it has no arguments to be formatted.
+    /// Get the formatted string, if it has no arguments to be formatted at runtime.
     ///
-    /// This can be used to avoid allocations in the most trivial case.
+    /// This can be used to avoid allocations in some cases.
+    ///
+    /// # Guarantees
+    ///
+    /// For `format_args!("just a literal")`, this function is guaranteed to
+    /// return `Some("just a literal")`.
+    ///
+    /// For most cases with placeholders, this function will return `None`.
+    ///
+    /// However, the compiler may perform optimizations that can cause this
+    /// function to return `Some(_)` even if the format string contains
+    /// placeholders. For example, `format_args!("Hello, {}!", "world")` may be
+    /// optimized to `format_args!("Hello, world!")`, such that `as_str()`
+    /// returns `Some("Hello, world!")`.
+    ///
+    /// The behavior for anything but the trivial case (without placeholders)
+    /// is not guaranteed, and should not be relied upon for anything other
+    /// than optimization.
     ///
     /// # Examples
     ///
@@ -512,7 +531,7 @@ impl<'a> Arguments<'a> {
     /// ```rust
     /// assert_eq!(format_args!("hello").as_str(), Some("hello"));
     /// assert_eq!(format_args!("").as_str(), Some(""));
-    /// assert_eq!(format_args!("{}", 1).as_str(), None);
+    /// assert_eq!(format_args!("{:?}", std::env::current_dir()).as_str(), None);
     /// ```
     #[stable(feature = "fmt_as_str", since = "1.52.0")]
     #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "103900")]
@@ -1355,11 +1374,11 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{}", Foo::new(2)), "2");
-    /// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
-    /// assert_eq!(&format!("{}", Foo::new(0)), "0");
-    /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
-    /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
+    /// assert_eq!(format!("{}", Foo::new(2)), "2");
+    /// assert_eq!(format!("{}", Foo::new(-1)), "-1");
+    /// assert_eq!(format!("{}", Foo::new(0)), "0");
+    /// assert_eq!(format!("{:#}", Foo::new(-1)), "-Foo 1");
+    /// assert_eq!(format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
@@ -1452,8 +1471,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo:<4}"), "Foo ");
-    /// assert_eq!(&format!("{Foo:0>4}"), "0Foo");
+    /// assert_eq!(format!("{Foo:<4}"), "Foo ");
+    /// assert_eq!(format!("{Foo:0>4}"), "0Foo");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pad(&mut self, s: &str) -> Result {
@@ -1636,8 +1655,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo}"), "Foo");
-    /// assert_eq!(&format!("{Foo:0>8}"), "Foo");
+    /// assert_eq!(format!("{Foo}"), "Foo");
+    /// assert_eq!(format!("{Foo:0>8}"), "Foo");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_str(&mut self, data: &str) -> Result {
@@ -1659,8 +1678,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
-    /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
+    /// assert_eq!(format!("{}", Foo(-1)), "Foo -1");
+    /// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
@@ -1703,8 +1722,8 @@ impl<'a> Formatter<'a> {
     /// }
     ///
     /// // We set alignment to the right with ">".
-    /// assert_eq!(&format!("{Foo:G>3}"), "GGG");
-    /// assert_eq!(&format!("{Foo:t>6}"), "tttttt");
+    /// assert_eq!(format!("{Foo:G>3}"), "GGG");
+    /// assert_eq!(format!("{Foo:t>6}"), "tttttt");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1738,10 +1757,10 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{Foo:<}"), "left");
-    /// assert_eq!(&format!("{Foo:>}"), "right");
-    /// assert_eq!(&format!("{Foo:^}"), "center");
-    /// assert_eq!(&format!("{Foo}"), "into the void");
+    /// assert_eq!(format!("{Foo:<}"), "left");
+    /// assert_eq!(format!("{Foo:>}"), "right");
+    /// assert_eq!(format!("{Foo:^}"), "center");
+    /// assert_eq!(format!("{Foo}"), "into the void");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags_align", since = "1.28.0")]
@@ -1767,7 +1786,7 @@ impl<'a> Formatter<'a> {
     ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
     ///         if let Some(width) = formatter.width() {
     ///             // If we received a width, we use it
-    ///             write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
+    ///             write!(formatter, "{:width$}", format!("Foo({})", self.0), width = width)
     ///         } else {
     ///             // Otherwise we do nothing special
     ///             write!(formatter, "Foo({})", self.0)
@@ -1775,8 +1794,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:10}", Foo(23)), "Foo(23)   ");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1806,8 +1825,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
-    /// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");
+    /// assert_eq!(format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
+    /// assert_eq!(format!("{}", Foo(23.2)), "Foo(23.20)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1837,9 +1856,9 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
-    /// assert_eq!(&format!("{:+}", Foo(-23)), "Foo(-23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:+}", Foo(23)), "Foo(+23)");
+    /// assert_eq!(format!("{:+}", Foo(-23)), "Foo(-23)");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1867,8 +1886,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{:-}", Foo(23)), "-Foo(23)");
+    /// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1895,8 +1914,8 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
-    /// assert_eq!(&format!("{}", Foo(23)), "23");
+    /// assert_eq!(format!("{:#}", Foo(23)), "Foo(23)");
+    /// assert_eq!(format!("{}", Foo(23)), "23");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
@@ -1922,7 +1941,7 @@ impl<'a> Formatter<'a> {
     ///     }
     /// }
     ///
-    /// assert_eq!(&format!("{:04}", Foo(23)), "23");
+    /// assert_eq!(format!("{:04}", Foo(23)), "23");
     /// ```
     #[must_use]
     #[stable(feature = "fmt_flags", since = "1.5.0")]
diff --git a/library/core/src/fmt/rt/v1.rs b/library/core/src/fmt/rt/v1.rs
index 37202b277..11a50951a 100644
--- a/library/core/src/fmt/rt/v1.rs
+++ b/library/core/src/fmt/rt/v1.rs
@@ -5,7 +5,9 @@
 //! these can be statically allocated and are slightly optimized for the runtime
 #![allow(missing_debug_implementations)]
 
+#[cfg_attr(not(bootstrap), lang = "format_placeholder")]
 #[derive(Copy, Clone)]
+// FIXME: Rename this to Placeholder
 pub struct Argument {
     pub position: usize,
     pub format: FormatSpec,
@@ -20,7 +22,22 @@ pub struct FormatSpec {
     pub width: Count,
 }
 
+impl Argument {
+    #[inline(always)]
+    pub const fn new(
+        position: usize,
+        fill: char,
+        align: Alignment,
+        flags: u32,
+        precision: Count,
+        width: Count,
+    ) -> Self {
+        Self { position, format: FormatSpec { fill, align, flags, precision, width } }
+    }
+}
+
 /// Possible alignments that can be requested as part of a formatting directive.
+#[cfg_attr(not(bootstrap), lang = "format_alignment")]
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum Alignment {
     /// Indication that contents should be left-aligned.
@@ -34,6 +51,7 @@ pub enum Alignment {
 }
 
 /// Used by [width](https://doc.rust-lang.org/std/fmt/#width) and [precision](https://doc.rust-lang.org/std/fmt/#precision) specifiers.
+#[cfg_attr(not(bootstrap), lang = "format_count")]
 #[derive(Copy, Clone)]
 pub enum Count {
     /// Specified with a literal number, stores the value
diff --git a/library/core/src/future/mod.rs b/library/core/src/future/mod.rs
index c4fb36209..46cbcd435 100644
--- a/library/core/src/future/mod.rs
+++ b/library/core/src/future/mod.rs
@@ -56,51 +56,6 @@ unsafe impl Send for ResumeTy {}
 #[unstable(feature = "gen_future", issue = "50547")]
 unsafe impl Sync for ResumeTy {}
 
-/// Wrap a generator in a future.
-///
-/// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give
-/// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`).
-// This is `const` to avoid extra errors after we recover from `const async fn`
-#[doc(hidden)]
-#[unstable(feature = "gen_future", issue = "50547")]
-#[rustc_const_unstable(feature = "gen_future", issue = "50547")]
-#[inline]
-pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
-where
-    T: crate::ops::Generator<ResumeTy, Yield = ()>,
-{
-    use crate::{
-        ops::{Generator, GeneratorState},
-        pin::Pin,
-        task::Poll,
-    };
-
-    #[rustc_diagnostic_item = "gen_future"]
-    struct GenFuture<T: Generator<ResumeTy, Yield = ()>>(T);
-
-    // We rely on the fact that async/await futures are immovable in order to create
-    // self-referential borrows in the underlying generator.
-    impl<T: Generator<ResumeTy, Yield = ()>> !Unpin for GenFuture<T> {}
-
-    impl<T: Generator<ResumeTy, Yield = ()>> Future for GenFuture<T> {
-        type Output = T::Return;
-        #[track_caller]
-        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-            // SAFETY: Safe because we're !Unpin + !Drop, and this is just a field projection.
-            let gen = unsafe { Pin::map_unchecked_mut(self, |s| &mut s.0) };
-
-            // Resume the generator, turning the `&mut Context` into a `NonNull` raw pointer. The
-            // `.await` lowering will safely cast that back to a `&mut Context`.
-            match gen.resume(ResumeTy(NonNull::from(cx).cast::<Context<'static>>())) {
-                GeneratorState::Yielded(()) => Poll::Pending,
-                GeneratorState::Complete(x) => Poll::Ready(x),
-            }
-        }
-    }
-
-    GenFuture(gen)
-}
-
 #[lang = "get_context"]
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
diff --git a/library/core/src/hint.rs b/library/core/src/hint.rs
index 5a76e8669..ee13dae60 100644
--- a/library/core/src/hint.rs
+++ b/library/core/src/hint.rs
@@ -216,7 +216,8 @@ pub fn spin_loop() {
 ///
 /// Note however, that `black_box` is only (and can only be) provided on a "best-effort" basis. The
 /// extent to which it can block optimisations may vary depending upon the platform and code-gen
-/// backend used. Programs cannot rely on `black_box` for *correctness* in any way.
+/// backend used. Programs cannot rely on `black_box` for *correctness*, beyond it behaving as the
+/// identity function.
 ///
 /// [`std::convert::identity`]: crate::convert::identity
 ///
diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index a315a28fb..18a90599c 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -58,7 +58,6 @@ use crate::marker::DiscriminantKind;
 use crate::marker::Tuple;
 use crate::mem;
 
-#[cfg(not(bootstrap))]
 pub mod mir;
 
 // These imports are used for simplifying intra-doc links
@@ -963,7 +962,6 @@ extern "rust-intrinsic" {
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
     #[rustc_safe_intrinsic]
-    #[cfg(not(bootstrap))]
     pub fn assert_mem_uninitialized_valid<T>();
 
     /// Gets a reference to a static `Location` indicating where it was called.
@@ -2095,6 +2093,10 @@ extern "rust-intrinsic" {
     /// Above some backend-decided threshold this will emit calls to `memcmp`,
     /// like slice equality does, instead of causing massive code size.
     ///
+    /// Since this works by comparing the underlying bytes, the actual `T` is
+    /// not particularly important.  It will be used for its size and alignment,
+    /// but any validity restrictions will be ignored, not enforced.
+    ///
     /// # Safety
     ///
     /// It's UB to call this if any of the *bytes* in `*a` or `*b` are uninitialized or carry a
diff --git a/library/core/src/intrinsics/mir.rs b/library/core/src/intrinsics/mir.rs
index e3157b669..72db1d87c 100644
--- a/library/core/src/intrinsics/mir.rs
+++ b/library/core/src/intrinsics/mir.rs
@@ -42,7 +42,7 @@
 //! another function. The `dialect` and `phase` parameters indicate which [version of MIR][dialect
 //! docs] you are inserting here. Generally you'll want to use `#![custom_mir(dialect = "built")]`
 //! if you want your MIR to be modified by the full MIR pipeline, or `#![custom_mir(dialect =
-//! "runtime", phase = "optimized")] if you don't.
+//! "runtime", phase = "optimized")]` if you don't.
 //!
 //! [dialect docs]:
 //!     https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/enum.MirPhase.html
@@ -60,8 +60,7 @@
 //!
 //! # Examples
 //!
-#![cfg_attr(bootstrap, doc = "```rust,compile_fail")]
-#![cfg_attr(not(bootstrap), doc = "```rust")]
+//! ```rust
 //! #![feature(core_intrinsics, custom_mir)]
 //!
 //! extern crate core;
@@ -211,13 +210,16 @@
 //!
 //! #### Statements
 //!  - Assign statements work via normal Rust assignment.
-//!  - [`Retag`] statements have an associated function.
+//!  - [`Retag`], [`StorageLive`], [`StorageDead`], [`Deinit`] statements have an associated function.
 //!
 //! #### Rvalues
 //!
 //!  - Operands implicitly convert to `Use` rvalues.
 //!  - `&`, `&mut`, `addr_of!`, and `addr_of_mut!` all work to create their associated rvalue.
-//!  - [`Discriminant`] has an associated function.
+//!  - [`Discriminant`] and [`Len`] have associated functions.
+//!  - Unary and binary operations use their normal Rust syntax - `a * b`, `!c`, etc.
+//!  - Checked binary operations are represented by wrapping the associated binop in [`Checked`].
+//!  - Array repetition syntax (`[foo; 10]`) creates the associated rvalue.
 //!
 //! #### Terminators
 //!
@@ -261,6 +263,9 @@ define!("mir_drop_and_replace", fn DropAndReplace<T>(place: T, value: T, goto: B
 define!("mir_call", fn Call<T>(place: T, goto: BasicBlock, call: T));
 define!("mir_storage_live", fn StorageLive<T>(local: T));
 define!("mir_storage_dead", fn StorageDead<T>(local: T));
+define!("mir_deinit", fn Deinit<T>(place: T));
+define!("mir_checked", fn Checked<T>(binop: T) -> (T, bool));
+define!("mir_len", fn Len<T>(place: T) -> usize);
 define!("mir_retag", fn Retag<T>(place: T));
 define!("mir_move", fn Move<T>(place: T) -> T);
 define!("mir_static", fn Static<T>(s: T) -> &'static T);
@@ -294,8 +299,7 @@ define!(
     ///
     /// # Examples
     ///
-    #[cfg_attr(bootstrap, doc = "```rust,compile_fail")]
-    #[cfg_attr(not(bootstrap), doc = "```rust")]
+    /// ```rust
     /// #![feature(custom_mir, core_intrinsics)]
     ///
     /// extern crate core;
diff --git a/library/core/src/iter/adapters/array_chunks.rs b/library/core/src/iter/adapters/array_chunks.rs
index 5e4211058..13719c727 100644
--- a/library/core/src/iter/adapters/array_chunks.rs
+++ b/library/core/src/iter/adapters/array_chunks.rs
@@ -1,7 +1,5 @@
 use crate::array;
-use crate::const_closure::ConstFnMutClosure;
 use crate::iter::{ByRefSized, FusedIterator, Iterator, TrustedRandomAccessNoCoerce};
-use crate::mem::{self, MaybeUninit};
 use crate::ops::{ControlFlow, NeverShortCircuit, Try};
 
 /// An iterator over `N` elements of the iterator at a time.
@@ -189,13 +187,12 @@ where
     I: Iterator,
 {
     #[inline]
-    default fn fold<B, F>(mut self, init: B, mut f: F) -> B
+    default fn fold<B, F>(mut self, init: B, f: F) -> B
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> B,
     {
-        let fold = ConstFnMutClosure::new(&mut f, NeverShortCircuit::wrap_mut_2_imp);
-        self.try_fold(init, fold).0
+        self.try_fold(init, NeverShortCircuit::wrap_mut_2(f)).0
     }
 }
 
@@ -214,19 +211,14 @@ where
         let mut i = 0;
         // Use a while loop because (0..len).step_by(N) doesn't optimize well.
         while inner_len - i >= N {
-            let mut chunk = MaybeUninit::uninit_array();
-            let mut guard = array::Guard { array_mut: &mut chunk, initialized: 0 };
-            while guard.initialized < N {
+            let chunk = crate::array::from_fn(|local| {
                 // SAFETY: The method consumes the iterator and the loop condition ensures that
                 // all accesses are in bounds and only happen once.
                 unsafe {
-                    let idx = i + guard.initialized;
-                    guard.push_unchecked(self.iter.__iterator_get_unchecked(idx));
+                    let idx = i + local;
+                    self.iter.__iterator_get_unchecked(idx)
                 }
-            }
-            mem::forget(guard);
-            // SAFETY: The loop above initialized all elements
-            let chunk = unsafe { MaybeUninit::array_assume_init(chunk) };
+            });
             accum = f(accum, chunk);
             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 1945e402f..477e7117c 100644
--- a/library/core/src/iter/adapters/by_ref_sized.rs
+++ b/library/core/src/iter/adapters/by_ref_sized.rs
@@ -1,7 +1,4 @@
-use crate::{
-    const_closure::ConstFnMutClosure,
-    ops::{NeverShortCircuit, Try},
-};
+use crate::ops::{NeverShortCircuit, Try};
 
 /// Like `Iterator::by_ref`, but requiring `Sized` so it can forward generics.
 ///
@@ -39,13 +36,12 @@ impl<I: Iterator> Iterator for ByRefSized<'_, I> {
     }
 
     #[inline]
-    fn fold<B, F>(self, init: B, mut f: F) -> B
+    fn fold<B, F>(self, init: B, 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, ConstFnMutClosure::new(&mut f, NeverShortCircuit::wrap_mut_2_imp))
-            .0
+        I::try_fold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
     }
 
     #[inline]
@@ -76,17 +72,12 @@ impl<I: DoubleEndedIterator> DoubleEndedIterator for ByRefSized<'_, I> {
     }
 
     #[inline]
-    fn rfold<B, F>(self, init: B, mut f: F) -> B
+    fn rfold<B, F>(self, init: B, 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,
-            ConstFnMutClosure::new(&mut f, NeverShortCircuit::wrap_mut_2_imp),
-        )
-        .0
+        I::try_rfold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
     }
 
     #[inline]
diff --git a/library/core/src/iter/adapters/cloned.rs b/library/core/src/iter/adapters/cloned.rs
index aba24a79d..914ff86c1 100644
--- a/library/core/src/iter/adapters/cloned.rs
+++ b/library/core/src/iter/adapters/cloned.rs
@@ -1,7 +1,7 @@
 use crate::iter::adapters::{
     zip::try_get_unchecked, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
 };
-use crate::iter::{FusedIterator, TrustedLen};
+use crate::iter::{FusedIterator, TrustedLen, UncheckedIterator};
 use crate::ops::Try;
 
 /// An iterator that clones the elements of an underlying iterator.
@@ -140,3 +140,16 @@ where
     T: Clone,
 {
 }
+
+impl<'a, I, T: 'a> UncheckedIterator for Cloned<I>
+where
+    I: UncheckedIterator<Item = &'a T>,
+    T: Clone,
+{
+    unsafe fn next_unchecked(&mut self) -> T {
+        // SAFETY: `Cloned` is 1:1 with the inner iterator, so if the caller promised
+        // that there's an element left, the inner iterator has one too.
+        let item = unsafe { self.it.next_unchecked() };
+        item.clone()
+    }
+}
diff --git a/library/core/src/iter/adapters/filter_map.rs b/library/core/src/iter/adapters/filter_map.rs
index e0d665c9e..6bdf53f7f 100644
--- a/library/core/src/iter/adapters/filter_map.rs
+++ b/library/core/src/iter/adapters/filter_map.rs
@@ -99,7 +99,7 @@ where
         ) -> impl FnMut((), T) -> ControlFlow<B> + '_ {
             move |(), x| match f(x) {
                 Some(x) => ControlFlow::Break(x),
-                None => ControlFlow::CONTINUE,
+                None => ControlFlow::Continue(()),
             }
         }
 
diff --git a/library/core/src/iter/adapters/flatten.rs b/library/core/src/iter/adapters/flatten.rs
index 307016c26..b040a0ea9 100644
--- a/library/core/src/iter/adapters/flatten.rs
+++ b/library/core/src/iter/adapters/flatten.rs
@@ -539,7 +539,7 @@ where
         #[rustc_inherit_overflow_checks]
         fn advance<U: Iterator>(n: usize, iter: &mut U) -> ControlFlow<(), usize> {
             match iter.advance_by(n) {
-                Ok(()) => ControlFlow::BREAK,
+                Ok(()) => ControlFlow::Break(()),
                 Err(advanced) => ControlFlow::Continue(n - advanced),
             }
         }
@@ -629,7 +629,7 @@ where
         #[rustc_inherit_overflow_checks]
         fn advance<U: DoubleEndedIterator>(n: usize, iter: &mut U) -> ControlFlow<(), usize> {
             match iter.advance_back_by(n) {
-                Ok(()) => ControlFlow::BREAK,
+                Ok(()) => ControlFlow::Break(()),
                 Err(advanced) => ControlFlow::Continue(n - advanced),
             }
         }
diff --git a/library/core/src/iter/adapters/map.rs b/library/core/src/iter/adapters/map.rs
index 9e25dbe46..31d02a4da 100644
--- a/library/core/src/iter/adapters/map.rs
+++ b/library/core/src/iter/adapters/map.rs
@@ -2,7 +2,7 @@ use crate::fmt;
 use crate::iter::adapters::{
     zip::try_get_unchecked, SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
 };
-use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
+use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen, UncheckedIterator};
 use crate::ops::Try;
 
 /// An iterator that maps the values of `iter` with `f`.
@@ -187,6 +187,19 @@ where
 {
 }
 
+impl<B, I, F> UncheckedIterator for Map<I, F>
+where
+    I: UncheckedIterator,
+    F: FnMut(I::Item) -> B,
+{
+    unsafe fn next_unchecked(&mut self) -> B {
+        // SAFETY: `Map` is 1:1 with the inner iterator, so if the caller promised
+        // that there's an element left, the inner iterator has one too.
+        let item = unsafe { self.iter.next_unchecked() };
+        (self.f)(item)
+    }
+}
+
 #[doc(hidden)]
 #[unstable(feature = "trusted_random_access", issue = "none")]
 unsafe impl<I, F> TrustedRandomAccess for Map<I, F> where I: TrustedRandomAccess {}
diff --git a/library/core/src/iter/adapters/zip.rs b/library/core/src/iter/adapters/zip.rs
index 8153c8cfe..b6b0c90cb 100644
--- a/library/core/src/iter/adapters/zip.rs
+++ b/library/core/src/iter/adapters/zip.rs
@@ -1,7 +1,7 @@
 use crate::cmp;
 use crate::fmt::{self, Debug};
 use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, Iterator};
-use crate::iter::{InPlaceIterable, SourceIter, TrustedLen};
+use crate::iter::{InPlaceIterable, SourceIter, TrustedLen, UncheckedIterator};
 
 /// An iterator that iterates two other iterators simultaneously.
 ///
@@ -417,6 +417,13 @@ where
 {
 }
 
+impl<A, B> UncheckedIterator for Zip<A, B>
+where
+    A: UncheckedIterator,
+    B: UncheckedIterator,
+{
+}
+
 // Arbitrarily selects the left side of the zip iteration as extractable "source"
 // it would require negative trait bounds to be able to try both
 #[unstable(issue = "none", feature = "inplace_iteration")]
diff --git a/library/core/src/iter/mod.rs b/library/core/src/iter/mod.rs
index bb35d50b4..ae00232c1 100644
--- a/library/core/src/iter/mod.rs
+++ b/library/core/src/iter/mod.rs
@@ -278,6 +278,7 @@
 //!
 //! ```
 //! # #![allow(unused_must_use)]
+//! # #![cfg_attr(not(bootstrap), allow(map_unit_fn))]
 //! let v = vec![1, 2, 3, 4, 5];
 //! v.iter().map(|x| println!("{x}"));
 //! ```
@@ -362,15 +363,13 @@ macro_rules! impl_fold_via_try_fold {
     };
     (@internal $fold:ident -> $try_fold:ident) => {
         #[inline]
-        fn $fold<AAA, FFF>(mut self, init: AAA, mut fold: FFF) -> AAA
+        fn $fold<AAA, FFF>(mut self, init: AAA, 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.$try_fold(init, fold).0
+            self.$try_fold(init, NeverShortCircuit::wrap_mut_2(fold)).0
         }
     };
 }
@@ -452,6 +451,7 @@ pub use self::adapters::{
 pub use self::adapters::{Intersperse, IntersperseWith};
 
 pub(crate) use self::adapters::try_process;
+pub(crate) use self::traits::UncheckedIterator;
 
 mod adapters;
 mod range;
diff --git a/library/core/src/iter/range.rs b/library/core/src/iter/range.rs
index b5739f2f3..78e27d730 100644
--- a/library/core/src/iter/range.rs
+++ b/library/core/src/iter/range.rs
@@ -1,4 +1,3 @@
-use crate::char;
 use crate::convert::TryFrom;
 use crate::mem;
 use crate::ops::{self, Try};
diff --git a/library/core/src/iter/traits/double_ended.rs b/library/core/src/iter/traits/double_ended.rs
index bdf94c792..ed23873cd 100644
--- a/library/core/src/iter/traits/double_ended.rs
+++ b/library/core/src/iter/traits/double_ended.rs
@@ -352,7 +352,7 @@ pub trait DoubleEndedIterator: Iterator {
         #[inline]
         fn check<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut((), T) -> ControlFlow<T> {
             move |(), x| {
-                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE }
+                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::Continue(()) }
             }
         }
 
diff --git a/library/core/src/iter/traits/exact_size.rs b/library/core/src/iter/traits/exact_size.rs
index 1757e37ec..908830d8a 100644
--- a/library/core/src/iter/traits/exact_size.rs
+++ b/library/core/src/iter/traits/exact_size.rs
@@ -21,6 +21,16 @@
 ///
 /// [`len`]: ExactSizeIterator::len
 ///
+/// # When *shouldn't* an adapter be `ExactSizeIterator`?
+///
+/// If an adapter makes an iterator *longer*, then it's usually incorrect for
+/// that adapter to implement `ExactSizeIterator`.  The inner exact-sized
+/// iterator might already be `usize::MAX`-long, and thus the length of the
+/// longer adapted iterator would no longer be exactly representable in `usize`.
+///
+/// This is why [`Chain<A, B>`](crate::iter::Chain) isn't `ExactSizeIterator`,
+/// even when `A` and `B` are both `ExactSizeIterator`.
+///
 /// # Examples
 ///
 /// Basic usage:
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index a4a665d48..b8e7d0a68 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -69,6 +69,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
 #[doc(notable_trait)]
 #[rustc_diagnostic_item = "Iterator"]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Iterator {
     /// The type of the elements being iterated over.
     #[rustc_diagnostic_item = "IteratorItem"]
@@ -141,6 +142,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_next_chunk", reason = "recently added", issue = "98326")]
+    #[rustc_do_not_const_check]
     fn next_chunk<const N: usize>(
         &mut self,
     ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>>
@@ -218,6 +220,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn size_hint(&self) -> (usize, Option<usize>) {
         (0, None)
     }
@@ -255,6 +258,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn count(self) -> usize
     where
         Self: Sized,
@@ -285,6 +289,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn last(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -331,6 +336,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")]
+    #[rustc_do_not_const_check]
     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
         for i in 0..n {
             self.next().ok_or(i)?;
@@ -379,6 +385,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         self.advance_by(n).ok()?;
         self.next()
@@ -431,6 +438,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_step_by", since = "1.28.0")]
+    #[rustc_do_not_const_check]
     fn step_by(self, step: usize) -> StepBy<Self>
     where
         Self: Sized,
@@ -502,6 +510,7 @@ pub trait Iterator {
     /// [`OsStr`]: ../../std/ffi/struct.OsStr.html
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter>
     where
         Self: Sized,
@@ -620,6 +629,7 @@ pub trait Iterator {
     /// [`zip`]: crate::iter::zip
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter>
     where
         Self: Sized,
@@ -662,6 +672,7 @@ pub trait Iterator {
     /// [`intersperse_with`]: Iterator::intersperse_with
     #[inline]
     #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
+    #[rustc_do_not_const_check]
     fn intersperse(self, separator: Self::Item) -> Intersperse<Self>
     where
         Self: Sized,
@@ -720,6 +731,7 @@ pub trait Iterator {
     /// [`intersperse`]: Iterator::intersperse
     #[inline]
     #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
+    #[rustc_do_not_const_check]
     fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>
     where
         Self: Sized,
@@ -777,8 +789,10 @@ pub trait Iterator {
     ///     println!("{x}");
     /// }
     /// ```
+    #[rustc_diagnostic_item = "IteratorMap"]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn map<B, F>(self, f: F) -> Map<Self, F>
     where
         Self: Sized,
@@ -824,6 +838,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_for_each", since = "1.21.0")]
+    #[rustc_do_not_const_check]
     fn for_each<F>(self, f: F)
     where
         Self: Sized,
@@ -899,6 +914,7 @@ pub trait Iterator {
     /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn filter<P>(self, predicate: P) -> Filter<Self, P>
     where
         Self: Sized,
@@ -944,6 +960,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
     where
         Self: Sized,
@@ -990,6 +1007,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn enumerate(self) -> Enumerate<Self>
     where
         Self: Sized,
@@ -1061,6 +1079,7 @@ pub trait Iterator {
     /// [`next`]: Iterator::next
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn peekable(self) -> Peekable<Self>
     where
         Self: Sized,
@@ -1126,6 +1145,7 @@ pub trait Iterator {
     #[inline]
     #[doc(alias = "drop_while")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
     where
         Self: Sized,
@@ -1207,6 +1227,7 @@ pub trait Iterator {
     /// the iteration should stop, but wasn't placed back into the iterator.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
     where
         Self: Sized,
@@ -1295,6 +1316,7 @@ pub trait Iterator {
     /// [`fuse`]: Iterator::fuse
     #[inline]
     #[stable(feature = "iter_map_while", since = "1.57.0")]
+    #[rustc_do_not_const_check]
     fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>
     where
         Self: Sized,
@@ -1326,6 +1348,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn skip(self, n: usize) -> Skip<Self>
     where
         Self: Sized,
@@ -1379,6 +1402,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn take(self, n: usize) -> Take<Self>
     where
         Self: Sized,
@@ -1428,6 +1452,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
     where
         Self: Sized,
@@ -1468,6 +1493,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
     where
         Self: Sized,
@@ -1552,6 +1578,7 @@ pub trait Iterator {
     /// [`flat_map()`]: Iterator::flat_map
     #[inline]
     #[stable(feature = "iterator_flatten", since = "1.29.0")]
+    #[rustc_do_not_const_check]
     fn flatten(self) -> Flatten<Self>
     where
         Self: Sized,
@@ -1620,6 +1647,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn fuse(self) -> Fuse<Self>
     where
         Self: Sized,
@@ -1704,6 +1732,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn inspect<F>(self, f: F) -> Inspect<Self, F>
     where
         Self: Sized,
@@ -1734,6 +1763,7 @@ pub trait Iterator {
     /// assert_eq!(of_rust, vec!["of", "Rust"]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn by_ref(&mut self) -> &mut Self
     where
         Self: Sized,
@@ -1853,6 +1883,7 @@ pub trait Iterator {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]
     #[cfg_attr(not(test), rustc_diagnostic_item = "iterator_collect_fn")]
+    #[rustc_do_not_const_check]
     fn collect<B: FromIterator<Self::Item>>(self) -> B
     where
         Self: Sized,
@@ -1931,6 +1962,7 @@ pub trait Iterator {
     /// [`collect`]: Iterator::collect
     #[inline]
     #[unstable(feature = "iterator_try_collect", issue = "94047")]
+    #[rustc_do_not_const_check]
     fn try_collect<B>(&mut self) -> ChangeOutputType<Self::Item, B>
     where
         Self: Sized,
@@ -2004,6 +2036,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_collect_into", reason = "new API", issue = "94780")]
+    #[rustc_do_not_const_check]
     fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E
     where
         Self: Sized,
@@ -2038,6 +2071,7 @@ pub trait Iterator {
     /// assert_eq!(odd, vec![1, 3]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn partition<B, F>(self, f: F) -> (B, B)
     where
         Self: Sized,
@@ -2100,6 +2134,7 @@ pub trait Iterator {
     /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds
     /// ```
     #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")]
+    #[rustc_do_not_const_check]
     fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize
     where
         Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
@@ -2157,6 +2192,7 @@ pub trait Iterator {
     /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));
     /// ```
     #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")]
+    #[rustc_do_not_const_check]
     fn is_partitioned<P>(mut self, mut predicate: P) -> bool
     where
         Self: Sized,
@@ -2251,6 +2287,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
+    #[rustc_do_not_const_check]
     fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
     where
         Self: Sized,
@@ -2309,6 +2346,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
+    #[rustc_do_not_const_check]
     fn try_for_each<F, R>(&mut self, f: F) -> R
     where
         Self: Sized,
@@ -2428,6 +2466,7 @@ pub trait Iterator {
     #[doc(alias = "inject", alias = "foldl")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn fold<B, F>(mut self, init: B, mut f: F) -> B
     where
         Self: Sized,
@@ -2465,6 +2504,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_fold_self", since = "1.51.0")]
+    #[rustc_do_not_const_check]
     fn reduce<F>(mut self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -2536,6 +2576,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")]
+    #[rustc_do_not_const_check]
     fn try_reduce<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<R::Output>>
     where
         Self: Sized,
@@ -2593,6 +2634,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn all<F>(&mut self, f: F) -> bool
     where
         Self: Sized,
@@ -2601,10 +2643,10 @@ pub trait Iterator {
         #[inline]
         fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> {
             move |(), x| {
-                if f(x) { ControlFlow::CONTINUE } else { ControlFlow::BREAK }
+                if f(x) { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
             }
         }
-        self.try_fold((), check(f)) == ControlFlow::CONTINUE
+        self.try_fold((), check(f)) == ControlFlow::Continue(())
     }
 
     /// Tests if any element of the iterator matches a predicate.
@@ -2646,6 +2688,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn any<F>(&mut self, f: F) -> bool
     where
         Self: Sized,
@@ -2654,11 +2697,11 @@ pub trait Iterator {
         #[inline]
         fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<()> {
             move |(), x| {
-                if f(x) { ControlFlow::BREAK } else { ControlFlow::CONTINUE }
+                if f(x) { ControlFlow::Break(()) } else { ControlFlow::Continue(()) }
             }
         }
 
-        self.try_fold((), check(f)) == ControlFlow::BREAK
+        self.try_fold((), check(f)) == ControlFlow::Break(())
     }
 
     /// Searches for an element of an iterator that satisfies a predicate.
@@ -2709,6 +2752,7 @@ pub trait Iterator {
     /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
     where
         Self: Sized,
@@ -2717,7 +2761,7 @@ pub trait Iterator {
         #[inline]
         fn check<T>(mut predicate: impl FnMut(&T) -> bool) -> impl FnMut((), T) -> ControlFlow<T> {
             move |(), x| {
-                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE }
+                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::Continue(()) }
             }
         }
 
@@ -2740,6 +2784,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_find_map", since = "1.30.0")]
+    #[rustc_do_not_const_check]
     fn find_map<B, F>(&mut self, f: F) -> Option<B>
     where
         Self: Sized,
@@ -2749,7 +2794,7 @@ pub trait Iterator {
         fn check<T, B>(mut f: impl FnMut(T) -> Option<B>) -> impl FnMut((), T) -> ControlFlow<B> {
             move |(), x| match f(x) {
                 Some(x) => ControlFlow::Break(x),
-                None => ControlFlow::CONTINUE,
+                None => ControlFlow::Continue(()),
             }
         }
 
@@ -2796,6 +2841,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
+    #[rustc_do_not_const_check]
     fn try_find<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<Self::Item>>
     where
         Self: Sized,
@@ -2812,7 +2858,7 @@ pub trait Iterator {
             R: Residual<Option<I>>,
         {
             move |(), x| match f(&x).branch() {
-                ControlFlow::Continue(false) => ControlFlow::CONTINUE,
+                ControlFlow::Continue(false) => ControlFlow::Continue(()),
                 ControlFlow::Continue(true) => ControlFlow::Break(Try::from_output(Some(x))),
                 ControlFlow::Break(r) => ControlFlow::Break(FromResidual::from_residual(r)),
             }
@@ -2878,6 +2924,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn position<P>(&mut self, predicate: P) -> Option<usize>
     where
         Self: Sized,
@@ -2935,6 +2982,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn rposition<P>(&mut self, predicate: P) -> Option<usize>
     where
         P: FnMut(Self::Item) -> bool,
@@ -2986,6 +3034,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn max(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3024,6 +3073,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn min(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3046,6 +3096,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    #[rustc_do_not_const_check]
     fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3079,6 +3130,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_max_by", since = "1.15.0")]
+    #[rustc_do_not_const_check]
     fn max_by<F>(self, compare: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3106,6 +3158,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    #[rustc_do_not_const_check]
     fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3139,6 +3192,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_min_by", since = "1.15.0")]
+    #[rustc_do_not_const_check]
     fn min_by<F>(self, compare: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3176,6 +3230,7 @@ pub trait Iterator {
     #[inline]
     #[doc(alias = "reverse")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn rev(self) -> Rev<Self>
     where
         Self: Sized + DoubleEndedIterator,
@@ -3214,6 +3269,7 @@ pub trait Iterator {
     /// assert_eq!(z, [3, 6]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
     where
         FromA: Default + Extend<A>,
@@ -3246,6 +3302,7 @@ pub trait Iterator {
     /// assert_eq!(v_map, vec![1, 2, 3]);
     /// ```
     #[stable(feature = "iter_copied", since = "1.36.0")]
+    #[rustc_do_not_const_check]
     fn copied<'a, T: 'a>(self) -> Copied<Self>
     where
         Self: Sized + Iterator<Item = &'a T>,
@@ -3293,6 +3350,7 @@ pub trait Iterator {
     /// assert_eq!(&[vec![23]], &faster[..]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn cloned<'a, T: 'a>(self) -> Cloned<Self>
     where
         Self: Sized + Iterator<Item = &'a T>,
@@ -3327,6 +3385,7 @@ pub trait Iterator {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[rustc_do_not_const_check]
     fn cycle(self) -> Cycle<Self>
     where
         Self: Sized + Clone,
@@ -3370,6 +3429,7 @@ pub trait Iterator {
     /// ```
     #[track_caller]
     #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "100450")]
+    #[rustc_do_not_const_check]
     fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>
     where
         Self: Sized,
@@ -3400,6 +3460,7 @@ pub trait Iterator {
     /// assert_eq!(sum, 6);
     /// ```
     #[stable(feature = "iter_arith", since = "1.11.0")]
+    #[rustc_do_not_const_check]
     fn sum<S>(self) -> S
     where
         Self: Sized,
@@ -3429,6 +3490,7 @@ pub trait Iterator {
     /// assert_eq!(factorial(5), 120);
     /// ```
     #[stable(feature = "iter_arith", since = "1.11.0")]
+    #[rustc_do_not_const_check]
     fn product<P>(self) -> P
     where
         Self: Sized,
@@ -3450,6 +3512,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn cmp<I>(self, other: I) -> Ordering
     where
         I: IntoIterator<Item = Self::Item>,
@@ -3479,6 +3542,7 @@ 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")]
+    #[rustc_do_not_const_check]
     fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
     where
         Self: Sized,
@@ -3491,7 +3555,7 @@ pub trait Iterator {
             F: FnMut(X, Y) -> Ordering,
         {
             move |x, y| match cmp(x, y) {
-                Ordering::Equal => ControlFlow::CONTINUE,
+                Ordering::Equal => ControlFlow::Continue(()),
                 non_eq => ControlFlow::Break(non_eq),
             }
         }
@@ -3502,8 +3566,10 @@ pub trait Iterator {
         }
     }
 
-    /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
-    /// of another.
+    /// [Lexicographically](Ord#lexicographical-comparison) compares the [`PartialOrd`] elements of
+    /// this [`Iterator`] with those of another. The comparison works like short-circuit
+    /// evaluation, returning a result without comparing the remaining elements.
+    /// As soon as an order can be determined, the evaluation stops and a result is returned.
     ///
     /// # Examples
     ///
@@ -3513,10 +3579,27 @@ pub trait Iterator {
     /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal));
     /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less));
     /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater));
+    /// ```
     ///
+    /// For floating-point numbers, NaN does not have a total order and will result
+    /// in `None` when compared:
+    ///
+    /// ```
     /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None);
     /// ```
+    ///
+    /// The results are determined by the order of evaluation.
+    ///
+    /// ```
+    /// use std::cmp::Ordering;
+    ///
+    /// assert_eq!([1.0, f64::NAN].iter().partial_cmp([2.0, f64::NAN].iter()), Some(Ordering::Less));
+    /// assert_eq!([2.0, f64::NAN].iter().partial_cmp([1.0, f64::NAN].iter()), Some(Ordering::Greater));
+    /// assert_eq!([f64::NAN, 1.0].iter().partial_cmp([f64::NAN, 2.0].iter()), None);
+    /// ```
+    ///
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn partial_cmp<I>(self, other: I) -> Option<Ordering>
     where
         I: IntoIterator,
@@ -3555,6 +3638,7 @@ pub trait Iterator {
     /// );
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
+    #[rustc_do_not_const_check]
     fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
     where
         Self: Sized,
@@ -3567,7 +3651,7 @@ pub trait Iterator {
             F: FnMut(X, Y) -> Option<Ordering>,
         {
             move |x, y| match partial_cmp(x, y) {
-                Some(Ordering::Equal) => ControlFlow::CONTINUE,
+                Some(Ordering::Equal) => ControlFlow::Continue(()),
                 non_eq => ControlFlow::Break(non_eq),
             }
         }
@@ -3588,6 +3672,7 @@ pub trait Iterator {
     /// assert_eq!([1].iter().eq([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn eq<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3613,6 +3698,7 @@ pub trait Iterator {
     /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y));
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
+    #[rustc_do_not_const_check]
     fn eq_by<I, F>(self, other: I, eq: F) -> bool
     where
         Self: Sized,
@@ -3625,7 +3711,7 @@ pub trait Iterator {
             F: FnMut(X, Y) -> bool,
         {
             move |x, y| {
-                if eq(x, y) { ControlFlow::CONTINUE } else { ControlFlow::BREAK }
+                if eq(x, y) { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
             }
         }
 
@@ -3645,6 +3731,7 @@ pub trait Iterator {
     /// assert_eq!([1].iter().ne([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn ne<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3666,6 +3753,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().lt([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn lt<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3687,6 +3775,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().le([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn le<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3708,6 +3797,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().gt([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn gt<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3729,6 +3819,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().ge([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn ge<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3760,6 +3851,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted(self) -> bool
     where
         Self: Sized,
@@ -3788,6 +3880,7 @@ pub trait Iterator {
     ///
     /// [`is_sorted`]: Iterator::is_sorted
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted_by<F>(mut self, compare: F) -> bool
     where
         Self: Sized,
@@ -3834,6 +3927,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted_by_key<F, K>(self, f: F) -> bool
     where
         Self: Sized,
@@ -3849,6 +3943,7 @@ pub trait Iterator {
     #[inline]
     #[doc(hidden)]
     #[unstable(feature = "trusted_random_access", issue = "none")]
+    #[rustc_do_not_const_check]
     unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccessNoCoerce,
@@ -3859,7 +3954,7 @@ 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
+/// 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
diff --git a/library/core/src/iter/traits/marker.rs b/library/core/src/iter/traits/marker.rs
index da7537457..af0284823 100644
--- a/library/core/src/iter/traits/marker.rs
+++ b/library/core/src/iter/traits/marker.rs
@@ -31,6 +31,17 @@ impl<I: FusedIterator + ?Sized> FusedIterator for &mut I {}
 /// The iterator must produce exactly the number of elements it reported
 /// or diverge before reaching the end.
 ///
+/// # When *shouldn't* an adapter be `TrustedLen`?
+///
+/// If an adapter makes an iterator *shorter* by a given amount, then it's
+/// usually incorrect for that adapter to implement `TrustedLen`.  The inner
+/// iterator might return more than `usize::MAX` items, but there's no way to
+/// know what `k` elements less than that will be, since the `size_hint` from
+/// the inner iterator has already saturated and lost that information.
+///
+/// This is why [`Skip<I>`](crate::iter::Skip) isn't `TrustedLen`, even when
+/// `I` implements `TrustedLen`.
+///
 /// # Safety
 ///
 /// This trait must only be implemented when the contract is upheld. Consumers
diff --git a/library/core/src/iter/traits/mod.rs b/library/core/src/iter/traits/mod.rs
index ed0fb634d..41ea29e6a 100644
--- a/library/core/src/iter/traits/mod.rs
+++ b/library/core/src/iter/traits/mod.rs
@@ -4,6 +4,7 @@ mod double_ended;
 mod exact_size;
 mod iterator;
 mod marker;
+mod unchecked_iterator;
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::{
@@ -19,3 +20,5 @@ pub use self::{
 pub use self::marker::InPlaceIterable;
 #[unstable(feature = "trusted_step", issue = "85731")]
 pub use self::marker::TrustedStep;
+
+pub(crate) use self::unchecked_iterator::UncheckedIterator;
diff --git a/library/core/src/iter/traits/unchecked_iterator.rs b/library/core/src/iter/traits/unchecked_iterator.rs
new file mode 100644
index 000000000..ae4bfcad4
--- /dev/null
+++ b/library/core/src/iter/traits/unchecked_iterator.rs
@@ -0,0 +1,36 @@
+use crate::iter::TrustedLen;
+
+/// [`TrustedLen`] cannot have methods, so this allows augmenting it.
+///
+/// It currently requires `TrustedLen` because it's unclear whether it's
+/// reasonably possible to depend on the `size_hint` of anything else.
+pub(crate) trait UncheckedIterator: TrustedLen {
+    /// Gets the next item from a non-empty iterator.
+    ///
+    /// Because there's always a value to return, that means it can return
+    /// the `Item` type directly, without wrapping it in an `Option`.
+    ///
+    /// # Safety
+    ///
+    /// This can only be called if `size_hint().0 != 0`, guaranteeing that
+    /// there's at least one item available.
+    ///
+    /// Otherwise (aka when `size_hint().1 == Some(0)`), this is UB.
+    ///
+    /// # Note to Implementers
+    ///
+    /// This has a default implementation using [`Option::unwrap_unchecked`].
+    /// That's probably sufficient if your `next` *always* returns `Some`,
+    /// such as for infinite iterators.  In more complicated situations, however,
+    /// sometimes there can still be `insertvalue`/`assume`/`extractvalue`
+    /// instructions remaining in the IR from the `Option` handling, at which
+    /// point you might want to implement this manually instead.
+    #[unstable(feature = "trusted_len_next_unchecked", issue = "37572")]
+    #[inline]
+    unsafe fn next_unchecked(&mut self) -> Self::Item {
+        let opt = self.next();
+        // SAFETY: The caller promised that we're not empty, and
+        // `Self: TrustedLen` so we can actually trust the `size_hint`.
+        unsafe { opt.unwrap_unchecked() }
+    }
+}
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 8790649ab..24bad799f 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -95,6 +95,7 @@
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
 #![allow(incomplete_features)]
+#![cfg_attr(not(bootstrap), warn(multiple_supertrait_upcastable))]
 //
 // Library features:
 #![feature(const_align_offset)]
@@ -123,6 +124,8 @@
 #![feature(const_inherent_unchecked_arith)]
 #![feature(const_int_unchecked_arith)]
 #![feature(const_intrinsic_forget)]
+#![feature(const_ipv4)]
+#![feature(const_ipv6)]
 #![feature(const_likely)]
 #![feature(const_maybe_uninit_uninit_array)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
@@ -133,6 +136,7 @@
 #![feature(const_option)]
 #![feature(const_option_ext)]
 #![feature(const_pin)]
+#![feature(const_pointer_byte_offsets)]
 #![feature(const_pointer_is_aligned)]
 #![feature(const_ptr_sub_ptr)]
 #![feature(const_replace)]
@@ -178,6 +182,7 @@
 #![feature(const_slice_index)]
 #![feature(const_is_char_boundary)]
 #![feature(const_cstr_methods)]
+#![feature(ip)]
 #![feature(is_ascii_octdigit)]
 //
 // Language features:
@@ -191,8 +196,9 @@
 #![feature(cfg_sanitize)]
 #![feature(cfg_target_has_atomic)]
 #![feature(cfg_target_has_atomic_equal_alignment)]
-#![cfg_attr(not(bootstrap), feature(const_closures))]
+#![feature(const_closures)]
 #![feature(const_fn_floating_point_arithmetic)]
+#![feature(const_for)]
 #![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
 #![feature(const_refs_to_cell)]
@@ -235,11 +241,11 @@
 #![feature(unsized_fn_params)]
 #![feature(asm_const)]
 #![feature(const_transmute_copy)]
+#![cfg_attr(not(bootstrap), feature(multiple_supertrait_upcastable))]
 //
 // Target features:
 #![feature(arm_target_feature)]
 #![feature(avx512_target_feature)]
-#![feature(cmpxchg16b_target_feature)]
 #![feature(hexagon_target_feature)]
 #![feature(mips_target_feature)]
 #![feature(powerpc_target_feature)]
@@ -248,7 +254,7 @@
 #![feature(sse4a_target_feature)]
 #![feature(tbm_target_feature)]
 #![feature(wasm_target_feature)]
-#![cfg_attr(bootstrap, feature(f16c_target_feature))]
+#![cfg_attr(bootstrap, feature(cmpxchg16b_target_feature))]
 
 // allow using `core::` in intra-doc links
 #[allow(unused_extern_crates)]
@@ -347,6 +353,7 @@ pub mod cell;
 pub mod char;
 pub mod ffi;
 pub mod iter;
+pub mod net;
 pub mod option;
 pub mod panic;
 pub mod panicking;
@@ -375,8 +382,6 @@ 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 1326fc9ab..520ae0edb 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -97,6 +97,7 @@ unsafe impl<T: Sync + ?Sized> Send for &T {}
 #[fundamental] // for Default, for example, which requires that `[T]: !Default` be evaluatable
 #[rustc_specialization_trait]
 #[rustc_deny_explicit_impl]
+#[cfg_attr(not(bootstrap), rustc_coinductive)]
 pub trait Sized {
     // Empty.
 }
@@ -469,6 +470,62 @@ pub macro Copy($item:item) {
 #[cfg_attr(not(test), rustc_diagnostic_item = "Sync")]
 #[lang = "sync"]
 #[rustc_on_unimplemented(
+    on(
+        _Self = "std::cell::OnceCell<T>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::OnceLock` instead"
+    ),
+    on(
+        _Self = "std::cell::Cell<u8>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU8` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<u16>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU16` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<u32>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU32` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<u64>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicU64` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<usize>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicUsize` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<i8>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI8` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<i16>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI16` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<i32>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI32` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<i64>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicI64` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<isize>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicIsize` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<bool>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` or `std::sync::atomic::AtomicBool` instead",
+    ),
+    on(
+        _Self = "std::cell::Cell<T>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`",
+    ),
+    on(
+        _Self = "std::cell::RefCell<T>",
+        note = "if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` instead",
+    ),
     message = "`{Self}` cannot be shared between threads safely",
     label = "`{Self}` cannot be shared between threads safely"
 )]
@@ -815,14 +872,18 @@ pub trait Destruct {}
 #[rustc_deny_explicit_impl]
 pub trait Tuple {}
 
-/// A marker for things
-#[unstable(feature = "pointer_sized_trait", issue = "none")]
-#[lang = "pointer_sized"]
+/// A marker for pointer-like types.
+///
+/// All types that have the same size and alignment as a `usize` or
+/// `*const ()` automatically implement this trait.
+#[unstable(feature = "pointer_like_trait", issue = "none")]
+#[cfg_attr(bootstrap, lang = "pointer_sized")]
+#[cfg_attr(not(bootstrap), lang = "pointer_like")]
 #[rustc_on_unimplemented(
-    message = "`{Self}` needs to be a pointer-sized type",
-    label = "`{Self}` needs to be a pointer-sized type"
+    message = "`{Self}` needs to have the same alignment and size as a pointer",
+    label = "`{Self}` needs to be a pointer-like type"
 )]
-pub trait PointerSized {}
+pub trait PointerLike {}
 
 /// Implementations of `Copy` for primitive types.
 ///
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 5e01ccc07..a67df7ed5 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -682,7 +682,6 @@ pub unsafe fn zeroed<T>() -> T {
 pub unsafe fn uninitialized<T>() -> T {
     // SAFETY: the caller must guarantee that an uninitialized value is valid for `T`.
     unsafe {
-        #[cfg(not(bootstrap))] // If the compiler hits this itself then it deserves the UB.
         intrinsics::assert_mem_uninitialized_valid::<T>();
         let mut val = MaybeUninit::<T>::uninit();
 
diff --git a/library/core/src/net/display_buffer.rs b/library/core/src/net/display_buffer.rs
new file mode 100644
index 000000000..7aadf06e9
--- /dev/null
+++ b/library/core/src/net/display_buffer.rs
@@ -0,0 +1,40 @@
+use crate::fmt;
+use crate::mem::MaybeUninit;
+use crate::str;
+
+/// Used for slow path in `Display` implementations when alignment is required.
+pub struct DisplayBuffer<const SIZE: usize> {
+    buf: [MaybeUninit<u8>; SIZE],
+    len: usize,
+}
+
+impl<const SIZE: usize> DisplayBuffer<SIZE> {
+    #[inline]
+    pub const fn new() -> Self {
+        Self { buf: MaybeUninit::uninit_array(), len: 0 }
+    }
+
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        // SAFETY: `buf` is only written to by the `fmt::Write::write_str` implementation
+        // which writes a valid UTF-8 string to `buf` and correctly sets `len`.
+        unsafe {
+            let s = MaybeUninit::slice_assume_init_ref(&self.buf[..self.len]);
+            str::from_utf8_unchecked(s)
+        }
+    }
+}
+
+impl<const SIZE: usize> fmt::Write for DisplayBuffer<SIZE> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        let bytes = s.as_bytes();
+
+        if let Some(buf) = self.buf.get_mut(self.len..(self.len + bytes.len())) {
+            MaybeUninit::write_slice(buf, bytes);
+            self.len += bytes.len();
+            Ok(())
+        } else {
+            Err(fmt::Error)
+        }
+    }
+}
diff --git a/library/core/src/net/ip_addr.rs b/library/core/src/net/ip_addr.rs
new file mode 100644
index 000000000..954d88d54
--- /dev/null
+++ b/library/core/src/net/ip_addr.rs
@@ -0,0 +1,2070 @@
+use crate::cmp::Ordering;
+use crate::fmt::{self, Write};
+use crate::mem::transmute;
+
+use super::display_buffer::DisplayBuffer;
+
+/// An IP address, either IPv4 or IPv6.
+///
+/// This enum can contain either an [`Ipv4Addr`] or an [`Ipv6Addr`], see their
+/// respective documentation for more details.
+///
+/// # Examples
+///
+/// ```
+/// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+///
+/// let localhost_v4 = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
+/// let localhost_v6 = IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+///
+/// assert_eq!("127.0.0.1".parse(), Ok(localhost_v4));
+/// assert_eq!("::1".parse(), Ok(localhost_v6));
+///
+/// assert_eq!(localhost_v4.is_ipv6(), false);
+/// assert_eq!(localhost_v4.is_ipv4(), true);
+/// ```
+#[cfg_attr(not(test), rustc_diagnostic_item = "IpAddr")]
+#[stable(feature = "ip_addr", since = "1.7.0")]
+#[derive(Copy, Clone, Eq, PartialEq, Hash, PartialOrd, Ord)]
+pub enum IpAddr {
+    /// An IPv4 address.
+    #[stable(feature = "ip_addr", since = "1.7.0")]
+    V4(#[stable(feature = "ip_addr", since = "1.7.0")] Ipv4Addr),
+    /// An IPv6 address.
+    #[stable(feature = "ip_addr", since = "1.7.0")]
+    V6(#[stable(feature = "ip_addr", since = "1.7.0")] Ipv6Addr),
+}
+
+/// An IPv4 address.
+///
+/// IPv4 addresses are defined as 32-bit integers in [IETF RFC 791].
+/// They are usually represented as four octets.
+///
+/// See [`IpAddr`] for a type encompassing both IPv4 and IPv6 addresses.
+///
+/// [IETF RFC 791]: https://tools.ietf.org/html/rfc791
+///
+/// # Textual representation
+///
+/// `Ipv4Addr` provides a [`FromStr`] implementation. The four octets are in decimal
+/// notation, divided by `.` (this is called "dot-decimal notation").
+/// Notably, octal numbers (which are indicated with a leading `0`) and hexadecimal numbers (which
+/// are indicated with a leading `0x`) are not allowed per [IETF RFC 6943].
+///
+/// [IETF RFC 6943]: https://tools.ietf.org/html/rfc6943#section-3.1.1
+/// [`FromStr`]: crate::str::FromStr
+///
+/// # Examples
+///
+/// ```
+/// use std::net::Ipv4Addr;
+///
+/// let localhost = Ipv4Addr::new(127, 0, 0, 1);
+/// assert_eq!("127.0.0.1".parse(), Ok(localhost));
+/// assert_eq!(localhost.is_loopback(), true);
+/// assert!("012.004.002.000".parse::<Ipv4Addr>().is_err()); // all octets are in octal
+/// assert!("0000000.0.0.0".parse::<Ipv4Addr>().is_err()); // first octet is a zero in octal
+/// assert!("0xcb.0x0.0x71.0x00".parse::<Ipv4Addr>().is_err()); // all octets are in hex
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Ipv4Addr {
+    octets: [u8; 4],
+}
+
+/// An IPv6 address.
+///
+/// IPv6 addresses are defined as 128-bit integers in [IETF RFC 4291].
+/// They are usually represented as eight 16-bit segments.
+///
+/// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
+///
+/// # Embedding IPv4 Addresses
+///
+/// See [`IpAddr`] for a type encompassing both IPv4 and IPv6 addresses.
+///
+/// To assist in the transition from IPv4 to IPv6 two types of IPv6 addresses that embed an IPv4 address were defined:
+/// IPv4-compatible and IPv4-mapped addresses. Of these IPv4-compatible addresses have been officially deprecated.
+///
+/// Both types of addresses are not assigned any special meaning by this implementation,
+/// other than what the relevant standards prescribe. This means that an address like `::ffff:127.0.0.1`,
+/// while representing an IPv4 loopback address, is not itself an IPv6 loopback address; only `::1` is.
+/// To handle these so called "IPv4-in-IPv6" addresses, they have to first be converted to their canonical IPv4 address.
+///
+/// ### IPv4-Compatible IPv6 Addresses
+///
+/// IPv4-compatible IPv6 addresses are defined in [IETF RFC 4291 Section 2.5.5.1], and have been officially deprecated.
+/// The RFC describes the format of an "IPv4-Compatible IPv6 address" as follows:
+///
+/// ```text
+/// |                80 bits               | 16 |      32 bits        |
+/// +--------------------------------------+--------------------------+
+/// |0000..............................0000|0000|    IPv4 address     |
+/// +--------------------------------------+----+---------------------+
+/// ```
+/// So `::a.b.c.d` would be an IPv4-compatible IPv6 address representing the IPv4 address `a.b.c.d`.
+///
+/// To convert from an IPv4 address to an IPv4-compatible IPv6 address, use [`Ipv4Addr::to_ipv6_compatible`].
+/// Use [`Ipv6Addr::to_ipv4`] to convert an IPv4-compatible IPv6 address to the canonical IPv4 address.
+///
+/// [IETF RFC 4291 Section 2.5.5.1]: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.1
+///
+/// ### IPv4-Mapped IPv6 Addresses
+///
+/// IPv4-mapped IPv6 addresses are defined in [IETF RFC 4291 Section 2.5.5.2].
+/// The RFC describes the format of an "IPv4-Mapped IPv6 address" as follows:
+///
+/// ```text
+/// |                80 bits               | 16 |      32 bits        |
+/// +--------------------------------------+--------------------------+
+/// |0000..............................0000|FFFF|    IPv4 address     |
+/// +--------------------------------------+----+---------------------+
+/// ```
+/// So `::ffff:a.b.c.d` would be an IPv4-mapped IPv6 address representing the IPv4 address `a.b.c.d`.
+///
+/// To convert from an IPv4 address to an IPv4-mapped IPv6 address, use [`Ipv4Addr::to_ipv6_mapped`].
+/// Use [`Ipv6Addr::to_ipv4`] to convert an IPv4-mapped IPv6 address to the canonical IPv4 address.
+/// Note that this will also convert the IPv6 loopback address `::1` to `0.0.0.1`. Use
+/// [`Ipv6Addr::to_ipv4_mapped`] to avoid this.
+///
+/// [IETF RFC 4291 Section 2.5.5.2]: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2
+///
+/// # Textual representation
+///
+/// `Ipv6Addr` provides a [`FromStr`] implementation. There are many ways to represent
+/// an IPv6 address in text, but in general, each segments is written in hexadecimal
+/// notation, and segments are separated by `:`. For more information, see
+/// [IETF RFC 5952].
+///
+/// [`FromStr`]: crate::str::FromStr
+/// [IETF RFC 5952]: https://tools.ietf.org/html/rfc5952
+///
+/// # Examples
+///
+/// ```
+/// use std::net::Ipv6Addr;
+///
+/// let localhost = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
+/// assert_eq!("::1".parse(), Ok(localhost));
+/// assert_eq!(localhost.is_loopback(), true);
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Ipv6Addr {
+    octets: [u8; 16],
+}
+
+/// Scope of an [IPv6 multicast address] as defined in [IETF RFC 7346 section 2].
+///
+/// # Stability Guarantees
+///
+/// Not all possible values for a multicast scope have been assigned.
+/// Future RFCs may introduce new scopes, which will be added as variants to this enum;
+/// because of this the enum is marked as `#[non_exhaustive]`.
+///
+/// # Examples
+/// ```
+/// #![feature(ip)]
+///
+/// use std::net::Ipv6Addr;
+/// use std::net::Ipv6MulticastScope::*;
+///
+/// // An IPv6 multicast address with global scope (`ff0e::`).
+/// let address = Ipv6Addr::new(0xff0e, 0, 0, 0, 0, 0, 0, 0);
+///
+/// // Will print "Global scope".
+/// match address.multicast_scope() {
+///     Some(InterfaceLocal) => println!("Interface-Local scope"),
+///     Some(LinkLocal) => println!("Link-Local scope"),
+///     Some(RealmLocal) => println!("Realm-Local scope"),
+///     Some(AdminLocal) => println!("Admin-Local scope"),
+///     Some(SiteLocal) => println!("Site-Local scope"),
+///     Some(OrganizationLocal) => println!("Organization-Local scope"),
+///     Some(Global) => println!("Global scope"),
+///     Some(_) => println!("Unknown scope"),
+///     None => println!("Not a multicast address!")
+/// }
+///
+/// ```
+///
+/// [IPv6 multicast address]: Ipv6Addr
+/// [IETF RFC 7346 section 2]: https://tools.ietf.org/html/rfc7346#section-2
+#[derive(Copy, PartialEq, Eq, Clone, Hash, Debug)]
+#[unstable(feature = "ip", issue = "27709")]
+#[non_exhaustive]
+pub enum Ipv6MulticastScope {
+    /// Interface-Local scope.
+    InterfaceLocal,
+    /// Link-Local scope.
+    LinkLocal,
+    /// Realm-Local scope.
+    RealmLocal,
+    /// Admin-Local scope.
+    AdminLocal,
+    /// Site-Local scope.
+    SiteLocal,
+    /// Organization-Local scope.
+    OrganizationLocal,
+    /// Global scope.
+    Global,
+}
+
+impl IpAddr {
+    /// Returns [`true`] for the special 'unspecified' address.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_unspecified()`] and
+    /// [`Ipv6Addr::is_unspecified()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(0, 0, 0, 0)).is_unspecified(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)).is_unspecified(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "ip_shared", since = "1.12.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unspecified(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_unspecified(),
+            IpAddr::V6(ip) => ip.is_unspecified(),
+        }
+    }
+
+    /// Returns [`true`] if this is a loopback address.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_loopback()`] and
+    /// [`Ipv6Addr::is_loopback()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)).is_loopback(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1)).is_loopback(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "ip_shared", since = "1.12.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_loopback(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_loopback(),
+            IpAddr::V6(ip) => ip.is_loopback(),
+        }
+    }
+
+    /// Returns [`true`] if the address appears to be globally routable.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_global()`] and
+    /// [`Ipv6Addr::is_global()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(80, 9, 12, 3)).is_global(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0x1c9, 0, 0, 0xafc8, 0, 0x1)).is_global(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_global(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_global(),
+            IpAddr::V6(ip) => ip.is_global(),
+        }
+    }
+
+    /// Returns [`true`] if this is a multicast address.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_multicast()`] and
+    /// [`Ipv6Addr::is_multicast()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(224, 254, 0, 0)).is_multicast(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0)).is_multicast(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "ip_shared", since = "1.12.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_multicast(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_multicast(),
+            IpAddr::V6(ip) => ip.is_multicast(),
+        }
+    }
+
+    /// Returns [`true`] if this address is in a range designated for documentation.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_documentation()`] and
+    /// [`Ipv6Addr::is_documentation()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_documentation(), true);
+    /// assert_eq!(
+    ///     IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_documentation(),
+    ///     true
+    /// );
+    /// ```
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_documentation(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_documentation(),
+            IpAddr::V6(ip) => ip.is_documentation(),
+        }
+    }
+
+    /// Returns [`true`] if this address is in a range designated for benchmarking.
+    ///
+    /// See the documentation for [`Ipv4Addr::is_benchmarking()`] and
+    /// [`Ipv6Addr::is_benchmarking()`] for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(198, 19, 255, 255)).is_benchmarking(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0x2, 0, 0, 0, 0, 0, 0)).is_benchmarking(), true);
+    /// ```
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_benchmarking(&self) -> bool {
+        match self {
+            IpAddr::V4(ip) => ip.is_benchmarking(),
+            IpAddr::V6(ip) => ip.is_benchmarking(),
+        }
+    }
+
+    /// Returns [`true`] if this address is an [`IPv4` address], and [`false`]
+    /// otherwise.
+    ///
+    /// [`IPv4` address]: IpAddr::V4
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_ipv4(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_ipv4(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "ipaddr_checker", since = "1.16.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_ipv4(&self) -> bool {
+        matches!(self, IpAddr::V4(_))
+    }
+
+    /// Returns [`true`] if this address is an [`IPv6` address], and [`false`]
+    /// otherwise.
+    ///
+    /// [`IPv6` address]: IpAddr::V6
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(203, 0, 113, 6)).is_ipv6(), false);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0)).is_ipv6(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "ipaddr_checker", since = "1.16.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_ipv6(&self) -> bool {
+        matches!(self, IpAddr::V6(_))
+    }
+
+    /// Converts this address to an `IpAddr::V4` if it is an IPv4-mapped IPv6 addresses, otherwise it
+    /// return `self` as-is.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)).to_canonical().is_loopback(), true);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1)).is_loopback(), false);
+    /// assert_eq!(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1)).to_canonical().is_loopback(), true);
+    /// ```
+    #[inline]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[rustc_const_unstable(feature = "const_ip", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    pub const fn to_canonical(&self) -> IpAddr {
+        match self {
+            &v4 @ IpAddr::V4(_) => v4,
+            IpAddr::V6(v6) => v6.to_canonical(),
+        }
+    }
+}
+
+impl Ipv4Addr {
+    /// Creates a new IPv4 address from four eight-bit octets.
+    ///
+    /// The result will represent the IP address `a`.`b`.`c`.`d`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[inline]
+    pub const fn new(a: u8, b: u8, c: u8, d: u8) -> Ipv4Addr {
+        Ipv4Addr { octets: [a, b, c, d] }
+    }
+
+    /// An IPv4 address with the address pointing to localhost: `127.0.0.1`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::LOCALHOST;
+    /// assert_eq!(addr, Ipv4Addr::new(127, 0, 0, 1));
+    /// ```
+    #[stable(feature = "ip_constructors", since = "1.30.0")]
+    pub const LOCALHOST: Self = Ipv4Addr::new(127, 0, 0, 1);
+
+    /// An IPv4 address representing an unspecified address: `0.0.0.0`
+    ///
+    /// This corresponds to the constant `INADDR_ANY` in other languages.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::UNSPECIFIED;
+    /// assert_eq!(addr, Ipv4Addr::new(0, 0, 0, 0));
+    /// ```
+    #[doc(alias = "INADDR_ANY")]
+    #[stable(feature = "ip_constructors", since = "1.30.0")]
+    pub const UNSPECIFIED: Self = Ipv4Addr::new(0, 0, 0, 0);
+
+    /// An IPv4 address representing the broadcast address: `255.255.255.255`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::BROADCAST;
+    /// assert_eq!(addr, Ipv4Addr::new(255, 255, 255, 255));
+    /// ```
+    #[stable(feature = "ip_constructors", since = "1.30.0")]
+    pub const BROADCAST: Self = Ipv4Addr::new(255, 255, 255, 255);
+
+    /// Returns the four eight-bit integers that make up this address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
+    /// assert_eq!(addr.octets(), [127, 0, 0, 1]);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[inline]
+    pub const fn octets(&self) -> [u8; 4] {
+        self.octets
+    }
+
+    /// Returns [`true`] for the special 'unspecified' address (`0.0.0.0`).
+    ///
+    /// This property is defined in _UNIX Network Programming, Second Edition_,
+    /// W. Richard Stevens, p. 891; see also [ip7].
+    ///
+    /// [ip7]: https://man7.org/linux/man-pages/man7/ip.7.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(0, 0, 0, 0).is_unspecified(), true);
+    /// assert_eq!(Ipv4Addr::new(45, 22, 13, 197).is_unspecified(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
+    #[stable(feature = "ip_shared", since = "1.12.0")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unspecified(&self) -> bool {
+        u32::from_be_bytes(self.octets) == 0
+    }
+
+    /// Returns [`true`] if this is a loopback address (`127.0.0.0/8`).
+    ///
+    /// This property is defined by [IETF RFC 1122].
+    ///
+    /// [IETF RFC 1122]: https://tools.ietf.org/html/rfc1122
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(127, 0, 0, 1).is_loopback(), true);
+    /// assert_eq!(Ipv4Addr::new(45, 22, 13, 197).is_loopback(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_loopback(&self) -> bool {
+        self.octets()[0] == 127
+    }
+
+    /// Returns [`true`] if this is a private address.
+    ///
+    /// The private address ranges are defined in [IETF RFC 1918] and include:
+    ///
+    ///  - `10.0.0.0/8`
+    ///  - `172.16.0.0/12`
+    ///  - `192.168.0.0/16`
+    ///
+    /// [IETF RFC 1918]: https://tools.ietf.org/html/rfc1918
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(10, 0, 0, 1).is_private(), true);
+    /// assert_eq!(Ipv4Addr::new(10, 10, 10, 10).is_private(), true);
+    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 10).is_private(), true);
+    /// assert_eq!(Ipv4Addr::new(172, 29, 45, 14).is_private(), true);
+    /// assert_eq!(Ipv4Addr::new(172, 32, 0, 2).is_private(), false);
+    /// assert_eq!(Ipv4Addr::new(192, 168, 0, 2).is_private(), true);
+    /// assert_eq!(Ipv4Addr::new(192, 169, 0, 2).is_private(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_private(&self) -> bool {
+        match self.octets() {
+            [10, ..] => true,
+            [172, b, ..] if b >= 16 && b <= 31 => true,
+            [192, 168, ..] => true,
+            _ => false,
+        }
+    }
+
+    /// Returns [`true`] if the address is link-local (`169.254.0.0/16`).
+    ///
+    /// This property is defined by [IETF RFC 3927].
+    ///
+    /// [IETF RFC 3927]: https://tools.ietf.org/html/rfc3927
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(169, 254, 0, 0).is_link_local(), true);
+    /// assert_eq!(Ipv4Addr::new(169, 254, 10, 65).is_link_local(), true);
+    /// assert_eq!(Ipv4Addr::new(16, 89, 10, 65).is_link_local(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_link_local(&self) -> bool {
+        matches!(self.octets(), [169, 254, ..])
+    }
+
+    /// Returns [`true`] if the address appears to be globally reachable
+    /// as specified by the [IANA IPv4 Special-Purpose Address Registry].
+    /// Whether or not an address is practically reachable will depend on your network configuration.
+    ///
+    /// Most IPv4 addresses are globally reachable;
+    /// unless they are specifically defined as *not* globally reachable.
+    ///
+    /// Non-exhaustive list of notable addresses that are not globally reachable:
+    ///
+    /// - The [unspecified address] ([`is_unspecified`](Ipv4Addr::is_unspecified))
+    /// - Addresses reserved for private use ([`is_private`](Ipv4Addr::is_private))
+    /// - Addresses in the shared address space ([`is_shared`](Ipv4Addr::is_shared))
+    /// - Loopback addresses ([`is_loopback`](Ipv4Addr::is_loopback))
+    /// - Link-local addresses ([`is_link_local`](Ipv4Addr::is_link_local))
+    /// - Addresses reserved for documentation ([`is_documentation`](Ipv4Addr::is_documentation))
+    /// - Addresses reserved for benchmarking ([`is_benchmarking`](Ipv4Addr::is_benchmarking))
+    /// - Reserved addresses ([`is_reserved`](Ipv4Addr::is_reserved))
+    /// - The [broadcast address] ([`is_broadcast`](Ipv4Addr::is_broadcast))
+    ///
+    /// For the complete overview of which addresses are globally reachable, see the table at the [IANA IPv4 Special-Purpose Address Registry].
+    ///
+    /// [IANA IPv4 Special-Purpose Address Registry]: https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
+    /// [unspecified address]: Ipv4Addr::UNSPECIFIED
+    /// [broadcast address]: Ipv4Addr::BROADCAST
+
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv4Addr;
+    ///
+    /// // Most IPv4 addresses are globally reachable:
+    /// assert_eq!(Ipv4Addr::new(80, 9, 12, 3).is_global(), true);
+    ///
+    /// // However some addresses have been assigned a special meaning
+    /// // that makes them not globally reachable. Some examples are:
+    ///
+    /// // The unspecified address (`0.0.0.0`)
+    /// assert_eq!(Ipv4Addr::UNSPECIFIED.is_global(), false);
+    ///
+    /// // Addresses reserved for private use (`10.0.0.0/8`, `172.16.0.0/12`, 192.168.0.0/16)
+    /// assert_eq!(Ipv4Addr::new(10, 254, 0, 0).is_global(), false);
+    /// assert_eq!(Ipv4Addr::new(192, 168, 10, 65).is_global(), false);
+    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 65).is_global(), false);
+    ///
+    /// // Addresses in the shared address space (`100.64.0.0/10`)
+    /// assert_eq!(Ipv4Addr::new(100, 100, 0, 0).is_global(), false);
+    ///
+    /// // The loopback addresses (`127.0.0.0/8`)
+    /// assert_eq!(Ipv4Addr::LOCALHOST.is_global(), false);
+    ///
+    /// // Link-local addresses (`169.254.0.0/16`)
+    /// assert_eq!(Ipv4Addr::new(169, 254, 45, 1).is_global(), false);
+    ///
+    /// // Addresses reserved for documentation (`192.0.2.0/24`, `198.51.100.0/24`, `203.0.113.0/24`)
+    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).is_global(), false);
+    /// assert_eq!(Ipv4Addr::new(198, 51, 100, 65).is_global(), false);
+    /// assert_eq!(Ipv4Addr::new(203, 0, 113, 6).is_global(), false);
+    ///
+    /// // Addresses reserved for benchmarking (`198.18.0.0/15`)
+    /// assert_eq!(Ipv4Addr::new(198, 18, 0, 0).is_global(), false);
+    ///
+    /// // Reserved addresses (`240.0.0.0/4`)
+    /// assert_eq!(Ipv4Addr::new(250, 10, 20, 30).is_global(), false);
+    ///
+    /// // The broadcast address (`255.255.255.255`)
+    /// assert_eq!(Ipv4Addr::BROADCAST.is_global(), false);
+    ///
+    /// // For a complete overview see the IANA IPv4 Special-Purpose Address Registry.
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_global(&self) -> bool {
+        !(self.octets()[0] == 0 // "This network"
+            || self.is_private()
+            || self.is_shared()
+            || self.is_loopback()
+            || self.is_link_local()
+            // addresses reserved for future protocols (`192.0.0.0/24`)
+            ||(self.octets()[0] == 192 && self.octets()[1] == 0 && self.octets()[2] == 0)
+            || self.is_documentation()
+            || self.is_benchmarking()
+            || self.is_reserved()
+            || self.is_broadcast())
+    }
+
+    /// Returns [`true`] if this address is part of the Shared Address Space defined in
+    /// [IETF RFC 6598] (`100.64.0.0/10`).
+    ///
+    /// [IETF RFC 6598]: https://tools.ietf.org/html/rfc6598
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(100, 64, 0, 0).is_shared(), true);
+    /// assert_eq!(Ipv4Addr::new(100, 127, 255, 255).is_shared(), true);
+    /// assert_eq!(Ipv4Addr::new(100, 128, 0, 0).is_shared(), false);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_shared(&self) -> bool {
+        self.octets()[0] == 100 && (self.octets()[1] & 0b1100_0000 == 0b0100_0000)
+    }
+
+    /// Returns [`true`] if this address part of the `198.18.0.0/15` range, which is reserved for
+    /// network devices benchmarking. This range is defined in [IETF RFC 2544] as `192.18.0.0`
+    /// through `198.19.255.255` but [errata 423] corrects it to `198.18.0.0/15`.
+    ///
+    /// [IETF RFC 2544]: https://tools.ietf.org/html/rfc2544
+    /// [errata 423]: https://www.rfc-editor.org/errata/eid423
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(198, 17, 255, 255).is_benchmarking(), false);
+    /// assert_eq!(Ipv4Addr::new(198, 18, 0, 0).is_benchmarking(), true);
+    /// assert_eq!(Ipv4Addr::new(198, 19, 255, 255).is_benchmarking(), true);
+    /// assert_eq!(Ipv4Addr::new(198, 20, 0, 0).is_benchmarking(), false);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_benchmarking(&self) -> bool {
+        self.octets()[0] == 198 && (self.octets()[1] & 0xfe) == 18
+    }
+
+    /// Returns [`true`] if this address is reserved by IANA for future use. [IETF RFC 1112]
+    /// defines the block of reserved addresses as `240.0.0.0/4`. This range normally includes the
+    /// broadcast address `255.255.255.255`, but this implementation explicitly excludes it, since
+    /// it is obviously not reserved for future use.
+    ///
+    /// [IETF RFC 1112]: https://tools.ietf.org/html/rfc1112
+    ///
+    /// # Warning
+    ///
+    /// As IANA assigns new addresses, this method will be
+    /// updated. This may result in non-reserved addresses being
+    /// treated as reserved in code that relies on an outdated version
+    /// of this method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(240, 0, 0, 0).is_reserved(), true);
+    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 254).is_reserved(), true);
+    ///
+    /// assert_eq!(Ipv4Addr::new(239, 255, 255, 255).is_reserved(), false);
+    /// // The broadcast address is not considered as reserved for future use by this implementation
+    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 255).is_reserved(), false);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv4", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_reserved(&self) -> bool {
+        self.octets()[0] & 240 == 240 && !self.is_broadcast()
+    }
+
+    /// Returns [`true`] if this is a multicast address (`224.0.0.0/4`).
+    ///
+    /// Multicast addresses have a most significant octet between `224` and `239`,
+    /// and is defined by [IETF RFC 5771].
+    ///
+    /// [IETF RFC 5771]: https://tools.ietf.org/html/rfc5771
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(224, 254, 0, 0).is_multicast(), true);
+    /// assert_eq!(Ipv4Addr::new(236, 168, 10, 65).is_multicast(), true);
+    /// assert_eq!(Ipv4Addr::new(172, 16, 10, 65).is_multicast(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_multicast(&self) -> bool {
+        self.octets()[0] >= 224 && self.octets()[0] <= 239
+    }
+
+    /// Returns [`true`] if this is a broadcast address (`255.255.255.255`).
+    ///
+    /// A broadcast address has all octets set to `255` as defined in [IETF RFC 919].
+    ///
+    /// [IETF RFC 919]: https://tools.ietf.org/html/rfc919
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(255, 255, 255, 255).is_broadcast(), true);
+    /// assert_eq!(Ipv4Addr::new(236, 168, 10, 65).is_broadcast(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_broadcast(&self) -> bool {
+        u32::from_be_bytes(self.octets()) == u32::from_be_bytes(Self::BROADCAST.octets())
+    }
+
+    /// Returns [`true`] if this address is in a range designated for documentation.
+    ///
+    /// This is defined in [IETF RFC 5737]:
+    ///
+    /// - `192.0.2.0/24` (TEST-NET-1)
+    /// - `198.51.100.0/24` (TEST-NET-2)
+    /// - `203.0.113.0/24` (TEST-NET-3)
+    ///
+    /// [IETF RFC 5737]: https://tools.ietf.org/html/rfc5737
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).is_documentation(), true);
+    /// assert_eq!(Ipv4Addr::new(198, 51, 100, 65).is_documentation(), true);
+    /// assert_eq!(Ipv4Addr::new(203, 0, 113, 6).is_documentation(), true);
+    /// assert_eq!(Ipv4Addr::new(193, 34, 17, 19).is_documentation(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_documentation(&self) -> bool {
+        matches!(self.octets(), [192, 0, 2, _] | [198, 51, 100, _] | [203, 0, 113, _])
+    }
+
+    /// Converts this address to an [IPv4-compatible] [`IPv6` address].
+    ///
+    /// `a.b.c.d` becomes `::a.b.c.d`
+    ///
+    /// Note that IPv4-compatible addresses have been officially deprecated.
+    /// If you don't explicitly need an IPv4-compatible address for legacy reasons, consider using `to_ipv6_mapped` instead.
+    ///
+    /// [IPv4-compatible]: Ipv6Addr#ipv4-compatible-ipv6-addresses
+    /// [`IPv6` address]: Ipv6Addr
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(
+    ///     Ipv4Addr::new(192, 0, 2, 255).to_ipv6_compatible(),
+    ///     Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc000, 0x2ff)
+    /// );
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[inline]
+    pub const fn to_ipv6_compatible(&self) -> Ipv6Addr {
+        let [a, b, c, d] = self.octets();
+        Ipv6Addr { octets: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, a, b, c, d] }
+    }
+
+    /// Converts this address to an [IPv4-mapped] [`IPv6` address].
+    ///
+    /// `a.b.c.d` becomes `::ffff:a.b.c.d`
+    ///
+    /// [IPv4-mapped]: Ipv6Addr#ipv4-mapped-ipv6-addresses
+    /// [`IPv6` address]: Ipv6Addr
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(Ipv4Addr::new(192, 0, 2, 255).to_ipv6_mapped(),
+    ///            Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc000, 0x2ff));
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[inline]
+    pub const fn to_ipv6_mapped(&self) -> Ipv6Addr {
+        let [a, b, c, d] = self.octets();
+        Ipv6Addr { octets: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xFF, 0xFF, a, b, c, d] }
+    }
+}
+
+#[stable(feature = "ip_addr", since = "1.7.0")]
+impl fmt::Display for IpAddr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            IpAddr::V4(ip) => ip.fmt(fmt),
+            IpAddr::V6(ip) => ip.fmt(fmt),
+        }
+    }
+}
+
+#[stable(feature = "ip_addr", since = "1.7.0")]
+impl fmt::Debug for IpAddr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "ip_from_ip", since = "1.16.0")]
+impl From<Ipv4Addr> for IpAddr {
+    /// Copies this address to a new `IpAddr::V4`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr};
+    ///
+    /// let addr = Ipv4Addr::new(127, 0, 0, 1);
+    ///
+    /// assert_eq!(
+    ///     IpAddr::V4(addr),
+    ///     IpAddr::from(addr)
+    /// )
+    /// ```
+    #[inline]
+    fn from(ipv4: Ipv4Addr) -> IpAddr {
+        IpAddr::V4(ipv4)
+    }
+}
+
+#[stable(feature = "ip_from_ip", since = "1.16.0")]
+impl From<Ipv6Addr> for IpAddr {
+    /// Copies this address to a new `IpAddr::V6`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv6Addr};
+    ///
+    /// let addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff);
+    ///
+    /// assert_eq!(
+    ///     IpAddr::V6(addr),
+    ///     IpAddr::from(addr)
+    /// );
+    /// ```
+    #[inline]
+    fn from(ipv6: Ipv6Addr) -> IpAddr {
+        IpAddr::V6(ipv6)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for Ipv4Addr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let octets = self.octets();
+
+        // If there are no alignment requirements, write the IP address directly to `f`.
+        // Otherwise, write it to a local buffer and then use `f.pad`.
+        if fmt.precision().is_none() && fmt.width().is_none() {
+            write!(fmt, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3])
+        } else {
+            const LONGEST_IPV4_ADDR: &str = "255.255.255.255";
+
+            let mut buf = DisplayBuffer::<{ LONGEST_IPV4_ADDR.len() }>::new();
+            // Buffer is long enough for the longest possible IPv4 address, so this should never fail.
+            write!(buf, "{}.{}.{}.{}", octets[0], octets[1], octets[2], octets[3]).unwrap();
+
+            fmt.pad(buf.as_str())
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for Ipv4Addr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialEq<Ipv4Addr> for IpAddr {
+    #[inline]
+    fn eq(&self, other: &Ipv4Addr) -> bool {
+        match self {
+            IpAddr::V4(v4) => v4 == other,
+            IpAddr::V6(_) => false,
+        }
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialEq<IpAddr> for Ipv4Addr {
+    #[inline]
+    fn eq(&self, other: &IpAddr) -> bool {
+        match other {
+            IpAddr::V4(v4) => self == v4,
+            IpAddr::V6(_) => false,
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl PartialOrd for Ipv4Addr {
+    #[inline]
+    fn partial_cmp(&self, other: &Ipv4Addr) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialOrd<Ipv4Addr> for IpAddr {
+    #[inline]
+    fn partial_cmp(&self, other: &Ipv4Addr) -> Option<Ordering> {
+        match self {
+            IpAddr::V4(v4) => v4.partial_cmp(other),
+            IpAddr::V6(_) => Some(Ordering::Greater),
+        }
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialOrd<IpAddr> for Ipv4Addr {
+    #[inline]
+    fn partial_cmp(&self, other: &IpAddr) -> Option<Ordering> {
+        match other {
+            IpAddr::V4(v4) => self.partial_cmp(v4),
+            IpAddr::V6(_) => Some(Ordering::Less),
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Ord for Ipv4Addr {
+    #[inline]
+    fn cmp(&self, other: &Ipv4Addr) -> Ordering {
+        self.octets.cmp(&other.octets)
+    }
+}
+
+#[stable(feature = "ip_u32", since = "1.1.0")]
+impl From<Ipv4Addr> for u32 {
+    /// Converts an `Ipv4Addr` into a host byte order `u32`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::new(0x12, 0x34, 0x56, 0x78);
+    /// assert_eq!(0x12345678, u32::from(addr));
+    /// ```
+    #[inline]
+    fn from(ip: Ipv4Addr) -> u32 {
+        u32::from_be_bytes(ip.octets)
+    }
+}
+
+#[stable(feature = "ip_u32", since = "1.1.0")]
+impl From<u32> for Ipv4Addr {
+    /// Converts a host byte order `u32` into an `Ipv4Addr`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::from(0x12345678);
+    /// assert_eq!(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78), addr);
+    /// ```
+    #[inline]
+    fn from(ip: u32) -> Ipv4Addr {
+        Ipv4Addr { octets: ip.to_be_bytes() }
+    }
+}
+
+#[stable(feature = "from_slice_v4", since = "1.9.0")]
+impl From<[u8; 4]> for Ipv4Addr {
+    /// Creates an `Ipv4Addr` from a four element byte array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::from([13u8, 12u8, 11u8, 10u8]);
+    /// assert_eq!(Ipv4Addr::new(13, 12, 11, 10), addr);
+    /// ```
+    #[inline]
+    fn from(octets: [u8; 4]) -> Ipv4Addr {
+        Ipv4Addr { octets }
+    }
+}
+
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u8; 4]> for IpAddr {
+    /// Creates an `IpAddr::V4` from a four element byte array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr};
+    ///
+    /// let addr = IpAddr::from([13u8, 12u8, 11u8, 10u8]);
+    /// assert_eq!(IpAddr::V4(Ipv4Addr::new(13, 12, 11, 10)), addr);
+    /// ```
+    #[inline]
+    fn from(octets: [u8; 4]) -> IpAddr {
+        IpAddr::V4(Ipv4Addr::from(octets))
+    }
+}
+
+impl Ipv6Addr {
+    /// Creates a new IPv6 address from eight 16-bit segments.
+    ///
+    /// The result will represent the IP address `a:b:c:d:e:f:g:h`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[inline]
+    pub const fn new(a: u16, b: u16, c: u16, d: u16, e: u16, f: u16, g: u16, h: u16) -> Ipv6Addr {
+        let addr16 = [
+            a.to_be(),
+            b.to_be(),
+            c.to_be(),
+            d.to_be(),
+            e.to_be(),
+            f.to_be(),
+            g.to_be(),
+            h.to_be(),
+        ];
+        Ipv6Addr {
+            // All elements in `addr16` are big endian.
+            // SAFETY: `[u16; 8]` is always safe to transmute to `[u8; 16]`.
+            octets: unsafe { transmute::<_, [u8; 16]>(addr16) },
+        }
+    }
+
+    /// An IPv6 address representing localhost: `::1`.
+    ///
+    /// This corresponds to constant `IN6ADDR_LOOPBACK_INIT` or `in6addr_loopback` in other
+    /// languages.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::LOCALHOST;
+    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+    /// ```
+    #[doc(alias = "IN6ADDR_LOOPBACK_INIT")]
+    #[doc(alias = "in6addr_loopback")]
+    #[stable(feature = "ip_constructors", since = "1.30.0")]
+    pub const LOCALHOST: Self = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
+
+    /// An IPv6 address representing the unspecified address: `::`
+    ///
+    /// This corresponds to constant `IN6ADDR_ANY_INIT` or `in6addr_any` in other languages.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::UNSPECIFIED;
+    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
+    /// ```
+    #[doc(alias = "IN6ADDR_ANY_INIT")]
+    #[doc(alias = "in6addr_any")]
+    #[stable(feature = "ip_constructors", since = "1.30.0")]
+    pub const UNSPECIFIED: Self = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0);
+
+    /// Returns the eight 16-bit segments that make up this address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).segments(),
+    ///            [0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff]);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[inline]
+    pub const fn segments(&self) -> [u16; 8] {
+        // All elements in `self.octets` must be big endian.
+        // SAFETY: `[u8; 16]` is always safe to transmute to `[u16; 8]`.
+        let [a, b, c, d, e, f, g, h] = unsafe { transmute::<_, [u16; 8]>(self.octets) };
+        // We want native endian u16
+        [
+            u16::from_be(a),
+            u16::from_be(b),
+            u16::from_be(c),
+            u16::from_be(d),
+            u16::from_be(e),
+            u16::from_be(f),
+            u16::from_be(g),
+            u16::from_be(h),
+        ]
+    }
+
+    /// Returns [`true`] for the special 'unspecified' address (`::`).
+    ///
+    /// This property is defined in [IETF RFC 4291].
+    ///
+    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unspecified(), false);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0).is_unspecified(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unspecified(&self) -> bool {
+        u128::from_be_bytes(self.octets()) == u128::from_be_bytes(Ipv6Addr::UNSPECIFIED.octets())
+    }
+
+    /// Returns [`true`] if this is the [loopback address] (`::1`),
+    /// as defined in [IETF RFC 4291 section 2.5.3].
+    ///
+    /// Contrary to IPv4, in IPv6 there is only one loopback address.
+    ///
+    /// [loopback address]: Ipv6Addr::LOCALHOST
+    /// [IETF RFC 4291 section 2.5.3]: https://tools.ietf.org/html/rfc4291#section-2.5.3
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_loopback(), false);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1).is_loopback(), true);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_loopback(&self) -> bool {
+        u128::from_be_bytes(self.octets()) == u128::from_be_bytes(Ipv6Addr::LOCALHOST.octets())
+    }
+
+    /// Returns [`true`] if the address appears to be globally reachable
+    /// as specified by the [IANA IPv6 Special-Purpose Address Registry].
+    /// Whether or not an address is practically reachable will depend on your network configuration.
+    ///
+    /// Most IPv6 addresses are globally reachable;
+    /// unless they are specifically defined as *not* globally reachable.
+    ///
+    /// Non-exhaustive list of notable addresses that are not globally reachable:
+    /// - The [unspecified address] ([`is_unspecified`](Ipv6Addr::is_unspecified))
+    /// - The [loopback address] ([`is_loopback`](Ipv6Addr::is_loopback))
+    /// - IPv4-mapped addresses
+    /// - Addresses reserved for benchmarking
+    /// - Addresses reserved for documentation ([`is_documentation`](Ipv6Addr::is_documentation))
+    /// - Unique local addresses ([`is_unique_local`](Ipv6Addr::is_unique_local))
+    /// - Unicast addresses with link-local scope ([`is_unicast_link_local`](Ipv6Addr::is_unicast_link_local))
+    ///
+    /// For the complete overview of which addresses are globally reachable, see the table at the [IANA IPv6 Special-Purpose Address Registry].
+    ///
+    /// Note that an address having global scope is not the same as being globally reachable,
+    /// and there is no direct relation between the two concepts: There exist addresses with global scope
+    /// that are not globally reachable (for example unique local addresses),
+    /// and addresses that are globally reachable without having global scope
+    /// (multicast addresses with non-global scope).
+    ///
+    /// [IANA IPv6 Special-Purpose Address Registry]: https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml
+    /// [unspecified address]: Ipv6Addr::UNSPECIFIED
+    /// [loopback address]: Ipv6Addr::LOCALHOST
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// // Most IPv6 addresses are globally reachable:
+    /// assert_eq!(Ipv6Addr::new(0x26, 0, 0x1c9, 0, 0, 0xafc8, 0x10, 0x1).is_global(), true);
+    ///
+    /// // However some addresses have been assigned a special meaning
+    /// // that makes them not globally reachable. Some examples are:
+    ///
+    /// // The unspecified address (`::`)
+    /// assert_eq!(Ipv6Addr::UNSPECIFIED.is_global(), false);
+    ///
+    /// // The loopback address (`::1`)
+    /// assert_eq!(Ipv6Addr::LOCALHOST.is_global(), false);
+    ///
+    /// // IPv4-mapped addresses (`::ffff:0:0/96`)
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_global(), false);
+    ///
+    /// // Addresses reserved for benchmarking (`2001:2::/48`)
+    /// assert_eq!(Ipv6Addr::new(0x2001, 2, 0, 0, 0, 0, 0, 1,).is_global(), false);
+    ///
+    /// // Addresses reserved for documentation (`2001:db8::/32`)
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1).is_global(), false);
+    ///
+    /// // Unique local addresses (`fc00::/7`)
+    /// assert_eq!(Ipv6Addr::new(0xfc02, 0, 0, 0, 0, 0, 0, 1).is_global(), false);
+    ///
+    /// // Unicast addresses with link-local scope (`fe80::/10`)
+    /// assert_eq!(Ipv6Addr::new(0xfe81, 0, 0, 0, 0, 0, 0, 1).is_global(), false);
+    ///
+    /// // For a complete overview see the IANA IPv6 Special-Purpose Address Registry.
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_global(&self) -> bool {
+        !(self.is_unspecified()
+            || self.is_loopback()
+            // IPv4-mapped Address (`::ffff:0:0/96`)
+            || matches!(self.segments(), [0, 0, 0, 0, 0, 0xffff, _, _])
+            // IPv4-IPv6 Translat. (`64:ff9b:1::/48`)
+            || matches!(self.segments(), [0x64, 0xff9b, 1, _, _, _, _, _])
+            // Discard-Only Address Block (`100::/64`)
+            || matches!(self.segments(), [0x100, 0, 0, 0, _, _, _, _])
+            // IETF Protocol Assignments (`2001::/23`)
+            || (matches!(self.segments(), [0x2001, b, _, _, _, _, _, _] if b < 0x200)
+                && !(
+                    // Port Control Protocol Anycast (`2001:1::1`)
+                    u128::from_be_bytes(self.octets()) == 0x2001_0001_0000_0000_0000_0000_0000_0001
+                    // Traversal Using Relays around NAT Anycast (`2001:1::2`)
+                    || u128::from_be_bytes(self.octets()) == 0x2001_0001_0000_0000_0000_0000_0000_0002
+                    // AMT (`2001:3::/32`)
+                    || matches!(self.segments(), [0x2001, 3, _, _, _, _, _, _])
+                    // AS112-v6 (`2001:4:112::/48`)
+                    || matches!(self.segments(), [0x2001, 4, 0x112, _, _, _, _, _])
+                    // ORCHIDv2 (`2001:20::/28`)
+                    || matches!(self.segments(), [0x2001, b, _, _, _, _, _, _] if b >= 0x20 && b <= 0x2F)
+                ))
+            || self.is_documentation()
+            || self.is_unique_local()
+            || self.is_unicast_link_local())
+    }
+
+    /// Returns [`true`] if this is a unique local address (`fc00::/7`).
+    ///
+    /// This property is defined in [IETF RFC 4193].
+    ///
+    /// [IETF RFC 4193]: https://tools.ietf.org/html/rfc4193
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unique_local(), false);
+    /// assert_eq!(Ipv6Addr::new(0xfc02, 0, 0, 0, 0, 0, 0, 0).is_unique_local(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unique_local(&self) -> bool {
+        (self.segments()[0] & 0xfe00) == 0xfc00
+    }
+
+    /// Returns [`true`] if this is a unicast address, as defined by [IETF RFC 4291].
+    /// Any address that is not a [multicast address] (`ff00::/8`) is unicast.
+    ///
+    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
+    /// [multicast address]: Ipv6Addr::is_multicast
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// // The unspecified and loopback addresses are unicast.
+    /// assert_eq!(Ipv6Addr::UNSPECIFIED.is_unicast(), true);
+    /// assert_eq!(Ipv6Addr::LOCALHOST.is_unicast(), true);
+    ///
+    /// // Any address that is not a multicast address (`ff00::/8`) is unicast.
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast(), true);
+    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).is_unicast(), false);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unicast(&self) -> bool {
+        !self.is_multicast()
+    }
+
+    /// Returns `true` if the address is a unicast address with link-local scope,
+    /// as defined in [RFC 4291].
+    ///
+    /// A unicast address has link-local scope if it has the prefix `fe80::/10`, as per [RFC 4291 section 2.4].
+    /// Note that this encompasses more addresses than those defined in [RFC 4291 section 2.5.6],
+    /// which describes "Link-Local IPv6 Unicast Addresses" as having the following stricter format:
+    ///
+    /// ```text
+    /// | 10 bits  |         54 bits         |          64 bits           |
+    /// +----------+-------------------------+----------------------------+
+    /// |1111111010|           0             |       interface ID         |
+    /// +----------+-------------------------+----------------------------+
+    /// ```
+    /// So while currently the only addresses with link-local scope an application will encounter are all in `fe80::/64`,
+    /// this might change in the future with the publication of new standards. More addresses in `fe80::/10` could be allocated,
+    /// and those addresses will have link-local scope.
+    ///
+    /// Also note that while [RFC 4291 section 2.5.3] mentions about the [loopback address] (`::1`) that "it is treated as having Link-Local scope",
+    /// this does not mean that the loopback address actually has link-local scope and this method will return `false` on it.
+    ///
+    /// [RFC 4291]: https://tools.ietf.org/html/rfc4291
+    /// [RFC 4291 section 2.4]: https://tools.ietf.org/html/rfc4291#section-2.4
+    /// [RFC 4291 section 2.5.3]: https://tools.ietf.org/html/rfc4291#section-2.5.3
+    /// [RFC 4291 section 2.5.6]: https://tools.ietf.org/html/rfc4291#section-2.5.6
+    /// [loopback address]: Ipv6Addr::LOCALHOST
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// // The loopback address (`::1`) does not actually have link-local scope.
+    /// assert_eq!(Ipv6Addr::LOCALHOST.is_unicast_link_local(), false);
+    ///
+    /// // Only addresses in `fe80::/10` have link-local scope.
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), false);
+    /// assert_eq!(Ipv6Addr::new(0xfe80, 0, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), true);
+    ///
+    /// // Addresses outside the stricter `fe80::/64` also have link-local scope.
+    /// assert_eq!(Ipv6Addr::new(0xfe80, 0, 0, 1, 0, 0, 0, 0).is_unicast_link_local(), true);
+    /// assert_eq!(Ipv6Addr::new(0xfe81, 0, 0, 0, 0, 0, 0, 0).is_unicast_link_local(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unicast_link_local(&self) -> bool {
+        (self.segments()[0] & 0xffc0) == 0xfe80
+    }
+
+    /// Returns [`true`] if this is an address reserved for documentation
+    /// (`2001:db8::/32`).
+    ///
+    /// This property is defined in [IETF RFC 3849].
+    ///
+    /// [IETF RFC 3849]: https://tools.ietf.org/html/rfc3849
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_documentation(), false);
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_documentation(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_documentation(&self) -> bool {
+        (self.segments()[0] == 0x2001) && (self.segments()[1] == 0xdb8)
+    }
+
+    /// Returns [`true`] if this is an address reserved for benchmarking (`2001:2::/48`).
+    ///
+    /// This property is defined in [IETF RFC 5180], where it is mistakenly specified as covering the range `2001:0200::/48`.
+    /// This is corrected in [IETF RFC Errata 1752] to `2001:0002::/48`.
+    ///
+    /// [IETF RFC 5180]: https://tools.ietf.org/html/rfc5180
+    /// [IETF RFC Errata 1752]: https://www.rfc-editor.org/errata_search.php?eid=1752
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc613, 0x0).is_benchmarking(), false);
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0x2, 0, 0, 0, 0, 0, 0).is_benchmarking(), true);
+    /// ```
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_benchmarking(&self) -> bool {
+        (self.segments()[0] == 0x2001) && (self.segments()[1] == 0x2) && (self.segments()[2] == 0)
+    }
+
+    /// Returns [`true`] if the address is a globally routable unicast address.
+    ///
+    /// The following return false:
+    ///
+    /// - the loopback address
+    /// - the link-local addresses
+    /// - unique local addresses
+    /// - the unspecified address
+    /// - the address range reserved for documentation
+    ///
+    /// This method returns [`true`] for site-local addresses as per [RFC 4291 section 2.5.7]
+    ///
+    /// ```no_rust
+    /// The special behavior of [the site-local unicast] prefix defined in [RFC3513] must no longer
+    /// be supported in new implementations (i.e., new implementations must treat this prefix as
+    /// Global Unicast).
+    /// ```
+    ///
+    /// [RFC 4291 section 2.5.7]: https://tools.ietf.org/html/rfc4291#section-2.5.7
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 0).is_unicast_global(), false);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_unicast_global(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn is_unicast_global(&self) -> bool {
+        self.is_unicast()
+            && !self.is_loopback()
+            && !self.is_unicast_link_local()
+            && !self.is_unique_local()
+            && !self.is_unspecified()
+            && !self.is_documentation()
+            && !self.is_benchmarking()
+    }
+
+    /// Returns the address's multicast scope if the address is multicast.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    ///
+    /// use std::net::{Ipv6Addr, Ipv6MulticastScope};
+    ///
+    /// assert_eq!(
+    ///     Ipv6Addr::new(0xff0e, 0, 0, 0, 0, 0, 0, 0).multicast_scope(),
+    ///     Some(Ipv6MulticastScope::Global)
+    /// );
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).multicast_scope(), None);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use]
+    #[inline]
+    pub const fn multicast_scope(&self) -> Option<Ipv6MulticastScope> {
+        if self.is_multicast() {
+            match self.segments()[0] & 0x000f {
+                1 => Some(Ipv6MulticastScope::InterfaceLocal),
+                2 => Some(Ipv6MulticastScope::LinkLocal),
+                3 => Some(Ipv6MulticastScope::RealmLocal),
+                4 => Some(Ipv6MulticastScope::AdminLocal),
+                5 => Some(Ipv6MulticastScope::SiteLocal),
+                8 => Some(Ipv6MulticastScope::OrganizationLocal),
+                14 => Some(Ipv6MulticastScope::Global),
+                _ => None,
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Returns [`true`] if this is a multicast address (`ff00::/8`).
+    ///
+    /// This property is defined by [IETF RFC 4291].
+    ///
+    /// [IETF RFC 4291]: https://tools.ietf.org/html/rfc4291
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).is_multicast(), true);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).is_multicast(), false);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(since = "1.7.0", feature = "ip_17")]
+    #[must_use]
+    #[inline]
+    pub const fn is_multicast(&self) -> bool {
+        (self.segments()[0] & 0xff00) == 0xff00
+    }
+
+    /// Converts this address to an [`IPv4` address] if it's an [IPv4-mapped] address,
+    /// as defined in [IETF RFC 4291 section 2.5.5.2], otherwise returns [`None`].
+    ///
+    /// `::ffff:a.b.c.d` becomes `a.b.c.d`.
+    /// All addresses *not* starting with `::ffff` will return `None`.
+    ///
+    /// [`IPv4` address]: Ipv4Addr
+    /// [IPv4-mapped]: Ipv6Addr
+    /// [IETF RFC 4291 section 2.5.5.2]: https://tools.ietf.org/html/rfc4291#section-2.5.5.2
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).to_ipv4_mapped(), None);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).to_ipv4_mapped(),
+    ///            Some(Ipv4Addr::new(192, 10, 2, 255)));
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).to_ipv4_mapped(), None);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[stable(feature = "ipv6_to_ipv4_mapped", since = "1.63.0")]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[inline]
+    pub const fn to_ipv4_mapped(&self) -> Option<Ipv4Addr> {
+        match self.octets() {
+            [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, a, b, c, d] => {
+                Some(Ipv4Addr::new(a, b, c, d))
+            }
+            _ => None,
+        }
+    }
+
+    /// Converts this address to an [`IPv4` address] if it is either
+    /// an [IPv4-compatible] address as defined in [IETF RFC 4291 section 2.5.5.1],
+    /// or an [IPv4-mapped] address as defined in [IETF RFC 4291 section 2.5.5.2],
+    /// otherwise returns [`None`].
+    ///
+    /// Note that this will return an [`IPv4` address] for the IPv6 loopback address `::1`. Use
+    /// [`Ipv6Addr::to_ipv4_mapped`] to avoid this.
+    ///
+    /// `::a.b.c.d` and `::ffff:a.b.c.d` become `a.b.c.d`. `::1` becomes `0.0.0.1`.
+    /// All addresses *not* starting with either all zeroes or `::ffff` will return `None`.
+    ///
+    /// [`IPv4` address]: Ipv4Addr
+    /// [IPv4-compatible]: Ipv6Addr#ipv4-compatible-ipv6-addresses
+    /// [IPv4-mapped]: Ipv6Addr#ipv4-mapped-ipv6-addresses
+    /// [IETF RFC 4291 section 2.5.5.1]: https://tools.ietf.org/html/rfc4291#section-2.5.5.1
+    /// [IETF RFC 4291 section 2.5.5.2]: https://tools.ietf.org/html/rfc4291#section-2.5.5.2
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{Ipv4Addr, Ipv6Addr};
+    ///
+    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).to_ipv4(), None);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff).to_ipv4(),
+    ///            Some(Ipv4Addr::new(192, 10, 2, 255)));
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).to_ipv4(),
+    ///            Some(Ipv4Addr::new(0, 0, 0, 1)));
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_50", since = "1.50.0")]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[inline]
+    pub const fn to_ipv4(&self) -> Option<Ipv4Addr> {
+        if let [0, 0, 0, 0, 0, 0 | 0xffff, ab, cd] = self.segments() {
+            let [a, b] = ab.to_be_bytes();
+            let [c, d] = cd.to_be_bytes();
+            Some(Ipv4Addr::new(a, b, c, d))
+        } else {
+            None
+        }
+    }
+
+    /// Converts this address to an `IpAddr::V4` if it is an IPv4-mapped addresses, otherwise it
+    /// returns self wrapped in an `IpAddr::V6`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip)]
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1).is_loopback(), false);
+    /// assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x7f00, 0x1).to_canonical().is_loopback(), true);
+    /// ```
+    #[rustc_const_unstable(feature = "const_ipv6", issue = "76205")]
+    #[unstable(feature = "ip", issue = "27709")]
+    #[must_use = "this returns the result of the operation, \
+                  without modifying the original"]
+    #[inline]
+    pub const fn to_canonical(&self) -> IpAddr {
+        if let Some(mapped) = self.to_ipv4_mapped() {
+            return IpAddr::V4(mapped);
+        }
+        IpAddr::V6(*self)
+    }
+
+    /// Returns the sixteen eight-bit integers the IPv6 address consists of.
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// assert_eq!(Ipv6Addr::new(0xff00, 0, 0, 0, 0, 0, 0, 0).octets(),
+    ///            [255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
+    /// ```
+    #[rustc_const_stable(feature = "const_ip_32", since = "1.32.0")]
+    #[stable(feature = "ipv6_to_octets", since = "1.12.0")]
+    #[must_use]
+    #[inline]
+    pub const fn octets(&self) -> [u8; 16] {
+        self.octets
+    }
+}
+
+/// Write an Ipv6Addr, conforming to the canonical style described by
+/// [RFC 5952](https://tools.ietf.org/html/rfc5952).
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for Ipv6Addr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // If there are no alignment requirements, write the IP address directly to `f`.
+        // Otherwise, write it to a local buffer and then use `f.pad`.
+        if f.precision().is_none() && f.width().is_none() {
+            let segments = self.segments();
+
+            // Special case for :: and ::1; otherwise they get written with the
+            // IPv4 formatter
+            if self.is_unspecified() {
+                f.write_str("::")
+            } else if self.is_loopback() {
+                f.write_str("::1")
+            } else if let Some(ipv4) = self.to_ipv4() {
+                match segments[5] {
+                    // IPv4 Compatible address
+                    0 => write!(f, "::{}", ipv4),
+                    // IPv4 Mapped address
+                    0xffff => write!(f, "::ffff:{}", ipv4),
+                    _ => unreachable!(),
+                }
+            } else {
+                #[derive(Copy, Clone, Default)]
+                struct Span {
+                    start: usize,
+                    len: usize,
+                }
+
+                // Find the inner 0 span
+                let zeroes = {
+                    let mut longest = Span::default();
+                    let mut current = Span::default();
+
+                    for (i, &segment) in segments.iter().enumerate() {
+                        if segment == 0 {
+                            if current.len == 0 {
+                                current.start = i;
+                            }
+
+                            current.len += 1;
+
+                            if current.len > longest.len {
+                                longest = current;
+                            }
+                        } else {
+                            current = Span::default();
+                        }
+                    }
+
+                    longest
+                };
+
+                /// Write a colon-separated part of the address
+                #[inline]
+                fn fmt_subslice(f: &mut fmt::Formatter<'_>, chunk: &[u16]) -> fmt::Result {
+                    if let Some((first, tail)) = chunk.split_first() {
+                        write!(f, "{:x}", first)?;
+                        for segment in tail {
+                            f.write_char(':')?;
+                            write!(f, "{:x}", segment)?;
+                        }
+                    }
+                    Ok(())
+                }
+
+                if zeroes.len > 1 {
+                    fmt_subslice(f, &segments[..zeroes.start])?;
+                    f.write_str("::")?;
+                    fmt_subslice(f, &segments[zeroes.start + zeroes.len..])
+                } else {
+                    fmt_subslice(f, &segments)
+                }
+            }
+        } else {
+            const LONGEST_IPV6_ADDR: &str = "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff";
+
+            let mut buf = DisplayBuffer::<{ LONGEST_IPV6_ADDR.len() }>::new();
+            // Buffer is long enough for the longest possible IPv6 address, so this should never fail.
+            write!(buf, "{}", self).unwrap();
+
+            f.pad(buf.as_str())
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for Ipv6Addr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialEq<IpAddr> for Ipv6Addr {
+    #[inline]
+    fn eq(&self, other: &IpAddr) -> bool {
+        match other {
+            IpAddr::V4(_) => false,
+            IpAddr::V6(v6) => self == v6,
+        }
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialEq<Ipv6Addr> for IpAddr {
+    #[inline]
+    fn eq(&self, other: &Ipv6Addr) -> bool {
+        match self {
+            IpAddr::V4(_) => false,
+            IpAddr::V6(v6) => v6 == other,
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl PartialOrd for Ipv6Addr {
+    #[inline]
+    fn partial_cmp(&self, other: &Ipv6Addr) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialOrd<Ipv6Addr> for IpAddr {
+    #[inline]
+    fn partial_cmp(&self, other: &Ipv6Addr) -> Option<Ordering> {
+        match self {
+            IpAddr::V4(_) => Some(Ordering::Less),
+            IpAddr::V6(v6) => v6.partial_cmp(other),
+        }
+    }
+}
+
+#[stable(feature = "ip_cmp", since = "1.16.0")]
+impl PartialOrd<IpAddr> for Ipv6Addr {
+    #[inline]
+    fn partial_cmp(&self, other: &IpAddr) -> Option<Ordering> {
+        match other {
+            IpAddr::V4(_) => Some(Ordering::Greater),
+            IpAddr::V6(v6) => self.partial_cmp(v6),
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Ord for Ipv6Addr {
+    #[inline]
+    fn cmp(&self, other: &Ipv6Addr) -> Ordering {
+        self.segments().cmp(&other.segments())
+    }
+}
+
+#[stable(feature = "i128", since = "1.26.0")]
+impl From<Ipv6Addr> for u128 {
+    /// Convert an `Ipv6Addr` into a host byte order `u128`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::new(
+    ///     0x1020, 0x3040, 0x5060, 0x7080,
+    ///     0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
+    /// );
+    /// assert_eq!(0x102030405060708090A0B0C0D0E0F00D_u128, u128::from(addr));
+    /// ```
+    #[inline]
+    fn from(ip: Ipv6Addr) -> u128 {
+        u128::from_be_bytes(ip.octets)
+    }
+}
+#[stable(feature = "i128", since = "1.26.0")]
+impl From<u128> for Ipv6Addr {
+    /// Convert a host byte order `u128` into an `Ipv6Addr`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::from(0x102030405060708090A0B0C0D0E0F00D_u128);
+    /// assert_eq!(
+    ///     Ipv6Addr::new(
+    ///         0x1020, 0x3040, 0x5060, 0x7080,
+    ///         0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
+    ///     ),
+    ///     addr);
+    /// ```
+    #[inline]
+    fn from(ip: u128) -> Ipv6Addr {
+        Ipv6Addr::from(ip.to_be_bytes())
+    }
+}
+
+#[stable(feature = "ipv6_from_octets", since = "1.9.0")]
+impl From<[u8; 16]> for Ipv6Addr {
+    /// Creates an `Ipv6Addr` from a sixteen element byte array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::from([
+    ///     25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
+    ///     17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
+    /// ]);
+    /// assert_eq!(
+    ///     Ipv6Addr::new(
+    ///         0x1918, 0x1716,
+    ///         0x1514, 0x1312,
+    ///         0x1110, 0x0f0e,
+    ///         0x0d0c, 0x0b0a
+    ///     ),
+    ///     addr
+    /// );
+    /// ```
+    #[inline]
+    fn from(octets: [u8; 16]) -> Ipv6Addr {
+        Ipv6Addr { octets }
+    }
+}
+
+#[stable(feature = "ipv6_from_segments", since = "1.16.0")]
+impl From<[u16; 8]> for Ipv6Addr {
+    /// Creates an `Ipv6Addr` from an eight element 16-bit array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::from([
+    ///     525u16, 524u16, 523u16, 522u16,
+    ///     521u16, 520u16, 519u16, 518u16,
+    /// ]);
+    /// assert_eq!(
+    ///     Ipv6Addr::new(
+    ///         0x20d, 0x20c,
+    ///         0x20b, 0x20a,
+    ///         0x209, 0x208,
+    ///         0x207, 0x206
+    ///     ),
+    ///     addr
+    /// );
+    /// ```
+    #[inline]
+    fn from(segments: [u16; 8]) -> Ipv6Addr {
+        let [a, b, c, d, e, f, g, h] = segments;
+        Ipv6Addr::new(a, b, c, d, e, f, g, h)
+    }
+}
+
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u8; 16]> for IpAddr {
+    /// Creates an `IpAddr::V6` from a sixteen element byte array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv6Addr};
+    ///
+    /// let addr = IpAddr::from([
+    ///     25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
+    ///     17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
+    /// ]);
+    /// assert_eq!(
+    ///     IpAddr::V6(Ipv6Addr::new(
+    ///         0x1918, 0x1716,
+    ///         0x1514, 0x1312,
+    ///         0x1110, 0x0f0e,
+    ///         0x0d0c, 0x0b0a
+    ///     )),
+    ///     addr
+    /// );
+    /// ```
+    #[inline]
+    fn from(octets: [u8; 16]) -> IpAddr {
+        IpAddr::V6(Ipv6Addr::from(octets))
+    }
+}
+
+#[stable(feature = "ip_from_slice", since = "1.17.0")]
+impl From<[u16; 8]> for IpAddr {
+    /// Creates an `IpAddr::V6` from an eight element 16-bit array.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv6Addr};
+    ///
+    /// let addr = IpAddr::from([
+    ///     525u16, 524u16, 523u16, 522u16,
+    ///     521u16, 520u16, 519u16, 518u16,
+    /// ]);
+    /// assert_eq!(
+    ///     IpAddr::V6(Ipv6Addr::new(
+    ///         0x20d, 0x20c,
+    ///         0x20b, 0x20a,
+    ///         0x209, 0x208,
+    ///         0x207, 0x206
+    ///     )),
+    ///     addr
+    /// );
+    /// ```
+    #[inline]
+    fn from(segments: [u16; 8]) -> IpAddr {
+        IpAddr::V6(Ipv6Addr::from(segments))
+    }
+}
diff --git a/library/core/src/net/mod.rs b/library/core/src/net/mod.rs
new file mode 100644
index 000000000..31f5f5d3c
--- /dev/null
+++ b/library/core/src/net/mod.rs
@@ -0,0 +1,24 @@
+//! Networking primitives for IP communication.
+//!
+//! This module provides types for IP and socket addresses.
+//!
+//! # Organization
+//!
+//! * [`IpAddr`] represents IP addresses of either IPv4 or IPv6; [`Ipv4Addr`] and
+//!   [`Ipv6Addr`] are respectively IPv4 and IPv6 addresses
+//! * [`SocketAddr`] represents socket addresses of either IPv4 or IPv6; [`SocketAddrV4`]
+//!   and [`SocketAddrV6`] are respectively IPv4 and IPv6 socket addresses
+
+#![unstable(feature = "ip_in_core", issue = "108443")]
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::ip_addr::{IpAddr, Ipv4Addr, Ipv6Addr, Ipv6MulticastScope};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::parser::AddrParseError;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use self::socket_addr::{SocketAddr, SocketAddrV4, SocketAddrV6};
+
+mod display_buffer;
+mod ip_addr;
+mod parser;
+mod socket_addr;
diff --git a/library/core/src/net/parser.rs b/library/core/src/net/parser.rs
new file mode 100644
index 000000000..a08d2792d
--- /dev/null
+++ b/library/core/src/net/parser.rs
@@ -0,0 +1,498 @@
+//! A private parser implementation of IPv4, IPv6, and socket addresses.
+//!
+//! This module is "publicly exported" through the `FromStr` implementations
+//! below.
+
+use crate::convert::TryInto;
+use crate::error::Error;
+use crate::fmt;
+use crate::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+use crate::str::FromStr;
+
+trait ReadNumberHelper: crate::marker::Sized {
+    const ZERO: Self;
+    fn checked_mul(&self, other: u32) -> Option<Self>;
+    fn checked_add(&self, other: u32) -> Option<Self>;
+}
+
+macro_rules! impl_helper {
+    ($($t:ty)*) => ($(impl ReadNumberHelper for $t {
+        const ZERO: Self = 0;
+        #[inline]
+        fn checked_mul(&self, other: u32) -> Option<Self> {
+            Self::checked_mul(*self, other.try_into().ok()?)
+        }
+        #[inline]
+        fn checked_add(&self, other: u32) -> Option<Self> {
+            Self::checked_add(*self, other.try_into().ok()?)
+        }
+    })*)
+}
+
+impl_helper! { u8 u16 u32 }
+
+struct Parser<'a> {
+    // Parsing as ASCII, so can use byte array.
+    state: &'a [u8],
+}
+
+impl<'a> Parser<'a> {
+    fn new(input: &'a [u8]) -> Parser<'a> {
+        Parser { state: input }
+    }
+
+    /// Run a parser, and restore the pre-parse state if it fails.
+    fn read_atomically<T, F>(&mut self, inner: F) -> Option<T>
+    where
+        F: FnOnce(&mut Parser<'_>) -> Option<T>,
+    {
+        let state = self.state;
+        let result = inner(self);
+        if result.is_none() {
+            self.state = state;
+        }
+        result
+    }
+
+    /// Run a parser, but fail if the entire input wasn't consumed.
+    /// Doesn't run atomically.
+    fn parse_with<T, F>(&mut self, inner: F, kind: AddrKind) -> Result<T, AddrParseError>
+    where
+        F: FnOnce(&mut Parser<'_>) -> Option<T>,
+    {
+        let result = inner(self);
+        if self.state.is_empty() { result } else { None }.ok_or(AddrParseError(kind))
+    }
+
+    /// Peek the next character from the input
+    fn peek_char(&self) -> Option<char> {
+        self.state.first().map(|&b| char::from(b))
+    }
+
+    /// Read the next character from the input
+    fn read_char(&mut self) -> Option<char> {
+        self.state.split_first().map(|(&b, tail)| {
+            self.state = tail;
+            char::from(b)
+        })
+    }
+
+    #[must_use]
+    /// Read the next character from the input if it matches the target.
+    fn read_given_char(&mut self, target: char) -> Option<()> {
+        self.read_atomically(|p| {
+            p.read_char().and_then(|c| if c == target { Some(()) } else { None })
+        })
+    }
+
+    /// Helper for reading separators in an indexed loop. Reads the separator
+    /// character iff index > 0, then runs the parser. When used in a loop,
+    /// the separator character will only be read on index > 0 (see
+    /// read_ipv4_addr for an example)
+    fn read_separator<T, F>(&mut self, sep: char, index: usize, inner: F) -> Option<T>
+    where
+        F: FnOnce(&mut Parser<'_>) -> Option<T>,
+    {
+        self.read_atomically(move |p| {
+            if index > 0 {
+                p.read_given_char(sep)?;
+            }
+            inner(p)
+        })
+    }
+
+    // Read a number off the front of the input in the given radix, stopping
+    // at the first non-digit character or eof. Fails if the number has more
+    // digits than max_digits or if there is no number.
+    fn read_number<T: ReadNumberHelper>(
+        &mut self,
+        radix: u32,
+        max_digits: Option<usize>,
+        allow_zero_prefix: bool,
+    ) -> Option<T> {
+        self.read_atomically(move |p| {
+            let mut result = T::ZERO;
+            let mut digit_count = 0;
+            let has_leading_zero = p.peek_char() == Some('0');
+
+            while let Some(digit) = p.read_atomically(|p| p.read_char()?.to_digit(radix)) {
+                result = result.checked_mul(radix)?;
+                result = result.checked_add(digit)?;
+                digit_count += 1;
+                if let Some(max_digits) = max_digits {
+                    if digit_count > max_digits {
+                        return None;
+                    }
+                }
+            }
+
+            if digit_count == 0 {
+                None
+            } else if !allow_zero_prefix && has_leading_zero && digit_count > 1 {
+                None
+            } else {
+                Some(result)
+            }
+        })
+    }
+
+    /// Read an IPv4 address.
+    fn read_ipv4_addr(&mut self) -> Option<Ipv4Addr> {
+        self.read_atomically(|p| {
+            let mut groups = [0; 4];
+
+            for (i, slot) in groups.iter_mut().enumerate() {
+                *slot = p.read_separator('.', i, |p| {
+                    // Disallow octal number in IP string.
+                    // https://tools.ietf.org/html/rfc6943#section-3.1.1
+                    p.read_number(10, Some(3), false)
+                })?;
+            }
+
+            Some(groups.into())
+        })
+    }
+
+    /// Read an IPv6 Address.
+    fn read_ipv6_addr(&mut self) -> Option<Ipv6Addr> {
+        /// Read a chunk of an IPv6 address into `groups`. Returns the number
+        /// of groups read, along with a bool indicating if an embedded
+        /// trailing IPv4 address was read. Specifically, read a series of
+        /// colon-separated IPv6 groups (0x0000 - 0xFFFF), with an optional
+        /// trailing embedded IPv4 address.
+        fn read_groups(p: &mut Parser<'_>, groups: &mut [u16]) -> (usize, bool) {
+            let limit = groups.len();
+
+            for (i, slot) in groups.iter_mut().enumerate() {
+                // Try to read a trailing embedded IPv4 address. There must be
+                // at least two groups left.
+                if i < limit - 1 {
+                    let ipv4 = p.read_separator(':', i, |p| p.read_ipv4_addr());
+
+                    if let Some(v4_addr) = ipv4 {
+                        let [one, two, three, four] = v4_addr.octets();
+                        groups[i + 0] = u16::from_be_bytes([one, two]);
+                        groups[i + 1] = u16::from_be_bytes([three, four]);
+                        return (i + 2, true);
+                    }
+                }
+
+                let group = p.read_separator(':', i, |p| p.read_number(16, Some(4), true));
+
+                match group {
+                    Some(g) => *slot = g,
+                    None => return (i, false),
+                }
+            }
+            (groups.len(), false)
+        }
+
+        self.read_atomically(|p| {
+            // Read the front part of the address; either the whole thing, or up
+            // to the first ::
+            let mut head = [0; 8];
+            let (head_size, head_ipv4) = read_groups(p, &mut head);
+
+            if head_size == 8 {
+                return Some(head.into());
+            }
+
+            // IPv4 part is not allowed before `::`
+            if head_ipv4 {
+                return None;
+            }
+
+            // Read `::` if previous code parsed less than 8 groups.
+            // `::` indicates one or more groups of 16 bits of zeros.
+            p.read_given_char(':')?;
+            p.read_given_char(':')?;
+
+            // Read the back part of the address. The :: must contain at least one
+            // set of zeroes, so our max length is 7.
+            let mut tail = [0; 7];
+            let limit = 8 - (head_size + 1);
+            let (tail_size, _) = read_groups(p, &mut tail[..limit]);
+
+            // Concat the head and tail of the IP address
+            head[(8 - tail_size)..8].copy_from_slice(&tail[..tail_size]);
+
+            Some(head.into())
+        })
+    }
+
+    /// Read an IP Address, either IPv4 or IPv6.
+    fn read_ip_addr(&mut self) -> Option<IpAddr> {
+        self.read_ipv4_addr().map(IpAddr::V4).or_else(move || self.read_ipv6_addr().map(IpAddr::V6))
+    }
+
+    /// Read a `:` followed by a port in base 10.
+    fn read_port(&mut self) -> Option<u16> {
+        self.read_atomically(|p| {
+            p.read_given_char(':')?;
+            p.read_number(10, None, true)
+        })
+    }
+
+    /// Read a `%` followed by a scope ID in base 10.
+    fn read_scope_id(&mut self) -> Option<u32> {
+        self.read_atomically(|p| {
+            p.read_given_char('%')?;
+            p.read_number(10, None, true)
+        })
+    }
+
+    /// Read an IPv4 address with a port.
+    fn read_socket_addr_v4(&mut self) -> Option<SocketAddrV4> {
+        self.read_atomically(|p| {
+            let ip = p.read_ipv4_addr()?;
+            let port = p.read_port()?;
+            Some(SocketAddrV4::new(ip, port))
+        })
+    }
+
+    /// Read an IPv6 address with a port.
+    fn read_socket_addr_v6(&mut self) -> Option<SocketAddrV6> {
+        self.read_atomically(|p| {
+            p.read_given_char('[')?;
+            let ip = p.read_ipv6_addr()?;
+            let scope_id = p.read_scope_id().unwrap_or(0);
+            p.read_given_char(']')?;
+
+            let port = p.read_port()?;
+            Some(SocketAddrV6::new(ip, port, 0, scope_id))
+        })
+    }
+
+    /// Read an IP address with a port
+    fn read_socket_addr(&mut self) -> Option<SocketAddr> {
+        self.read_socket_addr_v4()
+            .map(SocketAddr::V4)
+            .or_else(|| self.read_socket_addr_v6().map(SocketAddr::V6))
+    }
+}
+
+impl IpAddr {
+    /// Parse an IP address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+    ///
+    /// let localhost_v4 = IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1));
+    /// let localhost_v6 = IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+    ///
+    /// assert_eq!(IpAddr::parse_ascii(b"127.0.0.1"), Ok(localhost_v4));
+    /// assert_eq!(IpAddr::parse_ascii(b"::1"), Ok(localhost_v6));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        Parser::new(b).parse_with(|p| p.read_ip_addr(), AddrKind::Ip)
+    }
+}
+
+#[stable(feature = "ip_addr", since = "1.7.0")]
+impl FromStr for IpAddr {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<IpAddr, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+impl Ipv4Addr {
+    /// Parse an IPv4 address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let localhost = Ipv4Addr::new(127, 0, 0, 1);
+    ///
+    /// assert_eq!(Ipv4Addr::parse_ascii(b"127.0.0.1"), Ok(localhost));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        // don't try to parse if too long
+        if b.len() > 15 {
+            Err(AddrParseError(AddrKind::Ipv4))
+        } else {
+            Parser::new(b).parse_with(|p| p.read_ipv4_addr(), AddrKind::Ipv4)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl FromStr for Ipv4Addr {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<Ipv4Addr, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+impl Ipv6Addr {
+    /// Parse an IPv6 address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let localhost = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
+    ///
+    /// assert_eq!(Ipv6Addr::parse_ascii(b"::1"), Ok(localhost));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        Parser::new(b).parse_with(|p| p.read_ipv6_addr(), AddrKind::Ipv6)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl FromStr for Ipv6Addr {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<Ipv6Addr, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+impl SocketAddrV4 {
+    /// Parse an IPv4 socket address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::{Ipv4Addr, SocketAddrV4};
+    ///
+    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    ///
+    /// assert_eq!(SocketAddrV4::parse_ascii(b"127.0.0.1:8080"), Ok(socket));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        Parser::new(b).parse_with(|p| p.read_socket_addr_v4(), AddrKind::SocketV4)
+    }
+}
+
+#[stable(feature = "socket_addr_from_str", since = "1.5.0")]
+impl FromStr for SocketAddrV4 {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<SocketAddrV4, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+impl SocketAddrV6 {
+    /// Parse an IPv6 socket address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::{Ipv6Addr, SocketAddrV6};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    ///
+    /// assert_eq!(SocketAddrV6::parse_ascii(b"[2001:db8::1]:8080"), Ok(socket));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        Parser::new(b).parse_with(|p| p.read_socket_addr_v6(), AddrKind::SocketV6)
+    }
+}
+
+#[stable(feature = "socket_addr_from_str", since = "1.5.0")]
+impl FromStr for SocketAddrV6 {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<SocketAddrV6, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+impl SocketAddr {
+    /// Parse a socket address from a slice of bytes.
+    ///
+    /// ```
+    /// #![feature(addr_parse_ascii)]
+    ///
+    /// use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};
+    ///
+    /// let socket_v4 = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// let socket_v6 = SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)), 8080);
+    ///
+    /// assert_eq!(SocketAddr::parse_ascii(b"127.0.0.1:8080"), Ok(socket_v4));
+    /// assert_eq!(SocketAddr::parse_ascii(b"[::1]:8080"), Ok(socket_v6));
+    /// ```
+    #[unstable(feature = "addr_parse_ascii", issue = "101035")]
+    pub fn parse_ascii(b: &[u8]) -> Result<Self, AddrParseError> {
+        Parser::new(b).parse_with(|p| p.read_socket_addr(), AddrKind::Socket)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl FromStr for SocketAddr {
+    type Err = AddrParseError;
+    fn from_str(s: &str) -> Result<SocketAddr, AddrParseError> {
+        Self::parse_ascii(s.as_bytes())
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum AddrKind {
+    Ip,
+    Ipv4,
+    Ipv6,
+    Socket,
+    SocketV4,
+    SocketV6,
+}
+
+/// An error which can be returned when parsing an IP address or a socket address.
+///
+/// This error is used as the error type for the [`FromStr`] implementation for
+/// [`IpAddr`], [`Ipv4Addr`], [`Ipv6Addr`], [`SocketAddr`], [`SocketAddrV4`], and
+/// [`SocketAddrV6`].
+///
+/// # Potential causes
+///
+/// `AddrParseError` may be thrown because the provided string does not parse as the given type,
+/// often because it includes information only handled by a different address type.
+///
+/// ```should_panic
+/// use std::net::IpAddr;
+/// let _foo: IpAddr = "127.0.0.1:8080".parse().expect("Cannot handle the socket port");
+/// ```
+///
+/// [`IpAddr`] doesn't handle the port. Use [`SocketAddr`] instead.
+///
+/// ```
+/// use std::net::SocketAddr;
+///
+/// // No problem, the `panic!` message has disappeared.
+/// let _foo: SocketAddr = "127.0.0.1:8080".parse().expect("unreachable panic");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AddrParseError(AddrKind);
+
+#[stable(feature = "addr_parse_error_error", since = "1.4.0")]
+impl fmt::Display for AddrParseError {
+    #[allow(deprecated, deprecated_in_future)]
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.write_str(self.description())
+    }
+}
+
+#[stable(feature = "addr_parse_error_error", since = "1.4.0")]
+impl Error for AddrParseError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        match self.0 {
+            AddrKind::Ip => "invalid IP address syntax",
+            AddrKind::Ipv4 => "invalid IPv4 address syntax",
+            AddrKind::Ipv6 => "invalid IPv6 address syntax",
+            AddrKind::Socket => "invalid socket address syntax",
+            AddrKind::SocketV4 => "invalid IPv4 socket address syntax",
+            AddrKind::SocketV6 => "invalid IPv6 socket address syntax",
+        }
+    }
+}
diff --git a/library/core/src/net/socket_addr.rs b/library/core/src/net/socket_addr.rs
new file mode 100644
index 000000000..2d48e2715
--- /dev/null
+++ b/library/core/src/net/socket_addr.rs
@@ -0,0 +1,664 @@
+use crate::cmp::Ordering;
+use crate::fmt::{self, Write};
+use crate::hash;
+use crate::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+
+use super::display_buffer::DisplayBuffer;
+
+/// An internet socket address, either IPv4 or IPv6.
+///
+/// Internet socket addresses consist of an [IP address], a 16-bit port number, as well
+/// as possibly some version-dependent additional information. See [`SocketAddrV4`]'s and
+/// [`SocketAddrV6`]'s respective documentation for more details.
+///
+/// The size of a `SocketAddr` instance may vary depending on the target operating
+/// system.
+///
+/// [IP address]: IpAddr
+///
+/// # Examples
+///
+/// ```
+/// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+///
+/// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+///
+/// assert_eq!("127.0.0.1:8080".parse(), Ok(socket));
+/// assert_eq!(socket.port(), 8080);
+/// assert_eq!(socket.is_ipv4(), true);
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub enum SocketAddr {
+    /// An IPv4 socket address.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    V4(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV4),
+    /// An IPv6 socket address.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    V6(#[stable(feature = "rust1", since = "1.0.0")] SocketAddrV6),
+}
+
+/// An IPv4 socket address.
+///
+/// IPv4 socket addresses consist of an [`IPv4` address] and a 16-bit port number, as
+/// stated in [IETF RFC 793].
+///
+/// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
+///
+/// The size of a `SocketAddrV4` struct may vary depending on the target operating
+/// system. Do not assume that this type has the same memory layout as the underlying
+/// system representation.
+///
+/// [IETF RFC 793]: https://tools.ietf.org/html/rfc793
+/// [`IPv4` address]: Ipv4Addr
+///
+/// # Examples
+///
+/// ```
+/// use std::net::{Ipv4Addr, SocketAddrV4};
+///
+/// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+///
+/// assert_eq!("127.0.0.1:8080".parse(), Ok(socket));
+/// assert_eq!(socket.ip(), &Ipv4Addr::new(127, 0, 0, 1));
+/// assert_eq!(socket.port(), 8080);
+/// ```
+#[derive(Copy, Clone, Eq, PartialEq)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct SocketAddrV4 {
+    ip: Ipv4Addr,
+    port: u16,
+}
+
+/// An IPv6 socket address.
+///
+/// IPv6 socket addresses consist of an [`IPv6` address], a 16-bit port number, as well
+/// as fields containing the traffic class, the flow label, and a scope identifier
+/// (see [IETF RFC 2553, Section 3.3] for more details).
+///
+/// See [`SocketAddr`] for a type encompassing both IPv4 and IPv6 socket addresses.
+///
+/// The size of a `SocketAddrV6` struct may vary depending on the target operating
+/// system. Do not assume that this type has the same memory layout as the underlying
+/// system representation.
+///
+/// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
+/// [`IPv6` address]: Ipv6Addr
+///
+/// # Examples
+///
+/// ```
+/// use std::net::{Ipv6Addr, SocketAddrV6};
+///
+/// let socket = SocketAddrV6::new(Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+///
+/// assert_eq!("[2001:db8::1]:8080".parse(), Ok(socket));
+/// assert_eq!(socket.ip(), &Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0, 1));
+/// assert_eq!(socket.port(), 8080);
+/// ```
+#[derive(Copy, Clone, Eq, PartialEq)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct SocketAddrV6 {
+    ip: Ipv6Addr,
+    port: u16,
+    flowinfo: u32,
+    scope_id: u32,
+}
+
+impl SocketAddr {
+    /// Creates a new socket address from an [IP address] and a port number.
+    ///
+    /// [IP address]: IpAddr
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)));
+    /// assert_eq!(socket.port(), 8080);
+    /// ```
+    #[stable(feature = "ip_addr", since = "1.7.0")]
+    #[must_use]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn new(ip: IpAddr, port: u16) -> SocketAddr {
+        match ip {
+            IpAddr::V4(a) => SocketAddr::V4(SocketAddrV4::new(a, port)),
+            IpAddr::V6(a) => SocketAddr::V6(SocketAddrV6::new(a, port, 0, 0)),
+        }
+    }
+
+    /// Returns the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)));
+    /// ```
+    #[must_use]
+    #[stable(feature = "ip_addr", since = "1.7.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn ip(&self) -> IpAddr {
+        match *self {
+            SocketAddr::V4(ref a) => IpAddr::V4(*a.ip()),
+            SocketAddr::V6(ref a) => IpAddr::V6(*a.ip()),
+        }
+    }
+
+    /// Changes the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let mut socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// socket.set_ip(IpAddr::V4(Ipv4Addr::new(10, 10, 0, 1)));
+    /// assert_eq!(socket.ip(), IpAddr::V4(Ipv4Addr::new(10, 10, 0, 1)));
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_ip(&mut self, new_ip: IpAddr) {
+        // `match (*self, new_ip)` would have us mutate a copy of self only to throw it away.
+        match (self, new_ip) {
+            (&mut SocketAddr::V4(ref mut a), IpAddr::V4(new_ip)) => a.set_ip(new_ip),
+            (&mut SocketAddr::V6(ref mut a), IpAddr::V6(new_ip)) => a.set_ip(new_ip),
+            (self_, new_ip) => *self_ = Self::new(new_ip, self_.port()),
+        }
+    }
+
+    /// Returns the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// assert_eq!(socket.port(), 8080);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn port(&self) -> u16 {
+        match *self {
+            SocketAddr::V4(ref a) => a.port(),
+            SocketAddr::V6(ref a) => a.port(),
+        }
+    }
+
+    /// Changes the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let mut socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// socket.set_port(1025);
+    /// assert_eq!(socket.port(), 1025);
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_port(&mut self, new_port: u16) {
+        match *self {
+            SocketAddr::V4(ref mut a) => a.set_port(new_port),
+            SocketAddr::V6(ref mut a) => a.set_port(new_port),
+        }
+    }
+
+    /// Returns [`true`] if the [IP address] in this `SocketAddr` is an
+    /// [`IPv4` address], and [`false`] otherwise.
+    ///
+    /// [IP address]: IpAddr
+    /// [`IPv4` address]: IpAddr::V4
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+    ///
+    /// let socket = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080);
+    /// assert_eq!(socket.is_ipv4(), true);
+    /// assert_eq!(socket.is_ipv6(), false);
+    /// ```
+    #[must_use]
+    #[stable(feature = "sockaddr_checker", since = "1.16.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn is_ipv4(&self) -> bool {
+        matches!(*self, SocketAddr::V4(_))
+    }
+
+    /// Returns [`true`] if the [IP address] in this `SocketAddr` is an
+    /// [`IPv6` address], and [`false`] otherwise.
+    ///
+    /// [IP address]: IpAddr
+    /// [`IPv6` address]: IpAddr::V6
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{IpAddr, Ipv6Addr, SocketAddr};
+    ///
+    /// let socket = SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 65535, 0, 1)), 8080);
+    /// assert_eq!(socket.is_ipv4(), false);
+    /// assert_eq!(socket.is_ipv6(), true);
+    /// ```
+    #[must_use]
+    #[stable(feature = "sockaddr_checker", since = "1.16.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn is_ipv6(&self) -> bool {
+        matches!(*self, SocketAddr::V6(_))
+    }
+}
+
+impl SocketAddrV4 {
+    /// Creates a new socket address from an [`IPv4` address] and a port number.
+    ///
+    /// [`IPv4` address]: Ipv4Addr
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV4, Ipv4Addr};
+    ///
+    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn new(ip: Ipv4Addr, port: u16) -> SocketAddrV4 {
+        SocketAddrV4 { ip, port }
+    }
+
+    /// Returns the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV4, Ipv4Addr};
+    ///
+    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    /// assert_eq!(socket.ip(), &Ipv4Addr::new(127, 0, 0, 1));
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn ip(&self) -> &Ipv4Addr {
+        &self.ip
+    }
+
+    /// Changes the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV4, Ipv4Addr};
+    ///
+    /// let mut socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    /// socket.set_ip(Ipv4Addr::new(192, 168, 0, 1));
+    /// assert_eq!(socket.ip(), &Ipv4Addr::new(192, 168, 0, 1));
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_ip(&mut self, new_ip: Ipv4Addr) {
+        self.ip = new_ip;
+    }
+
+    /// Returns the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV4, Ipv4Addr};
+    ///
+    /// let socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    /// assert_eq!(socket.port(), 8080);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn port(&self) -> u16 {
+        self.port
+    }
+
+    /// Changes the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV4, Ipv4Addr};
+    ///
+    /// let mut socket = SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080);
+    /// socket.set_port(4242);
+    /// assert_eq!(socket.port(), 4242);
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_port(&mut self, new_port: u16) {
+        self.port = new_port;
+    }
+}
+
+impl SocketAddrV6 {
+    /// Creates a new socket address from an [`IPv6` address], a 16-bit port number,
+    /// and the `flowinfo` and `scope_id` fields.
+    ///
+    /// For more information on the meaning and layout of the `flowinfo` and `scope_id`
+    /// parameters, see [IETF RFC 2553, Section 3.3].
+    ///
+    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
+    /// [`IPv6` address]: Ipv6Addr
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[must_use]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn new(ip: Ipv6Addr, port: u16, flowinfo: u32, scope_id: u32) -> SocketAddrV6 {
+        SocketAddrV6 { ip, port, flowinfo, scope_id }
+    }
+
+    /// Returns the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    /// assert_eq!(socket.ip(), &Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn ip(&self) -> &Ipv6Addr {
+        &self.ip
+    }
+
+    /// Changes the IP address associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    /// socket.set_ip(Ipv6Addr::new(76, 45, 0, 0, 0, 0, 0, 0));
+    /// assert_eq!(socket.ip(), &Ipv6Addr::new(76, 45, 0, 0, 0, 0, 0, 0));
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_ip(&mut self, new_ip: Ipv6Addr) {
+        self.ip = new_ip;
+    }
+
+    /// Returns the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    /// assert_eq!(socket.port(), 8080);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn port(&self) -> u16 {
+        self.port
+    }
+
+    /// Changes the port number associated with this socket address.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 0);
+    /// socket.set_port(4242);
+    /// assert_eq!(socket.port(), 4242);
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_port(&mut self, new_port: u16) {
+        self.port = new_port;
+    }
+
+    /// Returns the flow information associated with this address.
+    ///
+    /// This information corresponds to the `sin6_flowinfo` field in C's `netinet/in.h`,
+    /// as specified in [IETF RFC 2553, Section 3.3].
+    /// It combines information about the flow label and the traffic class as specified
+    /// in [IETF RFC 2460], respectively [Section 6] and [Section 7].
+    ///
+    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
+    /// [IETF RFC 2460]: https://tools.ietf.org/html/rfc2460
+    /// [Section 6]: https://tools.ietf.org/html/rfc2460#section-6
+    /// [Section 7]: https://tools.ietf.org/html/rfc2460#section-7
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 10, 0);
+    /// assert_eq!(socket.flowinfo(), 10);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn flowinfo(&self) -> u32 {
+        self.flowinfo
+    }
+
+    /// Changes the flow information associated with this socket address.
+    ///
+    /// See [`SocketAddrV6::flowinfo`]'s documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 10, 0);
+    /// socket.set_flowinfo(56);
+    /// assert_eq!(socket.flowinfo(), 56);
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_flowinfo(&mut self, new_flowinfo: u32) {
+        self.flowinfo = new_flowinfo;
+    }
+
+    /// Returns the scope ID associated with this address.
+    ///
+    /// This information corresponds to the `sin6_scope_id` field in C's `netinet/in.h`,
+    /// as specified in [IETF RFC 2553, Section 3.3].
+    ///
+    /// [IETF RFC 2553, Section 3.3]: https://tools.ietf.org/html/rfc2553#section-3.3
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 78);
+    /// assert_eq!(socket.scope_id(), 78);
+    /// ```
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "const_socketaddr", since = "1.69.0")]
+    pub const fn scope_id(&self) -> u32 {
+        self.scope_id
+    }
+
+    /// Changes the scope ID associated with this socket address.
+    ///
+    /// See [`SocketAddrV6::scope_id`]'s documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::net::{SocketAddrV6, Ipv6Addr};
+    ///
+    /// let mut socket = SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1), 8080, 0, 78);
+    /// socket.set_scope_id(42);
+    /// assert_eq!(socket.scope_id(), 42);
+    /// ```
+    #[stable(feature = "sockaddr_setters", since = "1.9.0")]
+    pub fn set_scope_id(&mut self, new_scope_id: u32) {
+        self.scope_id = new_scope_id;
+    }
+}
+
+#[stable(feature = "ip_from_ip", since = "1.16.0")]
+impl From<SocketAddrV4> for SocketAddr {
+    /// Converts a [`SocketAddrV4`] into a [`SocketAddr::V4`].
+    fn from(sock4: SocketAddrV4) -> SocketAddr {
+        SocketAddr::V4(sock4)
+    }
+}
+
+#[stable(feature = "ip_from_ip", since = "1.16.0")]
+impl From<SocketAddrV6> for SocketAddr {
+    /// Converts a [`SocketAddrV6`] into a [`SocketAddr::V6`].
+    fn from(sock6: SocketAddrV6) -> SocketAddr {
+        SocketAddr::V6(sock6)
+    }
+}
+
+#[stable(feature = "addr_from_into_ip", since = "1.17.0")]
+impl<I: Into<IpAddr>> From<(I, u16)> for SocketAddr {
+    /// Converts a tuple struct (Into<[`IpAddr`]>, `u16`) into a [`SocketAddr`].
+    ///
+    /// This conversion creates a [`SocketAddr::V4`] for an [`IpAddr::V4`]
+    /// and creates a [`SocketAddr::V6`] for an [`IpAddr::V6`].
+    ///
+    /// `u16` is treated as port of the newly created [`SocketAddr`].
+    fn from(pieces: (I, u16)) -> SocketAddr {
+        SocketAddr::new(pieces.0.into(), pieces.1)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for SocketAddr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            SocketAddr::V4(ref a) => a.fmt(f),
+            SocketAddr::V6(ref a) => a.fmt(f),
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for SocketAddr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for SocketAddrV4 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // If there are no alignment requirements, write the socket address directly to `f`.
+        // Otherwise, write it to a local buffer and then use `f.pad`.
+        if f.precision().is_none() && f.width().is_none() {
+            write!(f, "{}:{}", self.ip(), self.port())
+        } else {
+            const LONGEST_IPV4_SOCKET_ADDR: &str = "255.255.255.255:65536";
+
+            let mut buf = DisplayBuffer::<{ LONGEST_IPV4_SOCKET_ADDR.len() }>::new();
+            // Buffer is long enough for the longest possible IPv4 socket address, so this should never fail.
+            write!(buf, "{}:{}", self.ip(), self.port()).unwrap();
+
+            f.pad(buf.as_str())
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for SocketAddrV4 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Display for SocketAddrV6 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // If there are no alignment requirements, write the socket address directly to `f`.
+        // Otherwise, write it to a local buffer and then use `f.pad`.
+        if f.precision().is_none() && f.width().is_none() {
+            match self.scope_id() {
+                0 => write!(f, "[{}]:{}", self.ip(), self.port()),
+                scope_id => write!(f, "[{}%{}]:{}", self.ip(), scope_id, self.port()),
+            }
+        } else {
+            const LONGEST_IPV6_SOCKET_ADDR: &str =
+                "[ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff%4294967296]:65536";
+
+            let mut buf = DisplayBuffer::<{ LONGEST_IPV6_SOCKET_ADDR.len() }>::new();
+            match self.scope_id() {
+                0 => write!(buf, "[{}]:{}", self.ip(), self.port()),
+                scope_id => write!(buf, "[{}%{}]:{}", self.ip(), scope_id, self.port()),
+            }
+            // Buffer is long enough for the longest possible IPv6 socket address, so this should never fail.
+            .unwrap();
+
+            f.pad(buf.as_str())
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl fmt::Debug for SocketAddrV6 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
+impl PartialOrd for SocketAddrV4 {
+    fn partial_cmp(&self, other: &SocketAddrV4) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
+impl PartialOrd for SocketAddrV6 {
+    fn partial_cmp(&self, other: &SocketAddrV6) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
+impl Ord for SocketAddrV4 {
+    fn cmp(&self, other: &SocketAddrV4) -> Ordering {
+        self.ip().cmp(other.ip()).then(self.port().cmp(&other.port()))
+    }
+}
+
+#[stable(feature = "socketaddr_ordering", since = "1.45.0")]
+impl Ord for SocketAddrV6 {
+    fn cmp(&self, other: &SocketAddrV6) -> Ordering {
+        self.ip().cmp(other.ip()).then(self.port().cmp(&other.port()))
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl hash::Hash for SocketAddrV4 {
+    fn hash<H: hash::Hasher>(&self, s: &mut H) {
+        (self.port, self.ip).hash(s)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl hash::Hash for SocketAddrV6 {
+    fn hash<H: hash::Hasher>(&self, s: &mut H) {
+        (self.port, &self.ip, self.flowinfo, self.scope_id).hash(s)
+    }
+}
diff --git a/library/core/src/num/dec2flt/mod.rs b/library/core/src/num/dec2flt/mod.rs
index a888ced49..f8d493e8b 100644
--- a/library/core/src/num/dec2flt/mod.rs
+++ b/library/core/src/num/dec2flt/mod.rs
@@ -75,6 +75,7 @@
     issue = "none"
 )]
 
+use crate::error::Error;
 use crate::fmt;
 use crate::str::FromStr;
 
@@ -182,15 +183,10 @@ enum FloatErrorKind {
     Invalid,
 }
 
-impl ParseFloatError {
-    #[unstable(
-        feature = "int_error_internals",
-        reason = "available through Error trait and this method should \
-                  not be exposed publicly",
-        issue = "none"
-    )]
-    #[doc(hidden)]
-    pub fn __description(&self) -> &str {
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Error for ParseFloatError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
         match self.kind {
             FloatErrorKind::Empty => "cannot parse float from empty string",
             FloatErrorKind::Invalid => "invalid float literal",
@@ -201,7 +197,8 @@ impl ParseFloatError {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for ParseFloatError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.__description().fmt(f)
+        #[allow(deprecated)]
+        self.description().fmt(f)
     }
 }
 
diff --git a/library/core/src/num/error.rs b/library/core/src/num/error.rs
index 768dd8781..1bae4efe7 100644
--- a/library/core/src/num/error.rs
+++ b/library/core/src/num/error.rs
@@ -9,23 +9,19 @@ use crate::fmt;
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct TryFromIntError(pub(crate) ());
 
-impl TryFromIntError {
-    #[unstable(
-        feature = "int_error_internals",
-        reason = "available through Error trait and this method should \
-                  not be exposed publicly",
-        issue = "none"
-    )]
-    #[doc(hidden)]
-    pub fn __description(&self) -> &str {
-        "out of range integral type conversion attempted"
+#[stable(feature = "try_from", since = "1.34.0")]
+impl fmt::Display for TryFromIntError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        #[allow(deprecated)]
+        self.description().fmt(fmt)
     }
 }
 
 #[stable(feature = "try_from", since = "1.34.0")]
-impl fmt::Display for TryFromIntError {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.__description().fmt(fmt)
+impl Error for TryFromIntError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "out of range integral type conversion attempted"
     }
 }
 
@@ -121,28 +117,13 @@ impl ParseIntError {
     pub fn kind(&self) -> &IntErrorKind {
         &self.kind
     }
-    #[unstable(
-        feature = "int_error_internals",
-        reason = "available through Error trait and this method should \
-                  not be exposed publicly",
-        issue = "none"
-    )]
-    #[doc(hidden)]
-    pub fn __description(&self) -> &str {
-        match self.kind {
-            IntErrorKind::Empty => "cannot parse integer from empty string",
-            IntErrorKind::InvalidDigit => "invalid digit found in string",
-            IntErrorKind::PosOverflow => "number too large to fit in target type",
-            IntErrorKind::NegOverflow => "number too small to fit in target type",
-            IntErrorKind::Zero => "number would be zero for non-zero type",
-        }
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for ParseIntError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.__description().fmt(f)
+        #[allow(deprecated)]
+        self.description().fmt(f)
     }
 }
 
@@ -150,14 +131,12 @@ impl fmt::Display for ParseIntError {
 impl Error for ParseIntError {
     #[allow(deprecated)]
     fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
-#[stable(feature = "try_from", since = "1.34.0")]
-impl Error for TryFromIntError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
+        match self.kind {
+            IntErrorKind::Empty => "cannot parse integer from empty string",
+            IntErrorKind::InvalidDigit => "invalid digit found in string",
+            IntErrorKind::PosOverflow => "number too large to fit in target type",
+            IntErrorKind::NegOverflow => "number too small to fit in target type",
+            IntErrorKind::Zero => "number would be zero for non-zero type",
+        }
     }
 }
diff --git a/library/core/src/num/int_log10.rs b/library/core/src/num/int_log10.rs
index 80472528f..0ce31b40a 100644
--- a/library/core/src/num/int_log10.rs
+++ b/library/core/src/num/int_log10.rs
@@ -138,3 +138,11 @@ pub const fn i64(val: i64) -> u32 {
 pub const fn i128(val: i128) -> u32 {
     u128(val as u128)
 }
+
+/// Instantiate this panic logic once, rather than for all the ilog methods
+/// on every single primitive type.
+#[cold]
+#[track_caller]
+pub const fn panic_for_nonpositive_argument() -> ! {
+    panic!("argument of integer logarithm must be positive")
+}
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index 2cae98b8e..aec15212d 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -1,11 +1,31 @@
 macro_rules! int_impl {
-    ($SelfT:ty, $ActualT:ident, $UnsignedT:ty, $BITS:expr, $BITS_MINUS_ONE:expr, $Min:expr, $Max:expr,
-     $rot:expr, $rot_op:expr, $rot_result:expr, $swap_op:expr, $swapped:expr,
-     $reversed:expr, $le_bytes:expr, $be_bytes:expr,
-     $to_xe_bytes_doc:expr, $from_xe_bytes_doc:expr,
-     $bound_condition:expr) => {
+    (
+        Self = $SelfT:ty,
+        ActualT = $ActualT:ident,
+        UnsignedT = $UnsignedT:ty,
+
+        // There are all for use *only* in doc comments.
+        // As such, they're all passed as literals -- passing them as a string
+        // literal is fine if they need to be multiple code tokens.
+        // In non-comments, use the associated constants rather than these.
+        BITS = $BITS:literal,
+        BITS_MINUS_ONE = $BITS_MINUS_ONE:literal,
+        Min = $Min:literal,
+        Max = $Max:literal,
+        rot = $rot:literal,
+        rot_op = $rot_op:literal,
+        rot_result = $rot_result:literal,
+        swap_op = $swap_op:literal,
+        swapped = $swapped:literal,
+        reversed = $reversed:literal,
+        le_bytes = $le_bytes:literal,
+        be_bytes = $be_bytes:literal,
+        to_xe_bytes_doc = $to_xe_bytes_doc:expr,
+        from_xe_bytes_doc = $from_xe_bytes_doc:expr,
+        bound_condition = $bound_condition:literal,
+    ) => {
         /// The smallest value that can be represented by this integer type
-        #[doc = concat!("(&minus;2<sup>", $BITS_MINUS_ONE, "</sup>", $bound_condition, ")")]
+        #[doc = concat!("(&minus;2<sup>", $BITS_MINUS_ONE, "</sup>", $bound_condition, ").")]
         ///
         /// # Examples
         ///
@@ -15,10 +35,10 @@ macro_rules! int_impl {
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN, ", stringify!($Min), ");")]
         /// ```
         #[stable(feature = "assoc_int_consts", since = "1.43.0")]
-        pub const MIN: Self = !0 ^ ((!0 as $UnsignedT) >> 1) as Self;
+        pub const MIN: Self = !Self::MAX;
 
         /// The largest value that can be represented by this integer type
-        #[doc = concat!("(2<sup>", $BITS_MINUS_ONE, "</sup> &minus; 1", $bound_condition, ")")]
+        #[doc = concat!("(2<sup>", $BITS_MINUS_ONE, "</sup> &minus; 1", $bound_condition, ").")]
         ///
         /// # Examples
         ///
@@ -28,7 +48,7 @@ macro_rules! int_impl {
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX, ", stringify!($Max), ");")]
         /// ```
         #[stable(feature = "assoc_int_consts", since = "1.43.0")]
-        pub const MAX: Self = !Self::MIN;
+        pub const MAX: Self = (<$UnsignedT>::MAX >> 1) as Self;
 
         /// The size of this integer type in bits.
         ///
@@ -38,7 +58,7 @@ macro_rules! int_impl {
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::BITS, ", stringify!($BITS), ");")]
         /// ```
         #[stable(feature = "int_bits_const", since = "1.53.0")]
-        pub const BITS: u32 = $BITS;
+        pub const BITS: u32 = <$UnsignedT>::BITS;
 
         /// Converts a string slice in a given base to an integer.
         ///
@@ -1365,7 +1385,7 @@ macro_rules! int_impl {
             // SAFETY: the masking by the bitsize of the type ensures that we do not shift
             // out of bounds
             unsafe {
-                self.unchecked_shl(rhs & ($BITS - 1))
+                self.unchecked_shl(rhs & (Self::BITS - 1))
             }
         }
 
@@ -1395,7 +1415,7 @@ macro_rules! int_impl {
             // SAFETY: the masking by the bitsize of the type ensures that we do not shift
             // out of bounds
             unsafe {
-                self.unchecked_shr(rhs & ($BITS - 1))
+                self.unchecked_shr(rhs & (Self::BITS - 1))
             }
         }
 
@@ -1901,7 +1921,7 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn overflowing_shl(self, rhs: u32) -> (Self, bool) {
-            (self.wrapping_shl(rhs), (rhs > ($BITS - 1)))
+            (self.wrapping_shl(rhs), rhs >= Self::BITS)
         }
 
         /// Shifts self right by `rhs` bits.
@@ -1924,7 +1944,7 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn overflowing_shr(self, rhs: u32) -> (Self, bool) {
-            (self.wrapping_shr(rhs), (rhs > ($BITS - 1)))
+            (self.wrapping_shr(rhs), rhs >= Self::BITS)
         }
 
         /// Computes the absolute value of `self`.
@@ -2331,14 +2351,17 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog(self, base: Self) -> u32 {
             assert!(base >= 2, "base of integer logarithm must be at least 2");
-            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog(base) {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
@@ -2354,13 +2377,16 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog2(self) -> u32 {
-            self.checked_ilog2().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog2() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
@@ -2376,13 +2402,16 @@ macro_rules! int_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog10(self) -> u32 {
-            self.checked_ilog10().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog10() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,
@@ -2574,12 +2603,13 @@ macro_rules! int_impl {
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline(always)]
+        #[rustc_allow_const_fn_unstable(const_cmp)]
         pub const fn signum(self) -> Self {
-            match self {
-                n if n > 0 =>  1,
-                0          =>  0,
-                _          => -1,
-            }
+            // Picking the right way to phrase this is complicated
+            // (<https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>)
+            // so delegate it to `Ord` which is already producing -1/0/+1
+            // exactly like we need and can be the place to deal with the complexity.
+            self.cmp(&0) as _
         }
 
         /// Returns `true` if `self` is positive and `false` if the number is zero or
diff --git a/library/core/src/num/mod.rs b/library/core/src/num/mod.rs
index ac7f579eb..a50c91579 100644
--- a/library/core/src/num/mod.rs
+++ b/library/core/src/num/mod.rs
@@ -9,9 +9,6 @@ use crate::mem;
 use crate::ops::{Add, Mul, Sub};
 use crate::str::FromStr;
 
-#[cfg(not(no_fp_fmt_parse))]
-use crate::error::Error;
-
 // Used because the `?` operator is not allowed in a const context.
 macro_rules! try_opt {
     ($e:expr) => {
@@ -61,15 +58,6 @@ pub use wrapping::Wrapping;
 #[cfg(not(no_fp_fmt_parse))]
 pub use dec2flt::ParseFloatError;
 
-#[cfg(not(no_fp_fmt_parse))]
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Error for ParseFloatError {
-    #[allow(deprecated)]
-    fn description(&self) -> &str {
-        self.__description()
-    }
-}
-
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use error::ParseIntError;
 
@@ -238,72 +226,217 @@ macro_rules! widening_impl {
 }
 
 impl i8 {
-    int_impl! { i8, i8, u8, 8, 7, -128, 127, 2, "-0x7e", "0xa", "0x12", "0x12", "0x48",
-    "[0x12]", "[0x12]", "", "", "" }
+    int_impl! {
+        Self = i8,
+        ActualT = i8,
+        UnsignedT = u8,
+        BITS = 8,
+        BITS_MINUS_ONE = 7,
+        Min = -128,
+        Max = 127,
+        rot = 2,
+        rot_op = "-0x7e",
+        rot_result = "0xa",
+        swap_op = "0x12",
+        swapped = "0x12",
+        reversed = "0x48",
+        le_bytes = "[0x12]",
+        be_bytes = "[0x12]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 impl i16 {
-    int_impl! { i16, i16, u16, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234", "0x3412",
-    "0x2c48", "[0x34, 0x12]", "[0x12, 0x34]", "", "", "" }
+    int_impl! {
+        Self = i16,
+        ActualT = i16,
+        UnsignedT = u16,
+        BITS = 16,
+        BITS_MINUS_ONE = 15,
+        Min = -32768,
+        Max = 32767,
+        rot = 4,
+        rot_op = "-0x5ffd",
+        rot_result = "0x3a",
+        swap_op = "0x1234",
+        swapped = "0x3412",
+        reversed = "0x2c48",
+        le_bytes = "[0x34, 0x12]",
+        be_bytes = "[0x12, 0x34]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 impl i32 {
-    int_impl! { i32, i32, u32, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
-    "0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78]", "", "", "" }
+    int_impl! {
+        Self = i32,
+        ActualT = i32,
+        UnsignedT = u32,
+        BITS = 32,
+        BITS_MINUS_ONE = 31,
+        Min = -2147483648,
+        Max = 2147483647,
+        rot = 8,
+        rot_op = "0x10000b3",
+        rot_result = "0xb301",
+        swap_op = "0x12345678",
+        swapped = "0x78563412",
+        reversed = "0x1e6a2c48",
+        le_bytes = "[0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 impl i64 {
-    int_impl! { i64, i64, u64, 64, 63, -9223372036854775808, 9223372036854775807, 12,
-    "0xaa00000000006e1", "0x6e10aa", "0x1234567890123456", "0x5634129078563412",
-    "0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]", "", "", "" }
+    int_impl! {
+        Self = i64,
+        ActualT = i64,
+        UnsignedT = u64,
+        BITS = 64,
+        BITS_MINUS_ONE = 63,
+        Min = -9223372036854775808,
+        Max = 9223372036854775807,
+        rot = 12,
+        rot_op = "0xaa00000000006e1",
+        rot_result = "0x6e10aa",
+        swap_op = "0x1234567890123456",
+        swapped = "0x5634129078563412",
+        reversed = "0x6a2c48091e6a2c48",
+        le_bytes = "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 impl i128 {
-    int_impl! { i128, i128, u128, 128, 127, -170141183460469231731687303715884105728,
-    170141183460469231731687303715884105727, 16,
-    "0x13f40000000000000000000000004f76", "0x4f7613f4", "0x12345678901234567890123456789012",
-    "0x12907856341290785634129078563412", "0x48091e6a2c48091e6a2c48091e6a2c48",
-    "[0x12, 0x90, 0x78, 0x56, 0x34, 0x12, 0x90, 0x78, \
-      0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56, \
-      0x78, 0x90, 0x12, 0x34, 0x56, 0x78, 0x90, 0x12]", "", "", "" }
+    int_impl! {
+        Self = i128,
+        ActualT = i128,
+        UnsignedT = u128,
+        BITS = 128,
+        BITS_MINUS_ONE = 127,
+        Min = -170141183460469231731687303715884105728,
+        Max = 170141183460469231731687303715884105727,
+        rot = 16,
+        rot_op = "0x13f40000000000000000000000004f76",
+        rot_result = "0x4f7613f4",
+        swap_op = "0x12345678901234567890123456789012",
+        swapped = "0x12907856341290785634129078563412",
+        reversed = "0x48091e6a2c48091e6a2c48091e6a2c48",
+        le_bytes = "[0x12, 0x90, 0x78, 0x56, 0x34, 0x12, 0x90, 0x78, \
+            0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56, \
+            0x78, 0x90, 0x12, 0x34, 0x56, 0x78, 0x90, 0x12]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 #[cfg(target_pointer_width = "16")]
 impl isize {
-    int_impl! { isize, i16, usize, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234",
-    "0x3412", "0x2c48", "[0x34, 0x12]", "[0x12, 0x34]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 16-bit targets" }
+    int_impl! {
+        Self = isize,
+        ActualT = i16,
+        UnsignedT = usize,
+        BITS = 16,
+        BITS_MINUS_ONE = 15,
+        Min = -32768,
+        Max = 32767,
+        rot = 4,
+        rot_op = "-0x5ffd",
+        rot_result = "0x3a",
+        swap_op = "0x1234",
+        swapped = "0x3412",
+        reversed = "0x2c48",
+        le_bytes = "[0x34, 0x12]",
+        be_bytes = "[0x12, 0x34]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 16-bit targets",
+    }
 }
 
 #[cfg(target_pointer_width = "32")]
 impl isize {
-    int_impl! { isize, i32, usize, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
-    "0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 32-bit targets" }
+    int_impl! {
+        Self = isize,
+        ActualT = i32,
+        UnsignedT = usize,
+        BITS = 32,
+        BITS_MINUS_ONE = 31,
+        Min = -2147483648,
+        Max = 2147483647,
+        rot = 8,
+        rot_op = "0x10000b3",
+        rot_result = "0xb301",
+        swap_op = "0x12345678",
+        swapped = "0x78563412",
+        reversed = "0x1e6a2c48",
+        le_bytes = "[0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 32-bit targets",
+    }
 }
 
 #[cfg(target_pointer_width = "64")]
 impl isize {
-    int_impl! { isize, i64, usize, 64, 63, -9223372036854775808, 9223372036854775807,
-    12, "0xaa00000000006e1", "0x6e10aa",  "0x1234567890123456", "0x5634129078563412",
-    "0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 64-bit targets" }
+    int_impl! {
+        Self = isize,
+        ActualT = i64,
+        UnsignedT = usize,
+        BITS = 64,
+        BITS_MINUS_ONE = 63,
+        Min = -9223372036854775808,
+        Max = 9223372036854775807,
+        rot = 12,
+        rot_op = "0xaa00000000006e1",
+        rot_result = "0x6e10aa",
+        swap_op = "0x1234567890123456",
+        swapped = "0x5634129078563412",
+        reversed = "0x6a2c48091e6a2c48",
+        le_bytes = "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 64-bit targets",
+    }
 }
 
 /// If 6th bit set ascii is upper case.
 const ASCII_CASE_MASK: u8 = 0b0010_0000;
 
 impl u8 {
-    uint_impl! { u8, u8, i8, NonZeroU8, 8, 255, 2, "0x82", "0xa", "0x12", "0x12", "0x48", "[0x12]",
-    "[0x12]", "", "", "" }
+    uint_impl! {
+        Self = u8,
+        ActualT = u8,
+        SignedT = i8,
+        NonZeroT = NonZeroU8,
+        BITS = 8,
+        MAX = 255,
+        rot = 2,
+        rot_op = "0x82",
+        rot_result = "0xa",
+        swap_op = "0x12",
+        swapped = "0x12",
+        reversed = "0x48",
+        le_bytes = "[0x12]",
+        be_bytes = "[0x12]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
     widening_impl! { u8, u16, 8, unsigned }
 
     /// Checks if the value is within the ASCII range.
@@ -887,8 +1020,25 @@ impl u8 {
 }
 
 impl u16 {
-    uint_impl! { u16, u16, i16, NonZeroU16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
-    "[0x34, 0x12]", "[0x12, 0x34]", "", "", "" }
+    uint_impl! {
+        Self = u16,
+        ActualT = u16,
+        SignedT = i16,
+        NonZeroT = NonZeroU16,
+        BITS = 16,
+        MAX = 65535,
+        rot = 4,
+        rot_op = "0xa003",
+        rot_result = "0x3a",
+        swap_op = "0x1234",
+        swapped = "0x3412",
+        reversed = "0x2c48",
+        le_bytes = "[0x34, 0x12]",
+        be_bytes = "[0x12, 0x34]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
     widening_impl! { u16, u32, 16, unsigned }
 
     /// Checks if the value is a Unicode surrogate code point, which are disallowed values for [`char`].
@@ -918,56 +1068,144 @@ impl u16 {
 }
 
 impl u32 {
-    uint_impl! { u32, u32, i32, NonZeroU32, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
-    "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]", "", "", "" }
+    uint_impl! {
+        Self = u32,
+        ActualT = u32,
+        SignedT = i32,
+        NonZeroT = NonZeroU32,
+        BITS = 32,
+        MAX = 4294967295,
+        rot = 8,
+        rot_op = "0x10000b3",
+        rot_result = "0xb301",
+        swap_op = "0x12345678",
+        swapped = "0x78563412",
+        reversed = "0x1e6a2c48",
+        le_bytes = "[0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
     widening_impl! { u32, u64, 32, unsigned }
 }
 
 impl u64 {
-    uint_impl! { u64, u64, i64, NonZeroU64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
-    "0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
-    "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
-    "", "", ""}
+    uint_impl! {
+        Self = u64,
+        ActualT = u64,
+        SignedT = i64,
+        NonZeroT = NonZeroU64,
+        BITS = 64,
+        MAX = 18446744073709551615,
+        rot = 12,
+        rot_op = "0xaa00000000006e1",
+        rot_result = "0x6e10aa",
+        swap_op = "0x1234567890123456",
+        swapped = "0x5634129078563412",
+        reversed = "0x6a2c48091e6a2c48",
+        le_bytes = "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
     widening_impl! { u64, u128, 64, unsigned }
 }
 
 impl u128 {
-    uint_impl! { u128, u128, i128, NonZeroU128, 128, 340282366920938463463374607431768211455, 16,
-    "0x13f40000000000000000000000004f76", "0x4f7613f4", "0x12345678901234567890123456789012",
-    "0x12907856341290785634129078563412", "0x48091e6a2c48091e6a2c48091e6a2c48",
-    "[0x12, 0x90, 0x78, 0x56, 0x34, 0x12, 0x90, 0x78, \
-      0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56, \
-      0x78, 0x90, 0x12, 0x34, 0x56, 0x78, 0x90, 0x12]",
-     "", "", ""}
+    uint_impl! {
+        Self = u128,
+        ActualT = u128,
+        SignedT = i128,
+        NonZeroT = NonZeroU128,
+        BITS = 128,
+        MAX = 340282366920938463463374607431768211455,
+        rot = 16,
+        rot_op = "0x13f40000000000000000000000004f76",
+        rot_result = "0x4f7613f4",
+        swap_op = "0x12345678901234567890123456789012",
+        swapped = "0x12907856341290785634129078563412",
+        reversed = "0x48091e6a2c48091e6a2c48091e6a2c48",
+        le_bytes = "[0x12, 0x90, 0x78, 0x56, 0x34, 0x12, 0x90, 0x78, \
+            0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56, \
+            0x78, 0x90, 0x12, 0x34, 0x56, 0x78, 0x90, 0x12]",
+        to_xe_bytes_doc = "",
+        from_xe_bytes_doc = "",
+        bound_condition = "",
+    }
 }
 
 #[cfg(target_pointer_width = "16")]
 impl usize {
-    uint_impl! { usize, u16, isize, NonZeroUsize, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
-    "[0x34, 0x12]", "[0x12, 0x34]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 16-bit targets" }
+    uint_impl! {
+        Self = usize,
+        ActualT = u16,
+        SignedT = isize,
+        NonZeroT = NonZeroUsize,
+        BITS = 16,
+        MAX = 65535,
+        rot = 4,
+        rot_op = "0xa003",
+        rot_result = "0x3a",
+        swap_op = "0x1234",
+        swapped = "0x3412",
+        reversed = "0x2c48",
+        le_bytes = "[0x34, 0x12]",
+        be_bytes = "[0x12, 0x34]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 16-bit targets",
+    }
     widening_impl! { usize, u32, 16, unsigned }
 }
+
 #[cfg(target_pointer_width = "32")]
 impl usize {
-    uint_impl! { usize, u32, isize, NonZeroUsize, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
-    "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 32-bit targets" }
+    uint_impl! {
+        Self = usize,
+        ActualT = u32,
+        SignedT = isize,
+        NonZeroT = NonZeroUsize,
+        BITS = 32,
+        MAX = 4294967295,
+        rot = 8,
+        rot_op = "0x10000b3",
+        rot_result = "0xb301",
+        swap_op = "0x12345678",
+        swapped = "0x78563412",
+        reversed = "0x1e6a2c48",
+        le_bytes = "[0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 32-bit targets",
+    }
     widening_impl! { usize, u64, 32, unsigned }
 }
 
 #[cfg(target_pointer_width = "64")]
 impl usize {
-    uint_impl! { usize, u64, isize, NonZeroUsize, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
-    "0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
-    "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
-    "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
-    usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!(),
-    " on 64-bit targets" }
+    uint_impl! {
+        Self = usize,
+        ActualT = u64,
+        SignedT = isize,
+        NonZeroT = NonZeroUsize,
+        BITS = 64,
+        MAX = 18446744073709551615,
+        rot = 12,
+        rot_op = "0xaa00000000006e1",
+        rot_result = "0x6e10aa",
+        swap_op = "0x1234567890123456",
+        swapped = "0x5634129078563412",
+        reversed = "0x6a2c48091e6a2c48",
+        le_bytes = "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
+        be_bytes = "[0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]",
+        to_xe_bytes_doc = usize_isize_to_xe_bytes_doc!(),
+        from_xe_bytes_doc = usize_isize_from_xe_bytes_doc!(),
+        bound_condition = " on 64-bit targets",
+    }
     widening_impl! { usize, u128, 64, unsigned }
 }
 
diff --git a/library/core/src/num/shells/i128.rs b/library/core/src/num/shells/i128.rs
index 7b048dc52..b3b3d3b48 100644
--- a/library/core/src/num/shells/i128.rs
+++ b/library/core/src/num/shells/i128.rs
@@ -1,6 +1,4 @@
-//! Constants for the 128-bit signed integer type.
-//!
-//! *[See also the `i128` primitive type][i128].*
+//! Redundant constants module for the [`i128` primitive type][i128].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/i16.rs b/library/core/src/num/shells/i16.rs
index 5c5812d5c..70a452e19 100644
--- a/library/core/src/num/shells/i16.rs
+++ b/library/core/src/num/shells/i16.rs
@@ -1,6 +1,4 @@
-//! Constants for the 16-bit signed integer type.
-//!
-//! *[See also the `i16` primitive type][i16].*
+//! Redundant constants module for the [`i16` primitive type][i16].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/i32.rs b/library/core/src/num/shells/i32.rs
index b283ac644..c30849e25 100644
--- a/library/core/src/num/shells/i32.rs
+++ b/library/core/src/num/shells/i32.rs
@@ -1,6 +1,4 @@
-//! Constants for the 32-bit signed integer type.
-//!
-//! *[See also the `i32` primitive type][i32].*
+//! Redundant constants module for the [`i32` primitive type][i32].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/i64.rs b/library/core/src/num/shells/i64.rs
index a416fa7e9..77d95d712 100644
--- a/library/core/src/num/shells/i64.rs
+++ b/library/core/src/num/shells/i64.rs
@@ -1,6 +1,4 @@
-//! Constants for the 64-bit signed integer type.
-//!
-//! *[See also the `i64` primitive type][i64].*
+//! Redundant constants module for the [`i64` primitive type][i64].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/i8.rs b/library/core/src/num/shells/i8.rs
index 02465013a..516ba8cde 100644
--- a/library/core/src/num/shells/i8.rs
+++ b/library/core/src/num/shells/i8.rs
@@ -1,6 +1,4 @@
-//! Constants for the 8-bit signed integer type.
-//!
-//! *[See also the `i8` primitive type][i8].*
+//! Redundant constants module for the [`i8` primitive type][i8].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/isize.rs b/library/core/src/num/shells/isize.rs
index 1579fbab6..828f7345b 100644
--- a/library/core/src/num/shells/isize.rs
+++ b/library/core/src/num/shells/isize.rs
@@ -1,6 +1,4 @@
-//! Constants for the pointer-sized signed integer type.
-//!
-//! *[See also the `isize` primitive type][isize].*
+//! Redundant constants module for the [`isize` primitive type][isize].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/u128.rs b/library/core/src/num/shells/u128.rs
index fe08cee58..b1e30e384 100644
--- a/library/core/src/num/shells/u128.rs
+++ b/library/core/src/num/shells/u128.rs
@@ -1,6 +1,4 @@
-//! Constants for the 128-bit unsigned integer type.
-//!
-//! *[See also the `u128` primitive type][u128].*
+//! Redundant constants module for the [`u128` primitive type][u128].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/u16.rs b/library/core/src/num/shells/u16.rs
index 36f8c6978..b203806f4 100644
--- a/library/core/src/num/shells/u16.rs
+++ b/library/core/src/num/shells/u16.rs
@@ -1,6 +1,4 @@
-//! Constants for the 16-bit unsigned integer type.
-//!
-//! *[See also the `u16` primitive type][u16].*
+//! Redundant constants module for the [`i16` primitive type][i16].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/u32.rs b/library/core/src/num/shells/u32.rs
index 1c369097d..4c84274e7 100644
--- a/library/core/src/num/shells/u32.rs
+++ b/library/core/src/num/shells/u32.rs
@@ -1,6 +1,4 @@
-//! Constants for the 32-bit unsigned integer type.
-//!
-//! *[See also the `u32` primitive type][u32].*
+//! Redundant constants module for the [`u32` primitive type][u32].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/u64.rs b/library/core/src/num/shells/u64.rs
index e8b691d15..47a95c682 100644
--- a/library/core/src/num/shells/u64.rs
+++ b/library/core/src/num/shells/u64.rs
@@ -1,6 +1,4 @@
-//! Constants for the 64-bit unsigned integer type.
-//!
-//! *[See also the `u64` primitive type][u64].*
+//! Redundant constants module for the [`u64` primitive type][u64].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/u8.rs b/library/core/src/num/shells/u8.rs
index 817c6a18a..360baef72 100644
--- a/library/core/src/num/shells/u8.rs
+++ b/library/core/src/num/shells/u8.rs
@@ -1,6 +1,4 @@
-//! Constants for the 8-bit unsigned integer type.
-//!
-//! *[See also the `u8` primitive type][u8].*
+//! Redundant constants module for the [`u8` primitive type][u8].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/shells/usize.rs b/library/core/src/num/shells/usize.rs
index 3e1bec5ec..44c24dfc2 100644
--- a/library/core/src/num/shells/usize.rs
+++ b/library/core/src/num/shells/usize.rs
@@ -1,6 +1,4 @@
-//! Constants for the pointer-sized unsigned integer type.
-//!
-//! *[See also the `usize` primitive type][usize].*
+//! Redundant constants module for the [`usize` primitive type][usize].
 //!
 //! New code should use the associated constants directly on the primitive type.
 
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 1c97c4686..932038a0b 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -1,10 +1,28 @@
 macro_rules! uint_impl {
-    ($SelfT:ty, $ActualT:ident, $SignedT:ident, $NonZeroT:ident,
-        $BITS:expr, $MaxV:expr,
-        $rot:expr, $rot_op:expr, $rot_result:expr, $swap_op:expr, $swapped:expr,
-        $reversed:expr, $le_bytes:expr, $be_bytes:expr,
-        $to_xe_bytes_doc:expr, $from_xe_bytes_doc:expr,
-        $bound_condition:expr) => {
+    (
+        Self = $SelfT:ty,
+        ActualT = $ActualT:ident,
+        SignedT = $SignedT:ident,
+        NonZeroT = $NonZeroT:ident,
+
+        // There are all for use *only* in doc comments.
+        // As such, they're all passed as literals -- passing them as a string
+        // literal is fine if they need to be multiple code tokens.
+        // In non-comments, use the associated constants rather than these.
+        BITS = $BITS:literal,
+        MAX = $MaxV:literal,
+        rot = $rot:literal,
+        rot_op = $rot_op:literal,
+        rot_result = $rot_result:literal,
+        swap_op = $swap_op:literal,
+        swapped = $swapped:literal,
+        reversed = $reversed:literal,
+        le_bytes = $le_bytes:literal,
+        be_bytes = $be_bytes:literal,
+        to_xe_bytes_doc = $to_xe_bytes_doc:expr,
+        from_xe_bytes_doc = $from_xe_bytes_doc:expr,
+        bound_condition = $bound_condition:literal,
+    ) => {
         /// The smallest value that can be represented by this integer type.
         ///
         /// # Examples
@@ -18,7 +36,7 @@ macro_rules! uint_impl {
         pub const MIN: Self = 0;
 
         /// The largest value that can be represented by this integer type
-        #[doc = concat!("(2<sup>", $BITS, "</sup> &minus; 1", $bound_condition, ")")]
+        #[doc = concat!("(2<sup>", $BITS, "</sup> &minus; 1", $bound_condition, ").")]
         ///
         /// # Examples
         ///
@@ -38,7 +56,7 @@ macro_rules! uint_impl {
         #[doc = concat!("assert_eq!(", stringify!($SelfT), "::BITS, ", stringify!($BITS), ");")]
         /// ```
         #[stable(feature = "int_bits_const", since = "1.53.0")]
-        pub const BITS: u32 = $BITS;
+        pub const BITS: u32 = Self::MAX.count_ones();
 
         /// Converts a string slice in a given base to an integer.
         ///
@@ -705,14 +723,17 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog(self, base: Self) -> u32 {
             assert!(base >= 2, "base of integer logarithm must be at least 2");
-            self.checked_ilog(base).expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog(base) {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 2 logarithm of the number, rounded down.
@@ -728,13 +749,16 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog2(self) -> u32 {
-            self.checked_ilog2().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog2() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the base 10 logarithm of the number, rounded down.
@@ -750,13 +774,16 @@ macro_rules! uint_impl {
         /// ```
         #[stable(feature = "int_log", since = "1.67.0")]
         #[rustc_const_stable(feature = "int_log", since = "1.67.0")]
-        #[rustc_allow_const_fn_unstable(const_option)]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         #[inline]
         #[track_caller]
         pub const fn ilog10(self) -> u32 {
-            self.checked_ilog10().expect("argument of integer logarithm must be positive")
+            if let Some(log) = self.checked_ilog10() {
+                log
+            } else {
+                int_log10::panic_for_nonpositive_argument()
+            }
         }
 
         /// Returns the logarithm of the number with respect to an arbitrary base,
@@ -1381,7 +1408,7 @@ macro_rules! uint_impl {
             // SAFETY: the masking by the bitsize of the type ensures that we do not shift
             // out of bounds
             unsafe {
-                self.unchecked_shl(rhs & ($BITS - 1))
+                self.unchecked_shl(rhs & (Self::BITS - 1))
             }
         }
 
@@ -1414,7 +1441,7 @@ macro_rules! uint_impl {
             // SAFETY: the masking by the bitsize of the type ensures that we do not shift
             // out of bounds
             unsafe {
-                self.unchecked_shr(rhs & ($BITS - 1))
+                self.unchecked_shr(rhs & (Self::BITS - 1))
             }
         }
 
@@ -1838,7 +1865,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline(always)]
         pub const fn overflowing_shl(self, rhs: u32) -> (Self, bool) {
-            (self.wrapping_shl(rhs), (rhs > ($BITS - 1)))
+            (self.wrapping_shl(rhs), rhs >= Self::BITS)
         }
 
         /// Shifts self right by `rhs` bits.
@@ -1863,7 +1890,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline(always)]
         pub const fn overflowing_shr(self, rhs: u32) -> (Self, bool) {
-            (self.wrapping_shr(rhs), (rhs > ($BITS - 1)))
+            (self.wrapping_shr(rhs), rhs >= Self::BITS)
         }
 
         /// Raises self to the power of `exp`, using exponentiation by squaring.
diff --git a/library/core/src/ops/arith.rs b/library/core/src/ops/arith.rs
index 75c52d3ec..0c7ee9630 100644
--- a/library/core/src/ops/arith.rs
+++ b/library/core/src/ops/arith.rs
@@ -86,7 +86,8 @@ pub trait Add<Rhs = Self> {
     /// ```
     /// assert_eq!(12 + 1, 13);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "add"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn add(self, rhs: Rhs) -> Self::Output;
 }
@@ -195,7 +196,8 @@ pub trait Sub<Rhs = Self> {
     /// ```
     /// assert_eq!(12 - 1, 11);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "sub"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn sub(self, rhs: Rhs) -> Self::Output;
 }
@@ -325,7 +327,8 @@ pub trait Mul<Rhs = Self> {
     /// ```
     /// assert_eq!(12 * 2, 24);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "mul"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn mul(self, rhs: Rhs) -> Self::Output;
 }
@@ -459,7 +462,8 @@ pub trait Div<Rhs = Self> {
     /// ```
     /// assert_eq!(12 / 2, 6);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "div"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn div(self, rhs: Rhs) -> Self::Output;
 }
@@ -545,7 +549,7 @@ div_impl_float! { f32 f64 }
 #[lang = "rem"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
-    message = "cannot mod `{Self}` by `{Rhs}`",
+    message = "cannot calculate the remainder of `{Self}` divided by `{Rhs}`",
     label = "no implementation for `{Self} % {Rhs}`"
 )]
 #[doc(alias = "%")]
@@ -562,7 +566,8 @@ pub trait Rem<Rhs = Self> {
     /// ```
     /// assert_eq!(12 % 10, 2);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "rem"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn rem(self, rhs: Rhs) -> Self::Output;
 }
@@ -678,7 +683,8 @@ pub trait Neg {
     /// let x: i32 = 12;
     /// assert_eq!(-x, -12);
     /// ```
-    #[must_use]
+    #[must_use = "this returns the result of the operation, without modifying the original"]
+    #[rustc_diagnostic_item = "neg"]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn neg(self) -> Self::Output;
 }
@@ -981,7 +987,7 @@ div_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 #[lang = "rem_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
 #[rustc_on_unimplemented(
-    message = "cannot mod-assign `{Self}` by `{Rhs}``",
+    message = "cannot calculate and assign the remainder of `{Self}` divided by `{Rhs}`",
     label = "no implementation for `{Self} %= {Rhs}`"
 )]
 #[doc(alias = "%")]
diff --git a/library/core/src/ops/control_flow.rs b/library/core/src/ops/control_flow.rs
index cd183540c..117706fb4 100644
--- a/library/core/src/ops/control_flow.rs
+++ b/library/core/src/ops/control_flow.rs
@@ -259,46 +259,3 @@ impl<R: ops::Try> ControlFlow<R, R::Output> {
         }
     }
 }
-
-impl<B> ControlFlow<B, ()> {
-    /// It's frequently the case that there's no value needed with `Continue`,
-    /// so this provides a way to avoid typing `(())`, if you prefer it.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(control_flow_enum)]
-    /// use std::ops::ControlFlow;
-    ///
-    /// let mut partial_sum = 0;
-    /// let last_used = (1..10).chain(20..25).try_for_each(|x| {
-    ///     partial_sum += x;
-    ///     if partial_sum > 100 { ControlFlow::Break(x) }
-    ///     else { ControlFlow::CONTINUE }
-    /// });
-    /// assert_eq!(last_used.break_value(), Some(22));
-    /// ```
-    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
-    pub const CONTINUE: Self = ControlFlow::Continue(());
-}
-
-impl<C> ControlFlow<(), C> {
-    /// APIs like `try_for_each` don't need values with `Break`,
-    /// so this provides a way to avoid typing `(())`, if you prefer it.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(control_flow_enum)]
-    /// use std::ops::ControlFlow;
-    ///
-    /// let mut partial_sum = 0;
-    /// (1..10).chain(20..25).try_for_each(|x| {
-    ///     if partial_sum > 100 { ControlFlow::BREAK }
-    ///     else { partial_sum += x; ControlFlow::CONTINUE }
-    /// });
-    /// assert_eq!(partial_sum, 108);
-    /// ```
-    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
-    pub const BREAK: Self = ControlFlow::Break(());
-}
diff --git a/library/core/src/ops/range.rs b/library/core/src/ops/range.rs
index d29ae3561..b8ab26564 100644
--- a/library/core/src/ops/range.rs
+++ b/library/core/src/ops/range.rs
@@ -96,7 +96,7 @@ impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
     }
 }
 
-impl<Idx: PartialOrd<Idx>> Range<Idx> {
+impl<Idx: ~const PartialOrd<Idx>> Range<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///
     /// # Examples
@@ -116,10 +116,11 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
     /// assert!(!(f32::NAN..1.0).contains(&0.5));
     /// ```
     #[stable(feature = "range_contains", since = "1.35.0")]
-    pub fn contains<U>(&self, item: &U) -> bool
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn contains<U>(&self, item: &U) -> bool
     where
-        Idx: PartialOrd<U>,
-        U: ?Sized + PartialOrd<Idx>,
+        Idx: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<Idx>,
     {
         <Self as RangeBounds<Idx>>::contains(self, item)
     }
@@ -142,7 +143,8 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
     /// assert!( (f32::NAN..5.0).is_empty());
     /// ```
     #[stable(feature = "range_is_empty", since = "1.47.0")]
-    pub fn is_empty(&self) -> bool {
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn is_empty(&self) -> bool {
         !(self.start < self.end)
     }
 }
@@ -199,7 +201,7 @@ impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
     }
 }
 
-impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
+impl<Idx: ~const PartialOrd<Idx>> RangeFrom<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///
     /// # Examples
@@ -214,10 +216,11 @@ impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
     /// assert!(!(f32::NAN..).contains(&0.5));
     /// ```
     #[stable(feature = "range_contains", since = "1.35.0")]
-    pub fn contains<U>(&self, item: &U) -> bool
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn contains<U>(&self, item: &U) -> bool
     where
-        Idx: PartialOrd<U>,
-        U: ?Sized + PartialOrd<Idx>,
+        Idx: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<Idx>,
     {
         <Self as RangeBounds<Idx>>::contains(self, item)
     }
@@ -280,7 +283,7 @@ impl<Idx: fmt::Debug> fmt::Debug for RangeTo<Idx> {
     }
 }
 
-impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
+impl<Idx: ~const PartialOrd<Idx>> RangeTo<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///
     /// # Examples
@@ -295,10 +298,11 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
     /// assert!(!(..f32::NAN).contains(&0.5));
     /// ```
     #[stable(feature = "range_contains", since = "1.35.0")]
-    pub fn contains<U>(&self, item: &U) -> bool
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn contains<U>(&self, item: &U) -> bool
     where
-        Idx: PartialOrd<U>,
-        U: ?Sized + PartialOrd<Idx>,
+        Idx: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<Idx>,
     {
         <Self as RangeBounds<Idx>>::contains(self, item)
     }
@@ -437,7 +441,8 @@ impl<Idx> RangeInclusive<Idx> {
     /// ```
     #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
     #[inline]
-    pub fn into_inner(self) -> (Idx, Idx) {
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn into_inner(self) -> (Idx, Idx) {
         (self.start, self.end)
     }
 }
@@ -469,7 +474,7 @@ impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
     }
 }
 
-impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
+impl<Idx: ~const PartialOrd<Idx>> RangeInclusive<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///
     /// # Examples
@@ -500,10 +505,11 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// assert!(!r.contains(&3) && !r.contains(&5));
     /// ```
     #[stable(feature = "range_contains", since = "1.35.0")]
-    pub fn contains<U>(&self, item: &U) -> bool
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn contains<U>(&self, item: &U) -> bool
     where
-        Idx: PartialOrd<U>,
-        U: ?Sized + PartialOrd<Idx>,
+        Idx: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<Idx>,
     {
         <Self as RangeBounds<Idx>>::contains(self, item)
     }
@@ -535,8 +541,9 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// assert!(r.is_empty());
     /// ```
     #[stable(feature = "range_is_empty", since = "1.47.0")]
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
     #[inline]
-    pub fn is_empty(&self) -> bool {
+    pub const fn is_empty(&self) -> bool {
         self.exhausted || !(self.start <= self.end)
     }
 }
@@ -598,7 +605,7 @@ impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
     }
 }
 
-impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
+impl<Idx: ~const PartialOrd<Idx>> RangeToInclusive<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///
     /// # Examples
@@ -613,10 +620,11 @@ impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
     /// assert!(!(..=f32::NAN).contains(&0.5));
     /// ```
     #[stable(feature = "range_contains", since = "1.35.0")]
-    pub fn contains<U>(&self, item: &U) -> bool
+    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+    pub const fn contains<U>(&self, item: &U) -> bool
     where
-        Idx: PartialOrd<U>,
-        U: ?Sized + PartialOrd<Idx>,
+        Idx: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<Idx>,
     {
         <Self as RangeBounds<Idx>>::contains(self, item)
     }
@@ -757,6 +765,7 @@ impl<T: Clone> Bound<&T> {
 /// `RangeBounds` is implemented by Rust's built-in range types, produced
 /// by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
 #[stable(feature = "collections_range", since = "1.28.0")]
+#[const_trait]
 pub trait RangeBounds<T: ?Sized> {
     /// Start index bound.
     ///
@@ -809,8 +818,8 @@ pub trait RangeBounds<T: ?Sized> {
     #[stable(feature = "range_contains", since = "1.35.0")]
     fn contains<U>(&self, item: &U) -> bool
     where
-        T: PartialOrd<U>,
-        U: ?Sized + PartialOrd<T>,
+        T: ~const PartialOrd<U>,
+        U: ?Sized + ~const PartialOrd<T>,
     {
         (match self.start_bound() {
             Included(start) => start <= item,
@@ -827,7 +836,8 @@ pub trait RangeBounds<T: ?Sized> {
 use self::Bound::{Excluded, Included, Unbounded};
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T: ?Sized> RangeBounds<T> for RangeFull {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T: ?Sized> const RangeBounds<T> for RangeFull {
     fn start_bound(&self) -> Bound<&T> {
         Unbounded
     }
@@ -837,7 +847,8 @@ impl<T: ?Sized> RangeBounds<T> for RangeFull {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeFrom<T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeFrom<T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(&self.start)
     }
@@ -847,7 +858,8 @@ impl<T> RangeBounds<T> for RangeFrom<T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeTo<T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeTo<T> {
     fn start_bound(&self) -> Bound<&T> {
         Unbounded
     }
@@ -857,7 +869,8 @@ impl<T> RangeBounds<T> for RangeTo<T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for Range<T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for Range<T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(&self.start)
     }
@@ -867,7 +880,8 @@ impl<T> RangeBounds<T> for Range<T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeInclusive<T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeInclusive<T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(&self.start)
     }
@@ -883,7 +897,8 @@ impl<T> RangeBounds<T> for RangeInclusive<T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeToInclusive<T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeToInclusive<T> {
     fn start_bound(&self) -> Bound<&T> {
         Unbounded
     }
@@ -893,7 +908,8 @@ impl<T> RangeBounds<T> for RangeToInclusive<T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for (Bound<T>, Bound<T>) {
     fn start_bound(&self) -> Bound<&T> {
         match *self {
             (Included(ref start), _) => Included(start),
@@ -912,7 +928,8 @@ impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<'a, T: ?Sized + 'a> const RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
     fn start_bound(&self) -> Bound<&T> {
         self.0
     }
@@ -923,7 +940,8 @@ impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeFrom<&T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeFrom<&T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(self.start)
     }
@@ -933,7 +951,8 @@ impl<T> RangeBounds<T> for RangeFrom<&T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeTo<&T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeTo<&T> {
     fn start_bound(&self) -> Bound<&T> {
         Unbounded
     }
@@ -943,7 +962,8 @@ impl<T> RangeBounds<T> for RangeTo<&T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for Range<&T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for Range<&T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(self.start)
     }
@@ -953,7 +973,8 @@ impl<T> RangeBounds<T> for Range<&T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeInclusive<&T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeInclusive<&T> {
     fn start_bound(&self) -> Bound<&T> {
         Included(self.start)
     }
@@ -963,7 +984,8 @@ impl<T> RangeBounds<T> for RangeInclusive<&T> {
 }
 
 #[stable(feature = "collections_range", since = "1.28.0")]
-impl<T> RangeBounds<T> for RangeToInclusive<&T> {
+#[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
+impl<T> const RangeBounds<T> for RangeToInclusive<&T> {
     fn start_bound(&self) -> Bound<&T> {
         Unbounded
     }
diff --git a/library/core/src/ops/try_trait.rs b/library/core/src/ops/try_trait.rs
index 84a690468..86aa1e4fd 100644
--- a/library/core/src/ops/try_trait.rs
+++ b/library/core/src/ops/try_trait.rs
@@ -379,13 +379,27 @@ pub(crate) type ChangeOutputType<T, V> = <<T as Try>::Residual as Residual<V>>::
 pub(crate) struct NeverShortCircuit<T>(pub T);
 
 impl<T> NeverShortCircuit<T> {
-    /// Implementation for building `ConstFnMutClosure` for wrapping the output of a ~const FnMut in a `NeverShortCircuit`.
+    /// Wraps a unary function to produce one that wraps the output into a `NeverShortCircuit`.
+    ///
+    /// This is useful for implementing infallible functions in terms of the `try_` ones,
+    /// without accidentally capturing extra generic parameters in a closure.
+    #[inline]
+    pub fn wrap_mut_1<A>(mut f: impl FnMut(A) -> T) -> impl FnMut(A) -> NeverShortCircuit<T> {
+        move |a| NeverShortCircuit(f(a))
+    }
+
     #[inline]
-    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 fn wrap_mut_2<A, B>(
+        mut f: impl ~const FnMut(A, B) -> T,
+    ) -> impl ~const FnMut(A, B) -> Self {
+        cfg_if! {
+            if #[cfg(bootstrap)] {
+                #[allow(unused_parens)]
+                (const move |a, b| NeverShortCircuit(f(a, b)))
+            } else {
+                const move |a, b| NeverShortCircuit(f(a, b))
+            }
+        }
     }
 }
 
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index 7cc00e3f8..994c08d1f 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -551,8 +551,9 @@ use crate::marker::Destruct;
 use crate::panicking::{panic, panic_str};
 use crate::pin::Pin;
 use crate::{
-    convert, hint, mem,
+    cmp, convert, hint, mem,
     ops::{self, ControlFlow, Deref, DerefMut},
+    slice,
 };
 
 /// The `Option` type. See [the module level documentation](self) for more.
@@ -734,6 +735,124 @@ impl<T> Option<T> {
         }
     }
 
+    const fn get_some_offset() -> isize {
+        if mem::size_of::<Option<T>>() == mem::size_of::<T>() {
+            // niche optimization means the `T` is always stored at the same position as the Option.
+            0
+        } else {
+            assert!(mem::size_of::<Option<T>>() == mem::size_of::<Option<mem::MaybeUninit<T>>>());
+            let some_uninit = Some(mem::MaybeUninit::<T>::uninit());
+            // SAFETY: This gets the byte offset of the `Some(_)` value following the fact that
+            // niche optimization is not active, and thus Option<T> and Option<MaybeUninit<t>> share
+            // the same layout.
+            unsafe {
+                (some_uninit.as_ref().unwrap() as *const mem::MaybeUninit<T>)
+                    .byte_offset_from(&some_uninit as *const Option<mem::MaybeUninit<T>>)
+            }
+        }
+    }
+
+    /// Returns a slice of the contained value, if any. If this is `None`, an
+    /// empty slice is returned. This can be useful to have a single type of
+    /// iterator over an `Option` or slice.
+    ///
+    /// Note: Should you have an `Option<&T>` and wish to get a slice of `T`,
+    /// you can unpack it via `opt.map_or(&[], std::slice::from_ref)`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(option_as_slice)]
+    ///
+    /// assert_eq!(
+    ///     [Some(1234).as_slice(), None.as_slice()],
+    ///     [&[1234][..], &[][..]],
+    /// );
+    /// ```
+    ///
+    /// The inverse of this function is (discounting
+    /// borrowing) [`[_]::first`](slice::first):
+    ///
+    /// ```rust
+    /// #![feature(option_as_slice)]
+    ///
+    /// for i in [Some(1234_u16), None] {
+    ///     assert_eq!(i.as_ref(), i.as_slice().first());
+    /// }
+    /// ```
+    #[inline]
+    #[must_use]
+    #[unstable(feature = "option_as_slice", issue = "108545")]
+    pub fn as_slice(&self) -> &[T] {
+        // SAFETY: This is sound as long as `get_some_offset` returns the
+        // correct offset. Though in the `None` case, the slice may be located
+        // at a pointer pointing into padding, the fact that the slice is
+        // empty, and the padding is at a properly aligned position for a
+        // value of that type makes it sound.
+        unsafe {
+            slice::from_raw_parts(
+                (self as *const Option<T>).wrapping_byte_offset(Self::get_some_offset())
+                    as *const T,
+                self.is_some() as usize,
+            )
+        }
+    }
+
+    /// Returns a mutable slice of the contained value, if any. If this is
+    /// `None`, an empty slice is returned. This can be useful to have a
+    /// single type of iterator over an `Option` or slice.
+    ///
+    /// Note: Should you have an `Option<&mut T>` instead of a
+    /// `&mut Option<T>`, which this method takes, you can obtain a mutable
+    /// slice via `opt.map_or(&mut [], std::slice::from_mut)`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// #![feature(option_as_slice)]
+    ///
+    /// assert_eq!(
+    ///     [Some(1234).as_mut_slice(), None.as_mut_slice()],
+    ///     [&mut [1234][..], &mut [][..]],
+    /// );
+    /// ```
+    ///
+    /// The result is a mutable slice of zero or one items that points into
+    /// our original `Option`:
+    ///
+    /// ```rust
+    /// #![feature(option_as_slice)]
+    ///
+    /// let mut x = Some(1234);
+    /// x.as_mut_slice()[0] += 1;
+    /// assert_eq!(x, Some(1235));
+    /// ```
+    ///
+    /// The inverse of this method (discounting borrowing)
+    /// is [`[_]::first_mut`](slice::first_mut):
+    ///
+    /// ```rust
+    /// #![feature(option_as_slice)]
+    ///
+    /// assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))
+    /// ```
+    #[inline]
+    #[must_use]
+    #[unstable(feature = "option_as_slice", issue = "108545")]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        // SAFETY: This is sound as long as `get_some_offset` returns the
+        // correct offset. Though in the `None` case, the slice may be located
+        // at a pointer pointing into padding, the fact that the slice is
+        // empty, and the padding is at a properly aligned position for a
+        // value of that type makes it sound.
+        unsafe {
+            slice::from_raw_parts_mut(
+                (self as *mut Option<T>).wrapping_byte_offset(Self::get_some_offset()) as *mut T,
+                self.is_some() as usize,
+            )
+        }
+    }
+
     /////////////////////////////////////////////////////////////////////////
     // Getting to contained values
     /////////////////////////////////////////////////////////////////////////
@@ -943,7 +1062,7 @@ impl<T> Option<T> {
     // Transforming contained values
     /////////////////////////////////////////////////////////////////////////
 
-    /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value.
+    /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value (if `Some`) or returns `None` (if `None`).
     ///
     /// # Examples
     ///
@@ -955,8 +1074,10 @@ impl<T> Option<T> {
     /// let maybe_some_string = Some(String::from("Hello, World!"));
     /// // `Option::map` takes self *by value*, consuming `maybe_some_string`
     /// let maybe_some_len = maybe_some_string.map(|s| s.len());
-    ///
     /// assert_eq!(maybe_some_len, Some(13));
+    ///
+    /// let x: Option<&str> = None;
+    /// assert_eq!(x.map(|s| s.len()), None);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -2090,6 +2211,12 @@ impl<T: PartialEq> PartialEq for Option<T> {
     }
 }
 
+/// This specialization trait is a workaround for LLVM not currently (2023-01)
+/// being able to optimize this itself, even though Alive confirms that it would
+/// be legal to do so: <https://github.com/llvm/llvm-project/issues/52622>
+///
+/// Once that's fixed, `Option` should go back to deriving `PartialEq`, as
+/// it used to do before <https://github.com/rust-lang/rust/pull/103556>.
 #[unstable(feature = "spec_option_partial_eq", issue = "none", reason = "exposed only for rustc")]
 #[doc(hidden)]
 pub trait SpecOptionPartialEq: Sized {
@@ -2146,6 +2273,14 @@ impl<T> SpecOptionPartialEq for crate::ptr::NonNull<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl SpecOptionPartialEq for cmp::Ordering {
+    #[inline]
+    fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
+        l.map_or(2, |x| x as i8) == r.map_or(2, |x| x as i8)
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Option Iterators
 /////////////////////////////////////////////////////////////////////////////
diff --git a/library/core/src/panicking.rs b/library/core/src/panicking.rs
index 48e90e6d7..805a1e51a 100644
--- a/library/core/src/panicking.rs
+++ b/library/core/src/panicking.rs
@@ -117,7 +117,7 @@ pub const fn panic(expr: &'static str) -> ! {
 /// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize.
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
-#[cfg_attr(not(bootstrap), lang = "panic_nounwind")] // needed by codegen for non-unwinding panics
+#[lang = "panic_nounwind"] // needed by codegen for non-unwinding panics
 #[rustc_nounwind]
 pub fn panic_nounwind(expr: &'static str) -> ! {
     panic_nounwind_fmt(fmt::Arguments::new_v1(&[expr], &[]));
@@ -165,8 +165,7 @@ fn panic_bounds_check(index: usize, len: usize) -> ! {
 /// any extra arguments (including those synthesized by track_caller).
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
-#[cfg_attr(bootstrap, lang = "panic_no_unwind")] // needed by codegen for panic in nounwind function
-#[cfg_attr(not(bootstrap), lang = "panic_cannot_unwind")] // needed by codegen for panic in nounwind function
+#[lang = "panic_cannot_unwind"] // needed by codegen for panic in nounwind function
 #[rustc_nounwind]
 fn panic_cannot_unwind() -> ! {
     panic_nounwind("panic in a function that cannot unwind")
diff --git a/library/core/src/primitive_docs.rs b/library/core/src/primitive_docs.rs
index d6e9da187..6f78811a1 100644
--- a/library/core/src/primitive_docs.rs
+++ b/library/core/src/primitive_docs.rs
@@ -587,8 +587,10 @@ mod prim_pointer {}
 /// There are two syntactic forms for creating an array:
 ///
 /// * A list with each element, i.e., `[x, y, z]`.
-/// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.
-///   The type of `x` must be [`Copy`].
+/// * A repeat expression `[expr; N]` where `N` is how many times to repeat `expr` in the array. `expr` must either be:
+///
+///   * A value of a type implementing the [`Copy`] trait
+///   * A `const` value
 ///
 /// Note that `[expr; 0]` is allowed, and produces an empty array.
 /// This will still evaluate `expr`, however, and immediately drop the resulting value, so
diff --git a/library/core/src/ptr/alignment.rs b/library/core/src/ptr/alignment.rs
index 2123147c7..efe6d4183 100644
--- a/library/core/src/ptr/alignment.rs
+++ b/library/core/src/ptr/alignment.rs
@@ -41,7 +41,7 @@ impl Alignment {
     /// Returns the alignment for a type.
     ///
     /// This provides the same numerical value as [`mem::align_of`],
-    /// but in an `Alignment` instead of a `usize.
+    /// but in an `Alignment` instead of a `usize`.
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
     pub const fn of<T>() -> Self {
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index 7b1cb5488..57e2ffe5d 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -23,8 +23,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "Follow the rabbit";
     /// let ptr: *const u8 = s.as_ptr();
@@ -323,8 +321,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let ptr: *const u8 = &10u8 as *const u8;
     ///
@@ -384,8 +380,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// #![feature(ptr_as_uninit)]
     ///
@@ -449,8 +443,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "123";
     /// let ptr: *const u8 = s.as_ptr();
@@ -526,8 +518,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements
     /// let data = [1u8, 2, 3, 4, 5];
@@ -731,7 +721,7 @@ impl<T: ?Sized> *const T {
     /// This computes the same value that [`offset_from`](#method.offset_from)
     /// 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()`,
+    /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`,
     /// but it provides slightly more information to the optimizer, which can
     /// sometimes allow it to optimize slightly better with some backends.
     ///
@@ -908,8 +898,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "123";
     /// let ptr: *const u8 = s.as_ptr();
@@ -993,8 +981,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "123";
     ///
@@ -1072,8 +1058,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements
     /// let data = [1u8, 2, 3, 4, 5];
@@ -1152,8 +1136,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements (backwards)
     /// let data = [1u8, 2, 3, 4, 5];
@@ -1359,7 +1341,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
     /// ```
     /// #![feature(pointer_is_aligned)]
     /// #![feature(pointer_byte_offsets)]
@@ -1482,7 +1463,6 @@ impl<T: ?Sized> *const T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
     /// ```
     /// #![feature(pointer_is_aligned)]
     /// #![feature(pointer_byte_offsets)]
diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index ed1e3bd48..422d0f2b8 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -22,8 +22,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let mut s = [1, 2, 3];
     /// let ptr: *mut u32 = s.as_mut_ptr();
@@ -332,8 +330,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
     ///
@@ -396,8 +392,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// #![feature(ptr_as_uninit)]
     ///
@@ -461,8 +455,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let mut s = [1, 2, 3];
     /// let ptr: *mut u32 = s.as_mut_ptr();
@@ -539,8 +531,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements
     /// let mut data = [1u8, 2, 3, 4, 5];
@@ -660,8 +650,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let mut s = [1, 2, 3];
     /// let ptr: *mut u32 = s.as_mut_ptr();
@@ -904,7 +892,7 @@ impl<T: ?Sized> *mut T {
     /// This computes the same value that [`offset_from`](#method.offset_from)
     /// 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()`,
+    /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`,
     /// but it provides slightly more information to the optimizer, which can
     /// sometimes allow it to optimize slightly better with some backends.
     ///
@@ -1010,8 +998,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "123";
     /// let ptr: *const u8 = s.as_ptr();
@@ -1095,8 +1081,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let s: &str = "123";
     ///
@@ -1174,8 +1158,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements
     /// let data = [1u8, 2, 3, 4, 5];
@@ -1254,8 +1236,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// // Iterate using a raw pointer in increments of two elements (backwards)
     /// let data = [1u8, 2, 3, 4, 5];
@@ -1627,7 +1607,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
     /// ```
     /// #![feature(pointer_is_aligned)]
     /// #![feature(pointer_byte_offsets)]
@@ -1752,7 +1731,6 @@ impl<T: ?Sized> *mut T {
     ///
     /// # Examples
     ///
-    /// Basic usage:
     /// ```
     /// #![feature(pointer_is_aligned)]
     /// #![feature(pointer_byte_offsets)]
diff --git a/library/core/src/result.rs b/library/core/src/result.rs
index f00c40f35..208b220c2 100644
--- a/library/core/src/result.rs
+++ b/library/core/src/result.rs
@@ -458,7 +458,7 @@
 //! [`Result`] of a collection of each contained value of the original
 //! [`Result`] values, or [`Err`] if any of the elements was [`Err`].
 //!
-//! [impl-FromIterator]: Result#impl-FromIterator%3CResult%3CA%2C%20E%3E%3E-for-Result%3CV%2C%20E%3E
+//! [impl-FromIterator]: Result#impl-FromIterator%3CResult%3CA,+E%3E%3E-for-Result%3CV,+E%3E
 //!
 //! ```
 //! let v = [Ok(2), Ok(4), Err("err!"), Ok(8)];
@@ -474,8 +474,8 @@
 //! to provide the [`product`][Iterator::product] and
 //! [`sum`][Iterator::sum] methods.
 //!
-//! [impl-Product]: Result#impl-Product%3CResult%3CU%2C%20E%3E%3E-for-Result%3CT%2C%20E%3E
-//! [impl-Sum]: Result#impl-Sum%3CResult%3CU%2C%20E%3E%3E-for-Result%3CT%2C%20E%3E
+//! [impl-Product]: Result#impl-Product%3CResult%3CU,+E%3E%3E-for-Result%3CT,+E%3E
+//! [impl-Sum]: Result#impl-Sum%3CResult%3CU,+E%3E%3E-for-Result%3CT,+E%3E
 //!
 //! ```
 //! let v = [Err("error!"), Ok(1), Ok(2), Ok(3), Err("foo")];
@@ -525,8 +525,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<i32, &str> = Ok(-3);
     /// assert_eq!(x.is_ok(), true);
@@ -572,8 +570,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<i32, &str> = Ok(-3);
     /// assert_eq!(x.is_err(), false);
@@ -627,8 +623,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(2);
     /// assert_eq!(x.ok(), Some(2));
@@ -658,8 +652,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(2);
     /// assert_eq!(x.err(), None);
@@ -693,8 +685,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(2);
     /// assert_eq!(x.as_ref(), Ok(&2));
@@ -716,8 +706,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// fn mutate(r: &mut Result<i32, i32>) {
     ///     match r.as_mut() {
@@ -812,8 +800,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let k = 21;
     ///
@@ -841,8 +827,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// fn stringify(x: u32) -> String { format!("error code: {x}") }
     ///
@@ -968,8 +952,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(7);
     /// assert_eq!(x.iter().next(), Some(&7));
@@ -989,8 +971,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let mut x: Result<u32, &str> = Ok(7);
     /// match x.iter_mut().next() {
@@ -1031,8 +1011,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```should_panic
     /// let x: Result<u32, &str> = Err("emergency failure");
     /// x.expect("Testing expect"); // panics with `Testing expect: emergency failure`
@@ -1160,8 +1138,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```should_panic
     /// let x: Result<u32, &str> = Ok(10);
     /// x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`
@@ -1222,8 +1198,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// # #![feature(never_type)]
     /// # #![feature(unwrap_infallible)]
@@ -1259,8 +1233,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// # #![feature(never_type)]
     /// # #![feature(unwrap_infallible)]
@@ -1298,8 +1270,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(2);
     /// let y: Result<&str, &str> = Err("late error");
@@ -1383,8 +1353,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(2);
     /// let y: Result<u32, &str> = Err("late error");
@@ -1426,8 +1394,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// fn sq(x: u32) -> Result<u32, u32> { Ok(x * x) }
     /// fn err(x: u32) -> Result<u32, u32> { Err(x) }
@@ -1456,8 +1422,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let default = 2;
     /// let x: Result<u32, &str> = Ok(9);
@@ -1487,8 +1451,6 @@ impl<T, E> Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// fn count(x: &str) -> usize { x.len() }
     ///
@@ -1752,8 +1714,6 @@ impl<T, E> Result<Result<T, E>, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// #![feature(result_flattening)]
     /// let x: Result<Result<&'static str, u32>, u32> = Ok(Ok("hello"));
@@ -1842,8 +1802,6 @@ impl<T, E> IntoIterator for Result<T, E> {
     ///
     /// # Examples
     ///
-    /// Basic usage:
-    ///
     /// ```
     /// let x: Result<u32, &str> = Ok(5);
     /// let v: Vec<u32> = x.into_iter().collect();
diff --git a/library/core/src/slice/cmp.rs b/library/core/src/slice/cmp.rs
index 5e1b218e5..7601dd3c7 100644
--- a/library/core/src/slice/cmp.rs
+++ b/library/core/src/slice/cmp.rs
@@ -1,6 +1,6 @@
 //! Comparison traits for `[T]`.
 
-use crate::cmp::{self, Ordering};
+use crate::cmp::{self, BytewiseEq, Ordering};
 use crate::ffi;
 use crate::mem;
 
@@ -77,7 +77,7 @@ where
 // Use memcmp for bytewise equality when the types allow
 impl<A, B> SlicePartialEq<B> for [A]
 where
-    A: BytewiseEquality<B>,
+    A: BytewiseEq<B>,
 {
     fn equal(&self, other: &[B]) -> bool {
         if self.len() != other.len() {
@@ -203,29 +203,6 @@ impl SliceOrd for u8 {
     }
 }
 
-// Hack to allow specializing on `Eq` even though `Eq` has a method.
-#[rustc_unsafe_specialization_marker]
-trait MarkerEq<T>: PartialEq<T> {}
-
-impl<T: Eq> MarkerEq<T> for T {}
-
-#[doc(hidden)]
-/// Trait implemented for types that can be compared for equality using
-/// their bytewise representation
-#[rustc_specialization_trait]
-trait BytewiseEquality<T>: MarkerEq<T> + Copy {}
-
-macro_rules! impl_marker_for {
-    ($traitname:ident, $($ty:ty)*) => {
-        $(
-            impl $traitname<$ty> for $ty { }
-        )*
-    }
-}
-
-impl_marker_for!(BytewiseEquality,
-                 u8 i8 u16 i16 u32 i32 u64 i64 u128 i128 usize isize char bool);
-
 pub(super) trait SliceContains: Sized {
     fn slice_contains(&self, x: &[Self]) -> bool;
 }
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index 90ab43d12..c4317799b 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -7,7 +7,9 @@ use crate::cmp;
 use crate::cmp::Ordering;
 use crate::fmt;
 use crate::intrinsics::assume;
-use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use crate::iter::{
+    FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce, UncheckedIterator,
+};
 use crate::marker::{PhantomData, Send, Sized, Sync};
 use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
index 0fd57b197..89b92a7d5 100644
--- a/library/core/src/slice/iter/macros.rs
+++ b/library/core/src/slice/iter/macros.rs
@@ -384,6 +384,15 @@ macro_rules! iterator {
 
         #[unstable(feature = "trusted_len", issue = "37572")]
         unsafe impl<T> TrustedLen for $name<'_, T> {}
+
+        impl<'a, T> UncheckedIterator for $name<'a, T> {
+            unsafe fn next_unchecked(&mut self) -> $elem {
+                // SAFETY: The caller promised there's at least one more item.
+                unsafe {
+                    next_unchecked!(self)
+                }
+            }
+        }
     }
 }
 
diff --git a/library/core/src/slice/memchr.rs b/library/core/src/slice/memchr.rs
index c848c2e18..98c8349eb 100644
--- a/library/core/src/slice/memchr.rs
+++ b/library/core/src/slice/memchr.rs
@@ -16,25 +16,29 @@ const USIZE_BYTES: usize = mem::size_of::<usize>();
 /// bytes where the borrow propagated all the way to the most significant
 /// bit."
 #[inline]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 const fn contains_zero_byte(x: usize) -> bool {
     x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
 }
 
-#[cfg(target_pointer_width = "16")]
 #[inline]
+#[cfg(target_pointer_width = "16")]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 const fn repeat_byte(b: u8) -> usize {
     (b as usize) << 8 | b as usize
 }
 
-#[cfg(not(target_pointer_width = "16"))]
 #[inline]
+#[cfg(not(target_pointer_width = "16"))]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 const fn repeat_byte(b: u8) -> usize {
     (b as usize) * (usize::MAX / 255)
 }
 
 /// Returns the first index matching the byte `x` in `text`.
-#[must_use]
 #[inline]
+#[must_use]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 pub const fn memchr(x: u8, text: &[u8]) -> Option<usize> {
     // Fast path for small slices.
     if text.len() < 2 * USIZE_BYTES {
@@ -45,6 +49,7 @@ pub const fn memchr(x: u8, text: &[u8]) -> Option<usize> {
 }
 
 #[inline]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 const fn memchr_naive(x: u8, text: &[u8]) -> Option<usize> {
     let mut i = 0;
 
@@ -60,6 +65,10 @@ const fn memchr_naive(x: u8, text: &[u8]) -> Option<usize> {
     None
 }
 
+#[rustc_allow_const_fn_unstable(const_cmp)]
+#[rustc_allow_const_fn_unstable(const_slice_index)]
+#[rustc_allow_const_fn_unstable(const_align_offset)]
+#[rustc_const_stable(feature = "const_memchr", since = "1.65.0")]
 const fn memchr_aligned(x: u8, text: &[u8]) -> Option<usize> {
     // Scan for a single byte value by reading two `usize` words at a time.
     //
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index d93a3a57e..1cd86b445 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -805,8 +805,9 @@ impl<T> [T] {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[track_caller]
     pub fn windows(&self, size: usize) -> Windows<'_, T> {
-        let size = NonZeroUsize::new(size).expect("size is zero");
+        let size = NonZeroUsize::new(size).expect("window size must be non-zero");
         Windows::new(self, size)
     }
 
@@ -839,8 +840,9 @@ impl<T> [T] {
     /// [`rchunks`]: slice::rchunks
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[track_caller]
     pub fn chunks(&self, chunk_size: usize) -> Chunks<'_, T> {
-        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         Chunks::new(self, chunk_size)
     }
 
@@ -877,8 +879,9 @@ impl<T> [T] {
     /// [`rchunks_mut`]: slice::rchunks_mut
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[track_caller]
     pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
-        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         ChunksMut::new(self, chunk_size)
     }
 
@@ -914,8 +917,9 @@ impl<T> [T] {
     /// [`rchunks_exact`]: slice::rchunks_exact
     #[stable(feature = "chunks_exact", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn chunks_exact(&self, chunk_size: usize) -> ChunksExact<'_, T> {
-        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         ChunksExact::new(self, chunk_size)
     }
 
@@ -956,8 +960,9 @@ impl<T> [T] {
     /// [`rchunks_exact_mut`]: slice::rchunks_exact_mut
     #[stable(feature = "chunks_exact", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn chunks_exact_mut(&mut self, chunk_size: usize) -> ChunksExactMut<'_, T> {
-        assert_ne!(chunk_size, 0, "chunks cannot have a size of zero");
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         ChunksExactMut::new(self, chunk_size)
     }
 
@@ -1037,9 +1042,10 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_as_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     #[must_use]
     pub fn as_chunks<const N: usize>(&self) -> (&[[T; N]], &[T]) {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         let len = self.len() / N;
         let (multiple_of_n, remainder) = self.split_at(len * N);
         // SAFETY: We already panicked for zero, and ensured by construction
@@ -1068,9 +1074,10 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_as_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     #[must_use]
     pub fn as_rchunks<const N: usize>(&self) -> (&[T], &[[T; N]]) {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         let len = self.len() / N;
         let (remainder, multiple_of_n) = self.split_at(self.len() - len * N);
         // SAFETY: We already panicked for zero, and ensured by construction
@@ -1108,8 +1115,9 @@ impl<T> [T] {
     /// [`chunks_exact`]: slice::chunks_exact
     #[unstable(feature = "array_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     pub fn array_chunks<const N: usize>(&self) -> ArrayChunks<'_, T, N> {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         ArrayChunks::new(self)
     }
 
@@ -1186,9 +1194,10 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_as_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     #[must_use]
     pub fn as_chunks_mut<const N: usize>(&mut self) -> (&mut [[T; N]], &mut [T]) {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         let len = self.len() / N;
         let (multiple_of_n, remainder) = self.split_at_mut(len * N);
         // SAFETY: We already panicked for zero, and ensured by construction
@@ -1223,9 +1232,10 @@ impl<T> [T] {
     /// ```
     #[unstable(feature = "slice_as_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     #[must_use]
     pub fn as_rchunks_mut<const N: usize>(&mut self) -> (&mut [T], &mut [[T; N]]) {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         let len = self.len() / N;
         let (remainder, multiple_of_n) = self.split_at_mut(self.len() - len * N);
         // SAFETY: We already panicked for zero, and ensured by construction
@@ -1265,8 +1275,9 @@ impl<T> [T] {
     /// [`chunks_exact_mut`]: slice::chunks_exact_mut
     #[unstable(feature = "array_chunks", issue = "74985")]
     #[inline]
+    #[track_caller]
     pub fn array_chunks_mut<const N: usize>(&mut self) -> ArrayChunksMut<'_, T, N> {
-        assert_ne!(N, 0, "chunks cannot have a size of zero");
+        assert!(N != 0, "chunk size must be non-zero");
         ArrayChunksMut::new(self)
     }
 
@@ -1297,8 +1308,9 @@ impl<T> [T] {
     /// [`windows`]: slice::windows
     #[unstable(feature = "array_windows", issue = "75027")]
     #[inline]
+    #[track_caller]
     pub fn array_windows<const N: usize>(&self) -> ArrayWindows<'_, T, N> {
-        assert_ne!(N, 0, "windows cannot have a size of zero");
+        assert!(N != 0, "window size must be non-zero");
         ArrayWindows::new(self)
     }
 
@@ -1331,8 +1343,9 @@ impl<T> [T] {
     /// [`chunks`]: slice::chunks
     #[stable(feature = "rchunks", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn rchunks(&self, chunk_size: usize) -> RChunks<'_, T> {
-        assert!(chunk_size != 0);
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         RChunks::new(self, chunk_size)
     }
 
@@ -1369,8 +1382,9 @@ impl<T> [T] {
     /// [`chunks_mut`]: slice::chunks_mut
     #[stable(feature = "rchunks", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn rchunks_mut(&mut self, chunk_size: usize) -> RChunksMut<'_, T> {
-        assert!(chunk_size != 0);
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         RChunksMut::new(self, chunk_size)
     }
 
@@ -1408,8 +1422,9 @@ impl<T> [T] {
     /// [`chunks_exact`]: slice::chunks_exact
     #[stable(feature = "rchunks", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn rchunks_exact(&self, chunk_size: usize) -> RChunksExact<'_, T> {
-        assert!(chunk_size != 0);
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         RChunksExact::new(self, chunk_size)
     }
 
@@ -1451,8 +1466,9 @@ impl<T> [T] {
     /// [`chunks_exact_mut`]: slice::chunks_exact_mut
     #[stable(feature = "rchunks", since = "1.31.0")]
     #[inline]
+    #[track_caller]
     pub fn rchunks_exact_mut(&mut self, chunk_size: usize) -> RChunksExactMut<'_, T> {
-        assert!(chunk_size != 0);
+        assert!(chunk_size != 0, "chunk size must be non-zero");
         RChunksExactMut::new(self, chunk_size)
     }
 
@@ -2714,8 +2730,10 @@ impl<T> [T] {
     /// This reordering has the additional property that any value at position `i < index` will be
     /// 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 from the reordered slice:
+    /// (i.e. does not allocate), and *O*(*n*) on average. The worst-case performance is *O*(*n* log *n*).
+    /// This function is also known as "kth 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`.
@@ -2761,8 +2779,11 @@ impl<T> [T] {
     /// This reordering has the additional property that any value at position `i < index` will be
     /// 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 from
+    /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) on average.
+    /// The worst-case performance is *O*(*n* log *n*). This 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
@@ -2813,8 +2834,11 @@ impl<T> [T] {
     /// This reordering has the additional property that any value at position `i < index` will be
     /// 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 from
+    /// position `index`), in-place (i.e. does not allocate), and *O*(*n*) on average.
+    /// The worst-case performance is *O*(*n* log *n*).
+    /// This 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
@@ -2931,7 +2955,7 @@ impl<T> [T] {
         // This operation is still `O(n)`.
         //
         // Example: We start in this state, where `r` represents "next
-        // read" and `w` represents "next_write`.
+        // read" and `w` represents "next_write".
         //
         //           r
         //     +---+---+---+---+---+---+
diff --git a/library/core/src/slice/sort.rs b/library/core/src/slice/sort.rs
index 2181f9a81..2333f60a8 100644
--- a/library/core/src/slice/sort.rs
+++ b/library/core/src/slice/sort.rs
@@ -13,115 +13,184 @@ use crate::cmp;
 use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::ptr;
 
-/// When dropped, copies from `src` into `dest`.
-struct CopyOnDrop<T> {
+// When dropped, copies from `src` into `dest`.
+struct InsertionHole<T> {
     src: *const T,
     dest: *mut T,
 }
 
-impl<T> Drop for CopyOnDrop<T> {
+impl<T> Drop for InsertionHole<T> {
     fn drop(&mut self) {
-        // SAFETY: This is a helper class.
-        //         Please refer to its usage for correctness.
-        //         Namely, one must be sure that `src` and `dst` does not overlap as required by `ptr::copy_nonoverlapping`.
+        // SAFETY: This is a helper class. Please refer to its usage for correctness. Namely, one
+        // must be sure that `src` and `dst` does not overlap as required by
+        // `ptr::copy_nonoverlapping` and are both valid for writes.
         unsafe {
             ptr::copy_nonoverlapping(self.src, self.dest, 1);
         }
     }
 }
 
-/// Shifts the first element to the right until it encounters a greater or equal element.
-fn shift_head<T, F>(v: &mut [T], is_less: &mut F)
+/// Inserts `v[v.len() - 1]` into pre-sorted sequence `v[..v.len() - 1]` so that whole `v[..]`
+/// becomes sorted.
+unsafe fn insert_tail<T, F>(v: &mut [T], is_less: &mut F)
 where
     F: FnMut(&T, &T) -> bool,
 {
-    let len = v.len();
-    // SAFETY: The unsafe operations below involves indexing without a bounds check (by offsetting a
-    // pointer) and copying memory (`ptr::copy_nonoverlapping`).
-    //
-    // a. Indexing:
-    //  1. We checked the size of the array to >=2.
-    //  2. All the indexing that we will do is always between {0 <= index < len} at most.
-    //
-    // b. Memory copying
-    //  1. We are obtaining pointers to references which are guaranteed to be valid.
-    //  2. They cannot overlap because we obtain pointers to difference indices of the slice.
-    //     Namely, `i` and `i-1`.
-    //  3. If the slice is properly aligned, the elements are properly aligned.
-    //     It is the caller's responsibility to make sure the slice is properly aligned.
-    //
-    // See comments below for further detail.
+    debug_assert!(v.len() >= 2);
+
+    let arr_ptr = v.as_mut_ptr();
+    let i = v.len() - 1;
+
+    // SAFETY: caller must ensure v is at least len 2.
     unsafe {
-        // If the first two elements are out-of-order...
-        if len >= 2 && is_less(v.get_unchecked(1), v.get_unchecked(0)) {
-            // Read the first element into a stack-allocated variable. If a following comparison
-            // operation panics, `hole` will get dropped and automatically write the element back
-            // into the slice.
-            let tmp = mem::ManuallyDrop::new(ptr::read(v.get_unchecked(0)));
-            let v = v.as_mut_ptr();
-            let mut hole = CopyOnDrop { src: &*tmp, dest: v.add(1) };
-            ptr::copy_nonoverlapping(v.add(1), v.add(0), 1);
-
-            for i in 2..len {
-                if !is_less(&*v.add(i), &*tmp) {
+        // See insert_head which talks about why this approach is beneficial.
+        let i_ptr = arr_ptr.add(i);
+
+        // It's important that we use i_ptr here. If this check is positive and we continue,
+        // We want to make sure that no other copy of the value was seen by is_less.
+        // Otherwise we would have to copy it back.
+        if is_less(&*i_ptr, &*i_ptr.sub(1)) {
+            // It's important, that we use tmp for comparison from now on. As it is the value that
+            // will be copied back. And notionally we could have created a divergence if we copy
+            // back the wrong value.
+            let tmp = mem::ManuallyDrop::new(ptr::read(i_ptr));
+            // Intermediate state of the insertion process is always tracked by `hole`, which
+            // serves two purposes:
+            // 1. Protects integrity of `v` from panics in `is_less`.
+            // 2. Fills the remaining hole in `v` in the end.
+            //
+            // Panic safety:
+            //
+            // If `is_less` panics at any point during the process, `hole` will get dropped and
+            // fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
+            // initially held exactly once.
+            let mut hole = InsertionHole { src: &*tmp, dest: i_ptr.sub(1) };
+            ptr::copy_nonoverlapping(hole.dest, i_ptr, 1);
+
+            // SAFETY: We know i is at least 1.
+            for j in (0..(i - 1)).rev() {
+                let j_ptr = arr_ptr.add(j);
+                if !is_less(&*tmp, &*j_ptr) {
                     break;
                 }
 
-                // Move `i`-th element one place to the left, thus shifting the hole to the right.
-                ptr::copy_nonoverlapping(v.add(i), v.add(i - 1), 1);
-                hole.dest = v.add(i);
+                ptr::copy_nonoverlapping(j_ptr, hole.dest, 1);
+                hole.dest = j_ptr;
             }
             // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
         }
     }
 }
 
-/// Shifts the last element to the left until it encounters a smaller or equal element.
-fn shift_tail<T, F>(v: &mut [T], is_less: &mut F)
+/// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted.
+///
+/// This is the integral subroutine of insertion sort.
+unsafe fn insert_head<T, F>(v: &mut [T], is_less: &mut F)
 where
     F: FnMut(&T, &T) -> bool,
 {
-    let len = v.len();
-    // SAFETY: The unsafe operations below involves indexing without a bound check (by offsetting a
-    // pointer) and copying memory (`ptr::copy_nonoverlapping`).
-    //
-    // a. Indexing:
-    //  1. We checked the size of the array to >= 2.
-    //  2. All the indexing that we will do is always between `0 <= index < len-1` at most.
-    //
-    // b. Memory copying
-    //  1. We are obtaining pointers to references which are guaranteed to be valid.
-    //  2. They cannot overlap because we obtain pointers to difference indices of the slice.
-    //     Namely, `i` and `i+1`.
-    //  3. If the slice is properly aligned, the elements are properly aligned.
-    //     It is the caller's responsibility to make sure the slice is properly aligned.
-    //
-    // See comments below for further detail.
+    debug_assert!(v.len() >= 2);
+
+    // SAFETY: caller must ensure v is at least len 2.
     unsafe {
-        // If the last two elements are out-of-order...
-        if len >= 2 && is_less(v.get_unchecked(len - 1), v.get_unchecked(len - 2)) {
-            // Read the last element into a stack-allocated variable. If a following comparison
-            // operation panics, `hole` will get dropped and automatically write the element back
-            // into the slice.
-            let tmp = mem::ManuallyDrop::new(ptr::read(v.get_unchecked(len - 1)));
-            let v = v.as_mut_ptr();
-            let mut hole = CopyOnDrop { src: &*tmp, dest: v.add(len - 2) };
-            ptr::copy_nonoverlapping(v.add(len - 2), v.add(len - 1), 1);
-
-            for i in (0..len - 2).rev() {
-                if !is_less(&*tmp, &*v.add(i)) {
+        if is_less(v.get_unchecked(1), v.get_unchecked(0)) {
+            let arr_ptr = v.as_mut_ptr();
+
+            // There are three ways to implement insertion here:
+            //
+            // 1. Swap adjacent elements until the first one gets to its final destination.
+            //    However, this way we copy data around more than is necessary. If elements are big
+            //    structures (costly to copy), this method will be slow.
+            //
+            // 2. Iterate until the right place for the first element is found. Then shift the
+            //    elements succeeding it to make room for it and finally place it into the
+            //    remaining hole. This is a good method.
+            //
+            // 3. Copy the first element into a temporary variable. Iterate until the right place
+            //    for it is found. As we go along, copy every traversed element into the slot
+            //    preceding it. Finally, copy data from the temporary variable into the remaining
+            //    hole. This method is very good. Benchmarks demonstrated slightly better
+            //    performance than with the 2nd method.
+            //
+            // All methods were benchmarked, and the 3rd showed best results. So we chose that one.
+            let tmp = mem::ManuallyDrop::new(ptr::read(arr_ptr));
+
+            // Intermediate state of the insertion process is always tracked by `hole`, which
+            // serves two purposes:
+            // 1. Protects integrity of `v` from panics in `is_less`.
+            // 2. Fills the remaining hole in `v` in the end.
+            //
+            // Panic safety:
+            //
+            // If `is_less` panics at any point during the process, `hole` will get dropped and
+            // fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
+            // initially held exactly once.
+            let mut hole = InsertionHole { src: &*tmp, dest: arr_ptr.add(1) };
+            ptr::copy_nonoverlapping(arr_ptr.add(1), arr_ptr.add(0), 1);
+
+            for i in 2..v.len() {
+                if !is_less(&v.get_unchecked(i), &*tmp) {
                     break;
                 }
-
-                // Move `i`-th element one place to the right, thus shifting the hole to the left.
-                ptr::copy_nonoverlapping(v.add(i), v.add(i + 1), 1);
-                hole.dest = v.add(i);
+                ptr::copy_nonoverlapping(arr_ptr.add(i), arr_ptr.add(i - 1), 1);
+                hole.dest = arr_ptr.add(i);
             }
             // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
         }
     }
 }
 
+/// Sort `v` assuming `v[..offset]` is already sorted.
+///
+/// Never inline this function to avoid code bloat. It still optimizes nicely and has practically no
+/// performance impact. Even improving performance in some cases.
+#[inline(never)]
+fn insertion_sort_shift_left<T, F>(v: &mut [T], offset: usize, is_less: &mut F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+
+    // Using assert here improves performance.
+    assert!(offset != 0 && offset <= len);
+
+    // Shift each element of the unsorted region v[i..] as far left as is needed to make v sorted.
+    for i in offset..len {
+        // SAFETY: we tested that `offset` must be at least 1, so this loop is only entered if len
+        // >= 2. The range is exclusive and we know `i` must be at least 1 so this slice has at
+        // >least len 2.
+        unsafe {
+            insert_tail(&mut v[..=i], is_less);
+        }
+    }
+}
+
+/// Sort `v` assuming `v[offset..]` is already sorted.
+///
+/// Never inline this function to avoid code bloat. It still optimizes nicely and has practically no
+/// performance impact. Even improving performance in some cases.
+#[inline(never)]
+fn insertion_sort_shift_right<T, F>(v: &mut [T], offset: usize, is_less: &mut F)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+
+    // Using assert here improves performance.
+    assert!(offset != 0 && offset <= len && len >= 2);
+
+    // Shift each element of the unsorted region v[..i] as far left as is needed to make v sorted.
+    for i in (0..offset).rev() {
+        // SAFETY: we tested that `offset` must be at least 1, so this loop is only entered if len
+        // >= 2.We ensured that the slice length is always at least 2 long. We know that start_found
+        // will be at least one less than end, and the range is exclusive. Which gives us i always
+        // <= (end - 2).
+        unsafe {
+            insert_head(&mut v[i..len], is_less);
+        }
+    }
+}
+
 /// Partially sorts a slice by shifting several out-of-order elements around.
 ///
 /// Returns `true` if the slice is sorted at the end. This function is *O*(*n*) worst-case.
@@ -161,26 +230,19 @@ where
         // Swap the found pair of elements. This puts them in correct order.
         v.swap(i - 1, i);
 
-        // Shift the smaller element to the left.
-        shift_tail(&mut v[..i], is_less);
-        // Shift the greater element to the right.
-        shift_head(&mut v[i..], is_less);
+        if i >= 2 {
+            // Shift the smaller element to the left.
+            insertion_sort_shift_left(&mut v[..i], i - 1, is_less);
+
+            // Shift the greater element to the right.
+            insertion_sort_shift_right(&mut v[..i], 1, is_less);
+        }
     }
 
     // Didn't manage to sort the slice in the limited number of steps.
     false
 }
 
-/// Sorts a slice using insertion sort, which is *O*(*n*^2) worst-case.
-fn insertion_sort<T, F>(v: &mut [T], is_less: &mut F)
-where
-    F: FnMut(&T, &T) -> bool,
-{
-    for i in 1..v.len() {
-        shift_tail(&mut v[..i + 1], is_less);
-    }
-}
-
 /// Sorts `v` using heapsort, which guarantees *O*(*n* \* log(*n*)) worst-case.
 #[cold]
 #[unstable(feature = "sort_internals", reason = "internal to sort module", issue = "none")]
@@ -198,8 +260,11 @@ where
             }
 
             // Choose the greater child.
-            if child + 1 < v.len() && is_less(&v[child], &v[child + 1]) {
-                child += 1;
+            if child + 1 < v.len() {
+                // We need a branch to be sure not to out-of-bounds index,
+                // but it's highly predictable.  The comparison, however,
+                // is better done branchless, especially for primitives.
+                child += is_less(&v[child], &v[child + 1]) as usize;
             }
 
             // Stop if the invariant holds at `node`.
@@ -252,7 +317,7 @@ where
     // 1. `block` - Number of elements in the block.
     // 2. `start` - Start pointer into the `offsets` array.
     // 3. `end` - End pointer into the `offsets` array.
-    // 4. `offsets - Indices of out-of-order elements within the block.
+    // 4. `offsets` - Indices of out-of-order elements within the block.
 
     // The current block on the left side (from `l` to `l.add(block_l)`).
     let mut l = v.as_mut_ptr();
@@ -262,7 +327,7 @@ where
     let mut offsets_l = [MaybeUninit::<u8>::uninit(); BLOCK];
 
     // The current block on the right side (from `r.sub(block_r)` to `r`).
-    // SAFETY: The documentation for .add() specifically mention that `vec.as_ptr().add(vec.len())` is always safe`
+    // SAFETY: The documentation for .add() specifically mention that `vec.as_ptr().add(vec.len())` is always safe
     let mut r = unsafe { l.add(v.len()) };
     let mut block_r = BLOCK;
     let mut start_r = ptr::null_mut();
@@ -507,7 +572,7 @@ where
 
         // SAFETY: `pivot` is a reference to the first element of `v`, so `ptr::read` is safe.
         let tmp = mem::ManuallyDrop::new(unsafe { ptr::read(pivot) });
-        let _pivot_guard = CopyOnDrop { src: &*tmp, dest: pivot };
+        let _pivot_guard = InsertionHole { src: &*tmp, dest: pivot };
         let pivot = &*tmp;
 
         // Find the first pair of out-of-order elements.
@@ -560,7 +625,7 @@ where
     // operation panics, the pivot will be automatically written back into the slice.
     // SAFETY: The pointer here is valid because it is obtained from a reference to a slice.
     let tmp = mem::ManuallyDrop::new(unsafe { ptr::read(pivot) });
-    let _pivot_guard = CopyOnDrop { src: &*tmp, dest: pivot };
+    let _pivot_guard = InsertionHole { src: &*tmp, dest: pivot };
     let pivot = &*tmp;
 
     // Now partition the slice.
@@ -608,19 +673,23 @@ where
 fn break_patterns<T>(v: &mut [T]) {
     let len = v.len();
     if len >= 8 {
-        // Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
-        let mut random = len as u32;
-        let mut gen_u32 = || {
-            random ^= random << 13;
-            random ^= random >> 17;
-            random ^= random << 5;
-            random
-        };
+        let mut seed = len;
         let mut gen_usize = || {
+            // Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
             if usize::BITS <= 32 {
-                gen_u32() as usize
+                let mut r = seed as u32;
+                r ^= r << 13;
+                r ^= r >> 17;
+                r ^= r << 5;
+                seed = r as usize;
+                seed
             } else {
-                (((gen_u32() as u64) << 32) | (gen_u32() as u64)) as usize
+                let mut r = seed as u64;
+                r ^= r << 13;
+                r ^= r >> 7;
+                r ^= r << 17;
+                seed = r as usize;
+                seed
             }
         };
 
@@ -742,7 +811,9 @@ where
 
         // Very short slices get sorted using insertion sort.
         if len <= MAX_INSERTION {
-            insertion_sort(v, is_less);
+            if len >= 2 {
+                insertion_sort_shift_left(v, 1, is_less);
+            }
             return;
         }
 
@@ -844,10 +915,14 @@ fn partition_at_index_loop<'a, T, F>(
     let mut was_balanced = true;
 
     loop {
+        let len = v.len();
+
         // For slices of up to this length it's probably faster to simply sort them.
         const MAX_INSERTION: usize = 10;
-        if v.len() <= MAX_INSERTION {
-            insertion_sort(v, is_less);
+        if len <= MAX_INSERTION {
+            if len >= 2 {
+                insertion_sort_shift_left(v, 1, is_less);
+            }
             return;
         }
 
@@ -887,7 +962,7 @@ fn partition_at_index_loop<'a, T, F>(
         }
 
         let (mid, _) = partition(v, pivot, is_less);
-        was_balanced = cmp::min(mid, v.len() - mid) >= v.len() / 8;
+        was_balanced = cmp::min(mid, len - mid) >= len / 8;
 
         // Split the slice into `left`, `pivot`, and `right`.
         let (left, right) = v.split_at_mut(mid);
@@ -954,75 +1029,6 @@ where
     (left, pivot, right)
 }
 
-/// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted.
-///
-/// This is the integral subroutine of insertion sort.
-fn insert_head<T, F>(v: &mut [T], is_less: &mut F)
-where
-    F: FnMut(&T, &T) -> bool,
-{
-    if v.len() >= 2 && is_less(&v[1], &v[0]) {
-        // SAFETY: Copy tmp back even if panic, and ensure unique observation.
-        unsafe {
-            // There are three ways to implement insertion here:
-            //
-            // 1. Swap adjacent elements until the first one gets to its final destination.
-            //    However, this way we copy data around more than is necessary. If elements are big
-            //    structures (costly to copy), this method will be slow.
-            //
-            // 2. Iterate until the right place for the first element is found. Then shift the
-            //    elements succeeding it to make room for it and finally place it into the
-            //    remaining hole. This is a good method.
-            //
-            // 3. Copy the first element into a temporary variable. Iterate until the right place
-            //    for it is found. As we go along, copy every traversed element into the slot
-            //    preceding it. Finally, copy data from the temporary variable into the remaining
-            //    hole. This method is very good. Benchmarks demonstrated slightly better
-            //    performance than with the 2nd method.
-            //
-            // All methods were benchmarked, and the 3rd showed best results. So we chose that one.
-            let tmp = mem::ManuallyDrop::new(ptr::read(&v[0]));
-
-            // Intermediate state of the insertion process is always tracked by `hole`, which
-            // serves two purposes:
-            // 1. Protects integrity of `v` from panics in `is_less`.
-            // 2. Fills the remaining hole in `v` in the end.
-            //
-            // Panic safety:
-            //
-            // If `is_less` panics at any point during the process, `hole` will get dropped and
-            // fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
-            // initially held exactly once.
-            let mut hole = InsertionHole { src: &*tmp, dest: &mut v[1] };
-            ptr::copy_nonoverlapping(&v[1], &mut v[0], 1);
-
-            for i in 2..v.len() {
-                if !is_less(&v[i], &*tmp) {
-                    break;
-                }
-                ptr::copy_nonoverlapping(&v[i], &mut v[i - 1], 1);
-                hole.dest = &mut v[i];
-            }
-            // `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
-        }
-    }
-
-    // When dropped, copies from `src` into `dest`.
-    struct InsertionHole<T> {
-        src: *const T,
-        dest: *mut T,
-    }
-
-    impl<T> Drop for InsertionHole<T> {
-        fn drop(&mut self) {
-            // SAFETY: The caller must ensure that src and dest are correctly set.
-            unsafe {
-                ptr::copy_nonoverlapping(self.src, self.dest, 1);
-            }
-        }
-    }
-}
-
 /// Merges non-decreasing runs `v[..mid]` and `v[mid..]` using `buf` as temporary storage, and
 /// stores the result into `v[..]`.
 ///
@@ -1180,8 +1186,6 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
 {
     // Slices of up to this length get sorted using insertion sort.
     const MAX_INSERTION: usize = 20;
-    // Very short runs are extended using insertion sort to span at least this many elements.
-    const MIN_RUN: usize = 10;
 
     // The caller should have already checked that.
     debug_assert!(!T::IS_ZST);
@@ -1191,9 +1195,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
     // Short arrays get sorted in-place via insertion sort to avoid allocations.
     if len <= MAX_INSERTION {
         if len >= 2 {
-            for i in (0..len - 1).rev() {
-                insert_head(&mut v[i..], is_less);
-            }
+            insertion_sort_shift_left(v, 1, is_less);
         }
         return;
     }
@@ -1203,59 +1205,43 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
     // `is_less` panics. When merging two sorted runs, this buffer holds a copy of the shorter run,
     // which will always have length at most `len / 2`.
     let buf = BufGuard::new(len / 2, elem_alloc_fn, elem_dealloc_fn);
-    let buf_ptr = buf.buf_ptr;
+    let buf_ptr = buf.buf_ptr.as_ptr();
 
     let mut runs = RunVec::new(run_alloc_fn, run_dealloc_fn);
 
-    // In order to identify natural runs in `v`, we traverse it backwards. That might seem like a
-    // strange decision, but consider the fact that merges more often go in the opposite direction
-    // (forwards). According to benchmarks, merging forwards is slightly faster than merging
-    // backwards. To conclude, identifying runs by traversing backwards improves performance.
-    let mut end = len;
-    while end > 0 {
-        // Find the next natural run, and reverse it if it's strictly descending.
-        let mut start = end - 1;
-        if start > 0 {
-            start -= 1;
-
-            // SAFETY: The v.get_unchecked must be fed with correct inbound indicies.
-            unsafe {
-                if is_less(v.get_unchecked(start + 1), v.get_unchecked(start)) {
-                    while start > 0 && is_less(v.get_unchecked(start), v.get_unchecked(start - 1)) {
-                        start -= 1;
-                    }
-                    v[start..end].reverse();
-                } else {
-                    while start > 0 && !is_less(v.get_unchecked(start), v.get_unchecked(start - 1))
-                    {
-                        start -= 1;
-                    }
-                }
-            }
+    let mut end = 0;
+    let mut start = 0;
+
+    // Scan forward. Memory pre-fetching prefers forward scanning vs backwards scanning, and the
+    // code-gen is usually better. For the most sensitive types such as integers, these are merged
+    // bidirectionally at once. So there is no benefit in scanning backwards.
+    while end < len {
+        let (streak_end, was_reversed) = find_streak(&v[start..], is_less);
+        end += streak_end;
+        if was_reversed {
+            v[start..end].reverse();
         }
 
         // Insert some more elements into the run if it's too short. Insertion sort is faster than
         // merge sort on short sequences, so this significantly improves performance.
-        while start > 0 && end - start < MIN_RUN {
-            start -= 1;
-            insert_head(&mut v[start..end], is_less);
-        }
+        end = provide_sorted_batch(v, start, end, is_less);
 
         // Push this run onto the stack.
         runs.push(TimSortRun { start, len: end - start });
-        end = start;
+        start = end;
 
         // Merge some pairs of adjacent runs to satisfy the invariants.
-        while let Some(r) = collapse(runs.as_slice()) {
-            let left = runs[r + 1];
-            let right = runs[r];
+        while let Some(r) = collapse(runs.as_slice(), len) {
+            let left = runs[r];
+            let right = runs[r + 1];
+            let merge_slice = &mut v[left.start..right.start + right.len];
             // SAFETY: `buf_ptr` must hold enough capacity for the shorter of the two sides, and
             // neither side may be on length 0.
             unsafe {
-                merge(&mut v[left.start..right.start + right.len], left.len, buf_ptr, is_less);
+                merge(merge_slice, left.len, buf_ptr, is_less);
             }
-            runs[r] = TimSortRun { start: left.start, len: left.len + right.len };
-            runs.remove(r + 1);
+            runs[r + 1] = TimSortRun { start: left.start, len: left.len + right.len };
+            runs.remove(r);
         }
     }
 
@@ -1277,10 +1263,10 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
     // run starts at index 0, it will always demand a merge operation until the stack is fully
     // collapsed, in order to complete the sort.
     #[inline]
-    fn collapse(runs: &[TimSortRun]) -> Option<usize> {
+    fn collapse(runs: &[TimSortRun], stop: usize) -> Option<usize> {
         let n = runs.len();
         if n >= 2
-            && (runs[n - 1].start == 0
+            && (runs[n - 1].start + runs[n - 1].len == stop
                 || runs[n - 2].len <= runs[n - 1].len
                 || (n >= 3 && runs[n - 3].len <= runs[n - 2].len + runs[n - 1].len)
                 || (n >= 4 && runs[n - 4].len <= runs[n - 3].len + runs[n - 2].len))
@@ -1298,7 +1284,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
     where
         ElemDeallocF: Fn(*mut T, usize),
     {
-        buf_ptr: *mut T,
+        buf_ptr: ptr::NonNull<T>,
         capacity: usize,
         elem_dealloc_fn: ElemDeallocF,
     }
@@ -1315,7 +1301,11 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
         where
             ElemAllocF: Fn(usize) -> *mut T,
         {
-            Self { buf_ptr: elem_alloc_fn(len), capacity: len, elem_dealloc_fn }
+            Self {
+                buf_ptr: ptr::NonNull::new(elem_alloc_fn(len)).unwrap(),
+                capacity: len,
+                elem_dealloc_fn,
+            }
         }
     }
 
@@ -1324,7 +1314,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
         ElemDeallocF: Fn(*mut T, usize),
     {
         fn drop(&mut self) {
-            (self.elem_dealloc_fn)(self.buf_ptr, self.capacity);
+            (self.elem_dealloc_fn)(self.buf_ptr.as_ptr(), self.capacity);
         }
     }
 
@@ -1333,7 +1323,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
         RunAllocF: Fn(usize) -> *mut TimSortRun,
         RunDeallocF: Fn(*mut TimSortRun, usize),
     {
-        buf_ptr: *mut TimSortRun,
+        buf_ptr: ptr::NonNull<TimSortRun>,
         capacity: usize,
         len: usize,
         run_alloc_fn: RunAllocF,
@@ -1350,7 +1340,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
             const START_RUN_CAPACITY: usize = 16;
 
             Self {
-                buf_ptr: run_alloc_fn(START_RUN_CAPACITY),
+                buf_ptr: ptr::NonNull::new(run_alloc_fn(START_RUN_CAPACITY)).unwrap(),
                 capacity: START_RUN_CAPACITY,
                 len: 0,
                 run_alloc_fn,
@@ -1361,15 +1351,15 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
         fn push(&mut self, val: TimSortRun) {
             if self.len == self.capacity {
                 let old_capacity = self.capacity;
-                let old_buf_ptr = self.buf_ptr;
+                let old_buf_ptr = self.buf_ptr.as_ptr();
 
                 self.capacity = self.capacity * 2;
-                self.buf_ptr = (self.run_alloc_fn)(self.capacity);
+                self.buf_ptr = ptr::NonNull::new((self.run_alloc_fn)(self.capacity)).unwrap();
 
                 // SAFETY: buf_ptr new and old were correctly allocated and old_buf_ptr has
                 // old_capacity valid elements.
                 unsafe {
-                    ptr::copy_nonoverlapping(old_buf_ptr, self.buf_ptr, old_capacity);
+                    ptr::copy_nonoverlapping(old_buf_ptr, self.buf_ptr.as_ptr(), old_capacity);
                 }
 
                 (self.run_dealloc_fn)(old_buf_ptr, old_capacity);
@@ -1377,7 +1367,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
 
             // SAFETY: The invariant was just checked.
             unsafe {
-                self.buf_ptr.add(self.len).write(val);
+                self.buf_ptr.as_ptr().add(self.len).write(val);
             }
             self.len += 1;
         }
@@ -1390,7 +1380,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
             // SAFETY: buf_ptr needs to be valid and len invariant upheld.
             unsafe {
                 // the place we are taking from.
-                let ptr = self.buf_ptr.add(index);
+                let ptr = self.buf_ptr.as_ptr().add(index);
 
                 // Shift everything down to fill in that spot.
                 ptr::copy(ptr.add(1), ptr, self.len - index - 1);
@@ -1400,7 +1390,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
 
         fn as_slice(&self) -> &[TimSortRun] {
             // SAFETY: Safe as long as buf_ptr is valid and len invariant was upheld.
-            unsafe { &*ptr::slice_from_raw_parts(self.buf_ptr, self.len) }
+            unsafe { &*ptr::slice_from_raw_parts(self.buf_ptr.as_ptr(), self.len) }
         }
 
         fn len(&self) -> usize {
@@ -1419,7 +1409,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
             if index < self.len {
                 // SAFETY: buf_ptr and len invariant must be upheld.
                 unsafe {
-                    return &*(self.buf_ptr.add(index));
+                    return &*(self.buf_ptr.as_ptr().add(index));
                 }
             }
 
@@ -1436,7 +1426,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
             if index < self.len {
                 // SAFETY: buf_ptr and len invariant must be upheld.
                 unsafe {
-                    return &mut *(self.buf_ptr.add(index));
+                    return &mut *(self.buf_ptr.as_ptr().add(index));
                 }
             }
 
@@ -1452,7 +1442,7 @@ pub fn merge_sort<T, CmpF, ElemAllocF, ElemDeallocF, RunAllocF, RunDeallocF>(
         fn drop(&mut self) {
             // As long as TimSortRun is Copy we don't need to drop them individually but just the
             // whole allocation.
-            (self.run_dealloc_fn)(self.buf_ptr, self.capacity);
+            (self.run_dealloc_fn)(self.buf_ptr.as_ptr(), self.capacity);
         }
     }
 }
@@ -1463,3 +1453,71 @@ pub struct TimSortRun {
     len: usize,
     start: usize,
 }
+
+/// Takes a range as denoted by start and end, that is already sorted and extends it to the right if
+/// necessary with sorts optimized for smaller ranges such as insertion sort.
+#[cfg(not(no_global_oom_handling))]
+fn provide_sorted_batch<T, F>(v: &mut [T], start: usize, mut end: usize, is_less: &mut F) -> usize
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+    assert!(end >= start && end <= len);
+
+    // This value is a balance between least comparisons and best performance, as
+    // influenced by for example cache locality.
+    const MIN_INSERTION_RUN: usize = 10;
+
+    // Insert some more elements into the run if it's too short. Insertion sort is faster than
+    // merge sort on short sequences, so this significantly improves performance.
+    let start_end_diff = end - start;
+
+    if start_end_diff < MIN_INSERTION_RUN && end < len {
+        // v[start_found..end] are elements that are already sorted in the input. We want to extend
+        // the sorted region to the left, so we push up MIN_INSERTION_RUN - 1 to the right. Which is
+        // more efficient that trying to push those already sorted elements to the left.
+        end = cmp::min(start + MIN_INSERTION_RUN, len);
+        let presorted_start = cmp::max(start_end_diff, 1);
+
+        insertion_sort_shift_left(&mut v[start..end], presorted_start, is_less);
+    }
+
+    end
+}
+
+/// Finds a streak of presorted elements starting at the beginning of the slice. Returns the first
+/// value that is not part of said streak, and a bool denoting wether the streak was reversed.
+/// Streaks can be increasing or decreasing.
+fn find_streak<T, F>(v: &[T], is_less: &mut F) -> (usize, bool)
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    let len = v.len();
+
+    if len < 2 {
+        return (len, false);
+    }
+
+    let mut end = 2;
+
+    // SAFETY: See below specific.
+    unsafe {
+        // SAFETY: We checked that len >= 2, so 0 and 1 are valid indices.
+        let assume_reverse = is_less(v.get_unchecked(1), v.get_unchecked(0));
+
+        // SAFETY: We know end >= 2 and check end < len.
+        // From that follows that accessing v at end and end - 1 is safe.
+        if assume_reverse {
+            while end < len && is_less(v.get_unchecked(end), v.get_unchecked(end - 1)) {
+                end += 1;
+            }
+
+            (end, true)
+        } else {
+            while end < len && !is_less(v.get_unchecked(end), v.get_unchecked(end - 1)) {
+                end += 1;
+            }
+            (end, false)
+        }
+    }
+}
diff --git a/library/core/src/str/iter.rs b/library/core/src/str/iter.rs
index d969475aa..95c682f42 100644
--- a/library/core/src/str/iter.rs
+++ b/library/core/src/str/iter.rs
@@ -1,6 +1,6 @@
 //! Iterators for `str` methods.
 
-use crate::char;
+use crate::char as char_mod;
 use crate::fmt::{self, Write};
 use crate::iter::{Chain, FlatMap, Flatten};
 use crate::iter::{Copied, Filter, FusedIterator, Map, TrustedLen};
@@ -1455,8 +1455,8 @@ impl FusedIterator for EncodeUtf16<'_> {}
 #[derive(Clone, Debug)]
 pub struct EscapeDebug<'a> {
     pub(super) inner: Chain<
-        Flatten<option::IntoIter<char::EscapeDebug>>,
-        FlatMap<Chars<'a>, char::EscapeDebug, CharEscapeDebugContinue>,
+        Flatten<option::IntoIter<char_mod::EscapeDebug>>,
+        FlatMap<Chars<'a>, char_mod::EscapeDebug, CharEscapeDebugContinue>,
     >,
 }
 
@@ -1464,14 +1464,14 @@ pub struct EscapeDebug<'a> {
 #[stable(feature = "str_escape", since = "1.34.0")]
 #[derive(Clone, Debug)]
 pub struct EscapeDefault<'a> {
-    pub(super) inner: FlatMap<Chars<'a>, char::EscapeDefault, CharEscapeDefault>,
+    pub(super) inner: FlatMap<Chars<'a>, char_mod::EscapeDefault, CharEscapeDefault>,
 }
 
 /// The return type of [`str::escape_unicode`].
 #[stable(feature = "str_escape", since = "1.34.0")]
 #[derive(Clone, Debug)]
 pub struct EscapeUnicode<'a> {
-    pub(super) inner: FlatMap<Chars<'a>, char::EscapeUnicode, CharEscapeUnicode>,
+    pub(super) inner: FlatMap<Chars<'a>, char_mod::EscapeUnicode, CharEscapeUnicode>,
 }
 
 macro_rules! escape_types_impls {
diff --git a/library/core/src/str/traits.rs b/library/core/src/str/traits.rs
index d3ed811b1..68f62ce8b 100644
--- a/library/core/src/str/traits.rs
+++ b/library/core/src/str/traits.rs
@@ -28,10 +28,6 @@ impl PartialEq for str {
     fn eq(&self, other: &str) -> bool {
         self.as_bytes() == other.as_bytes()
     }
-    #[inline]
-    fn ne(&self, other: &str) -> bool {
-        !(*self).eq(other)
-    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/core/src/sync/atomic.rs b/library/core/src/sync/atomic.rs
index 14367eb09..040a59184 100644
--- a/library/core/src/sync/atomic.rs
+++ b/library/core/src/sync/atomic.rs
@@ -305,6 +305,50 @@ impl AtomicBool {
         AtomicBool { v: UnsafeCell::new(v as u8) }
     }
 
+    /// Creates a new `AtomicBool` from a pointer.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(atomic_from_ptr, pointer_is_aligned)]
+    /// use std::sync::atomic::{self, AtomicBool};
+    /// use std::mem::align_of;
+    ///
+    /// // Get a pointer to an allocated value
+    /// let ptr: *mut bool = Box::into_raw(Box::new(false));
+    ///
+    /// assert!(ptr.is_aligned_to(align_of::<AtomicBool>()));
+    ///
+    /// {
+    ///     // Create an atomic view of the allocated value
+    ///     let atomic = unsafe { AtomicBool::from_ptr(ptr) };
+    ///
+    ///     // Use `atomic` for atomic operations, possibly share it with other threads
+    ///     atomic.store(true, atomic::Ordering::Relaxed);
+    /// }
+    ///
+    /// // It's ok to non-atomically access the value behind `ptr`,
+    /// // since the reference to the atomic ended its lifetime in the block above
+    /// assert_eq!(unsafe { *ptr }, true);
+    ///
+    /// // Deallocate the value
+    /// unsafe { drop(Box::from_raw(ptr)) }
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note that on some platforms this can be bigger than `align_of::<bool>()`).
+    /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
+    /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+    ///
+    /// [valid]: crate::ptr#safety
+    #[unstable(feature = "atomic_from_ptr", issue = "108652")]
+    #[rustc_const_unstable(feature = "atomic_from_ptr", issue = "108652")]
+    pub const unsafe fn from_ptr<'a>(ptr: *mut bool) -> &'a AtomicBool {
+        // SAFETY: guaranteed by the caller
+        unsafe { &*ptr.cast() }
+    }
+
     /// Returns a mutable reference to the underlying [`bool`].
     ///
     /// This is safe because the mutable reference guarantees that no other threads are
@@ -922,14 +966,14 @@ impl AtomicBool {
     ///
     /// let mut atomic = AtomicBool::new(true);
     /// unsafe {
-    ///     my_atomic_op(atomic.as_mut_ptr());
+    ///     my_atomic_op(atomic.as_ptr());
     /// }
     /// # }
     /// ```
     #[inline]
     #[unstable(feature = "atomic_mut_ptr", reason = "recently added", issue = "66893")]
-    pub fn as_mut_ptr(&self) -> *mut bool {
-        self.v.get() as *mut bool
+    pub const fn as_ptr(&self) -> *mut bool {
+        self.v.get().cast()
     }
 
     /// Fetches the value, and applies a function to it that returns an optional
@@ -1017,6 +1061,50 @@ impl<T> AtomicPtr<T> {
         AtomicPtr { p: UnsafeCell::new(p) }
     }
 
+    /// Creates a new `AtomicPtr` from a pointer.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(atomic_from_ptr, pointer_is_aligned)]
+    /// use std::sync::atomic::{self, AtomicPtr};
+    /// use std::mem::align_of;
+    ///
+    /// // Get a pointer to an allocated value
+    /// let ptr: *mut *mut u8 = Box::into_raw(Box::new(std::ptr::null_mut()));
+    ///
+    /// assert!(ptr.is_aligned_to(align_of::<AtomicPtr<u8>>()));
+    ///
+    /// {
+    ///     // Create an atomic view of the allocated value
+    ///     let atomic = unsafe { AtomicPtr::from_ptr(ptr) };
+    ///
+    ///     // Use `atomic` for atomic operations, possibly share it with other threads
+    ///     atomic.store(std::ptr::NonNull::dangling().as_ptr(), atomic::Ordering::Relaxed);
+    /// }
+    ///
+    /// // It's ok to non-atomically access the value behind `ptr`,
+    /// // since the reference to the atomic ended its lifetime in the block above
+    /// assert!(!unsafe { *ptr }.is_null());
+    ///
+    /// // Deallocate the value
+    /// unsafe { drop(Box::from_raw(ptr)) }
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// * `ptr` must be aligned to `align_of::<AtomicPtr<T>>()` (note that on some platforms this can be bigger than `align_of::<*mut T>()`).
+    /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
+    /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+    ///
+    /// [valid]: crate::ptr#safety
+    #[unstable(feature = "atomic_from_ptr", issue = "108652")]
+    #[rustc_const_unstable(feature = "atomic_from_ptr", issue = "108652")]
+    pub const unsafe fn from_ptr<'a>(ptr: *mut *mut T) -> &'a AtomicPtr<T> {
+        // SAFETY: guaranteed by the caller
+        unsafe { &*ptr.cast() }
+    }
+
     /// Returns a mutable reference to the underlying pointer.
     ///
     /// This is safe because the mutable reference guarantees that no other threads are
@@ -1803,7 +1891,7 @@ impl<T> AtomicPtr<T> {
     ///
     /// ```ignore (extern-declaration)
     /// #![feature(atomic_mut_ptr)]
-    //// use std::sync::atomic::AtomicPtr;
+    /// use std::sync::atomic::AtomicPtr;
     ///
     /// extern "C" {
     ///     fn my_atomic_op(arg: *mut *mut u32);
@@ -1814,12 +1902,12 @@ impl<T> AtomicPtr<T> {
     ///
     /// // SAFETY: Safe as long as `my_atomic_op` is atomic.
     /// unsafe {
-    ///     my_atomic_op(atomic.as_mut_ptr());
+    ///     my_atomic_op(atomic.as_ptr());
     /// }
     /// ```
     #[inline]
     #[unstable(feature = "atomic_mut_ptr", reason = "recently added", issue = "66893")]
-    pub fn as_mut_ptr(&self) -> *mut *mut T {
+    pub const fn as_ptr(&self) -> *mut *mut T {
         self.p.get()
     }
 }
@@ -1861,7 +1949,8 @@ macro_rules! if_not_8_bit {
     ($_:ident, $($tt:tt)*) => { $($tt)* };
 }
 
-#[cfg(target_has_atomic_load_store = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic_load_store))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic_load_store = "8"))]
 macro_rules! atomic_int {
     ($cfg_cas:meta,
      $cfg_align:meta,
@@ -1957,6 +2046,53 @@ macro_rules! atomic_int {
                 Self {v: UnsafeCell::new(v)}
             }
 
+            /// Creates a new reference to an atomic integer from a pointer.
+            ///
+            /// # Examples
+            ///
+            /// ```
+            /// #![feature(atomic_from_ptr, pointer_is_aligned)]
+            #[doc = concat!($extra_feature, "use std::sync::atomic::{self, ", stringify!($atomic_type), "};")]
+            /// use std::mem::align_of;
+            ///
+            /// // Get a pointer to an allocated value
+            #[doc = concat!("let ptr: *mut ", stringify!($int_type), " = Box::into_raw(Box::new(0));")]
+            ///
+            #[doc = concat!("assert!(ptr.is_aligned_to(align_of::<", stringify!($atomic_type), ">()));")]
+            ///
+            /// {
+            ///     // Create an atomic view of the allocated value
+            // SAFETY: this is a doc comment, tidy, it can't hurt you (also guaranteed by the construction of `ptr` and the assert above)
+            #[doc = concat!("    let atomic = unsafe {", stringify!($atomic_type), "::from_ptr(ptr) };")]
+            ///
+            ///     // Use `atomic` for atomic operations, possibly share it with other threads
+            ///     atomic.store(1, atomic::Ordering::Relaxed);
+            /// }
+            ///
+            /// // It's ok to non-atomically access the value behind `ptr`,
+            /// // since the reference to the atomic ended its lifetime in the block above
+            /// assert_eq!(unsafe { *ptr }, 1);
+            ///
+            /// // Deallocate the value
+            /// unsafe { drop(Box::from_raw(ptr)) }
+            /// ```
+            ///
+            /// # Safety
+            ///
+            /// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note that on some platforms this can be bigger than `align_of::<bool>()`).
+            #[doc = concat!(" * `ptr` must be aligned to `align_of::<", stringify!($atomic_type), ">()` (note that on some platforms this can be bigger than `align_of::<", stringify!($int_type), ">()`).")]
+            /// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
+            /// * The value behind `ptr` must not be accessed through non-atomic operations for the whole lifetime `'a`.
+            ///
+            /// [valid]: crate::ptr#safety
+            #[unstable(feature = "atomic_from_ptr", issue = "108652")]
+            #[rustc_const_unstable(feature = "atomic_from_ptr", issue = "108652")]
+            pub const unsafe fn from_ptr<'a>(ptr: *mut $int_type) -> &'a $atomic_type {
+                // SAFETY: guaranteed by the caller
+                unsafe { &*ptr.cast() }
+            }
+
+
             /// Returns a mutable reference to the underlying integer.
             ///
             /// This is safe because the mutable reference guarantees that no other threads are
@@ -2718,7 +2854,7 @@ macro_rules! atomic_int {
             ///
             /// // SAFETY: Safe as long as `my_atomic_op` is atomic.
             /// unsafe {
-            ///     my_atomic_op(atomic.as_mut_ptr());
+            ///     my_atomic_op(atomic.as_ptr());
             /// }
             /// # }
             /// ```
@@ -2726,7 +2862,7 @@ macro_rules! atomic_int {
             #[unstable(feature = "atomic_mut_ptr",
                    reason = "recently added",
                    issue = "66893")]
-            pub fn as_mut_ptr(&self) -> *mut $int_type {
+            pub const fn as_ptr(&self) -> *mut $int_type {
                 self.v.get()
             }
         }
@@ -2988,7 +3124,8 @@ atomic_int_ptr_sized! {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 fn strongest_failure_ordering(order: Ordering) -> Ordering {
     match order {
         Release => Relaxed,
@@ -3030,7 +3167,8 @@ unsafe fn atomic_load<T: Copy>(dst: *const T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_swap<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_swap`.
@@ -3047,7 +3185,8 @@ unsafe fn atomic_swap<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// Returns the previous value (like __sync_fetch_and_add).
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_add<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_add`.
@@ -3064,7 +3203,8 @@ unsafe fn atomic_add<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// Returns the previous value (like __sync_fetch_and_sub).
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_sub<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_sub`.
@@ -3080,7 +3220,8 @@ unsafe fn atomic_sub<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_compare_exchange<T: Copy>(
     dst: *mut T,
@@ -3115,7 +3256,8 @@ unsafe fn atomic_compare_exchange<T: Copy>(
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_compare_exchange_weak<T: Copy>(
     dst: *mut T,
@@ -3150,7 +3292,8 @@ unsafe fn atomic_compare_exchange_weak<T: Copy>(
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_and<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_and`
@@ -3166,7 +3309,8 @@ unsafe fn atomic_and<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_nand<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_nand`
@@ -3182,7 +3326,8 @@ unsafe fn atomic_nand<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_or<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_or`
@@ -3198,7 +3343,8 @@ unsafe fn atomic_or<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 }
 
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_xor<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_xor`
@@ -3215,7 +3361,8 @@ unsafe fn atomic_xor<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the max value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_max<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_max`
@@ -3232,7 +3379,8 @@ unsafe fn atomic_max<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the min value (signed comparison)
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_min<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_min`
@@ -3249,7 +3397,8 @@ unsafe fn atomic_min<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the max value (unsigned comparison)
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_umax<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_umax`
@@ -3266,7 +3415,8 @@ unsafe fn atomic_umax<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
 
 /// returns the min value (unsigned comparison)
 #[inline]
-#[cfg(target_has_atomic = "8")]
+#[cfg_attr(not(bootstrap), cfg(target_has_atomic))]
+#[cfg_attr(bootstrap, cfg(target_has_atomic = "8"))]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn atomic_umin<T: Copy>(dst: *mut T, val: T, order: Ordering) -> T {
     // SAFETY: the caller must uphold the safety contract for `atomic_umin`
diff --git a/library/core/src/task/poll.rs b/library/core/src/task/poll.rs
index 25b61c0e6..af5bf441b 100644
--- a/library/core/src/task/poll.rs
+++ b/library/core/src/task/poll.rs
@@ -45,6 +45,7 @@ impl<T> Poll<T> {
     /// assert_eq!(poll_some_len, Poll::Ready(13));
     /// ```
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[inline]
     pub fn map<U, F>(self, f: F) -> Poll<U>
     where
         F: FnOnce(T) -> U,
@@ -144,6 +145,7 @@ impl<T, E> Poll<Result<T, E>> {
     /// assert_eq!(squared, Poll::Ready(Ok(144)));
     /// ```
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[inline]
     pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
     where
         F: FnOnce(T) -> U,
@@ -171,6 +173,7 @@ impl<T, E> Poll<Result<T, E>> {
     /// assert_eq!(res, Poll::Ready(Err(0)));
     /// ```
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[inline]
     pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
     where
         F: FnOnce(E) -> U,
@@ -199,6 +202,7 @@ impl<T, E> Poll<Option<Result<T, E>>> {
     /// assert_eq!(squared, Poll::Ready(Some(Ok(144))));
     /// ```
     #[stable(feature = "poll_map", since = "1.51.0")]
+    #[inline]
     pub fn map_ok<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
     where
         F: FnOnce(T) -> U,
@@ -228,6 +232,7 @@ impl<T, E> Poll<Option<Result<T, E>>> {
     /// assert_eq!(res, Poll::Ready(Some(Err(0))));
     /// ```
     #[stable(feature = "poll_map", since = "1.51.0")]
+    #[inline]
     pub fn map_err<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
     where
         F: FnOnce(E) -> U,
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index 89adfccd9..808825326 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -174,7 +174,7 @@ impl RawWakerVTable {
 /// Currently, `Context` only serves to provide access to a [`&Waker`](Waker)
 /// which can be used to wake the current task.
 #[stable(feature = "futures_api", since = "1.36.0")]
-#[cfg_attr(not(bootstrap), lang = "Context")]
+#[lang = "Context"]
 pub struct Context<'a> {
     waker: &'a Waker,
     // Ensure we future-proof against variance changes by forcing
diff --git a/library/core/tests/array.rs b/library/core/tests/array.rs
index f268fe3ae..5327e4f81 100644
--- a/library/core/tests/array.rs
+++ b/library/core/tests/array.rs
@@ -700,3 +700,28 @@ fn array_into_iter_rfold() {
     let s = it.rfold(10, |a, b| 10 * a + b);
     assert_eq!(s, 10432);
 }
+
+#[cfg(not(panic = "abort"))]
+#[test]
+fn array_map_drops_unmapped_elements_on_panic() {
+    struct DropCounter<'a>(usize, &'a AtomicUsize);
+    impl Drop for DropCounter<'_> {
+        fn drop(&mut self) {
+            self.1.fetch_add(1, Ordering::SeqCst);
+        }
+    }
+
+    const MAX: usize = 11;
+    for panic_after in 0..MAX {
+        let counter = AtomicUsize::new(0);
+        let a = array::from_fn::<_, 11, _>(|i| DropCounter(i, &counter));
+        let success = std::panic::catch_unwind(|| {
+            let _ = a.map(|x| {
+                assert!(x.0 < panic_after);
+                assert_eq!(counter.load(Ordering::SeqCst), x.0);
+            });
+        });
+        assert!(success.is_err());
+        assert_eq!(counter.load(Ordering::SeqCst), MAX);
+    }
+}
diff --git a/library/core/tests/iter/adapters/mod.rs b/library/core/tests/iter/adapters/mod.rs
index ffd5f3857..ca3463aa7 100644
--- a/library/core/tests/iter/adapters/mod.rs
+++ b/library/core/tests/iter/adapters/mod.rs
@@ -24,7 +24,7 @@ mod zip;
 
 use core::cell::Cell;
 
-/// An iterator that panics whenever `next` or next_back` is called
+/// An iterator that panics whenever `next` or `next_back` is called
 /// after `None` has already been returned. This does not violate
 /// `Iterator`'s contract. Used to test that iterator adapters don't
 /// poll their inner iterators after exhausting them.
diff --git a/library/core/tests/iter/range.rs b/library/core/tests/iter/range.rs
index 84498a8ea..0f91ffe2d 100644
--- a/library/core/tests/iter/range.rs
+++ b/library/core/tests/iter/range.rs
@@ -26,7 +26,6 @@ fn test_range() {
 
 #[test]
 fn test_char_range() {
-    use std::char;
     // Miri is too slow
     let from = if cfg!(miri) { char::from_u32(0xD800 - 10).unwrap() } else { '\0' };
     let to = if cfg!(miri) { char::from_u32(0xDFFF + 10).unwrap() } else { char::MAX };
diff --git a/library/core/tests/iter/traits/iterator.rs b/library/core/tests/iter/traits/iterator.rs
index 37345c1d3..62566a950 100644
--- a/library/core/tests/iter/traits/iterator.rs
+++ b/library/core/tests/iter/traits/iterator.rs
@@ -582,6 +582,9 @@ fn test_next_chunk() {
     assert_eq!(it.next_chunk().unwrap(), []);
     assert_eq!(it.next_chunk().unwrap(), [4, 5, 6, 7, 8, 9]);
     assert_eq!(it.next_chunk::<4>().unwrap_err().as_slice(), &[10, 11]);
+
+    let mut it = std::iter::repeat_with(|| panic!());
+    assert_eq!(it.next_chunk::<0>().unwrap(), []);
 }
 
 // just tests by whether or not this compiles
diff --git a/library/core/tests/lib.rs b/library/core/tests/lib.rs
index 42a26ae16..ccb7be68e 100644
--- a/library/core/tests/lib.rs
+++ b/library/core/tests/lib.rs
@@ -66,6 +66,8 @@
 #![feature(try_trait_v2)]
 #![feature(slice_internals)]
 #![feature(slice_partition_dedup)]
+#![feature(ip)]
+#![feature(ip_in_core)]
 #![feature(iter_advance_by)]
 #![feature(iter_array_chunks)]
 #![feature(iter_collect_into)]
@@ -77,6 +79,9 @@
 #![feature(iter_repeat_n)]
 #![feature(iterator_try_collect)]
 #![feature(iterator_try_reduce)]
+#![feature(const_ip)]
+#![feature(const_ipv4)]
+#![feature(const_ipv6)]
 #![feature(const_mut_refs)]
 #![feature(const_pin)]
 #![feature(const_waker)]
@@ -135,6 +140,7 @@ mod lazy;
 mod macros;
 mod manually_drop;
 mod mem;
+mod net;
 mod nonzero;
 mod num;
 mod ops;
diff --git a/library/core/tests/net/ip_addr.rs b/library/core/tests/net/ip_addr.rs
new file mode 100644
index 000000000..5a6ac08c0
--- /dev/null
+++ b/library/core/tests/net/ip_addr.rs
@@ -0,0 +1,1035 @@
+use super::{sa4, sa6};
+use core::net::{
+    IpAddr, Ipv4Addr, Ipv6Addr, Ipv6MulticastScope, SocketAddr, SocketAddrV4, SocketAddrV6,
+};
+use core::str::FromStr;
+
+#[test]
+fn test_from_str_ipv4() {
+    assert_eq!(Ok(Ipv4Addr::new(127, 0, 0, 1)), "127.0.0.1".parse());
+    assert_eq!(Ok(Ipv4Addr::new(255, 255, 255, 255)), "255.255.255.255".parse());
+    assert_eq!(Ok(Ipv4Addr::new(0, 0, 0, 0)), "0.0.0.0".parse());
+
+    // out of range
+    let none: Option<Ipv4Addr> = "256.0.0.1".parse().ok();
+    assert_eq!(None, none);
+    // too short
+    let none: Option<Ipv4Addr> = "255.0.0".parse().ok();
+    assert_eq!(None, none);
+    // too long
+    let none: Option<Ipv4Addr> = "255.0.0.1.2".parse().ok();
+    assert_eq!(None, none);
+    // no number between dots
+    let none: Option<Ipv4Addr> = "255.0..1".parse().ok();
+    assert_eq!(None, none);
+    // octal
+    let none: Option<Ipv4Addr> = "255.0.0.01".parse().ok();
+    assert_eq!(None, none);
+    // octal zero
+    let none: Option<Ipv4Addr> = "255.0.0.00".parse().ok();
+    assert_eq!(None, none);
+    let none: Option<Ipv4Addr> = "255.0.00.0".parse().ok();
+    assert_eq!(None, none);
+}
+
+#[test]
+fn test_from_str_ipv6() {
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)), "0:0:0:0:0:0:0:0".parse());
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)), "0:0:0:0:0:0:0:1".parse());
+
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)), "::1".parse());
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)), "::".parse());
+
+    assert_eq!(Ok(Ipv6Addr::new(0x2a02, 0x6b8, 0, 0, 0, 0, 0x11, 0x11)), "2a02:6b8::11:11".parse());
+
+    // too long group
+    let none: Option<Ipv6Addr> = "::00000".parse().ok();
+    assert_eq!(None, none);
+    // too short
+    let none: Option<Ipv6Addr> = "1:2:3:4:5:6:7".parse().ok();
+    assert_eq!(None, none);
+    // too long
+    let none: Option<Ipv6Addr> = "1:2:3:4:5:6:7:8:9".parse().ok();
+    assert_eq!(None, none);
+    // triple colon
+    let none: Option<Ipv6Addr> = "1:2:::6:7:8".parse().ok();
+    assert_eq!(None, none);
+    // two double colons
+    let none: Option<Ipv6Addr> = "1:2::6::8".parse().ok();
+    assert_eq!(None, none);
+    // `::` indicating zero groups of zeros
+    let none: Option<Ipv6Addr> = "1:2:3:4::5:6:7:8".parse().ok();
+    assert_eq!(None, none);
+}
+
+#[test]
+fn test_from_str_ipv4_in_ipv6() {
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 49152, 545)), "::192.0.2.33".parse());
+    assert_eq!(Ok(Ipv6Addr::new(0, 0, 0, 0, 0, 0xFFFF, 49152, 545)), "::FFFF:192.0.2.33".parse());
+    assert_eq!(
+        Ok(Ipv6Addr::new(0x64, 0xff9b, 0, 0, 0, 0, 49152, 545)),
+        "64:ff9b::192.0.2.33".parse()
+    );
+    assert_eq!(
+        Ok(Ipv6Addr::new(0x2001, 0xdb8, 0x122, 0xc000, 0x2, 0x2100, 49152, 545)),
+        "2001:db8:122:c000:2:2100:192.0.2.33".parse()
+    );
+
+    // colon after v4
+    let none: Option<Ipv4Addr> = "::127.0.0.1:".parse().ok();
+    assert_eq!(None, none);
+    // not enough groups
+    let none: Option<Ipv6Addr> = "1:2:3:4:5:127.0.0.1".parse().ok();
+    assert_eq!(None, none);
+    // too many groups
+    let none: Option<Ipv6Addr> = "1:2:3:4:5:6:7:127.0.0.1".parse().ok();
+    assert_eq!(None, none);
+}
+
+#[test]
+fn test_from_str_socket_addr() {
+    assert_eq!(Ok(sa4(Ipv4Addr::new(77, 88, 21, 11), 80)), "77.88.21.11:80".parse());
+    assert_eq!(Ok(SocketAddrV4::new(Ipv4Addr::new(77, 88, 21, 11), 80)), "77.88.21.11:80".parse());
+    assert_eq!(
+        Ok(sa6(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 53)),
+        "[2a02:6b8:0:1::1]:53".parse()
+    );
+    assert_eq!(
+        Ok(SocketAddrV6::new(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 53, 0, 0)),
+        "[2a02:6b8:0:1::1]:53".parse()
+    );
+    assert_eq!(Ok(sa6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0x7F00, 1), 22)), "[::127.0.0.1]:22".parse());
+    assert_eq!(
+        Ok(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0x7F00, 1), 22, 0, 0)),
+        "[::127.0.0.1]:22".parse()
+    );
+
+    // without port
+    let none: Option<SocketAddr> = "127.0.0.1".parse().ok();
+    assert_eq!(None, none);
+    // without port
+    let none: Option<SocketAddr> = "127.0.0.1:".parse().ok();
+    assert_eq!(None, none);
+    // wrong brackets around v4
+    let none: Option<SocketAddr> = "[127.0.0.1]:22".parse().ok();
+    assert_eq!(None, none);
+    // port out of range
+    let none: Option<SocketAddr> = "127.0.0.1:123456".parse().ok();
+    assert_eq!(None, none);
+}
+
+#[test]
+fn ipv4_addr_to_string() {
+    assert_eq!(Ipv4Addr::new(127, 0, 0, 1).to_string(), "127.0.0.1");
+    // Short address
+    assert_eq!(Ipv4Addr::new(1, 1, 1, 1).to_string(), "1.1.1.1");
+    // Long address
+    assert_eq!(Ipv4Addr::new(127, 127, 127, 127).to_string(), "127.127.127.127");
+
+    // Test padding
+    assert_eq!(format!("{:16}", Ipv4Addr::new(1, 1, 1, 1)), "1.1.1.1         ");
+    assert_eq!(format!("{:>16}", Ipv4Addr::new(1, 1, 1, 1)), "         1.1.1.1");
+}
+
+#[test]
+fn ipv6_addr_to_string() {
+    // ipv4-mapped address
+    let a1 = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc000, 0x280);
+    assert_eq!(a1.to_string(), "::ffff:192.0.2.128");
+
+    // ipv4-compatible address
+    let a1 = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc000, 0x280);
+    assert_eq!(a1.to_string(), "::192.0.2.128");
+
+    // v6 address with no zero segments
+    assert_eq!(Ipv6Addr::new(8, 9, 10, 11, 12, 13, 14, 15).to_string(), "8:9:a:b:c:d:e:f");
+
+    // longest possible IPv6 length
+    assert_eq!(
+        Ipv6Addr::new(0x1111, 0x2222, 0x3333, 0x4444, 0x5555, 0x6666, 0x7777, 0x8888).to_string(),
+        "1111:2222:3333:4444:5555:6666:7777:8888"
+    );
+    // padding
+    assert_eq!(format!("{:20}", Ipv6Addr::new(1, 2, 3, 4, 5, 6, 7, 8)), "1:2:3:4:5:6:7:8     ");
+    assert_eq!(format!("{:>20}", Ipv6Addr::new(1, 2, 3, 4, 5, 6, 7, 8)), "     1:2:3:4:5:6:7:8");
+
+    // reduce a single run of zeros
+    assert_eq!(
+        "ae::ffff:102:304",
+        Ipv6Addr::new(0xae, 0, 0, 0, 0, 0xffff, 0x0102, 0x0304).to_string()
+    );
+
+    // don't reduce just a single zero segment
+    assert_eq!("1:2:3:4:5:6:0:8", Ipv6Addr::new(1, 2, 3, 4, 5, 6, 0, 8).to_string());
+
+    // 'any' address
+    assert_eq!("::", Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0).to_string());
+
+    // loopback address
+    assert_eq!("::1", Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1).to_string());
+
+    // ends in zeros
+    assert_eq!("1::", Ipv6Addr::new(1, 0, 0, 0, 0, 0, 0, 0).to_string());
+
+    // two runs of zeros, second one is longer
+    assert_eq!("1:0:0:4::8", Ipv6Addr::new(1, 0, 0, 4, 0, 0, 0, 8).to_string());
+
+    // two runs of zeros, equal length
+    assert_eq!("1::4:5:0:0:8", Ipv6Addr::new(1, 0, 0, 4, 5, 0, 0, 8).to_string());
+
+    // don't prefix `0x` to each segment in `dbg!`.
+    assert_eq!("1::4:5:0:0:8", &format!("{:#?}", Ipv6Addr::new(1, 0, 0, 4, 5, 0, 0, 8)));
+}
+
+#[test]
+fn ipv4_to_ipv6() {
+    assert_eq!(
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x1234, 0x5678),
+        Ipv4Addr::new(0x12, 0x34, 0x56, 0x78).to_ipv6_mapped()
+    );
+    assert_eq!(
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0x1234, 0x5678),
+        Ipv4Addr::new(0x12, 0x34, 0x56, 0x78).to_ipv6_compatible()
+    );
+}
+
+#[test]
+fn ipv6_to_ipv4_mapped() {
+    assert_eq!(
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x1234, 0x5678).to_ipv4_mapped(),
+        Some(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78))
+    );
+    assert_eq!(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0x1234, 0x5678).to_ipv4_mapped(), None);
+}
+
+#[test]
+fn ipv6_to_ipv4() {
+    assert_eq!(
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x1234, 0x5678).to_ipv4(),
+        Some(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78))
+    );
+    assert_eq!(
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0x1234, 0x5678).to_ipv4(),
+        Some(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78))
+    );
+    assert_eq!(Ipv6Addr::new(0, 0, 1, 0, 0, 0, 0x1234, 0x5678).to_ipv4(), None);
+}
+
+#[test]
+fn ip_properties() {
+    macro_rules! ip {
+        ($s:expr) => {
+            IpAddr::from_str($s).unwrap()
+        };
+    }
+
+    macro_rules! check {
+        ($s:expr) => {
+            check!($s, 0);
+        };
+
+        ($s:expr, $mask:expr) => {{
+            let unspec: u8 = 1 << 0;
+            let loopback: u8 = 1 << 1;
+            let global: u8 = 1 << 2;
+            let multicast: u8 = 1 << 3;
+            let doc: u8 = 1 << 4;
+            let benchmarking: u8 = 1 << 5;
+
+            if ($mask & unspec) == unspec {
+                assert!(ip!($s).is_unspecified());
+            } else {
+                assert!(!ip!($s).is_unspecified());
+            }
+
+            if ($mask & loopback) == loopback {
+                assert!(ip!($s).is_loopback());
+            } else {
+                assert!(!ip!($s).is_loopback());
+            }
+
+            if ($mask & global) == global {
+                assert!(ip!($s).is_global());
+            } else {
+                assert!(!ip!($s).is_global());
+            }
+
+            if ($mask & multicast) == multicast {
+                assert!(ip!($s).is_multicast());
+            } else {
+                assert!(!ip!($s).is_multicast());
+            }
+
+            if ($mask & doc) == doc {
+                assert!(ip!($s).is_documentation());
+            } else {
+                assert!(!ip!($s).is_documentation());
+            }
+
+            if ($mask & benchmarking) == benchmarking {
+                assert!(ip!($s).is_benchmarking());
+            } else {
+                assert!(!ip!($s).is_benchmarking());
+            }
+        }};
+    }
+
+    let unspec: u8 = 1 << 0;
+    let loopback: u8 = 1 << 1;
+    let global: u8 = 1 << 2;
+    let multicast: u8 = 1 << 3;
+    let doc: u8 = 1 << 4;
+    let benchmarking: u8 = 1 << 5;
+
+    check!("0.0.0.0", unspec);
+    check!("0.0.0.1");
+    check!("0.1.0.0");
+    check!("10.9.8.7");
+    check!("127.1.2.3", loopback);
+    check!("172.31.254.253");
+    check!("169.254.253.242");
+    check!("192.0.2.183", doc);
+    check!("192.1.2.183", global);
+    check!("192.168.254.253");
+    check!("198.51.100.0", doc);
+    check!("203.0.113.0", doc);
+    check!("203.2.113.0", global);
+    check!("224.0.0.0", global | multicast);
+    check!("239.255.255.255", global | multicast);
+    check!("255.255.255.255");
+    // make sure benchmarking addresses are not global
+    check!("198.18.0.0", benchmarking);
+    check!("198.18.54.2", benchmarking);
+    check!("198.19.255.255", benchmarking);
+    // make sure addresses reserved for protocol assignment are not global
+    check!("192.0.0.0");
+    check!("192.0.0.255");
+    check!("192.0.0.100");
+    // make sure reserved addresses are not global
+    check!("240.0.0.0");
+    check!("251.54.1.76");
+    check!("254.255.255.255");
+    // make sure shared addresses are not global
+    check!("100.64.0.0");
+    check!("100.127.255.255");
+    check!("100.100.100.0");
+
+    check!("::", unspec);
+    check!("::1", loopback);
+    check!("::0.0.0.2", global);
+    check!("1::", global);
+    check!("fc00::");
+    check!("fdff:ffff::");
+    check!("fe80:ffff::");
+    check!("febf:ffff::");
+    check!("fec0::", global);
+    check!("ff01::", global | multicast);
+    check!("ff02::", global | multicast);
+    check!("ff03::", global | multicast);
+    check!("ff04::", global | multicast);
+    check!("ff05::", global | multicast);
+    check!("ff08::", global | multicast);
+    check!("ff0e::", global | multicast);
+    check!("2001:db8:85a3::8a2e:370:7334", doc);
+    check!("2001:2::ac32:23ff:21", benchmarking);
+    check!("102:304:506:708:90a:b0c:d0e:f10", global);
+}
+
+#[test]
+fn ipv4_properties() {
+    macro_rules! ip {
+        ($s:expr) => {
+            Ipv4Addr::from_str($s).unwrap()
+        };
+    }
+
+    macro_rules! check {
+        ($s:expr) => {
+            check!($s, 0);
+        };
+
+        ($s:expr, $mask:expr) => {{
+            let unspec: u16 = 1 << 0;
+            let loopback: u16 = 1 << 1;
+            let private: u16 = 1 << 2;
+            let link_local: u16 = 1 << 3;
+            let global: u16 = 1 << 4;
+            let multicast: u16 = 1 << 5;
+            let broadcast: u16 = 1 << 6;
+            let documentation: u16 = 1 << 7;
+            let benchmarking: u16 = 1 << 8;
+            let reserved: u16 = 1 << 10;
+            let shared: u16 = 1 << 11;
+
+            if ($mask & unspec) == unspec {
+                assert!(ip!($s).is_unspecified());
+            } else {
+                assert!(!ip!($s).is_unspecified());
+            }
+
+            if ($mask & loopback) == loopback {
+                assert!(ip!($s).is_loopback());
+            } else {
+                assert!(!ip!($s).is_loopback());
+            }
+
+            if ($mask & private) == private {
+                assert!(ip!($s).is_private());
+            } else {
+                assert!(!ip!($s).is_private());
+            }
+
+            if ($mask & link_local) == link_local {
+                assert!(ip!($s).is_link_local());
+            } else {
+                assert!(!ip!($s).is_link_local());
+            }
+
+            if ($mask & global) == global {
+                assert!(ip!($s).is_global());
+            } else {
+                assert!(!ip!($s).is_global());
+            }
+
+            if ($mask & multicast) == multicast {
+                assert!(ip!($s).is_multicast());
+            } else {
+                assert!(!ip!($s).is_multicast());
+            }
+
+            if ($mask & broadcast) == broadcast {
+                assert!(ip!($s).is_broadcast());
+            } else {
+                assert!(!ip!($s).is_broadcast());
+            }
+
+            if ($mask & documentation) == documentation {
+                assert!(ip!($s).is_documentation());
+            } else {
+                assert!(!ip!($s).is_documentation());
+            }
+
+            if ($mask & benchmarking) == benchmarking {
+                assert!(ip!($s).is_benchmarking());
+            } else {
+                assert!(!ip!($s).is_benchmarking());
+            }
+
+            if ($mask & reserved) == reserved {
+                assert!(ip!($s).is_reserved());
+            } else {
+                assert!(!ip!($s).is_reserved());
+            }
+
+            if ($mask & shared) == shared {
+                assert!(ip!($s).is_shared());
+            } else {
+                assert!(!ip!($s).is_shared());
+            }
+        }};
+    }
+
+    let unspec: u16 = 1 << 0;
+    let loopback: u16 = 1 << 1;
+    let private: u16 = 1 << 2;
+    let link_local: u16 = 1 << 3;
+    let global: u16 = 1 << 4;
+    let multicast: u16 = 1 << 5;
+    let broadcast: u16 = 1 << 6;
+    let documentation: u16 = 1 << 7;
+    let benchmarking: u16 = 1 << 8;
+    let reserved: u16 = 1 << 10;
+    let shared: u16 = 1 << 11;
+
+    check!("0.0.0.0", unspec);
+    check!("0.0.0.1");
+    check!("0.1.0.0");
+    check!("10.9.8.7", private);
+    check!("127.1.2.3", loopback);
+    check!("172.31.254.253", private);
+    check!("169.254.253.242", link_local);
+    check!("192.0.2.183", documentation);
+    check!("192.1.2.183", global);
+    check!("192.168.254.253", private);
+    check!("198.51.100.0", documentation);
+    check!("203.0.113.0", documentation);
+    check!("203.2.113.0", global);
+    check!("224.0.0.0", global | multicast);
+    check!("239.255.255.255", global | multicast);
+    check!("255.255.255.255", broadcast);
+    check!("198.18.0.0", benchmarking);
+    check!("198.18.54.2", benchmarking);
+    check!("198.19.255.255", benchmarking);
+    check!("192.0.0.0");
+    check!("192.0.0.255");
+    check!("192.0.0.100");
+    check!("240.0.0.0", reserved);
+    check!("251.54.1.76", reserved);
+    check!("254.255.255.255", reserved);
+    check!("100.64.0.0", shared);
+    check!("100.127.255.255", shared);
+    check!("100.100.100.0", shared);
+}
+
+#[test]
+fn ipv6_properties() {
+    macro_rules! ip {
+        ($s:expr) => {
+            Ipv6Addr::from_str($s).unwrap()
+        };
+    }
+
+    macro_rules! check {
+        ($s:expr, &[$($octet:expr),*], $mask:expr) => {
+            assert_eq!($s, ip!($s).to_string());
+            let octets = &[$($octet),*];
+            assert_eq!(&ip!($s).octets(), octets);
+            assert_eq!(Ipv6Addr::from(*octets), ip!($s));
+
+            let unspecified: u32 = 1 << 0;
+            let loopback: u32 = 1 << 1;
+            let unique_local: u32 = 1 << 2;
+            let global: u32 = 1 << 3;
+            let unicast_link_local: u32 = 1 << 4;
+            let unicast_global: u32 = 1 << 7;
+            let documentation: u32 = 1 << 8;
+            let benchmarking: u32 = 1 << 16;
+            let multicast_interface_local: u32 = 1 << 9;
+            let multicast_link_local: u32 = 1 << 10;
+            let multicast_realm_local: u32 = 1 << 11;
+            let multicast_admin_local: u32 = 1 << 12;
+            let multicast_site_local: u32 = 1 << 13;
+            let multicast_organization_local: u32 = 1 << 14;
+            let multicast_global: u32 = 1 << 15;
+            let multicast: u32 = multicast_interface_local
+                | multicast_admin_local
+                | multicast_global
+                | multicast_link_local
+                | multicast_realm_local
+                | multicast_site_local
+                | multicast_organization_local;
+
+            if ($mask & unspecified) == unspecified {
+                assert!(ip!($s).is_unspecified());
+            } else {
+                assert!(!ip!($s).is_unspecified());
+            }
+            if ($mask & loopback) == loopback {
+                assert!(ip!($s).is_loopback());
+            } else {
+                assert!(!ip!($s).is_loopback());
+            }
+            if ($mask & unique_local) == unique_local {
+                assert!(ip!($s).is_unique_local());
+            } else {
+                assert!(!ip!($s).is_unique_local());
+            }
+            if ($mask & global) == global {
+                assert!(ip!($s).is_global());
+            } else {
+                assert!(!ip!($s).is_global());
+            }
+            if ($mask & unicast_link_local) == unicast_link_local {
+                assert!(ip!($s).is_unicast_link_local());
+            } else {
+                assert!(!ip!($s).is_unicast_link_local());
+            }
+            if ($mask & unicast_global) == unicast_global {
+                assert!(ip!($s).is_unicast_global());
+            } else {
+                assert!(!ip!($s).is_unicast_global());
+            }
+            if ($mask & documentation) == documentation {
+                assert!(ip!($s).is_documentation());
+            } else {
+                assert!(!ip!($s).is_documentation());
+            }
+            if ($mask & benchmarking) == benchmarking {
+                assert!(ip!($s).is_benchmarking());
+            } else {
+                assert!(!ip!($s).is_benchmarking());
+            }
+            if ($mask & multicast) != 0 {
+                assert!(ip!($s).multicast_scope().is_some());
+                assert!(ip!($s).is_multicast());
+            } else {
+                assert!(ip!($s).multicast_scope().is_none());
+                assert!(!ip!($s).is_multicast());
+            }
+            if ($mask & multicast_interface_local) == multicast_interface_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::InterfaceLocal);
+            }
+            if ($mask & multicast_link_local) == multicast_link_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::LinkLocal);
+            }
+            if ($mask & multicast_realm_local) == multicast_realm_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::RealmLocal);
+            }
+            if ($mask & multicast_admin_local) == multicast_admin_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::AdminLocal);
+            }
+            if ($mask & multicast_site_local) == multicast_site_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::SiteLocal);
+            }
+            if ($mask & multicast_organization_local) == multicast_organization_local {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::OrganizationLocal);
+            }
+            if ($mask & multicast_global) == multicast_global {
+                assert_eq!(ip!($s).multicast_scope().unwrap(),
+                           Ipv6MulticastScope::Global);
+            }
+        }
+    }
+
+    let unspecified: u32 = 1 << 0;
+    let loopback: u32 = 1 << 1;
+    let unique_local: u32 = 1 << 2;
+    let global: u32 = 1 << 3;
+    let unicast_link_local: u32 = 1 << 4;
+    let unicast_global: u32 = 1 << 7;
+    let documentation: u32 = 1 << 8;
+    let benchmarking: u32 = 1 << 16;
+    let multicast_interface_local: u32 = 1 << 9;
+    let multicast_link_local: u32 = 1 << 10;
+    let multicast_realm_local: u32 = 1 << 11;
+    let multicast_admin_local: u32 = 1 << 12;
+    let multicast_site_local: u32 = 1 << 13;
+    let multicast_organization_local: u32 = 1 << 14;
+    let multicast_global: u32 = 1 << 15;
+
+    check!("::", &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unspecified);
+
+    check!("::1", &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1], loopback);
+
+    check!("::0.0.0.2", &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2], global | unicast_global);
+
+    check!("1::", &[0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], global | unicast_global);
+
+    check!(
+        "::ffff:127.0.0.1",
+        &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, 0x7f, 0, 0, 1],
+        unicast_global
+    );
+
+    check!(
+        "64:ff9b:1::",
+        &[0, 0x64, 0xff, 0x9b, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        unicast_global
+    );
+
+    check!("100::", &[0x01, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_global);
+
+    check!("2001::", &[0x20, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_global);
+
+    check!(
+        "2001:1::1",
+        &[0x20, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
+        global | unicast_global
+    );
+
+    check!(
+        "2001:1::2",
+        &[0x20, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2],
+        global | unicast_global
+    );
+
+    check!(
+        "2001:3::",
+        &[0x20, 1, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        global | unicast_global
+    );
+
+    check!(
+        "2001:4:112::",
+        &[0x20, 1, 0, 4, 1, 0x12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        global | unicast_global
+    );
+
+    check!(
+        "2001:20::",
+        &[0x20, 1, 0, 0x20, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        global | unicast_global
+    );
+
+    check!("2001:30::", &[0x20, 1, 0, 0x30, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_global);
+
+    check!(
+        "2001:200::",
+        &[0x20, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        global | unicast_global
+    );
+
+    check!("fc00::", &[0xfc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unique_local);
+
+    check!(
+        "fdff:ffff::",
+        &[0xfd, 0xff, 0xff, 0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        unique_local
+    );
+
+    check!(
+        "fe80:ffff::",
+        &[0xfe, 0x80, 0xff, 0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        unicast_link_local
+    );
+
+    check!("fe80::", &[0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_link_local);
+
+    check!(
+        "febf:ffff::",
+        &[0xfe, 0xbf, 0xff, 0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        unicast_link_local
+    );
+
+    check!("febf::", &[0xfe, 0xbf, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], unicast_link_local);
+
+    check!(
+        "febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff",
+        &[
+            0xfe, 0xbf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+            0xff, 0xff
+        ],
+        unicast_link_local
+    );
+
+    check!(
+        "fe80::ffff:ffff:ffff:ffff",
+        &[
+            0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+            0xff, 0xff
+        ],
+        unicast_link_local
+    );
+
+    check!(
+        "fe80:0:0:1::",
+        &[0xfe, 0x80, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
+        unicast_link_local
+    );
+
+    check!(
+        "fec0::",
+        &[0xfe, 0xc0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        unicast_global | global
+    );
+
+    check!(
+        "ff01::",
+        &[0xff, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_interface_local | global
+    );
+
+    check!(
+        "ff02::",
+        &[0xff, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_link_local | global
+    );
+
+    check!(
+        "ff03::",
+        &[0xff, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_realm_local | global
+    );
+
+    check!(
+        "ff04::",
+        &[0xff, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_admin_local | global
+    );
+
+    check!(
+        "ff05::",
+        &[0xff, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_site_local | global
+    );
+
+    check!(
+        "ff08::",
+        &[0xff, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_organization_local | global
+    );
+
+    check!(
+        "ff0e::",
+        &[0xff, 0xe, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+        multicast_global | global
+    );
+
+    check!(
+        "2001:db8:85a3::8a2e:370:7334",
+        &[0x20, 1, 0xd, 0xb8, 0x85, 0xa3, 0, 0, 0, 0, 0x8a, 0x2e, 3, 0x70, 0x73, 0x34],
+        documentation
+    );
+
+    check!(
+        "2001:2::ac32:23ff:21",
+        &[0x20, 1, 0, 2, 0, 0, 0, 0, 0, 0, 0xac, 0x32, 0x23, 0xff, 0, 0x21],
+        benchmarking
+    );
+
+    check!(
+        "102:304:506:708:90a:b0c:d0e:f10",
+        &[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
+        global | unicast_global
+    );
+}
+
+#[test]
+fn test_ipv4_to_int() {
+    let a = Ipv4Addr::new(0x11, 0x22, 0x33, 0x44);
+    assert_eq!(u32::from(a), 0x11223344);
+}
+
+#[test]
+fn test_int_to_ipv4() {
+    let a = Ipv4Addr::new(0x11, 0x22, 0x33, 0x44);
+    assert_eq!(Ipv4Addr::from(0x11223344), a);
+}
+
+#[test]
+fn test_ipv6_to_int() {
+    let a = Ipv6Addr::new(0x1122, 0x3344, 0x5566, 0x7788, 0x99aa, 0xbbcc, 0xddee, 0xff11);
+    assert_eq!(u128::from(a), 0x112233445566778899aabbccddeeff11u128);
+}
+
+#[test]
+fn test_int_to_ipv6() {
+    let a = Ipv6Addr::new(0x1122, 0x3344, 0x5566, 0x7788, 0x99aa, 0xbbcc, 0xddee, 0xff11);
+    assert_eq!(Ipv6Addr::from(0x112233445566778899aabbccddeeff11u128), a);
+}
+
+#[test]
+fn ipv4_from_constructors() {
+    assert_eq!(Ipv4Addr::LOCALHOST, Ipv4Addr::new(127, 0, 0, 1));
+    assert!(Ipv4Addr::LOCALHOST.is_loopback());
+    assert_eq!(Ipv4Addr::UNSPECIFIED, Ipv4Addr::new(0, 0, 0, 0));
+    assert!(Ipv4Addr::UNSPECIFIED.is_unspecified());
+    assert_eq!(Ipv4Addr::BROADCAST, Ipv4Addr::new(255, 255, 255, 255));
+    assert!(Ipv4Addr::BROADCAST.is_broadcast());
+}
+
+#[test]
+fn ipv6_from_constructors() {
+    assert_eq!(Ipv6Addr::LOCALHOST, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+    assert!(Ipv6Addr::LOCALHOST.is_loopback());
+    assert_eq!(Ipv6Addr::UNSPECIFIED, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
+    assert!(Ipv6Addr::UNSPECIFIED.is_unspecified());
+}
+
+#[test]
+fn ipv4_from_octets() {
+    assert_eq!(Ipv4Addr::from([127, 0, 0, 1]), Ipv4Addr::new(127, 0, 0, 1))
+}
+
+#[test]
+fn ipv6_from_segments() {
+    let from_u16s =
+        Ipv6Addr::from([0x0011, 0x2233, 0x4455, 0x6677, 0x8899, 0xaabb, 0xccdd, 0xeeff]);
+    let new = Ipv6Addr::new(0x0011, 0x2233, 0x4455, 0x6677, 0x8899, 0xaabb, 0xccdd, 0xeeff);
+    assert_eq!(new, from_u16s);
+}
+
+#[test]
+fn ipv6_from_octets() {
+    let from_u16s =
+        Ipv6Addr::from([0x0011, 0x2233, 0x4455, 0x6677, 0x8899, 0xaabb, 0xccdd, 0xeeff]);
+    let from_u8s = Ipv6Addr::from([
+        0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee,
+        0xff,
+    ]);
+    assert_eq!(from_u16s, from_u8s);
+}
+
+#[test]
+fn cmp() {
+    let v41 = Ipv4Addr::new(100, 64, 3, 3);
+    let v42 = Ipv4Addr::new(192, 0, 2, 2);
+    let v61 = "2001:db8:f00::1002".parse::<Ipv6Addr>().unwrap();
+    let v62 = "2001:db8:f00::2001".parse::<Ipv6Addr>().unwrap();
+    assert!(v41 < v42);
+    assert!(v61 < v62);
+
+    assert_eq!(v41, IpAddr::V4(v41));
+    assert_eq!(v61, IpAddr::V6(v61));
+    assert!(v41 != IpAddr::V4(v42));
+    assert!(v61 != IpAddr::V6(v62));
+
+    assert!(v41 < IpAddr::V4(v42));
+    assert!(v61 < IpAddr::V6(v62));
+    assert!(IpAddr::V4(v41) < v42);
+    assert!(IpAddr::V6(v61) < v62);
+
+    assert!(v41 < IpAddr::V6(v61));
+    assert!(IpAddr::V4(v41) < v61);
+}
+
+#[test]
+fn is_v4() {
+    let ip = IpAddr::V4(Ipv4Addr::new(100, 64, 3, 3));
+    assert!(ip.is_ipv4());
+    assert!(!ip.is_ipv6());
+}
+
+#[test]
+fn is_v6() {
+    let ip = IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0x1234, 0x5678));
+    assert!(!ip.is_ipv4());
+    assert!(ip.is_ipv6());
+}
+
+#[test]
+fn ipv4_const() {
+    // test that the methods of `Ipv4Addr` are usable in a const context
+
+    const IP_ADDRESS: Ipv4Addr = Ipv4Addr::new(127, 0, 0, 1);
+    assert_eq!(IP_ADDRESS, Ipv4Addr::LOCALHOST);
+
+    const OCTETS: [u8; 4] = IP_ADDRESS.octets();
+    assert_eq!(OCTETS, [127, 0, 0, 1]);
+
+    const IS_UNSPECIFIED: bool = IP_ADDRESS.is_unspecified();
+    assert!(!IS_UNSPECIFIED);
+
+    const IS_LOOPBACK: bool = IP_ADDRESS.is_loopback();
+    assert!(IS_LOOPBACK);
+
+    const IS_PRIVATE: bool = IP_ADDRESS.is_private();
+    assert!(!IS_PRIVATE);
+
+    const IS_LINK_LOCAL: bool = IP_ADDRESS.is_link_local();
+    assert!(!IS_LINK_LOCAL);
+
+    const IS_GLOBAL: bool = IP_ADDRESS.is_global();
+    assert!(!IS_GLOBAL);
+
+    const IS_SHARED: bool = IP_ADDRESS.is_shared();
+    assert!(!IS_SHARED);
+
+    const IS_BENCHMARKING: bool = IP_ADDRESS.is_benchmarking();
+    assert!(!IS_BENCHMARKING);
+
+    const IS_RESERVED: bool = IP_ADDRESS.is_reserved();
+    assert!(!IS_RESERVED);
+
+    const IS_MULTICAST: bool = IP_ADDRESS.is_multicast();
+    assert!(!IS_MULTICAST);
+
+    const IS_BROADCAST: bool = IP_ADDRESS.is_broadcast();
+    assert!(!IS_BROADCAST);
+
+    const IS_DOCUMENTATION: bool = IP_ADDRESS.is_documentation();
+    assert!(!IS_DOCUMENTATION);
+
+    const IP_V6_COMPATIBLE: Ipv6Addr = IP_ADDRESS.to_ipv6_compatible();
+    assert_eq!(
+        IP_V6_COMPATIBLE,
+        Ipv6Addr::from([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 127, 0, 0, 1])
+    );
+
+    const IP_V6_MAPPED: Ipv6Addr = IP_ADDRESS.to_ipv6_mapped();
+    assert_eq!(
+        IP_V6_MAPPED,
+        Ipv6Addr::from([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 127, 0, 0, 1])
+    );
+}
+
+#[test]
+fn ipv6_const() {
+    // test that the methods of `Ipv6Addr` are usable in a const context
+
+    const IP_ADDRESS: Ipv6Addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1);
+    assert_eq!(IP_ADDRESS, Ipv6Addr::LOCALHOST);
+
+    const SEGMENTS: [u16; 8] = IP_ADDRESS.segments();
+    assert_eq!(SEGMENTS, [0, 0, 0, 0, 0, 0, 0, 1]);
+
+    const OCTETS: [u8; 16] = IP_ADDRESS.octets();
+    assert_eq!(OCTETS, [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]);
+
+    const IS_UNSPECIFIED: bool = IP_ADDRESS.is_unspecified();
+    assert!(!IS_UNSPECIFIED);
+
+    const IS_LOOPBACK: bool = IP_ADDRESS.is_loopback();
+    assert!(IS_LOOPBACK);
+
+    const IS_GLOBAL: bool = IP_ADDRESS.is_global();
+    assert!(!IS_GLOBAL);
+
+    const IS_UNIQUE_LOCAL: bool = IP_ADDRESS.is_unique_local();
+    assert!(!IS_UNIQUE_LOCAL);
+
+    const IS_UNICAST_LINK_LOCAL: bool = IP_ADDRESS.is_unicast_link_local();
+    assert!(!IS_UNICAST_LINK_LOCAL);
+
+    const IS_DOCUMENTATION: bool = IP_ADDRESS.is_documentation();
+    assert!(!IS_DOCUMENTATION);
+
+    const IS_BENCHMARKING: bool = IP_ADDRESS.is_benchmarking();
+    assert!(!IS_BENCHMARKING);
+
+    const IS_UNICAST_GLOBAL: bool = IP_ADDRESS.is_unicast_global();
+    assert!(!IS_UNICAST_GLOBAL);
+
+    const MULTICAST_SCOPE: Option<Ipv6MulticastScope> = IP_ADDRESS.multicast_scope();
+    assert_eq!(MULTICAST_SCOPE, None);
+
+    const IS_MULTICAST: bool = IP_ADDRESS.is_multicast();
+    assert!(!IS_MULTICAST);
+
+    const IP_V4: Option<Ipv4Addr> = IP_ADDRESS.to_ipv4();
+    assert_eq!(IP_V4.unwrap(), Ipv4Addr::new(0, 0, 0, 1));
+}
+
+#[test]
+fn ip_const() {
+    // test that the methods of `IpAddr` are usable in a const context
+
+    const IP_ADDRESS: IpAddr = IpAddr::V4(Ipv4Addr::LOCALHOST);
+
+    const IS_UNSPECIFIED: bool = IP_ADDRESS.is_unspecified();
+    assert!(!IS_UNSPECIFIED);
+
+    const IS_LOOPBACK: bool = IP_ADDRESS.is_loopback();
+    assert!(IS_LOOPBACK);
+
+    const IS_GLOBAL: bool = IP_ADDRESS.is_global();
+    assert!(!IS_GLOBAL);
+
+    const IS_MULTICAST: bool = IP_ADDRESS.is_multicast();
+    assert!(!IS_MULTICAST);
+
+    const IS_IP_V4: bool = IP_ADDRESS.is_ipv4();
+    assert!(IS_IP_V4);
+
+    const IS_IP_V6: bool = IP_ADDRESS.is_ipv6();
+    assert!(!IS_IP_V6);
+}
+
+#[test]
+fn structural_match() {
+    // test that all IP types can be structurally matched upon
+
+    const IPV4: Ipv4Addr = Ipv4Addr::LOCALHOST;
+    match IPV4 {
+        Ipv4Addr::LOCALHOST => {}
+        _ => unreachable!(),
+    }
+
+    const IPV6: Ipv6Addr = Ipv6Addr::LOCALHOST;
+    match IPV6 {
+        Ipv6Addr::LOCALHOST => {}
+        _ => unreachable!(),
+    }
+
+    const IP: IpAddr = IpAddr::V4(Ipv4Addr::LOCALHOST);
+    match IP {
+        IpAddr::V4(Ipv4Addr::LOCALHOST) => {}
+        _ => unreachable!(),
+    }
+}
diff --git a/library/core/tests/net/mod.rs b/library/core/tests/net/mod.rs
new file mode 100644
index 000000000..8f17bbe55
--- /dev/null
+++ b/library/core/tests/net/mod.rs
@@ -0,0 +1,13 @@
+use core::net::{Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+
+mod ip_addr;
+mod parser;
+mod socket_addr;
+
+pub fn sa4(a: Ipv4Addr, p: u16) -> SocketAddr {
+    SocketAddr::V4(SocketAddrV4::new(a, p))
+}
+
+pub fn sa6(a: Ipv6Addr, p: u16) -> SocketAddr {
+    SocketAddr::V6(SocketAddrV6::new(a, p, 0, 0))
+}
diff --git a/library/core/tests/net/parser.rs b/library/core/tests/net/parser.rs
new file mode 100644
index 000000000..36b87d7c1
--- /dev/null
+++ b/library/core/tests/net/parser.rs
@@ -0,0 +1,149 @@
+// FIXME: These tests are all excellent candidates for AFL fuzz testing
+use core::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+use core::str::FromStr;
+
+const PORT: u16 = 8080;
+const SCOPE_ID: u32 = 1337;
+
+const IPV4: Ipv4Addr = Ipv4Addr::new(192, 168, 0, 1);
+const IPV4_STR: &str = "192.168.0.1";
+const IPV4_STR_PORT: &str = "192.168.0.1:8080";
+const IPV4_STR_WITH_OCTAL: &str = "0127.0.0.1";
+const IPV4_STR_WITH_HEX: &str = "0x10.0.0.1";
+
+const IPV6: Ipv6Addr = Ipv6Addr::new(0x2001, 0xdb8, 0, 0, 0, 0, 0xc0a8, 0x1);
+const IPV6_STR_FULL: &str = "2001:db8:0:0:0:0:c0a8:1";
+const IPV6_STR_COMPRESS: &str = "2001:db8::c0a8:1";
+const IPV6_STR_V4: &str = "2001:db8::192.168.0.1";
+const IPV6_STR_V4_WITH_OCTAL: &str = "2001:db8::0127.0.0.1";
+const IPV6_STR_V4_WITH_HEX: &str = "2001:db8::0x10.0.0.1";
+const IPV6_STR_PORT: &str = "[2001:db8::c0a8:1]:8080";
+const IPV6_STR_PORT_SCOPE_ID: &str = "[2001:db8::c0a8:1%1337]:8080";
+
+#[test]
+fn parse_ipv4() {
+    let result: Ipv4Addr = IPV4_STR.parse().unwrap();
+    assert_eq!(result, IPV4);
+
+    assert!(Ipv4Addr::from_str(IPV4_STR_PORT).is_err());
+    assert!(Ipv4Addr::from_str(IPV4_STR_WITH_OCTAL).is_err());
+    assert!(Ipv4Addr::from_str(IPV4_STR_WITH_HEX).is_err());
+    assert!(Ipv4Addr::from_str(IPV6_STR_FULL).is_err());
+    assert!(Ipv4Addr::from_str(IPV6_STR_COMPRESS).is_err());
+    assert!(Ipv4Addr::from_str(IPV6_STR_V4).is_err());
+    assert!(Ipv4Addr::from_str(IPV6_STR_PORT).is_err());
+}
+
+#[test]
+fn parse_ipv6() {
+    let result: Ipv6Addr = IPV6_STR_FULL.parse().unwrap();
+    assert_eq!(result, IPV6);
+
+    let result: Ipv6Addr = IPV6_STR_COMPRESS.parse().unwrap();
+    assert_eq!(result, IPV6);
+
+    let result: Ipv6Addr = IPV6_STR_V4.parse().unwrap();
+    assert_eq!(result, IPV6);
+
+    assert!(Ipv6Addr::from_str(IPV6_STR_V4_WITH_OCTAL).is_err());
+    assert!(Ipv6Addr::from_str(IPV6_STR_V4_WITH_HEX).is_err());
+    assert!(Ipv6Addr::from_str(IPV4_STR).is_err());
+    assert!(Ipv6Addr::from_str(IPV4_STR_PORT).is_err());
+    assert!(Ipv6Addr::from_str(IPV6_STR_PORT).is_err());
+}
+
+#[test]
+fn parse_ip() {
+    let result: IpAddr = IPV4_STR.parse().unwrap();
+    assert_eq!(result, IpAddr::from(IPV4));
+
+    let result: IpAddr = IPV6_STR_FULL.parse().unwrap();
+    assert_eq!(result, IpAddr::from(IPV6));
+
+    let result: IpAddr = IPV6_STR_COMPRESS.parse().unwrap();
+    assert_eq!(result, IpAddr::from(IPV6));
+
+    let result: IpAddr = IPV6_STR_V4.parse().unwrap();
+    assert_eq!(result, IpAddr::from(IPV6));
+
+    assert!(IpAddr::from_str(IPV4_STR_PORT).is_err());
+    assert!(IpAddr::from_str(IPV6_STR_PORT).is_err());
+}
+
+#[test]
+fn parse_socket_v4() {
+    let result: SocketAddrV4 = IPV4_STR_PORT.parse().unwrap();
+    assert_eq!(result, SocketAddrV4::new(IPV4, PORT));
+
+    assert!(SocketAddrV4::from_str(IPV4_STR).is_err());
+    assert!(SocketAddrV4::from_str(IPV6_STR_FULL).is_err());
+    assert!(SocketAddrV4::from_str(IPV6_STR_COMPRESS).is_err());
+    assert!(SocketAddrV4::from_str(IPV6_STR_V4).is_err());
+    assert!(SocketAddrV4::from_str(IPV6_STR_PORT).is_err());
+}
+
+#[test]
+fn parse_socket_v6() {
+    assert_eq!(IPV6_STR_PORT.parse(), Ok(SocketAddrV6::new(IPV6, PORT, 0, 0)));
+    assert_eq!(IPV6_STR_PORT_SCOPE_ID.parse(), Ok(SocketAddrV6::new(IPV6, PORT, 0, SCOPE_ID)));
+
+    assert!(SocketAddrV6::from_str(IPV4_STR).is_err());
+    assert!(SocketAddrV6::from_str(IPV4_STR_PORT).is_err());
+    assert!(SocketAddrV6::from_str(IPV6_STR_FULL).is_err());
+    assert!(SocketAddrV6::from_str(IPV6_STR_COMPRESS).is_err());
+    assert!(SocketAddrV6::from_str(IPV6_STR_V4).is_err());
+}
+
+#[test]
+fn parse_socket() {
+    let result: SocketAddr = IPV4_STR_PORT.parse().unwrap();
+    assert_eq!(result, SocketAddr::from((IPV4, PORT)));
+
+    let result: SocketAddr = IPV6_STR_PORT.parse().unwrap();
+    assert_eq!(result, SocketAddr::from((IPV6, PORT)));
+
+    assert!(SocketAddr::from_str(IPV4_STR).is_err());
+    assert!(SocketAddr::from_str(IPV6_STR_FULL).is_err());
+    assert!(SocketAddr::from_str(IPV6_STR_COMPRESS).is_err());
+    assert!(SocketAddr::from_str(IPV6_STR_V4).is_err());
+}
+
+#[test]
+fn ipv6_corner_cases() {
+    let result: Ipv6Addr = "1::".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(1, 0, 0, 0, 0, 0, 0, 0));
+
+    let result: Ipv6Addr = "1:1::".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(1, 1, 0, 0, 0, 0, 0, 0));
+
+    let result: Ipv6Addr = "::1".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+
+    let result: Ipv6Addr = "::1:1".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 1, 1));
+
+    let result: Ipv6Addr = "::".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
+
+    let result: Ipv6Addr = "::192.168.0.1".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc0a8, 0x1));
+
+    let result: Ipv6Addr = "::1:192.168.0.1".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(0, 0, 0, 0, 0, 1, 0xc0a8, 0x1));
+
+    let result: Ipv6Addr = "1:1:1:1:1:1:192.168.0.1".parse().unwrap();
+    assert_eq!(result, Ipv6Addr::new(1, 1, 1, 1, 1, 1, 0xc0a8, 0x1));
+}
+
+// Things that might not seem like failures but are
+#[test]
+fn ipv6_corner_failures() {
+    // No IP address before the ::
+    assert!(Ipv6Addr::from_str("1:192.168.0.1::").is_err());
+
+    // :: must have at least 1 set of zeroes
+    assert!(Ipv6Addr::from_str("1:1:1:1::1:1:1:1").is_err());
+
+    // Need brackets for a port
+    assert!(SocketAddrV6::from_str("1:1:1:1:1:1:1:1:8080").is_err());
+}
diff --git a/library/core/tests/net/socket_addr.rs b/library/core/tests/net/socket_addr.rs
new file mode 100644
index 000000000..68c7cd94d
--- /dev/null
+++ b/library/core/tests/net/socket_addr.rs
@@ -0,0 +1,233 @@
+use core::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+
+#[test]
+fn ipv4_socket_addr_to_string() {
+    // Shortest possible IPv4 length.
+    assert_eq!(SocketAddrV4::new(Ipv4Addr::new(0, 0, 0, 0), 0).to_string(), "0.0.0.0:0");
+
+    // Longest possible IPv4 length.
+    assert_eq!(
+        SocketAddrV4::new(Ipv4Addr::new(255, 255, 255, 255), u16::MAX).to_string(),
+        "255.255.255.255:65535"
+    );
+
+    // Test padding.
+    assert_eq!(
+        &format!("{:16}", SocketAddrV4::new(Ipv4Addr::new(1, 1, 1, 1), 53)),
+        "1.1.1.1:53      "
+    );
+    assert_eq!(
+        &format!("{:>16}", SocketAddrV4::new(Ipv4Addr::new(1, 1, 1, 1), 53)),
+        "      1.1.1.1:53"
+    );
+}
+
+#[test]
+fn ipv6_socket_addr_to_string() {
+    // IPv4-mapped address.
+    assert_eq!(
+        SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc000, 0x280), 8080, 0, 0)
+            .to_string(),
+        "[::ffff:192.0.2.128]:8080"
+    );
+
+    // IPv4-compatible address.
+    assert_eq!(
+        SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0xc000, 0x280), 8080, 0, 0).to_string(),
+        "[::192.0.2.128]:8080"
+    );
+
+    // IPv6 address with no zero segments.
+    assert_eq!(
+        SocketAddrV6::new(Ipv6Addr::new(8, 9, 10, 11, 12, 13, 14, 15), 80, 0, 0).to_string(),
+        "[8:9:a:b:c:d:e:f]:80"
+    );
+
+    // Shortest possible IPv6 length.
+    assert_eq!(SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0, 0, 0).to_string(), "[::]:0");
+
+    // Longest possible IPv6 length.
+    assert_eq!(
+        SocketAddrV6::new(
+            Ipv6Addr::new(0x1111, 0x2222, 0x3333, 0x4444, 0x5555, 0x6666, 0x7777, 0x8888),
+            u16::MAX,
+            u32::MAX,
+            u32::MAX,
+        )
+        .to_string(),
+        "[1111:2222:3333:4444:5555:6666:7777:8888%4294967295]:65535"
+    );
+
+    // Test padding.
+    assert_eq!(
+        &format!("{:22}", SocketAddrV6::new(Ipv6Addr::new(1, 2, 3, 4, 5, 6, 7, 8), 9, 0, 0)),
+        "[1:2:3:4:5:6:7:8]:9   "
+    );
+    assert_eq!(
+        &format!("{:>22}", SocketAddrV6::new(Ipv6Addr::new(1, 2, 3, 4, 5, 6, 7, 8), 9, 0, 0)),
+        "   [1:2:3:4:5:6:7:8]:9"
+    );
+}
+
+#[test]
+fn set_ip() {
+    fn ip4(low: u8) -> Ipv4Addr {
+        Ipv4Addr::new(77, 88, 21, low)
+    }
+    fn ip6(low: u16) -> Ipv6Addr {
+        Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, low)
+    }
+
+    let mut v4 = SocketAddrV4::new(ip4(11), 80);
+    assert_eq!(v4.ip(), &ip4(11));
+    v4.set_ip(ip4(12));
+    assert_eq!(v4.ip(), &ip4(12));
+
+    let mut addr = SocketAddr::V4(v4);
+    assert_eq!(addr.ip(), IpAddr::V4(ip4(12)));
+    addr.set_ip(IpAddr::V4(ip4(13)));
+    assert_eq!(addr.ip(), IpAddr::V4(ip4(13)));
+    addr.set_ip(IpAddr::V6(ip6(14)));
+    assert_eq!(addr.ip(), IpAddr::V6(ip6(14)));
+
+    let mut v6 = SocketAddrV6::new(ip6(1), 80, 0, 0);
+    assert_eq!(v6.ip(), &ip6(1));
+    v6.set_ip(ip6(2));
+    assert_eq!(v6.ip(), &ip6(2));
+
+    let mut addr = SocketAddr::V6(v6);
+    assert_eq!(addr.ip(), IpAddr::V6(ip6(2)));
+    addr.set_ip(IpAddr::V6(ip6(3)));
+    assert_eq!(addr.ip(), IpAddr::V6(ip6(3)));
+    addr.set_ip(IpAddr::V4(ip4(4)));
+    assert_eq!(addr.ip(), IpAddr::V4(ip4(4)));
+}
+
+#[test]
+fn set_port() {
+    let mut v4 = SocketAddrV4::new(Ipv4Addr::new(77, 88, 21, 11), 80);
+    assert_eq!(v4.port(), 80);
+    v4.set_port(443);
+    assert_eq!(v4.port(), 443);
+
+    let mut addr = SocketAddr::V4(v4);
+    assert_eq!(addr.port(), 443);
+    addr.set_port(8080);
+    assert_eq!(addr.port(), 8080);
+
+    let mut v6 = SocketAddrV6::new(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 80, 0, 0);
+    assert_eq!(v6.port(), 80);
+    v6.set_port(443);
+    assert_eq!(v6.port(), 443);
+
+    let mut addr = SocketAddr::V6(v6);
+    assert_eq!(addr.port(), 443);
+    addr.set_port(8080);
+    assert_eq!(addr.port(), 8080);
+}
+
+#[test]
+fn set_flowinfo() {
+    let mut v6 = SocketAddrV6::new(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 80, 10, 0);
+    assert_eq!(v6.flowinfo(), 10);
+    v6.set_flowinfo(20);
+    assert_eq!(v6.flowinfo(), 20);
+}
+
+#[test]
+fn set_scope_id() {
+    let mut v6 = SocketAddrV6::new(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 80, 0, 10);
+    assert_eq!(v6.scope_id(), 10);
+    v6.set_scope_id(20);
+    assert_eq!(v6.scope_id(), 20);
+}
+
+#[test]
+fn is_v4() {
+    let v4 = SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(77, 88, 21, 11), 80));
+    assert!(v4.is_ipv4());
+    assert!(!v4.is_ipv6());
+}
+
+#[test]
+fn is_v6() {
+    let v6 = SocketAddr::V6(SocketAddrV6::new(
+        Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1),
+        80,
+        10,
+        0,
+    ));
+    assert!(!v6.is_ipv4());
+    assert!(v6.is_ipv6());
+}
+
+#[test]
+fn socket_v4_to_str() {
+    let socket = SocketAddrV4::new(Ipv4Addr::new(192, 168, 0, 1), 8080);
+
+    assert_eq!(format!("{socket}"), "192.168.0.1:8080");
+    assert_eq!(format!("{socket:<20}"), "192.168.0.1:8080    ");
+    assert_eq!(format!("{socket:>20}"), "    192.168.0.1:8080");
+    assert_eq!(format!("{socket:^20}"), "  192.168.0.1:8080  ");
+    assert_eq!(format!("{socket:.10}"), "192.168.0.");
+}
+
+#[test]
+fn socket_v6_to_str() {
+    let mut socket = SocketAddrV6::new(Ipv6Addr::new(0x2a02, 0x6b8, 0, 1, 0, 0, 0, 1), 53, 0, 0);
+
+    assert_eq!(format!("{socket}"), "[2a02:6b8:0:1::1]:53");
+    assert_eq!(format!("{socket:<24}"), "[2a02:6b8:0:1::1]:53    ");
+    assert_eq!(format!("{socket:>24}"), "    [2a02:6b8:0:1::1]:53");
+    assert_eq!(format!("{socket:^24}"), "  [2a02:6b8:0:1::1]:53  ");
+    assert_eq!(format!("{socket:.15}"), "[2a02:6b8:0:1::");
+
+    socket.set_scope_id(5);
+
+    assert_eq!(format!("{socket}"), "[2a02:6b8:0:1::1%5]:53");
+    assert_eq!(format!("{socket:<24}"), "[2a02:6b8:0:1::1%5]:53  ");
+    assert_eq!(format!("{socket:>24}"), "  [2a02:6b8:0:1::1%5]:53");
+    assert_eq!(format!("{socket:^24}"), " [2a02:6b8:0:1::1%5]:53 ");
+    assert_eq!(format!("{socket:.18}"), "[2a02:6b8:0:1::1%5");
+}
+
+#[test]
+fn compare() {
+    let v4_1 = "224.120.45.1:23456".parse::<SocketAddrV4>().unwrap();
+    let v4_2 = "224.210.103.5:12345".parse::<SocketAddrV4>().unwrap();
+    let v4_3 = "224.210.103.5:23456".parse::<SocketAddrV4>().unwrap();
+    let v6_1 = "[2001:db8:f00::1002]:23456".parse::<SocketAddrV6>().unwrap();
+    let v6_2 = "[2001:db8:f00::2001]:12345".parse::<SocketAddrV6>().unwrap();
+    let v6_3 = "[2001:db8:f00::2001]:23456".parse::<SocketAddrV6>().unwrap();
+
+    // equality
+    assert_eq!(v4_1, v4_1);
+    assert_eq!(v6_1, v6_1);
+    assert_eq!(SocketAddr::V4(v4_1), SocketAddr::V4(v4_1));
+    assert_eq!(SocketAddr::V6(v6_1), SocketAddr::V6(v6_1));
+    assert!(v4_1 != v4_2);
+    assert!(v6_1 != v6_2);
+
+    // compare different addresses
+    assert!(v4_1 < v4_2);
+    assert!(v6_1 < v6_2);
+    assert!(v4_2 > v4_1);
+    assert!(v6_2 > v6_1);
+
+    // compare the same address with different ports
+    assert!(v4_2 < v4_3);
+    assert!(v6_2 < v6_3);
+    assert!(v4_3 > v4_2);
+    assert!(v6_3 > v6_2);
+
+    // compare different addresses with the same port
+    assert!(v4_1 < v4_3);
+    assert!(v6_1 < v6_3);
+    assert!(v4_3 > v4_1);
+    assert!(v6_3 > v6_1);
+
+    // compare with an inferred right-hand side
+    assert_eq!(v4_1, "224.120.45.1:23456".parse().unwrap());
+    assert_eq!(v6_1, "[2001:db8:f00::1002]:23456".parse().unwrap());
+    assert_eq!(SocketAddr::V4(v4_1), "224.120.45.1:23456".parse().unwrap());
+}
diff --git a/library/core/tests/num/dec2flt/mod.rs b/library/core/tests/num/dec2flt/mod.rs
index c4e105cba..a2b9bb551 100644
--- a/library/core/tests/num/dec2flt/mod.rs
+++ b/library/core/tests/num/dec2flt/mod.rs
@@ -15,7 +15,7 @@ macro_rules! test_literal {
         for input in inputs {
             assert_eq!(input.parse(), Ok(x64));
             assert_eq!(input.parse(), Ok(x32));
-            let neg_input = &format!("-{input}");
+            let neg_input = format!("-{input}");
             assert_eq!(neg_input.parse(), Ok(-x64));
             assert_eq!(neg_input.parse(), Ok(-x32));
         }
diff --git a/library/core/tests/ptr.rs b/library/core/tests/ptr.rs
index 80d30f14c..c02cd99cc 100644
--- a/library/core/tests/ptr.rs
+++ b/library/core/tests/ptr.rs
@@ -25,7 +25,7 @@ fn test() {
             snd: isize,
         }
         let mut p = Pair { fst: 10, snd: 20 };
-        let pptr: *mut Pair = &mut p;
+        let pptr: *mut Pair = addr_of_mut!(p);
         let iptr: *mut isize = pptr as *mut isize;
         assert_eq!(*iptr, 10);
         *iptr = 30;
@@ -1070,8 +1070,8 @@ fn swap_copy_untyped() {
     let mut x = 5u8;
     let mut y = 6u8;
 
-    let ptr1 = &mut x as *mut u8 as *mut bool;
-    let ptr2 = &mut y as *mut u8 as *mut bool;
+    let ptr1 = addr_of_mut!(x).cast::<bool>();
+    let ptr2 = addr_of_mut!(y).cast::<bool>();
 
     unsafe {
         ptr::swap(ptr1, ptr2);