Merge pull request #19726 from lnicola/sync-from-rust

Sync from downstream again

17 files changed, 330 insertions, 365 deletions

diff --git a/library/core/src/fmt/rt.rs b/library/core/src/fmt/rt.rs
index adcfdd309b7..e409771362e 100644
--- a/library/core/src/fmt/rt.rs
+++ b/library/core/src/fmt/rt.rs
@@ -200,8 +200,15 @@ impl Argument<'_> {
     /// let f = format_args!("{}", "a");
     /// println!("{f}");
     /// ```
+    ///
+    /// This function should _not_ be const, to make sure we don't accept
+    /// format_args!() and panic!() with arguments in const, even when not evaluated:
+    ///
+    /// ```compile_fail,E0015
+    /// const _: () = if false { panic!("a {}", "a") };
+    /// ```
     #[inline]
-    pub const fn none() -> [Self; 0] {
+    pub fn none() -> [Self; 0] {
         []
     }
 }
diff --git a/library/core/src/future/async_drop.rs b/library/core/src/future/async_drop.rs
index f1778a4d782..fc4f95a98b4 100644
--- a/library/core/src/future/async_drop.rs
+++ b/library/core/src/future/async_drop.rs
@@ -1,284 +1,51 @@
 #![unstable(feature = "async_drop", issue = "126482")]
 
-use crate::fmt;
-use crate::future::{Future, IntoFuture};
-use crate::intrinsics::discriminant_value;
-use crate::marker::{DiscriminantKind, PhantomPinned};
-use crate::mem::MaybeUninit;
-use crate::pin::Pin;
-use crate::task::{Context, Poll, ready};
-
-/// Asynchronously drops a value by running `AsyncDrop::async_drop`
-/// on a value and its fields recursively.
-#[unstable(feature = "async_drop", issue = "126482")]
-pub fn async_drop<T>(value: T) -> AsyncDropOwning<T> {
-    AsyncDropOwning { value: MaybeUninit::new(value), dtor: None, _pinned: PhantomPinned }
-}
-
-/// A future returned by the [`async_drop`].
-#[unstable(feature = "async_drop", issue = "126482")]
-pub struct AsyncDropOwning<T> {
-    value: MaybeUninit<T>,
-    dtor: Option<AsyncDropInPlace<T>>,
-    _pinned: PhantomPinned,
-}
-
-#[unstable(feature = "async_drop", issue = "126482")]
-impl<T> fmt::Debug for AsyncDropOwning<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("AsyncDropOwning").finish_non_exhaustive()
-    }
-}
-
-#[unstable(feature = "async_drop", issue = "126482")]
-impl<T> Future for AsyncDropOwning<T> {
-    type Output = ();
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        // SAFETY: Self is pinned thus it is ok to store references to self
-        unsafe {
-            let this = self.get_unchecked_mut();
-            let dtor = Pin::new_unchecked(
-                this.dtor.get_or_insert_with(|| async_drop_in_place(this.value.as_mut_ptr())),
-            );
-            // AsyncDestuctors are idempotent so Self gets idempotency as well
-            dtor.poll(cx)
-        }
-    }
-}
+#[allow(unused_imports)]
+use core::future::Future;
 
-#[lang = "async_drop_in_place"]
-#[allow(unconditional_recursion)]
-// FIXME: Consider if `#[rustc_diagnostic_item = "ptr_drop_in_place"]` is needed?
-unsafe fn async_drop_in_place_raw<T: ?Sized>(
-    to_drop: *mut T,
-) -> <T as AsyncDestruct>::AsyncDestructor {
-    // Code here does not matter - this is replaced by the
-    // real async drop glue constructor by the compiler.
-
-    // SAFETY: see comment above
-    unsafe { async_drop_in_place_raw(to_drop) }
-}
+#[allow(unused_imports)]
+use crate::pin::Pin;
+#[allow(unused_imports)]
+use crate::task::{Context, Poll};
 
-/// Creates the asynchronous destructor of the pointed-to value.
-///
-/// # Safety
-///
-/// Behavior is undefined if any of the following conditions are violated:
-///
-/// * `to_drop` must be [valid](crate::ptr#safety) for both reads and writes.
-///
-/// * `to_drop` must be properly aligned, even if `T` has size 0.
+/// Async version of Drop trait.
 ///
-/// * `to_drop` must be nonnull, even if `T` has size 0.
+/// When a value is no longer needed, Rust will run a "destructor" on that value.
+/// The most common way that a value is no longer needed is when it goes out of
+/// scope. Destructors may still run in other circumstances, but we're going to
+/// focus on scope for the examples here. To learn about some of those other cases,
+/// please see [the reference] section on destructors.
 ///
-/// * The value `to_drop` points to must be valid for async dropping,
-///   which may mean it must uphold additional invariants. These
-///   invariants depend on the type of the value being dropped. For
-///   instance, when dropping a Box, the box's pointer to the heap must
-///   be valid.
+/// [the reference]: https://doc.rust-lang.org/reference/destructors.html
 ///
-/// * While `async_drop_in_place` is executing or the returned async
-///   destructor is alive, the only way to access parts of `to_drop`
-///   is through the `self: Pin<&mut Self>` references supplied to
-///   the `AsyncDrop::async_drop` methods that `async_drop_in_place`
-///   or `AsyncDropInPlace<T>::poll` invokes. This usually means the
-///   returned future stores the `to_drop` pointer and user is required
-///   to guarantee that dropped value doesn't move.
+/// ## `Copy` and ([`Drop`]|`AsyncDrop`) are exclusive
 ///
-#[unstable(feature = "async_drop", issue = "126482")]
-pub unsafe fn async_drop_in_place<T: ?Sized>(to_drop: *mut T) -> AsyncDropInPlace<T> {
-    // SAFETY: `async_drop_in_place_raw` has the same safety requirements
-    unsafe { AsyncDropInPlace(async_drop_in_place_raw(to_drop)) }
-}
-
-/// A future returned by the [`async_drop_in_place`].
-#[unstable(feature = "async_drop", issue = "126482")]
-pub struct AsyncDropInPlace<T: ?Sized>(<T as AsyncDestruct>::AsyncDestructor);
-
-#[unstable(feature = "async_drop", issue = "126482")]
-impl<T: ?Sized> fmt::Debug for AsyncDropInPlace<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("AsyncDropInPlace").finish_non_exhaustive()
-    }
-}
-
-#[unstable(feature = "async_drop", issue = "126482")]
-impl<T: ?Sized> Future for AsyncDropInPlace<T> {
-    type Output = ();
-
-    #[inline(always)]
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        // SAFETY: This code simply forwards poll call to the inner future
-        unsafe { Pin::new_unchecked(&mut self.get_unchecked_mut().0) }.poll(cx)
-    }
-}
-
-// FIXME(zetanumbers): Add same restrictions on AsyncDrop impls as
-//   with Drop impls
-/// Custom code within the asynchronous destructor.
+/// You cannot implement both [`Copy`] and ([`Drop`]|`AsyncDrop`) on the same type. Types that
+/// are `Copy` get implicitly duplicated by the compiler, making it very
+/// hard to predict when, and how often destructors will be executed. As such,
+/// these types cannot have destructors.
+#[cfg(not(bootstrap))]
 #[unstable(feature = "async_drop", issue = "126482")]
 #[lang = "async_drop"]
 pub trait AsyncDrop {
-    /// A future returned by the [`AsyncDrop::async_drop`] to be part
-    /// of the async destructor.
-    #[unstable(feature = "async_drop", issue = "126482")]
-    type Dropper<'a>: Future<Output = ()>
-    where
-        Self: 'a;
-
-    /// Constructs the asynchronous destructor for this type.
-    #[unstable(feature = "async_drop", issue = "126482")]
-    fn async_drop(self: Pin<&mut Self>) -> Self::Dropper<'_>;
-}
-
-#[lang = "async_destruct"]
-#[rustc_deny_explicit_impl]
-#[rustc_do_not_implement_via_object]
-trait AsyncDestruct {
-    type AsyncDestructor: Future<Output = ()>;
-}
-
-/// Basically calls `AsyncDrop::async_drop` with pointer. Used to simplify
-/// generation of the code for `async_drop_in_place_raw`
-#[lang = "surface_async_drop_in_place"]
-async unsafe fn surface_async_drop_in_place<T: AsyncDrop + ?Sized>(ptr: *mut T) {
-    // SAFETY: We call this from async drop `async_drop_in_place_raw`
-    //   which has the same safety requirements
-    unsafe { <T as AsyncDrop>::async_drop(Pin::new_unchecked(&mut *ptr)).await }
-}
-
-/// Basically calls `Drop::drop` with pointer. Used to simplify generation
-/// of the code for `async_drop_in_place_raw`
-#[allow(drop_bounds)]
-#[lang = "async_drop_surface_drop_in_place"]
-async unsafe fn surface_drop_in_place<T: Drop + ?Sized>(ptr: *mut T) {
-    // SAFETY: We call this from async drop `async_drop_in_place_raw`
-    //   which has the same safety requirements
-    unsafe { crate::ops::fallback_surface_drop(&mut *ptr) }
-}
-
-/// Wraps a future to continue outputting `Poll::Ready(())` once after
-/// wrapped future completes by returning `Poll::Ready(())` on poll. This
-/// is useful for constructing async destructors to guarantee this
-/// "fuse" property
-//
-// FIXME: Consider optimizing combinators to not have to use fuse in majority
-// of cases, perhaps by adding `#[(rustc_)idempotent(_future)]` attribute for
-// async functions and blocks with the unit return type. However current layout
-// optimizations currently encode `None` case into the async block's discriminant.
-struct Fuse<T> {
-    inner: Option<T>,
-}
-
-#[lang = "async_drop_fuse"]
-fn fuse<T>(inner: T) -> Fuse<T> {
-    Fuse { inner: Some(inner) }
-}
-
-impl<T> Future for Fuse<T>
-where
-    T: Future<Output = ()>,
-{
-    type Output = ();
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        // SAFETY: pin projection into `self.inner`
-        unsafe {
-            let this = self.get_unchecked_mut();
-            if let Some(inner) = &mut this.inner {
-                ready!(Pin::new_unchecked(inner).poll(cx));
-                this.inner = None;
-            }
-        }
-        Poll::Ready(())
-    }
-}
-
-/// Async destructor for arrays and slices.
-#[lang = "async_drop_slice"]
-async unsafe fn slice<T>(s: *mut [T]) {
-    let len = s.len();
-    let ptr = s.as_mut_ptr();
-    for i in 0..len {
-        // SAFETY: we iterate over elements of `s` slice
-        unsafe { async_drop_in_place_raw(ptr.add(i)).await }
-    }
-}
-
-/// Constructs a chain of two futures, which awaits them sequentially as
-/// a future.
-#[lang = "async_drop_chain"]
-async fn chain<F, G>(first: F, last: G)
-where
-    F: IntoFuture<Output = ()>,
-    G: IntoFuture<Output = ()>,
-{
-    first.await;
-    last.await;
-}
-
-/// Basically a lazy version of `async_drop_in_place`. Returns a future
-/// that would call `AsyncDrop::async_drop` on a first poll.
-///
-/// # Safety
-///
-/// Same as `async_drop_in_place` except is lazy to avoid creating
-/// multiple mutable references.
-#[lang = "async_drop_defer"]
-async unsafe fn defer<T: ?Sized>(to_drop: *mut T) {
-    // SAFETY: same safety requirements as `async_drop_in_place`
-    unsafe { async_drop_in_place(to_drop) }.await
-}
-
-/// If `T`'s discriminant is equal to the stored one then awaits `M`
-/// otherwise awaits the `O`.
-///
-/// # Safety
-///
-/// Users should carefully manage the returned future, since it would
-/// try creating an immutable reference from `this` and get pointee's
-/// discriminant.
-// FIXME(zetanumbers): Send and Sync impls
-#[lang = "async_drop_either"]
-async unsafe fn either<O: IntoFuture<Output = ()>, M: IntoFuture<Output = ()>, T>(
-    other: O,
-    matched: M,
-    this: *mut T,
-    discr: <T as DiscriminantKind>::Discriminant,
-) {
-    // SAFETY: Guaranteed by the safety section of this funtion's documentation
-    if unsafe { discriminant_value(&*this) } == discr {
-        drop(other);
-        matched.await
-    } else {
-        drop(matched);
-        other.await
-    }
-}
-
-#[lang = "async_drop_deferred_drop_in_place"]
-async unsafe fn deferred_drop_in_place<T>(to_drop: *mut T) {
-    // SAFETY: same safety requirements as with drop_in_place (implied by
-    // function's name)
-    unsafe { crate::ptr::drop_in_place(to_drop) }
-}
-
-/// Used for noop async destructors. We don't use [`core::future::Ready`]
-/// because it panics after its second poll, which could be potentially
-/// bad if that would happen during the cleanup.
-#[derive(Clone, Copy)]
-struct Noop;
-
-#[lang = "async_drop_noop"]
-fn noop() -> Noop {
-    Noop
-}
-
-impl Future for Noop {
-    type Output = ();
-
-    fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Self::Output> {
-        Poll::Ready(())
-    }
+    /// Executes the async destructor for this type.
+    ///
+    /// This method is called implicitly when the value goes out of scope,
+    /// and cannot be called explicitly.
+    ///
+    /// When this method has been called, `self` has not yet been deallocated.
+    /// That only happens after the method is over.
+    ///
+    /// # Panics
+    #[allow(async_fn_in_trait)]
+    async fn drop(self: Pin<&mut Self>);
+}
+
+/// Async drop.
+#[cfg(not(bootstrap))]
+#[unstable(feature = "async_drop", issue = "126482")]
+#[lang = "async_drop_in_place"]
+pub async unsafe fn async_drop_in_place<T: ?Sized>(_to_drop: *mut T) {
+    // Code here does not matter - this is replaced by the
+    // real implementation by the compiler.
 }
diff --git a/library/core/src/future/mod.rs b/library/core/src/future/mod.rs
index 65c0171c88d..4b5a2f34d3f 100644
--- a/library/core/src/future/mod.rs
+++ b/library/core/src/future/mod.rs
@@ -20,8 +20,9 @@ mod pending;
 mod poll_fn;
 mod ready;
 
+#[cfg(not(bootstrap))]
 #[unstable(feature = "async_drop", issue = "126482")]
-pub use async_drop::{AsyncDrop, AsyncDropInPlace, async_drop, async_drop_in_place};
+pub use async_drop::{AsyncDrop, async_drop_in_place};
 #[stable(feature = "into_future", since = "1.64.0")]
 pub use into_future::IntoFuture;
 #[stable(feature = "future_readiness_fns", since = "1.48.0")]
diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs
index a7563f918a2..c5d5bc000f1 100644
--- a/library/core/src/intrinsics/mod.rs
+++ b/library/core/src/intrinsics/mod.rs
@@ -2996,7 +2996,7 @@ pub unsafe fn nontemporal_store<T>(ptr: *mut T, val: T);
 #[rustc_intrinsic]
 pub const unsafe fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
 
-/// See documentation of `<*const T>::sub_ptr` for details.
+/// See documentation of `<*const T>::offset_from_unsigned` for details.
 #[rustc_nounwind]
 #[rustc_intrinsic]
 #[rustc_intrinsic_const_stable_indirect]
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 9625475e617..64a7ec8906b 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -118,7 +118,6 @@
 #![feature(ptr_metadata)]
 #![feature(set_ptr_value)]
 #![feature(slice_as_array)]
-#![feature(slice_as_chunks)]
 #![feature(slice_ptr_get)]
 #![feature(str_internals)]
 #![feature(str_split_inclusive_remainder)]
diff --git a/library/core/src/ops/drop.rs b/library/core/src/ops/drop.rs
index e024b7fb4d3..5d040804a8d 100644
--- a/library/core/src/ops/drop.rs
+++ b/library/core/src/ops/drop.rs
@@ -240,10 +240,3 @@ pub trait Drop {
     #[stable(feature = "rust1", since = "1.0.0")]
     fn drop(&mut self);
 }
-
-/// Fallback function to call surface level `Drop::drop` function
-#[allow(drop_bounds)]
-#[lang = "fallback_surface_drop"]
-pub(crate) fn fallback_surface_drop<T: Drop + ?Sized>(x: &mut T) {
-    <T as Drop>::drop(x)
-}
diff --git a/library/core/src/ops/index.rs b/library/core/src/ops/index.rs
index 37d9a28fb99..8106c088f0b 100644
--- a/library/core/src/ops/index.rs
+++ b/library/core/src/ops/index.rs
@@ -67,6 +67,7 @@ pub trait Index<Idx: ?Sized> {
     ///
     /// May panic if the index is out of bounds.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[track_caller]
     fn index(&self, index: Idx) -> &Self::Output;
 }
@@ -171,6 +172,7 @@ pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
     ///
     /// May panic if the index is out of bounds.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[track_caller]
     fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
 }
diff --git a/library/core/src/ops/mod.rs b/library/core/src/ops/mod.rs
index 627a875d9f7..1658f0e5a36 100644
--- a/library/core/src/ops/mod.rs
+++ b/library/core/src/ops/mod.rs
@@ -176,7 +176,6 @@ pub use self::deref::Receiver;
 pub use self::deref::{Deref, DerefMut};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::drop::Drop;
-pub(crate) use self::drop::fallback_surface_drop;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::function::{Fn, FnMut, FnOnce};
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/core/src/panicking.rs b/library/core/src/panicking.rs
index 33ad59916e3..83a45436b30 100644
--- a/library/core/src/panicking.rs
+++ b/library/core/src/panicking.rs
@@ -155,30 +155,26 @@ pub const fn panic(expr: &'static str) -> ! {
 // reducing binary size impact.
 macro_rules! panic_const {
     ($($lang:ident = $message:expr,)+) => {
-        pub mod panic_const {
-            use super::*;
-
-            $(
-                /// This is a panic called with a message that's a result of a MIR-produced Assert.
-                //
-                // never inline unless panic_immediate_abort to avoid code
-                // bloat at the call sites as much as possible
-                #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
-                #[cfg_attr(feature = "panic_immediate_abort", inline)]
-                #[track_caller]
-                #[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
-                #[lang = stringify!($lang)]
-                pub const fn $lang() -> ! {
-                    // Use Arguments::new_const instead of format_args!("{expr}") to potentially
-                    // reduce size overhead. The format_args! macro uses str's Display trait to
-                    // write expr, which calls Formatter::pad, which must accommodate string
-                    // truncation and padding (even though none is used here). Using
-                    // Arguments::new_const may allow the compiler to omit Formatter::pad from the
-                    // output binary, saving up to a few kilobytes.
-                    panic_fmt(fmt::Arguments::new_const(&[$message]));
-                }
-            )+
-        }
+        $(
+            /// This is a panic called with a message that's a result of a MIR-produced Assert.
+            //
+            // never inline unless panic_immediate_abort to avoid code
+            // bloat at the call sites as much as possible
+            #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
+            #[cfg_attr(feature = "panic_immediate_abort", inline)]
+            #[track_caller]
+            #[rustc_const_stable_indirect] // must follow stable const rules since it is exposed to stable
+            #[lang = stringify!($lang)]
+            pub const fn $lang() -> ! {
+                // Use Arguments::new_const instead of format_args!("{expr}") to potentially
+                // reduce size overhead. The format_args! macro uses str's Display trait to
+                // write expr, which calls Formatter::pad, which must accommodate string
+                // truncation and padding (even though none is used here). Using
+                // Arguments::new_const may allow the compiler to omit Formatter::pad from the
+                // output binary, saving up to a few kilobytes.
+                panic_fmt(fmt::Arguments::new_const(&[$message]));
+            }
+        )+
     }
 }
 
@@ -186,25 +182,37 @@ macro_rules! panic_const {
 // slightly different forms. It's not clear if there's a good way to deduplicate without adding
 // special cases to the compiler (e.g., a const generic function wouldn't have a single definition
 // shared across crates, which is exactly what we want here).
-panic_const! {
-    panic_const_add_overflow = "attempt to add with overflow",
-    panic_const_sub_overflow = "attempt to subtract with overflow",
-    panic_const_mul_overflow = "attempt to multiply with overflow",
-    panic_const_div_overflow = "attempt to divide with overflow",
-    panic_const_rem_overflow = "attempt to calculate the remainder with overflow",
-    panic_const_neg_overflow = "attempt to negate with overflow",
-    panic_const_shr_overflow = "attempt to shift right with overflow",
-    panic_const_shl_overflow = "attempt to shift left with overflow",
-    panic_const_div_by_zero = "attempt to divide by zero",
-    panic_const_rem_by_zero = "attempt to calculate the remainder with a divisor of zero",
-    panic_const_coroutine_resumed = "coroutine resumed after completion",
-    panic_const_async_fn_resumed = "`async fn` resumed after completion",
-    panic_const_async_gen_fn_resumed = "`async gen fn` resumed after completion",
-    panic_const_gen_fn_none = "`gen fn` should just keep returning `None` after completion",
-    panic_const_coroutine_resumed_panic = "coroutine resumed after panicking",
-    panic_const_async_fn_resumed_panic = "`async fn` resumed after panicking",
-    panic_const_async_gen_fn_resumed_panic = "`async gen fn` resumed after panicking",
-    panic_const_gen_fn_none_panic = "`gen fn` should just keep returning `None` after panicking",
+pub mod panic_const {
+    use super::*;
+    panic_const! {
+        panic_const_add_overflow = "attempt to add with overflow",
+        panic_const_sub_overflow = "attempt to subtract with overflow",
+        panic_const_mul_overflow = "attempt to multiply with overflow",
+        panic_const_div_overflow = "attempt to divide with overflow",
+        panic_const_rem_overflow = "attempt to calculate the remainder with overflow",
+        panic_const_neg_overflow = "attempt to negate with overflow",
+        panic_const_shr_overflow = "attempt to shift right with overflow",
+        panic_const_shl_overflow = "attempt to shift left with overflow",
+        panic_const_div_by_zero = "attempt to divide by zero",
+        panic_const_rem_by_zero = "attempt to calculate the remainder with a divisor of zero",
+        panic_const_coroutine_resumed = "coroutine resumed after completion",
+        panic_const_async_fn_resumed = "`async fn` resumed after completion",
+        panic_const_async_gen_fn_resumed = "`async gen fn` resumed after completion",
+        panic_const_gen_fn_none = "`gen fn` should just keep returning `None` after completion",
+        panic_const_coroutine_resumed_panic = "coroutine resumed after panicking",
+        panic_const_async_fn_resumed_panic = "`async fn` resumed after panicking",
+        panic_const_async_gen_fn_resumed_panic = "`async gen fn` resumed after panicking",
+        panic_const_gen_fn_none_panic = "`gen fn` should just keep returning `None` after panicking",
+    }
+    // Separated panic constants list for async drop feature
+    // (May be joined when the corresponding lang items will be in the bootstrap)
+    #[cfg(not(bootstrap))]
+    panic_const! {
+        panic_const_coroutine_resumed_drop = "coroutine resumed after async drop",
+        panic_const_async_fn_resumed_drop = "`async fn` resumed after async drop",
+        panic_const_async_gen_fn_resumed_drop = "`async gen fn` resumed after async drop",
+        panic_const_gen_fn_none_drop = "`gen fn` resumed after async drop",
+    }
 }
 
 /// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize on the caller.
diff --git a/library/core/src/pin.rs b/library/core/src/pin.rs
index 9e6acf04bf7..dd1c2f2c285 100644
--- a/library/core/src/pin.rs
+++ b/library/core/src/pin.rs
@@ -676,7 +676,7 @@
 //!             let data_ptr = unpinned_src.data.as_ptr() as *const u8;
 //!             let slice_ptr = unpinned_src.slice.as_ptr() as *const u8;
 //!             let offset = slice_ptr.offset_from(data_ptr) as usize;
-//!             let len = (*unpinned_src.slice.as_ptr()).len();
+//!             let len = unpinned_src.slice.as_ptr().len();
 //!
 //!             unpinned_self.slice = NonNull::from(&mut unpinned_self.data[offset..offset+len]);
 //!         }
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index 2d869958b85..5234fb83eb6 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -484,8 +484,9 @@ impl<T: ?Sized> *const T {
     ///
     /// This operation itself is always safe, but using the resulting pointer is not.
     ///
-    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
-    /// be used to read or write other allocated objects.
+    /// The resulting pointer "remembers" the [allocated object] that `self` points to
+    /// (this is called "[Provenance](ptr/index.html#provenance)").
+    /// The pointer must not be used to read or write other allocated objects.
     ///
     /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
     /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
@@ -804,8 +805,8 @@ impl<T: ?Sized> *const T {
     /// units of **bytes**.
     ///
     /// This is purely a convenience for casting to a `u8` pointer and
-    /// using [`sub_ptr`][pointer::offset_from_unsigned] on it. See that method for
-    /// documentation and safety requirements.
+    /// using [`offset_from_unsigned`][pointer::offset_from_unsigned] on it.
+    /// See that method for documentation and safety requirements.
     ///
     /// For non-`Sized` pointees this operation considers only the data pointers,
     /// ignoring the metadata.
@@ -814,7 +815,7 @@ impl<T: ?Sized> *const T {
     #[inline]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn byte_offset_from_unsigned<U: ?Sized>(self, origin: *const U) -> usize {
-        // SAFETY: the caller must uphold the safety contract for `sub_ptr`.
+        // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`.
         unsafe { self.cast::<u8>().offset_from_unsigned(origin.cast::<u8>()) }
     }
 
diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index df49eedb350..31b8d3b572c 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -482,8 +482,9 @@ impl<T: ?Sized> *mut T {
     ///
     /// This operation itself is always safe, but using the resulting pointer is not.
     ///
-    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
-    /// be used to read or write other allocated objects.
+    /// The resulting pointer "remembers" the [allocated object] that `self` points to
+    /// (this is called "[Provenance](ptr/index.html#provenance)").
+    /// The pointer must not be used to read or write other allocated objects.
     ///
     /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
     /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
@@ -937,6 +938,7 @@ impl<T: ?Sized> *mut T {
     ///
     /// // This would be incorrect, as the pointers are not correctly ordered:
     /// // ptr1.offset_from(ptr2)
+    /// ```
     #[stable(feature = "ptr_sub_ptr", since = "1.87.0")]
     #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")]
     #[inline]
@@ -945,7 +947,7 @@ impl<T: ?Sized> *mut T {
     where
         T: Sized,
     {
-        // SAFETY: the caller must uphold the safety contract for `sub_ptr`.
+        // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`.
         unsafe { (self as *const T).offset_from_unsigned(origin) }
     }
 
@@ -954,8 +956,8 @@ impl<T: ?Sized> *mut T {
     /// units of **bytes**.
     ///
     /// This is purely a convenience for casting to a `u8` pointer and
-    /// using [`sub_ptr`][pointer::offset_from_unsigned] on it. See that method for
-    /// documentation and safety requirements.
+    /// using [`offset_from_unsigned`][pointer::offset_from_unsigned] on it.
+    /// See that method for documentation and safety requirements.
     ///
     /// For non-`Sized` pointees this operation considers only the data pointers,
     /// ignoring the metadata.
@@ -964,7 +966,7 @@ impl<T: ?Sized> *mut T {
     #[inline]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn byte_offset_from_unsigned<U: ?Sized>(self, origin: *mut U) -> usize {
-        // SAFETY: the caller must uphold the safety contract for `byte_sub_ptr`.
+        // SAFETY: the caller must uphold the safety contract for `byte_offset_from_unsigned`.
         unsafe { (self as *const T).byte_offset_from_unsigned(origin) }
     }
 
diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index 68b8f0c3e4e..0864cc457b6 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -906,7 +906,7 @@ impl<T: ?Sized> NonNull<T> {
     where
         T: Sized,
     {
-        // SAFETY: the caller must uphold the safety contract for `sub_ptr`.
+        // SAFETY: the caller must uphold the safety contract for `offset_from_unsigned`.
         unsafe { self.as_ptr().offset_from_unsigned(subtracted.as_ptr()) }
     }
 
@@ -915,8 +915,8 @@ impl<T: ?Sized> NonNull<T> {
     /// units of **bytes**.
     ///
     /// This is purely a convenience for casting to a `u8` pointer and
-    /// using [`sub_ptr`][NonNull::offset_from_unsigned] on it. See that method for
-    /// documentation and safety requirements.
+    /// using [`offset_from_unsigned`][NonNull::offset_from_unsigned] on it.
+    /// See that method for documentation and safety requirements.
     ///
     /// For non-`Sized` pointees this operation considers only the data pointers,
     /// ignoring the metadata.
@@ -925,7 +925,7 @@ impl<T: ?Sized> NonNull<T> {
     #[stable(feature = "ptr_sub_ptr", since = "1.87.0")]
     #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "1.87.0")]
     pub const unsafe fn byte_offset_from_unsigned<U: ?Sized>(self, origin: NonNull<U>) -> usize {
-        // SAFETY: the caller must uphold the safety contract for `byte_sub_ptr`.
+        // SAFETY: the caller must uphold the safety contract for `byte_offset_from_unsigned`.
         unsafe { self.as_ptr().byte_offset_from_unsigned(origin.as_ptr()) }
     }
 
diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index f507ee563ac..85a5e89a49e 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -2335,7 +2335,6 @@ pub struct ArrayChunks<'a, T: 'a, const N: usize> {
 
 impl<'a, T, const N: usize> ArrayChunks<'a, T, N> {
     #[rustc_const_unstable(feature = "const_slice_make_iter", issue = "137737")]
-    // #[rustc_const_unstable(feature = "slice_as_chunks", issue = "74985")]
     #[inline]
     pub(super) const fn new(slice: &'a [T]) -> Self {
         let (array_slice, rem) = slice.as_chunks();
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 1ae0849db5b..81fe0166fd7 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -109,6 +109,7 @@ impl<T> [T] {
     #[lang = "slice_len_fn"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_len", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub const fn len(&self) -> usize {
@@ -128,6 +129,7 @@ impl<T> [T] {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_slice_is_empty", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub const fn is_empty(&self) -> bool {
@@ -562,6 +564,7 @@ impl<T> [T] {
     /// assert_eq!(None, v.get(0..4));
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub fn get<I>(&self, index: I) -> Option<&I::Output>
@@ -587,6 +590,7 @@ impl<T> [T] {
     /// assert_eq!(x, &[0, 42, 2]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
@@ -624,6 +628,7 @@ impl<T> [T] {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
@@ -666,6 +671,7 @@ impl<T> [T] {
     /// assert_eq!(x, &[1, 13, 4]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[inline]
     #[must_use]
     pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
@@ -1262,6 +1268,18 @@ impl<T> [T] {
     /// Splits the slice into a slice of `N`-element arrays,
     /// assuming that there's no remainder.
     ///
+    /// This is the inverse operation to [`as_flattened`].
+    ///
+    /// [`as_flattened`]: slice::as_flattened
+    ///
+    /// As this is `unsafe`, consider whether you could use [`as_chunks`] or
+    /// [`as_rchunks`] instead, perhaps via something like
+    /// `if let (chunks, []) = slice.as_chunks()` or
+    /// `let (chunks, []) = slice.as_chunks() else { unreachable!() };`.
+    ///
+    /// [`as_chunks`]: slice::as_chunks
+    /// [`as_rchunks`]: slice::as_rchunks
+    ///
     /// # Safety
     ///
     /// This may only be called when
@@ -1271,7 +1289,6 @@ impl<T> [T] {
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let slice: &[char] = &['l', 'o', 'r', 'e', 'm', '!'];
     /// let chunks: &[[char; 1]] =
     ///     // SAFETY: 1-element chunks never have remainder
@@ -1286,7 +1303,8 @@ impl<T> [T] {
     /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked() // The slice length is not a multiple of 5
     /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked() // Zero-length chunks are never allowed
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[must_use]
     pub const unsafe fn as_chunks_unchecked<const N: usize>(&self) -> &[[T; N]] {
@@ -1306,15 +1324,27 @@ impl<T> [T] {
     /// starting at the beginning of the slice,
     /// and a remainder slice with length strictly less than `N`.
     ///
+    /// The remainder is meaningful in the division sense.  Given
+    /// `let (chunks, remainder) = slice.as_chunks()`, then:
+    /// - `chunks.len()` equals `slice.len() / N`,
+    /// - `remainder.len()` equals `slice.len() % N`, and
+    /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
+    ///
+    /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
+    ///
+    /// [`as_flattened`]: slice::as_flattened
+    ///
     /// # Panics
     ///
-    /// Panics if `N` is zero. This check will most probably get changed to a compile time
-    /// error before this method gets stabilized.
+    /// Panics if `N` is zero.
+    ///
+    /// Note that this check is against a const generic parameter, not a runtime
+    /// value, and thus a particular monomorphization will either always panic
+    /// or it will never panic.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let slice = ['l', 'o', 'r', 'e', 'm'];
     /// let (chunks, remainder) = slice.as_chunks();
     /// assert_eq!(chunks, &[['l', 'o'], ['r', 'e']]);
@@ -1324,14 +1354,14 @@ impl<T> [T] {
     /// If you expect the slice to be an exact multiple, you can combine
     /// `let`-`else` with an empty slice pattern:
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let slice = ['R', 'u', 's', 't'];
     /// let (chunks, []) = slice.as_chunks::<2>() else {
     ///     panic!("slice didn't have even length")
     /// };
     /// assert_eq!(chunks, &[['R', 'u'], ['s', 't']]);
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[track_caller]
     #[must_use]
@@ -1351,21 +1381,34 @@ impl<T> [T] {
     /// starting at the end of the slice,
     /// and a remainder slice with length strictly less than `N`.
     ///
+    /// The remainder is meaningful in the division sense.  Given
+    /// `let (remainder, chunks) = slice.as_rchunks()`, then:
+    /// - `remainder.len()` equals `slice.len() % N`,
+    /// - `chunks.len()` equals `slice.len() / N`, and
+    /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
+    ///
+    /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened`].
+    ///
+    /// [`as_flattened`]: slice::as_flattened
+    ///
     /// # Panics
     ///
-    /// Panics if `N` is zero. This check will most probably get changed to a compile time
-    /// error before this method gets stabilized.
+    /// Panics if `N` is zero.
+    ///
+    /// Note that this check is against a const generic parameter, not a runtime
+    /// value, and thus a particular monomorphization will either always panic
+    /// or it will never panic.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let slice = ['l', 'o', 'r', 'e', 'm'];
     /// let (remainder, chunks) = slice.as_rchunks();
     /// assert_eq!(remainder, &['l']);
     /// assert_eq!(chunks, &[['o', 'r'], ['e', 'm']]);
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[track_caller]
     #[must_use]
@@ -1418,6 +1461,18 @@ impl<T> [T] {
     /// Splits the slice into a slice of `N`-element arrays,
     /// assuming that there's no remainder.
     ///
+    /// This is the inverse operation to [`as_flattened_mut`].
+    ///
+    /// [`as_flattened_mut`]: slice::as_flattened_mut
+    ///
+    /// As this is `unsafe`, consider whether you could use [`as_chunks_mut`] or
+    /// [`as_rchunks_mut`] instead, perhaps via something like
+    /// `if let (chunks, []) = slice.as_chunks_mut()` or
+    /// `let (chunks, []) = slice.as_chunks_mut() else { unreachable!() };`.
+    ///
+    /// [`as_chunks_mut`]: slice::as_chunks_mut
+    /// [`as_rchunks_mut`]: slice::as_rchunks_mut
+    ///
     /// # Safety
     ///
     /// This may only be called when
@@ -1427,7 +1482,6 @@ impl<T> [T] {
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let slice: &mut [char] = &mut ['l', 'o', 'r', 'e', 'm', '!'];
     /// let chunks: &mut [[char; 1]] =
     ///     // SAFETY: 1-element chunks never have remainder
@@ -1444,7 +1498,8 @@ impl<T> [T] {
     /// // let chunks: &[[_; 5]] = slice.as_chunks_unchecked_mut() // The slice length is not a multiple of 5
     /// // let chunks: &[[_; 0]] = slice.as_chunks_unchecked_mut() // Zero-length chunks are never allowed
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[must_use]
     pub const unsafe fn as_chunks_unchecked_mut<const N: usize>(&mut self) -> &mut [[T; N]] {
@@ -1464,15 +1519,27 @@ impl<T> [T] {
     /// starting at the beginning of the slice,
     /// and a remainder slice with length strictly less than `N`.
     ///
+    /// The remainder is meaningful in the division sense.  Given
+    /// `let (chunks, remainder) = slice.as_chunks_mut()`, then:
+    /// - `chunks.len()` equals `slice.len() / N`,
+    /// - `remainder.len()` equals `slice.len() % N`, and
+    /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
+    ///
+    /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
+    ///
+    /// [`as_flattened_mut`]: slice::as_flattened_mut
+    ///
     /// # Panics
     ///
-    /// Panics if `N` is zero. This check will most probably get changed to a compile time
-    /// error before this method gets stabilized.
+    /// Panics if `N` is zero.
+    ///
+    /// Note that this check is against a const generic parameter, not a runtime
+    /// value, and thus a particular monomorphization will either always panic
+    /// or it will never panic.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let v = &mut [0, 0, 0, 0, 0];
     /// let mut count = 1;
     ///
@@ -1484,7 +1551,8 @@ impl<T> [T] {
     /// }
     /// assert_eq!(v, &[1, 1, 2, 2, 9]);
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[track_caller]
     #[must_use]
@@ -1504,15 +1572,27 @@ impl<T> [T] {
     /// starting at the end of the slice,
     /// and a remainder slice with length strictly less than `N`.
     ///
+    /// The remainder is meaningful in the division sense.  Given
+    /// `let (remainder, chunks) = slice.as_rchunks_mut()`, then:
+    /// - `remainder.len()` equals `slice.len() % N`,
+    /// - `chunks.len()` equals `slice.len() / N`, and
+    /// - `slice.len()` equals `chunks.len() * N + remainder.len()`.
+    ///
+    /// You can flatten the chunks back into a slice-of-`T` with [`as_flattened_mut`].
+    ///
+    /// [`as_flattened_mut`]: slice::as_flattened_mut
+    ///
     /// # Panics
     ///
-    /// Panics if `N` is zero. This check will most probably get changed to a compile time
-    /// error before this method gets stabilized.
+    /// Panics if `N` is zero.
+    ///
+    /// Note that this check is against a const generic parameter, not a runtime
+    /// value, and thus a particular monomorphization will either always panic
+    /// or it will never panic.
     ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(slice_as_chunks)]
     /// let v = &mut [0, 0, 0, 0, 0];
     /// let mut count = 1;
     ///
@@ -1524,7 +1604,8 @@ impl<T> [T] {
     /// }
     /// assert_eq!(v, &[9, 1, 1, 2, 2]);
     /// ```
-    #[unstable(feature = "slice_as_chunks", issue = "74985")]
+    #[stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "slice_as_chunks", since = "CURRENT_RUSTC_VERSION")]
     #[inline]
     #[track_caller]
     #[must_use]
@@ -4810,6 +4891,11 @@ impl<T> [MaybeUninit<T>] {
 impl<T, const N: usize> [[T; N]] {
     /// Takes a `&[[T; N]]`, and flattens it to a `&[T]`.
     ///
+    /// For the opposite operation, see [`as_chunks`] and [`as_rchunks`].
+    ///
+    /// [`as_chunks`]: slice::as_chunks
+    /// [`as_rchunks`]: slice::as_rchunks
+    ///
     /// # Panics
     ///
     /// This panics if the length of the resulting slice would overflow a `usize`.
@@ -4850,6 +4936,11 @@ impl<T, const N: usize> [[T; N]] {
 
     /// Takes a `&mut [[T; N]]`, and flattens it to a `&mut [T]`.
     ///
+    /// For the opposite operation, see [`as_chunks_mut`] and [`as_rchunks_mut`].
+    ///
+    /// [`as_chunks_mut`]: slice::as_chunks_mut
+    /// [`as_rchunks_mut`]: slice::as_rchunks_mut
+    ///
     /// # Panics
     ///
     /// This panics if the length of the resulting slice would overflow a `usize`.
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index 818dcc2125f..dafabba645c 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -134,6 +134,7 @@ impl str {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_str_len", since = "1.39.0")]
     #[rustc_diagnostic_item = "str_len"]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[must_use]
     #[inline]
     pub const fn len(&self) -> usize {
@@ -153,6 +154,7 @@ impl str {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_str_is_empty", since = "1.39.0")]
+    #[cfg_attr(not(bootstrap), rustc_no_implicit_autorefs)]
     #[must_use]
     #[inline]
     pub const fn is_empty(&self) -> bool {
diff --git a/library/core/src/sync/atomic.rs b/library/core/src/sync/atomic.rs
index 9b1b13e7129..84c7f1aafe1 100644
--- a/library/core/src/sync/atomic.rs
+++ b/library/core/src/sync/atomic.rs
@@ -247,6 +247,100 @@ use crate::cell::UnsafeCell;
 use crate::hint::spin_loop;
 use crate::{fmt, intrinsics};
 
+trait Sealed {}
+
+/// A marker trait for primitive types which can be modified atomically.
+///
+/// This is an implementation detail for <code>[Atomic]\<T></code> which may disappear or be replaced at any time.
+///
+/// # Safety
+///
+/// Types implementing this trait must be primitives that can be modified atomically.
+///
+/// The associated `Self::AtomicInner` type must have the same size and bit validity as `Self`,
+/// but may have a higher alignment requirement, so the following `transmute`s are sound:
+///
+/// - `&mut Self::AtomicInner` as `&mut Self`
+/// - `Self` as `Self::AtomicInner` or the reverse
+#[unstable(
+    feature = "atomic_internals",
+    reason = "implementation detail which may disappear or be replaced at any time",
+    issue = "none"
+)]
+#[expect(private_bounds)]
+pub unsafe trait AtomicPrimitive: Sized + Copy + Sealed {
+    /// Temporary implementation detail.
+    type AtomicInner: Sized;
+}
+
+macro impl_atomic_primitive(
+    $Atom:ident $(<$T:ident>)? ($Primitive:ty),
+    size($size:literal),
+    align($align:literal) $(,)?
+) {
+    impl $(<$T>)? Sealed for $Primitive {}
+
+    #[unstable(
+        feature = "atomic_internals",
+        reason = "implementation detail which may disappear or be replaced at any time",
+        issue = "none"
+    )]
+    #[cfg(target_has_atomic_load_store = $size)]
+    unsafe impl $(<$T>)? AtomicPrimitive for $Primitive {
+        type AtomicInner = $Atom $(<$T>)?;
+    }
+}
+
+impl_atomic_primitive!(AtomicBool(bool), size("8"), align(1));
+impl_atomic_primitive!(AtomicI8(i8), size("8"), align(1));
+impl_atomic_primitive!(AtomicU8(u8), size("8"), align(1));
+impl_atomic_primitive!(AtomicI16(i16), size("16"), align(2));
+impl_atomic_primitive!(AtomicU16(u16), size("16"), align(2));
+impl_atomic_primitive!(AtomicI32(i32), size("32"), align(4));
+impl_atomic_primitive!(AtomicU32(u32), size("32"), align(4));
+impl_atomic_primitive!(AtomicI64(i64), size("64"), align(8));
+impl_atomic_primitive!(AtomicU64(u64), size("64"), align(8));
+impl_atomic_primitive!(AtomicI128(i128), size("128"), align(16));
+impl_atomic_primitive!(AtomicU128(u128), size("128"), align(16));
+
+#[cfg(target_pointer_width = "16")]
+impl_atomic_primitive!(AtomicIsize(isize), size("ptr"), align(2));
+#[cfg(target_pointer_width = "32")]
+impl_atomic_primitive!(AtomicIsize(isize), size("ptr"), align(4));
+#[cfg(target_pointer_width = "64")]
+impl_atomic_primitive!(AtomicIsize(isize), size("ptr"), align(8));
+
+#[cfg(target_pointer_width = "16")]
+impl_atomic_primitive!(AtomicUsize(usize), size("ptr"), align(2));
+#[cfg(target_pointer_width = "32")]
+impl_atomic_primitive!(AtomicUsize(usize), size("ptr"), align(4));
+#[cfg(target_pointer_width = "64")]
+impl_atomic_primitive!(AtomicUsize(usize), size("ptr"), align(8));
+
+#[cfg(target_pointer_width = "16")]
+impl_atomic_primitive!(AtomicPtr<T>(*mut T), size("ptr"), align(2));
+#[cfg(target_pointer_width = "32")]
+impl_atomic_primitive!(AtomicPtr<T>(*mut T), size("ptr"), align(4));
+#[cfg(target_pointer_width = "64")]
+impl_atomic_primitive!(AtomicPtr<T>(*mut T), size("ptr"), align(8));
+
+/// A memory location which can be safely modified from multiple threads.
+///
+/// This has the same size and bit validity as the underlying type `T`. However,
+/// the alignment of this type is always equal to its size, even on targets where
+/// `T` has alignment less than its size.
+///
+/// For more about the differences between atomic types and non-atomic types as
+/// well as information about the portability of this type, please see the
+/// [module-level documentation].
+///
+/// **Note:** This type is only available on platforms that support atomic loads
+/// and stores of `T`.
+///
+/// [module-level documentation]: crate::sync::atomic
+#[unstable(feature = "generic_atomic", issue = "130539")]
+pub type Atomic<T> = <T as AtomicPrimitive>::AtomicInner;
+
 // Some architectures don't have byte-sized atomics, which results in LLVM
 // emulating them using a LL/SC loop. However for AtomicBool we can take
 // advantage of the fact that it only ever contains 0 or 1 and use atomic OR/AND