Auto merge of #18183 - lnicola:sync-from-rust, r=lnicola

internal: Sync from downstream

36 files changed, 1051 insertions, 248 deletions

diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index db2d752cfde..a91659b6de5 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -89,6 +89,7 @@ pub use std::alloc::Global;
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
     unsafe {
         // Make sure we don't accidentally allow omitting the allocator shim in
@@ -113,6 +114,7 @@ pub unsafe fn alloc(layout: Layout) -> *mut u8 {
 /// See [`GlobalAlloc::dealloc`].
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
     unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
 }
@@ -132,6 +134,7 @@ pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
     unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
 }
@@ -166,13 +169,21 @@ pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8
 #[stable(feature = "global_alloc", since = "1.28.0")]
 #[must_use = "losing the pointer will leak memory"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
-    unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
+    unsafe {
+        // Make sure we don't accidentally allow omitting the allocator shim in
+        // stable code until it is actually stabilized.
+        core::ptr::read_volatile(&__rust_no_alloc_shim_is_unstable);
+
+        __rust_alloc_zeroed(layout.size(), layout.align())
+    }
 }
 
 #[cfg(not(test))]
 impl Global {
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
             0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
@@ -187,6 +198,7 @@ impl Global {
 
     // SAFETY: Same as `Allocator::grow`
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow_impl(
         &self,
         ptr: NonNull<u8>,
@@ -237,16 +249,19 @@ impl Global {
 #[cfg(not(test))]
 unsafe impl Allocator for Global {
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, false)
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, true)
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
         if layout.size() != 0 {
             // SAFETY: `layout` is non-zero in size,
@@ -256,6 +271,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow(
         &self,
         ptr: NonNull<u8>,
@@ -267,6 +283,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn grow_zeroed(
         &self,
         ptr: NonNull<u8>,
@@ -278,6 +295,7 @@ unsafe impl Allocator for Global {
     }
 
     #[inline]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     unsafe fn shrink(
         &self,
         ptr: NonNull<u8>,
@@ -325,6 +343,7 @@ unsafe impl Allocator for Global {
 #[cfg(all(not(no_global_oom_handling), not(test)))]
 #[lang = "exchange_malloc"]
 #[inline]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
     let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
     match Global.allocate(layout) {
@@ -372,6 +391,7 @@ extern "Rust" {
 #[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
 #[cfg(all(not(no_global_oom_handling), not(test)))]
 #[cold]
+#[optimize(size)]
 pub const fn handle_alloc_error(layout: Layout) -> ! {
     const fn ct_error(_: Layout) -> ! {
         panic!("allocation failed");
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 38b1766c174..f61a484499f 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -53,22 +53,20 @@
 //!
 //! # Memory layout
 //!
-//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for
-//! its allocation. It is valid to convert both ways between a [`Box`] and a
-//! raw pointer allocated with the [`Global`] allocator, given that the
-//! [`Layout`] used with the allocator is correct for the type. More precisely,
-//! a `value: *mut T` that has been allocated with the [`Global`] allocator
-//! with `Layout::for_value(&*value)` may be converted into a box using
-//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut
-//! T` obtained from [`Box::<T>::into_raw`] may be deallocated using the
-//! [`Global`] allocator with [`Layout::for_value(&*value)`].
+//! For non-zero-sized values, a [`Box`] will use the [`Global`] allocator for its allocation. It is
+//! valid to convert both ways between a [`Box`] and a raw pointer allocated with the [`Global`]
+//! allocator, given that the [`Layout`] used with the allocator is correct for the type and the raw
+//! pointer points to a valid value of the right type. More precisely, a `value: *mut T` that has
+//! been allocated with the [`Global`] allocator with `Layout::for_value(&*value)` may be converted
+//! into a box using [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut T`
+//! obtained from [`Box::<T>::into_raw`] may be deallocated using the [`Global`] allocator with
+//! [`Layout::for_value(&*value)`].
 //!
-//! For zero-sized values, the `Box` pointer still has to be [valid] for reads
-//! and writes and sufficiently aligned. In particular, casting any aligned
-//! non-zero integer literal to a raw pointer produces a valid pointer, but a
-//! pointer pointing into previously allocated memory that since got freed is
-//! not valid. The recommended way to build a Box to a ZST if `Box::new` cannot
-//! be used is to use [`ptr::NonNull::dangling`].
+//! For zero-sized values, the `Box` pointer has to be non-null and sufficiently aligned. The
+//! recommended way to build a Box to a ZST if `Box::new` cannot be used is to use
+//! [`ptr::NonNull::dangling`].
+//!
+//! On top of these basic layout requirements, a `Box<T>` must point to a valid value of `T`.
 //!
 //! So long as `T: Sized`, a `Box<T>` is guaranteed to be represented
 //! as a single pointer and is also ABI-compatible with C pointers
@@ -201,7 +199,7 @@ use core::ops::{
     DerefPure, DispatchFromDyn, Receiver,
 };
 use core::pin::{Pin, PinCoerceUnsized};
-use core::ptr::{self, addr_of_mut, NonNull, Unique};
+use core::ptr::{self, NonNull, Unique, addr_of_mut};
 use core::task::{Context, Poll};
 use core::{borrow, fmt, slice};
 
@@ -252,6 +250,7 @@ impl<T> Box<T> {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     #[rustc_diagnostic_item = "box_new"]
+    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub fn new(x: T) -> Self {
         #[rustc_box]
         Box::new(x)
@@ -274,7 +273,7 @@ impl<T> Box<T> {
     /// assert_eq!(*five, 5)
     /// ```
     #[cfg(not(no_global_oom_handling))]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     #[inline]
     pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
@@ -665,7 +664,7 @@ impl<T> Box<[T]> {
     /// assert_eq!(*values, [1, 2, 3])
     /// ```
     #[cfg(not(no_global_oom_handling))]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
         unsafe { RawVec::with_capacity(len).into_box(len) }
@@ -932,7 +931,7 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
     ///
     /// assert_eq!(*five, 5)
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[inline]
     pub unsafe fn assume_init(self) -> Box<T, A> {
         let (raw, alloc) = Box::into_raw_with_allocator(self);
@@ -1005,7 +1004,7 @@ impl<T, A: Allocator> Box<[mem::MaybeUninit<T>], A> {
     ///
     /// assert_eq!(*values, [1, 2, 3])
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[inline]
     pub unsafe fn assume_init(self) -> Box<[T], A> {
         let (raw, alloc) = Box::into_raw_with_allocator(self);
@@ -1061,6 +1060,59 @@ impl<T: ?Sized> Box<T> {
     pub unsafe fn from_raw(raw: *mut T) -> Self {
         unsafe { Self::from_raw_in(raw, Global) }
     }
+
+    /// Constructs a box from a `NonNull` pointer.
+    ///
+    /// After calling this function, the `NonNull` pointer is owned by
+    /// the resulting `Box`. Specifically, the `Box` destructor will call
+    /// the destructor of `T` and free the allocated memory. For this
+    /// to be safe, the memory must have been allocated in accordance
+    /// with the [memory layout] used by `Box` .
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because improper use may lead to
+    /// memory problems. For example, a double-free may occur if the
+    /// function is called twice on the same `NonNull` pointer.
+    ///
+    /// The safety conditions are described in the [memory layout] section.
+    ///
+    /// # Examples
+    ///
+    /// Recreate a `Box` which was previously converted to a `NonNull`
+    /// pointer using [`Box::into_non_null`]:
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// let x = Box::new(5);
+    /// let non_null = Box::into_non_null(x);
+    /// let x = unsafe { Box::from_non_null(non_null) };
+    /// ```
+    /// Manually create a `Box` from scratch by using the global allocator:
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// use std::alloc::{alloc, Layout};
+    /// use std::ptr::NonNull;
+    ///
+    /// unsafe {
+    ///     let non_null = NonNull::new(alloc(Layout::new::<i32>()).cast::<i32>())
+    ///         .expect("allocation failed");
+    ///     // In general .write is required to avoid attempting to destruct
+    ///     // the (uninitialized) previous contents of `non_null`.
+    ///     non_null.write(5);
+    ///     let x = Box::from_non_null(non_null);
+    /// }
+    /// ```
+    ///
+    /// [memory layout]: self#memory-layout
+    /// [`Layout`]: crate::Layout
+    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    #[inline]
+    #[must_use = "call `drop(Box::from_non_null(ptr))` if you intend to drop the `Box`"]
+    pub unsafe fn from_non_null(ptr: NonNull<T>) -> Self {
+        unsafe { Self::from_raw(ptr.as_ptr()) }
+    }
 }
 
 impl<T: ?Sized, A: Allocator> Box<T, A> {
@@ -1118,6 +1170,61 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
         Box(unsafe { Unique::new_unchecked(raw) }, alloc)
     }
 
+    /// Constructs a box from a `NonNull` pointer in the given allocator.
+    ///
+    /// After calling this function, the `NonNull` pointer is owned by
+    /// the resulting `Box`. Specifically, the `Box` destructor will call
+    /// the destructor of `T` and free the allocated memory. For this
+    /// to be safe, the memory must have been allocated in accordance
+    /// with the [memory layout] used by `Box` .
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because improper use may lead to
+    /// memory problems. For example, a double-free may occur if the
+    /// function is called twice on the same raw pointer.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// Recreate a `Box` which was previously converted to a `NonNull` pointer
+    /// using [`Box::into_non_null_with_allocator`]:
+    /// ```
+    /// #![feature(allocator_api, box_vec_non_null)]
+    ///
+    /// use std::alloc::System;
+    ///
+    /// let x = Box::new_in(5, System);
+    /// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
+    /// let x = unsafe { Box::from_non_null_in(non_null, alloc) };
+    /// ```
+    /// Manually create a `Box` from scratch by using the system allocator:
+    /// ```
+    /// #![feature(allocator_api, box_vec_non_null, slice_ptr_get)]
+    ///
+    /// use std::alloc::{Allocator, Layout, System};
+    ///
+    /// unsafe {
+    ///     let non_null = System.allocate(Layout::new::<i32>())?.cast::<i32>();
+    ///     // In general .write is required to avoid attempting to destruct
+    ///     // the (uninitialized) previous contents of `non_null`.
+    ///     non_null.write(5);
+    ///     let x = Box::from_non_null_in(non_null, System);
+    /// }
+    /// # Ok::<(), std::alloc::AllocError>(())
+    /// ```
+    ///
+    /// [memory layout]: self#memory-layout
+    /// [`Layout`]: crate::Layout
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    // #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
+    #[inline]
+    pub const unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Self {
+        // SAFETY: guaranteed by the caller.
+        unsafe { Box::from_raw_in(raw.as_ptr(), alloc) }
+    }
+
     /// Consumes the `Box`, returning a wrapped raw pointer.
     ///
     /// The pointer will be properly aligned and non-null.
@@ -1173,6 +1280,66 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
         unsafe { addr_of_mut!(*&mut *Self::into_raw_with_allocator(b).0) }
     }
 
+    /// Consumes the `Box`, returning a wrapped `NonNull` pointer.
+    ///
+    /// The pointer will be properly aligned.
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// memory previously managed by the `Box`. In particular, the
+    /// caller should properly destroy `T` and release the memory, taking
+    /// into account the [memory layout] used by `Box`. The easiest way to
+    /// do this is to convert the `NonNull` pointer back into a `Box` with the
+    /// [`Box::from_non_null`] function, allowing the `Box` destructor to
+    /// perform the cleanup.
+    ///
+    /// Note: this is an associated function, which means that you have
+    /// to call it as `Box::into_non_null(b)` instead of `b.into_non_null()`.
+    /// This is so that there is no conflict with a method on the inner type.
+    ///
+    /// # Examples
+    /// Converting the `NonNull` pointer back into a `Box` with [`Box::from_non_null`]
+    /// for automatic cleanup:
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// let x = Box::new(String::from("Hello"));
+    /// let non_null = Box::into_non_null(x);
+    /// let x = unsafe { Box::from_non_null(non_null) };
+    /// ```
+    /// Manual cleanup by explicitly running the destructor and deallocating
+    /// the memory:
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// use std::alloc::{dealloc, Layout};
+    ///
+    /// let x = Box::new(String::from("Hello"));
+    /// let non_null = Box::into_non_null(x);
+    /// unsafe {
+    ///     non_null.drop_in_place();
+    ///     dealloc(non_null.as_ptr().cast::<u8>(), Layout::new::<String>());
+    /// }
+    /// ```
+    /// Note: This is equivalent to the following:
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// let x = Box::new(String::from("Hello"));
+    /// let non_null = Box::into_non_null(x);
+    /// unsafe {
+    ///     drop(Box::from_non_null(non_null));
+    /// }
+    /// ```
+    ///
+    /// [memory layout]: self#memory-layout
+    #[must_use = "losing the pointer will leak memory"]
+    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    #[inline]
+    pub fn into_non_null(b: Self) -> NonNull<T> {
+        // SAFETY: `Box` is guaranteed to be non-null.
+        unsafe { NonNull::new_unchecked(Self::into_raw(b)) }
+    }
+
     /// Consumes the `Box`, returning a wrapped raw pointer and the allocator.
     ///
     /// The pointer will be properly aligned and non-null.
@@ -1234,6 +1401,61 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
         (ptr, alloc)
     }
 
+    /// Consumes the `Box`, returning a wrapped `NonNull` pointer and the allocator.
+    ///
+    /// The pointer will be properly aligned.
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// memory previously managed by the `Box`. In particular, the
+    /// caller should properly destroy `T` and release the memory, taking
+    /// into account the [memory layout] used by `Box`. The easiest way to
+    /// do this is to convert the `NonNull` pointer back into a `Box` with the
+    /// [`Box::from_non_null_in`] function, allowing the `Box` destructor to
+    /// perform the cleanup.
+    ///
+    /// Note: this is an associated function, which means that you have
+    /// to call it as `Box::into_non_null_with_allocator(b)` instead of
+    /// `b.into_non_null_with_allocator()`. This is so that there is no
+    /// conflict with a method on the inner type.
+    ///
+    /// # Examples
+    /// Converting the `NonNull` pointer back into a `Box` with
+    /// [`Box::from_non_null_in`] for automatic cleanup:
+    /// ```
+    /// #![feature(allocator_api, box_vec_non_null)]
+    ///
+    /// use std::alloc::System;
+    ///
+    /// let x = Box::new_in(String::from("Hello"), System);
+    /// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
+    /// let x = unsafe { Box::from_non_null_in(non_null, alloc) };
+    /// ```
+    /// Manual cleanup by explicitly running the destructor and deallocating
+    /// the memory:
+    /// ```
+    /// #![feature(allocator_api, box_vec_non_null)]
+    ///
+    /// use std::alloc::{Allocator, Layout, System};
+    ///
+    /// let x = Box::new_in(String::from("Hello"), System);
+    /// let (non_null, alloc) = Box::into_non_null_with_allocator(x);
+    /// unsafe {
+    ///     non_null.drop_in_place();
+    ///     alloc.deallocate(non_null.cast::<u8>(), Layout::new::<String>());
+    /// }
+    /// ```
+    ///
+    /// [memory layout]: self#memory-layout
+    #[must_use = "losing the pointer will leak memory"]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    // #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    #[inline]
+    pub fn into_non_null_with_allocator(b: Self) -> (NonNull<T>, A) {
+        let (ptr, alloc) = Box::into_raw_with_allocator(b);
+        // SAFETY: `Box` is guaranteed to be non-null.
+        unsafe { (NonNull::new_unchecked(ptr), alloc) }
+    }
+
     #[unstable(
         feature = "ptr_internals",
         issue = "none",
@@ -2258,7 +2480,10 @@ impl<Args: Tuple, F: AsyncFnOnce<Args> + ?Sized, A: Allocator> AsyncFnOnce<Args>
 
 #[unstable(feature = "async_fn_traits", issue = "none")]
 impl<Args: Tuple, F: AsyncFnMut<Args> + ?Sized, A: Allocator> AsyncFnMut<Args> for Box<F, A> {
-    type CallRefFuture<'a> = F::CallRefFuture<'a> where Self: 'a;
+    type CallRefFuture<'a>
+        = F::CallRefFuture<'a>
+    where
+        Self: 'a;
 
     extern "rust-call" fn async_call_mut(&mut self, args: Args) -> Self::CallRefFuture<'_> {
         F::async_call_mut(self, args)
diff --git a/library/alloc/src/collections/binary_heap/mod.rs b/library/alloc/src/collections/binary_heap/mod.rs
index 88701370c10..5e59abf54ee 100644
--- a/library/alloc/src/collections/binary_heap/mod.rs
+++ b/library/alloc/src/collections/binary_heap/mod.rs
@@ -145,7 +145,7 @@
 
 use core::alloc::Allocator;
 use core::iter::{FusedIterator, InPlaceIterable, SourceIter, TrustedFused, TrustedLen};
-use core::mem::{self, swap, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, swap};
 use core::num::NonZero;
 use core::ops::{Deref, DerefMut};
 use core::{fmt, ptr};
@@ -959,6 +959,7 @@ impl<T, A: Allocator> BinaryHeap<T, A> {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "binaryheap_iter")]
     pub fn iter(&self) -> Iter<'_, T> {
         Iter { iter: self.data.iter() }
     }
@@ -1433,7 +1434,7 @@ pub struct Iter<'a, T: 'a> {
     iter: slice::Iter<'a, T>,
 }
 
-#[stable(feature = "default_iters_sequel", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "default_iters_sequel", since = "1.82.0")]
 impl<T> Default for Iter<'_, T> {
     /// Creates an empty `binary_heap::Iter`.
     ///
diff --git a/library/alloc/src/collections/binary_heap/tests.rs b/library/alloc/src/collections/binary_heap/tests.rs
index 1cb07c62149..c18318724a4 100644
--- a/library/alloc/src/collections/binary_heap/tests.rs
+++ b/library/alloc/src/collections/binary_heap/tests.rs
@@ -1,4 +1,4 @@
-use std::panic::{catch_unwind, AssertUnwindSafe};
+use std::panic::{AssertUnwindSafe, catch_unwind};
 
 use super::*;
 use crate::boxed::Box;
diff --git a/library/alloc/src/collections/btree/fix.rs b/library/alloc/src/collections/btree/fix.rs
index 4c1e19ead40..95fb52b7f77 100644
--- a/library/alloc/src/collections/btree/fix.rs
+++ b/library/alloc/src/collections/btree/fix.rs
@@ -3,7 +3,7 @@ use core::alloc::Allocator;
 use super::map::MIN_LEN;
 use super::node::ForceResult::*;
 use super::node::LeftOrRight::*;
-use super::node::{marker, Handle, NodeRef, Root};
+use super::node::{Handle, NodeRef, Root, marker};
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     /// Stocks up a possibly underfull node by merging with or stealing from a
diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index f6f773cc42a..55649d865fc 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -13,7 +13,7 @@ use super::borrow::DormantMutRef;
 use super::dedup_sorted_iter::DedupSortedIter;
 use super::navigate::{LazyLeafRange, LeafRange};
 use super::node::ForceResult::*;
-use super::node::{self, marker, Handle, NodeRef, Root};
+use super::node::{self, Handle, NodeRef, Root, marker};
 use super::search::SearchBound;
 use super::search::SearchResult::*;
 use super::set_val::SetValZST;
@@ -22,9 +22,9 @@ use crate::vec::Vec;
 
 mod entry;
 
+use Entry::*;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use entry::{Entry, OccupiedEntry, OccupiedError, VacantEntry};
-use Entry::*;
 
 /// Minimum number of elements in a node that is not a root.
 /// We might temporarily have fewer elements during methods.
@@ -916,6 +916,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// assert_eq!(map.contains_key(&2), false);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "btreemap_contains_key")]
     pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
     where
         K: Borrow<Q> + Ord,
@@ -981,6 +982,7 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_confusables("push", "put", "set")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "btreemap_insert")]
     pub fn insert(&mut self, key: K, value: V) -> Option<V>
     where
         K: Ord,
@@ -2016,7 +2018,7 @@ impl<K, V> Default for Range<'_, K, V> {
     }
 }
 
-#[stable(feature = "default_iters_sequel", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "default_iters_sequel", since = "1.82.0")]
 impl<K, V> Default for RangeMut<'_, K, V> {
     /// Creates an empty `btree_map::RangeMut`.
     ///
@@ -2064,7 +2066,7 @@ impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
 
-#[stable(feature = "default_iters_sequel", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "default_iters_sequel", since = "1.82.0")]
 impl<K, V> Default for ValuesMut<'_, K, V> {
     /// Creates an empty `btree_map::ValuesMut`.
     ///
@@ -3302,7 +3304,7 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'a, K, V, A> {
         Some(kv)
     }
 
-    /// Removes the precending element from the `BTreeMap`.
+    /// Removes the preceding element from the `BTreeMap`.
     ///
     /// The element that was removed is returned. The cursor position is
     /// unchanged (after the removed element).
@@ -3408,7 +3410,7 @@ impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> {
         self.inner.remove_next()
     }
 
-    /// Removes the precending element from the `BTreeMap`.
+    /// Removes the preceding element from the `BTreeMap`.
     ///
     /// The element that was removed is returned. The cursor position is
     /// unchanged (after the removed element).
diff --git a/library/alloc/src/collections/btree/map/entry.rs b/library/alloc/src/collections/btree/map/entry.rs
index d128ad8ee5f..75bb86916a8 100644
--- a/library/alloc/src/collections/btree/map/entry.rs
+++ b/library/alloc/src/collections/btree/map/entry.rs
@@ -5,7 +5,7 @@ use core::mem;
 use Entry::*;
 
 use super::super::borrow::DormantMutRef;
-use super::super::node::{marker, Handle, NodeRef};
+use super::super::node::{Handle, NodeRef, marker};
 use super::BTreeMap;
 use crate::alloc::{Allocator, Global};
 
diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
index ff1254a5a0c..d0e413778f8 100644
--- a/library/alloc/src/collections/btree/map/tests.rs
+++ b/library/alloc/src/collections/btree/map/tests.rs
@@ -1,7 +1,7 @@
 use core::assert_matches::assert_matches;
 use std::iter;
 use std::ops::Bound::{Excluded, Included, Unbounded};
-use std::panic::{catch_unwind, AssertUnwindSafe};
+use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering::SeqCst;
 
diff --git a/library/alloc/src/collections/btree/navigate.rs b/library/alloc/src/collections/btree/navigate.rs
index f5c621e2c17..14b7d4ad71f 100644
--- a/library/alloc/src/collections/btree/navigate.rs
+++ b/library/alloc/src/collections/btree/navigate.rs
@@ -3,7 +3,7 @@ use core::ops::RangeBounds;
 use core::{hint, ptr};
 
 use super::node::ForceResult::*;
-use super::node::{marker, Handle, NodeRef};
+use super::node::{Handle, NodeRef, marker};
 use super::search::SearchBound;
 use crate::alloc::Allocator;
 // `front` and `back` are always both `None` or both `Some`.
diff --git a/library/alloc/src/collections/btree/node/tests.rs b/library/alloc/src/collections/btree/node/tests.rs
index d230749d712..4d2fa0f0941 100644
--- a/library/alloc/src/collections/btree/node/tests.rs
+++ b/library/alloc/src/collections/btree/node/tests.rs
@@ -90,7 +90,7 @@ fn test_partial_eq() {
 
 #[test]
 #[cfg(target_arch = "x86_64")]
-#[cfg_attr(miri, ignore)] // We'd like to run Miri with layout randomization
+#[cfg_attr(any(miri, randomized_layouts), ignore)] // We'd like to run Miri with layout randomization
 fn test_sizes() {
     assert_eq!(core::mem::size_of::<LeafNode<(), ()>>(), 16);
     assert_eq!(core::mem::size_of::<LeafNode<i64, i64>>(), 16 + CAPACITY * 2 * 8);
diff --git a/library/alloc/src/collections/btree/remove.rs b/library/alloc/src/collections/btree/remove.rs
index c46422c2f1d..56f2824b782 100644
--- a/library/alloc/src/collections/btree/remove.rs
+++ b/library/alloc/src/collections/btree/remove.rs
@@ -3,7 +3,7 @@ use core::alloc::Allocator;
 use super::map::MIN_LEN;
 use super::node::ForceResult::*;
 use super::node::LeftOrRight::*;
-use super::node::{marker, Handle, NodeRef};
+use super::node::{Handle, NodeRef, marker};
 
 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV> {
     /// Removes a key-value pair from the tree, and returns that pair, as well as
diff --git a/library/alloc/src/collections/btree/search.rs b/library/alloc/src/collections/btree/search.rs
index 1d5c927175e..22e015edac3 100644
--- a/library/alloc/src/collections/btree/search.rs
+++ b/library/alloc/src/collections/btree/search.rs
@@ -6,7 +6,7 @@ use SearchBound::*;
 use SearchResult::*;
 
 use super::node::ForceResult::*;
-use super::node::{marker, Handle, NodeRef};
+use super::node::{Handle, NodeRef, marker};
 
 pub enum SearchBound<T> {
     /// An inclusive bound to look for, just like `Bound::Included(T)`.
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 973e7c66067..a40209fa2e3 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -7,10 +7,10 @@ use core::iter::{FusedIterator, Peekable};
 use core::mem::ManuallyDrop;
 use core::ops::{BitAnd, BitOr, BitXor, Bound, RangeBounds, Sub};
 
+use super::Recover;
 use super::map::{BTreeMap, Keys};
 use super::merge_iter::MergeIterInner;
 use super::set_val::SetValZST;
-use super::Recover;
 use crate::alloc::{Allocator, Global};
 use crate::vec::Vec;
 
@@ -1132,6 +1132,7 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
     /// assert_eq!(set_iter.next(), None);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "btreeset_iter")]
     pub fn iter(&self) -> Iter<'_, T> {
         Iter { iter: self.map.keys() }
     }
@@ -2298,7 +2299,7 @@ impl<'a, T: Ord, A: Allocator + Clone> CursorMut<'a, T, A> {
         self.inner.remove_next().map(|(k, _)| k)
     }
 
-    /// Removes the precending element from the `BTreeSet`.
+    /// Removes the preceding element from the `BTreeSet`.
     ///
     /// The element that was removed is returned. The cursor position is
     /// unchanged (after the removed element).
@@ -2384,7 +2385,7 @@ impl<'a, T: Ord, A: Allocator + Clone> CursorMutKey<'a, T, A> {
         self.inner.remove_next().map(|(k, _)| k)
     }
 
-    /// Removes the precending element from the `BTreeSet`.
+    /// Removes the preceding element from the `BTreeSet`.
     ///
     /// The element that was removed is returned. The cursor position is
     /// unchanged (after the removed element).
diff --git a/library/alloc/src/collections/btree/set/tests.rs b/library/alloc/src/collections/btree/set/tests.rs
index f947b6108c9..990044e069f 100644
--- a/library/alloc/src/collections/btree/set/tests.rs
+++ b/library/alloc/src/collections/btree/set/tests.rs
@@ -1,5 +1,5 @@
 use std::ops::Bound::{Excluded, Included};
-use std::panic::{catch_unwind, AssertUnwindSafe};
+use std::panic::{AssertUnwindSafe, catch_unwind};
 
 use super::*;
 use crate::testing::crash_test::{CrashTestDummy, Panic};
@@ -132,11 +132,9 @@ fn test_difference() {
     check_difference(&[1, 3, 5, 9, 11], &[3, 6, 9], &[1, 5, 11]);
     check_difference(&[1, 3, 5, 9, 11], &[0, 1], &[3, 5, 9, 11]);
     check_difference(&[1, 3, 5, 9, 11], &[11, 12], &[1, 3, 5, 9]);
-    check_difference(
-        &[-5, 11, 22, 33, 40, 42],
-        &[-12, -5, 14, 23, 34, 38, 39, 50],
-        &[11, 22, 33, 40, 42],
-    );
+    check_difference(&[-5, 11, 22, 33, 40, 42], &[-12, -5, 14, 23, 34, 38, 39, 50], &[
+        11, 22, 33, 40, 42,
+    ]);
 
     if cfg!(miri) {
         // Miri is too slow
@@ -252,11 +250,9 @@ fn test_union() {
     check_union(&[], &[], &[]);
     check_union(&[1, 2, 3], &[2], &[1, 2, 3]);
     check_union(&[2], &[1, 2, 3], &[1, 2, 3]);
-    check_union(
-        &[1, 3, 5, 9, 11, 16, 19, 24],
-        &[-2, 1, 5, 9, 13, 19],
-        &[-2, 1, 3, 5, 9, 11, 13, 16, 19, 24],
-    );
+    check_union(&[1, 3, 5, 9, 11, 16, 19, 24], &[-2, 1, 5, 9, 13, 19], &[
+        -2, 1, 3, 5, 9, 11, 13, 16, 19, 24,
+    ]);
 }
 
 #[test]
diff --git a/library/alloc/src/collections/linked_list/tests.rs b/library/alloc/src/collections/linked_list/tests.rs
index 9b3c9ac5ce5..b7d4f8512a0 100644
--- a/library/alloc/src/collections/linked_list/tests.rs
+++ b/library/alloc/src/collections/linked_list/tests.rs
@@ -1,4 +1,7 @@
-use std::panic::{catch_unwind, AssertUnwindSafe};
+// FIXME(static_mut_refs): Do not allow `static_mut_refs` lint
+#![allow(static_mut_refs)]
+
+use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::thread;
 
 use rand::RngCore;
@@ -693,10 +696,9 @@ fn test_cursor_mut_insert() {
     cursor.splice_after(p);
     cursor.splice_before(q);
     check_links(&m);
-    assert_eq!(
-        m.iter().cloned().collect::<Vec<_>>(),
-        &[200, 201, 202, 203, 1, 100, 101, 102, 103, 8, 2, 3, 4, 5, 6]
-    );
+    assert_eq!(m.iter().cloned().collect::<Vec<_>>(), &[
+        200, 201, 202, 203, 1, 100, 101, 102, 103, 8, 2, 3, 4, 5, 6
+    ]);
     let mut cursor = m.cursor_front_mut();
     cursor.move_prev();
     let tmp = cursor.split_before();
@@ -913,10 +915,9 @@ fn extract_if_complex() {
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
         assert_eq!(list.len(), 14);
-        assert_eq!(
-            list.into_iter().collect::<Vec<_>>(),
-            vec![1, 7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]
-        );
+        assert_eq!(list.into_iter().collect::<Vec<_>>(), vec![
+            1, 7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39
+        ]);
     }
 
     {
@@ -931,10 +932,9 @@ fn extract_if_complex() {
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
         assert_eq!(list.len(), 13);
-        assert_eq!(
-            list.into_iter().collect::<Vec<_>>(),
-            vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]
-        );
+        assert_eq!(list.into_iter().collect::<Vec<_>>(), vec![
+            7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39
+        ]);
     }
 
     {
@@ -949,10 +949,9 @@ fn extract_if_complex() {
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
         assert_eq!(list.len(), 11);
-        assert_eq!(
-            list.into_iter().collect::<Vec<_>>(),
-            vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35]
-        );
+        assert_eq!(list.into_iter().collect::<Vec<_>>(), vec![
+            7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35
+        ]);
     }
 
     {
diff --git a/library/alloc/src/collections/vec_deque/into_iter.rs b/library/alloc/src/collections/vec_deque/into_iter.rs
index 7be3de16b2d..2b09a5e7ddc 100644
--- a/library/alloc/src/collections/vec_deque/into_iter.rs
+++ b/library/alloc/src/collections/vec_deque/into_iter.rs
@@ -121,8 +121,6 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
     {
         match self.try_fold(init, |b, item| Ok::<B, !>(f(b, item))) {
             Ok(b) => b,
-            #[cfg(bootstrap)]
-            Err(e) => match e {},
         }
     }
 
@@ -243,8 +241,6 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     {
         match self.try_rfold(init, |b, item| Ok::<B, !>(f(b, item))) {
             Ok(b) => b,
-            #[cfg(bootstrap)]
-            Err(e) => match e {},
         }
     }
 }
diff --git a/library/alloc/src/collections/vec_deque/iter.rs b/library/alloc/src/collections/vec_deque/iter.rs
index 67b5b91c4d4..6922ea9b79b 100644
--- a/library/alloc/src/collections/vec_deque/iter.rs
+++ b/library/alloc/src/collections/vec_deque/iter.rs
@@ -28,7 +28,7 @@ impl<T: fmt::Debug> fmt::Debug for Iter<'_, T> {
     }
 }
 
-#[stable(feature = "default_iters_sequel", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "default_iters_sequel", since = "1.82.0")]
 impl<T> Default for Iter<'_, T> {
     /// Creates an empty `vec_deque::Iter`.
     ///
@@ -73,7 +73,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
     fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         let remaining = self.i1.advance_by(n);
         match remaining {
-            Ok(()) => return Ok(()),
+            Ok(()) => Ok(()),
             Err(n) => {
                 mem::swap(&mut self.i1, &mut self.i2);
                 self.i1.advance_by(n.get())
@@ -144,7 +144,7 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 
     fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         match self.i2.advance_back_by(n) {
-            Ok(()) => return Ok(()),
+            Ok(()) => Ok(()),
             Err(n) => {
                 mem::swap(&mut self.i1, &mut self.i2);
                 self.i2.advance_back_by(n.get())
diff --git a/library/alloc/src/collections/vec_deque/iter_mut.rs b/library/alloc/src/collections/vec_deque/iter_mut.rs
index 2726e3e4252..84b74109580 100644
--- a/library/alloc/src/collections/vec_deque/iter_mut.rs
+++ b/library/alloc/src/collections/vec_deque/iter_mut.rs
@@ -28,7 +28,7 @@ impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
     }
 }
 
-#[stable(feature = "default_iters_sequel", since = "CURRENT_RUSTC_VERSION")]
+#[stable(feature = "default_iters_sequel", since = "1.82.0")]
 impl<T> Default for IterMut<'_, T> {
     /// Creates an empty `vec_deque::IterMut`.
     ///
@@ -64,7 +64,7 @@ impl<'a, T> Iterator for IterMut<'a, T> {
 
     fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         match self.i1.advance_by(n) {
-            Ok(()) => return Ok(()),
+            Ok(()) => Ok(()),
             Err(remaining) => {
                 mem::swap(&mut self.i1, &mut self.i2);
                 self.i1.advance_by(remaining.get())
@@ -135,7 +135,7 @@ impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
 
     fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
         match self.i2.advance_back_by(n) {
-            Ok(()) => return Ok(()),
+            Ok(()) => Ok(()),
             Err(remaining) => {
                 mem::swap(&mut self.i1, &mut self.i2);
                 self.i2.advance_back_by(remaining.get())
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index dc725ec0f56..b1759a486ac 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -9,7 +9,7 @@
 
 use core::cmp::{self, Ordering};
 use core::hash::{Hash, Hasher};
-use core::iter::{repeat_n, repeat_with, ByRefSized};
+use core::iter::{ByRefSized, repeat_n, repeat_with};
 // This is used in a bunch of intra-doc links.
 // FIXME: For some reason, `#[cfg(doc)]` wasn't sufficient, resulting in
 // failures in linkchecker even though rustdoc built the docs just fine.
@@ -554,8 +554,8 @@ impl<T> VecDeque<T> {
     #[rustc_const_stable(feature = "const_vec_deque_new", since = "1.68.0")]
     #[must_use]
     pub const fn new() -> VecDeque<T> {
-        // FIXME: This should just be `VecDeque::new_in(Global)` once that hits stable.
-        VecDeque { head: 0, len: 0, buf: RawVec::NEW }
+        // FIXME(const-hack): This should just be `VecDeque::new_in(Global)` once that hits stable.
+        VecDeque { head: 0, len: 0, buf: RawVec::new() }
     }
 
     /// Creates an empty deque with space for at least `capacity` elements.
@@ -1201,6 +1201,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// assert_eq!(&c[..], b);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vecdeque_iter")]
     pub fn iter(&self) -> Iter<'_, T> {
         let (a, b) = self.as_slices();
         Iter::new(a.iter(), b.iter())
diff --git a/library/alloc/src/collections/vec_deque/tests.rs b/library/alloc/src/collections/vec_deque/tests.rs
index f8ce4ca9788..6328b3b4db8 100644
--- a/library/alloc/src/collections/vec_deque/tests.rs
+++ b/library/alloc/src/collections/vec_deque/tests.rs
@@ -1,3 +1,6 @@
+// FIXME(static_mut_refs): Do not allow `static_mut_refs` lint
+#![allow(static_mut_refs)]
+
 use core::iter::TrustedLen;
 
 use super::*;
@@ -559,10 +562,9 @@ fn make_contiguous_head_to_end() {
         tester.push_front(i as char);
     }
 
-    assert_eq!(
-        tester,
-        ['P', 'O', 'N', 'M', 'L', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K']
-    );
+    assert_eq!(tester, [
+        'P', 'O', 'N', 'M', 'L', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K'
+    ]);
 
     // ABCDEFGHIJKPONML
     let expected_start = 0;
diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index e32676a6543..797d591a8b5 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -4,7 +4,7 @@
 mod tests;
 
 use core::borrow::Borrow;
-use core::ffi::{c_char, CStr};
+use core::ffi::{CStr, c_char};
 use core::num::NonZero;
 use core::slice::memchr;
 use core::str::{self, Utf8Error};
@@ -576,6 +576,7 @@ impl CString {
     #[inline]
     #[must_use]
     #[stable(feature = "as_c_str", since = "1.20.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "cstring_as_c_str")]
     pub fn as_c_str(&self) -> &CStr {
         &*self
     }
diff --git a/library/alloc/src/fmt.rs b/library/alloc/src/fmt.rs
index 571fcd177aa..3da71038a5e 100644
--- a/library/alloc/src/fmt.rs
+++ b/library/alloc/src/fmt.rs
@@ -580,10 +580,8 @@
 pub use core::fmt::Alignment;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::Error;
-#[unstable(feature = "debug_closure_helpers", issue = "117729")]
-pub use core::fmt::{from_fn, FromFn};
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::fmt::{write, Arguments};
+pub use core::fmt::{Arguments, write};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{Binary, Octal};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -592,6 +590,8 @@ pub use core::fmt::{Debug, Display};
 pub use core::fmt::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{Formatter, Result, Write};
+#[unstable(feature = "debug_closure_helpers", issue = "117729")]
+pub use core::fmt::{FromFn, from_fn};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::fmt::{LowerExp, UpperExp};
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index c459a8da820..ff5ddd16e07 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -93,6 +93,7 @@
 // tidy-alphabetical-start
 #![cfg_attr(not(no_global_oom_handling), feature(const_alloc_error))]
 #![cfg_attr(not(no_global_oom_handling), feature(const_btree_len))]
+#![cfg_attr(test, feature(str_as_str))]
 #![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(array_chunks)]
@@ -110,11 +111,9 @@
 #![feature(const_cow_is_borrowed)]
 #![feature(const_eval_select)]
 #![feature(const_heap)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_write)]
 #![feature(const_option)]
 #![feature(const_pin)]
-#![feature(const_refs_to_cell)]
 #![feature(const_size_of_val)]
 #![feature(core_intrinsics)]
 #![feature(deprecated_suggestion)]
@@ -164,13 +163,14 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
+#![cfg_attr(bootstrap, feature(const_refs_to_cell))]
 #![cfg_attr(not(test), feature(coroutine_trait))]
 #![cfg_attr(test, feature(panic_update_hook))]
 #![cfg_attr(test, feature(test))]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unstable)]
 #![feature(cfg_sanitize)]
-#![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
 #![feature(const_ptr_write)]
 #![feature(const_try)]
@@ -183,6 +183,7 @@
 #![feature(multiple_supertrait_upcastable)]
 #![feature(negative_impls)]
 #![feature(never_type)]
+#![feature(optimize_attribute)]
 #![feature(rustc_allow_const_fn_unstable)]
 #![feature(rustc_attrs)]
 #![feature(slice_internals)]
diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index 9c8fa7ceff4..436e0596e3d 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/library/alloc/src/raw_vec.rs
@@ -96,13 +96,6 @@ struct RawVecInner<A: Allocator = Global> {
 }
 
 impl<T> RawVec<T, Global> {
-    /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
-    /// they cannot call `Self::new()`.
-    ///
-    /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
-    /// that would truly const-call something unstable.
-    pub const NEW: Self = Self::new();
-
     /// Creates the biggest possible `RawVec` (on the system heap)
     /// without allocating. If `T` has positive size, then this makes a
     /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
@@ -111,7 +104,7 @@ impl<T> RawVec<T, Global> {
     #[must_use]
     #[rustc_const_stable(feature = "raw_vec_internals_const", since = "1.81")]
     pub const fn new() -> Self {
-        Self { inner: RawVecInner::new::<T>(), _marker: PhantomData }
+        Self::new_in(Global)
     }
 
     /// Creates a `RawVec` (on the system heap) with exactly the
@@ -149,12 +142,6 @@ impl<T> RawVec<T, Global> {
 }
 
 impl RawVecInner<Global> {
-    #[must_use]
-    #[rustc_const_stable(feature = "raw_vec_internals_const", since = "1.81")]
-    const fn new<T>() -> Self {
-        Self::new_in(Global, core::mem::align_of::<T>())
-    }
-
     #[cfg(not(any(no_global_oom_handling, test)))]
     #[must_use]
     #[inline]
@@ -782,6 +769,7 @@ where
 // Central function for reserve error handling.
 #[cfg(not(no_global_oom_handling))]
 #[cold]
+#[optimize(size)]
 fn handle_error(e: TryReserveError) -> ! {
     match e.kind() {
         CapacityOverflow => capacity_overflow(),
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 1b31a78394e..54669bd310a 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -251,13 +251,13 @@ use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
 use core::marker::{PhantomData, Unsize};
-use core::mem::{self, align_of_val_raw, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, align_of_val_raw};
 use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Receiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 #[cfg(not(no_global_oom_handling))]
 use core::pin::Pin;
 use core::pin::PinCoerceUnsized;
-use core::ptr::{self, drop_in_place, NonNull};
+use core::ptr::{self, NonNull, drop_in_place};
 #[cfg(not(no_global_oom_handling))]
 use core::slice::from_raw_parts_mut;
 use core::{borrow, fmt, hint};
@@ -460,42 +460,7 @@ impl<T> Rc<T> {
     where
         F: FnOnce(&Weak<T>) -> T,
     {
-        // Construct the inner in the "uninitialized" state with a single
-        // weak reference.
-        let uninit_ptr: NonNull<_> = Box::leak(Box::new(RcBox {
-            strong: Cell::new(0),
-            weak: Cell::new(1),
-            value: mem::MaybeUninit::<T>::uninit(),
-        }))
-        .into();
-
-        let init_ptr: NonNull<RcBox<T>> = uninit_ptr.cast();
-
-        let weak = Weak { ptr: init_ptr, alloc: Global };
-
-        // It's important we don't give up ownership of the weak pointer, or
-        // else the memory might be freed by the time `data_fn` returns. If
-        // we really wanted to pass ownership, we could create an additional
-        // weak pointer for ourselves, but this would result in additional
-        // updates to the weak reference count which might not be necessary
-        // otherwise.
-        let data = data_fn(&weak);
-
-        let strong = unsafe {
-            let inner = init_ptr.as_ptr();
-            ptr::write(ptr::addr_of_mut!((*inner).value), data);
-
-            let prev_value = (*inner).strong.get();
-            debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
-            (*inner).strong.set(1);
-
-            Rc::from_inner(init_ptr)
-        };
-
-        // Strong references should collectively own a shared weak reference,
-        // so don't run the destructor for our old weak reference.
-        mem::forget(weak);
-        strong
+        Self::new_cyclic_in(data_fn, Global)
     }
 
     /// Constructs a new `Rc` with uninitialized contents.
@@ -517,7 +482,7 @@ impl<T> Rc<T> {
     /// assert_eq!(*five, 5)
     /// ```
     #[cfg(not(no_global_oom_handling))]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> {
         unsafe {
@@ -762,6 +727,84 @@ impl<T, A: Allocator> Rc<T, A> {
         }
     }
 
+    /// Constructs a new `Rc<T, A>` in the given allocator while giving you a `Weak<T, A>` to the allocation,
+    /// to allow you to construct a `T` which holds a weak pointer to itself.
+    ///
+    /// Generally, a structure circularly referencing itself, either directly or
+    /// indirectly, should not hold a strong reference to itself to prevent a memory leak.
+    /// Using this function, you get access to the weak pointer during the
+    /// initialization of `T`, before the `Rc<T, A>` is created, such that you can
+    /// clone and store it inside the `T`.
+    ///
+    /// `new_cyclic_in` first allocates the managed allocation for the `Rc<T, A>`,
+    /// then calls your closure, giving it a `Weak<T, A>` to this allocation,
+    /// and only afterwards completes the construction of the `Rc<T, A>` by placing
+    /// the `T` returned from your closure into the allocation.
+    ///
+    /// Since the new `Rc<T, A>` is not fully-constructed until `Rc<T, A>::new_cyclic_in`
+    /// returns, calling [`upgrade`] on the weak reference inside your closure will
+    /// fail and result in a `None` value.
+    ///
+    /// # Panics
+    ///
+    /// If `data_fn` panics, the panic is propagated to the caller, and the
+    /// temporary [`Weak<T, A>`] is dropped normally.
+    ///
+    /// # Examples
+    ///
+    /// See [`new_cyclic`].
+    ///
+    /// [`new_cyclic`]: Rc::new_cyclic
+    /// [`upgrade`]: Weak::upgrade
+    #[cfg(not(no_global_oom_handling))]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    pub fn new_cyclic_in<F>(data_fn: F, alloc: A) -> Rc<T, A>
+    where
+        F: FnOnce(&Weak<T, A>) -> T,
+    {
+        // Construct the inner in the "uninitialized" state with a single
+        // weak reference.
+        let (uninit_raw_ptr, alloc) = Box::into_raw_with_allocator(Box::new_in(
+            RcBox {
+                strong: Cell::new(0),
+                weak: Cell::new(1),
+                value: mem::MaybeUninit::<T>::uninit(),
+            },
+            alloc,
+        ));
+        let uninit_ptr: NonNull<_> = (unsafe { &mut *uninit_raw_ptr }).into();
+        let init_ptr: NonNull<RcBox<T>> = uninit_ptr.cast();
+
+        let weak = Weak { ptr: init_ptr, alloc: alloc };
+
+        // It's important we don't give up ownership of the weak pointer, or
+        // else the memory might be freed by the time `data_fn` returns. If
+        // we really wanted to pass ownership, we could create an additional
+        // weak pointer for ourselves, but this would result in additional
+        // updates to the weak reference count which might not be necessary
+        // otherwise.
+        let data = data_fn(&weak);
+
+        let strong = unsafe {
+            let inner = init_ptr.as_ptr();
+            ptr::write(ptr::addr_of_mut!((*inner).value), data);
+
+            let prev_value = (*inner).strong.get();
+            debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
+            (*inner).strong.set(1);
+
+            // Strong references should collectively own a shared weak reference,
+            // so don't run the destructor for our old weak reference.
+            // Calling into_raw_with_allocator has the double effect of giving us back the allocator,
+            // and forgetting the weak reference.
+            let alloc = weak.into_raw_with_allocator().1;
+
+            Rc::from_inner_in(init_ptr, alloc)
+        };
+
+        strong
+    }
+
     /// Constructs a new `Rc<T>` in the provided allocator, returning an error if the allocation
     /// fails
     ///
@@ -980,7 +1023,7 @@ impl<T> Rc<[T]> {
     /// assert_eq!(*values, [1, 2, 3])
     /// ```
     #[cfg(not(no_global_oom_handling))]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
         unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) }
@@ -1127,7 +1170,7 @@ impl<T, A: Allocator> Rc<mem::MaybeUninit<T>, A> {
     ///
     /// assert_eq!(*five, 5)
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[inline]
     pub unsafe fn assume_init(self) -> Rc<T, A> {
         let (ptr, alloc) = Rc::into_inner_with_allocator(self);
@@ -1167,7 +1210,7 @@ impl<T, A: Allocator> Rc<[mem::MaybeUninit<T>], A> {
     ///
     /// assert_eq!(*values, [1, 2, 3])
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[inline]
     pub unsafe fn assume_init(self) -> Rc<[T], A> {
         let (ptr, alloc) = Rc::into_inner_with_allocator(self);
diff --git a/library/alloc/src/rc/tests.rs b/library/alloc/src/rc/tests.rs
index 84e8b325f71..333e1bde31c 100644
--- a/library/alloc/src/rc/tests.rs
+++ b/library/alloc/src/rc/tests.rs
@@ -448,7 +448,11 @@ fn test_from_box_str() {
     use std::string::String;
 
     let s = String::from("foo").into_boxed_str();
+    assert_eq!((&&&s).as_str(), "foo");
+
     let r: Rc<str> = Rc::from(s);
+    assert_eq!((&r).as_str(), "foo");
+    assert_eq!(r.as_str(), "foo");
 
     assert_eq!(&r[..], "foo");
 }
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index 9d704870326..f636f10d5c0 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -43,14 +43,6 @@ pub use core::slice::ArrayWindows;
 pub use core::slice::EscapeAscii;
 #[stable(feature = "slice_get_slice", since = "1.28.0")]
 pub use core::slice::SliceIndex;
-#[stable(feature = "from_ref", since = "1.28.0")]
-pub use core::slice::{from_mut, from_ref};
-#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
-pub use core::slice::{from_mut_ptr_range, from_ptr_range};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use core::slice::{from_raw_parts, from_raw_parts_mut};
-#[unstable(feature = "slice_range", issue = "76393")]
-pub use core::slice::{range, try_range};
 #[stable(feature = "slice_group_by", since = "1.77.0")]
 pub use core::slice::{ChunkBy, ChunkByMut};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -69,6 +61,14 @@ pub use core::slice::{RSplit, RSplitMut};
 pub use core::slice::{RSplitN, RSplitNMut, SplitN, SplitNMut};
 #[stable(feature = "split_inclusive", since = "1.51.0")]
 pub use core::slice::{SplitInclusive, SplitInclusiveMut};
+#[stable(feature = "from_ref", since = "1.28.0")]
+pub use core::slice::{from_mut, from_ref};
+#[unstable(feature = "slice_from_ptr_range", issue = "89792")]
+pub use core::slice::{from_mut_ptr_range, from_ptr_range};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::slice::{from_raw_parts, from_raw_parts_mut};
+#[unstable(feature = "slice_range", issue = "76393")]
+pub use core::slice::{range, try_range};
 
 ////////////////////////////////////////////////////////////////////////////////
 // Basic slice extension methods
@@ -96,6 +96,7 @@ pub(crate) mod hack {
     // We shouldn't add inline attribute to this since this is used in
     // `vec!` macro mostly and causes perf regression. See #71204 for
     // discussion and perf results.
+    #[allow(missing_docs)]
     pub fn into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A> {
         unsafe {
             let len = b.len();
@@ -105,6 +106,7 @@ pub(crate) mod hack {
     }
 
     #[cfg(not(no_global_oom_handling))]
+    #[allow(missing_docs)]
     #[inline]
     pub fn to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A> {
         T::to_vec(s, alloc)
@@ -494,6 +496,7 @@ impl<T> [T] {
     #[rustc_allow_incoherent_impl]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "slice_into_vec")]
     pub fn into_vec<A: Allocator>(self: Box<Self, A>) -> Vec<T, A> {
         // N.B., see the `hack` module in this file for more details.
         hack::into_vec(self)
diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
index d7fba3ae159..32212b61c6e 100644
--- a/library/alloc/src/str.rs
+++ b/library/alloc/src/str.rs
@@ -9,9 +9,6 @@
 
 use core::borrow::{Borrow, BorrowMut};
 use core::iter::FusedIterator;
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use core::str::pattern;
-use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
 #[stable(feature = "encode_utf16", since = "1.8.0")]
 pub use core::str::EncodeUtf16;
 #[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
@@ -20,12 +17,11 @@ pub use core::str::SplitAsciiWhitespace;
 pub use core::str::SplitInclusive;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::SplitWhitespace;
-#[unstable(feature = "str_from_raw_parts", issue = "119206")]
-pub use core::str::{from_raw_parts, from_raw_parts_mut};
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
+pub use core::str::pattern;
+use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
+pub use core::str::{Bytes, CharIndices, Chars, from_utf8, from_utf8_mut};
 #[stable(feature = "str_escape", since = "1.34.0")]
 pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -38,6 +34,8 @@ pub use core::str::{MatchIndices, RMatchIndices};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{Matches, RMatches};
 #[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{ParseBoolError, from_utf8_unchecked, from_utf8_unchecked_mut};
+#[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplit, Split};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::str::{RSplitN, SplitN};
@@ -45,6 +43,8 @@ pub use core::str::{RSplitN, SplitN};
 pub use core::str::{RSplitTerminator, SplitTerminator};
 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 pub use core::str::{Utf8Chunk, Utf8Chunks};
+#[unstable(feature = "str_from_raw_parts", issue = "119206")]
+pub use core::str::{from_raw_parts, from_raw_parts_mut};
 use core::unicode::conversions;
 use core::{mem, ptr};
 
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index e628be1546f..ee878e879e9 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -43,9 +43,9 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use core::error::Error;
+use core::iter::FusedIterator;
 #[cfg(not(no_global_oom_handling))]
 use core::iter::from_fn;
-use core::iter::FusedIterator;
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Add;
 #[cfg(not(no_global_oom_handling))]
@@ -62,9 +62,9 @@ use crate::alloc::Allocator;
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 use crate::collections::TryReserveError;
-use crate::str::{self, from_utf8_unchecked_mut, Chars, Utf8Error};
+use crate::str::{self, Chars, Utf8Error, from_utf8_unchecked_mut};
 #[cfg(not(no_global_oom_handling))]
-use crate::str::{from_boxed_utf8_unchecked, FromStr};
+use crate::str::{FromStr, from_boxed_utf8_unchecked};
 use crate::vec::Vec;
 
 /// A UTF-8–encoded, growable string.
@@ -440,6 +440,7 @@ impl String {
     /// ```
     #[inline]
     #[rustc_const_stable(feature = "const_string_new", since = "1.39.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_new")]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     pub const fn new() -> String {
@@ -508,6 +509,7 @@ impl String {
     // NB see the slice::hack module in slice.rs for more information
     #[inline]
     #[cfg(test)]
+    #[allow(missing_docs)]
     pub fn from_str(_: &str) -> String {
         panic!("not available with cfg(test)");
     }
@@ -570,6 +572,7 @@ impl String {
     /// [`into_bytes`]: String::into_bytes
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_from_utf8")]
     pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
         match str::from_utf8(&vec) {
             Ok(..) => Ok(String { vec }),
@@ -659,6 +662,56 @@ impl String {
         Cow::Owned(res)
     }
 
+    /// Converts a [`Vec<u8>`] to a `String`, substituting invalid UTF-8
+    /// sequences with replacement characters.
+    ///
+    /// See [`from_utf8_lossy`] for more details.
+    ///
+    /// [`from_utf8_lossy`]: String::from_utf8_lossy
+    ///
+    /// Note that this function does not guarantee reuse of the original `Vec`
+    /// allocation.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(string_from_utf8_lossy_owned)]
+    /// // some bytes, in a vector
+    /// let sparkle_heart = vec![240, 159, 146, 150];
+    ///
+    /// let sparkle_heart = String::from_utf8_lossy_owned(sparkle_heart);
+    ///
+    /// assert_eq!(String::from("💖"), sparkle_heart);
+    /// ```
+    ///
+    /// Incorrect bytes:
+    ///
+    /// ```
+    /// #![feature(string_from_utf8_lossy_owned)]
+    /// // some invalid bytes
+    /// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
+    /// let output = String::from_utf8_lossy_owned(input);
+    ///
+    /// assert_eq!(String::from("Hello �World"), output);
+    /// ```
+    #[must_use]
+    #[cfg(not(no_global_oom_handling))]
+    #[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
+    pub fn from_utf8_lossy_owned(v: Vec<u8>) -> String {
+        if let Cow::Owned(string) = String::from_utf8_lossy(&v) {
+            string
+        } else {
+            // SAFETY: `String::from_utf8_lossy`'s contract ensures that if
+            // it returns a `Cow::Borrowed`, it is a valid UTF-8 string.
+            // Otherwise, it returns a new allocation of an owned `String`, with
+            // replacement characters for invalid sequences, which is returned
+            // above.
+            unsafe { String::from_utf8_unchecked(v) }
+        }
+    }
+
     /// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
     /// if `v` contains any invalid data.
     ///
@@ -1022,6 +1075,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "string_as_str", since = "1.7.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_as_str")]
     pub fn as_str(&self) -> &str {
         self
     }
@@ -1041,6 +1095,7 @@ impl String {
     #[inline]
     #[must_use]
     #[stable(feature = "string_as_str", since = "1.7.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_as_mut_str")]
     pub fn as_mut_str(&mut self) -> &mut str {
         self
     }
@@ -1060,6 +1115,7 @@ impl String {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_confusables("append", "push")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_push_str")]
     pub fn push_str(&mut self, string: &str) {
         self.vec.extend_from_slice(string.as_bytes())
     }
@@ -1694,6 +1750,7 @@ impl String {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[stable(feature = "insert_str", since = "1.16.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_insert_str")]
     pub fn insert_str(&mut self, idx: usize, string: &str) {
         assert!(self.is_char_boundary(idx));
 
@@ -2009,6 +2066,54 @@ impl FromUtf8Error {
         &self.bytes[..]
     }
 
+    /// Converts the bytes into a `String` lossily, substituting invalid UTF-8
+    /// sequences with replacement characters.
+    ///
+    /// See [`String::from_utf8_lossy`] for more details on replacement of
+    /// invalid sequences, and [`String::from_utf8_lossy_owned`] for the
+    /// `String` function which corresponds to this function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(string_from_utf8_lossy_owned)]
+    /// // some invalid bytes
+    /// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
+    /// let output = String::from_utf8(input).unwrap_or_else(|e| e.into_utf8_lossy());
+    ///
+    /// assert_eq!(String::from("Hello �World"), output);
+    /// ```
+    #[must_use]
+    #[cfg(not(no_global_oom_handling))]
+    #[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
+    pub fn into_utf8_lossy(self) -> String {
+        const REPLACEMENT: &str = "\u{FFFD}";
+
+        let mut res = {
+            let mut v = Vec::with_capacity(self.bytes.len());
+
+            // `Utf8Error::valid_up_to` returns the maximum index of validated
+            // UTF-8 bytes. Copy the valid bytes into the output buffer.
+            v.extend_from_slice(&self.bytes[..self.error.valid_up_to()]);
+
+            // SAFETY: This is safe because the only bytes present in the buffer
+            // were validated as UTF-8 by the call to `String::from_utf8` which
+            // produced this `FromUtf8Error`.
+            unsafe { String::from_utf8_unchecked(v) }
+        };
+
+        let iter = self.bytes[self.error.valid_up_to()..].utf8_chunks();
+
+        for chunk in iter {
+            res.push_str(chunk.valid());
+            if !chunk.invalid().is_empty() {
+                res.push_str(REPLACEMENT);
+            }
+        }
+
+        res
+    }
+
     /// Returns the bytes that were attempted to convert to a `String`.
     ///
     /// This method is carefully constructed to avoid allocation. It will
@@ -2313,7 +2418,7 @@ impl<'b> Pattern for &'b String {
     }
 
     #[inline]
-    fn strip_suffix_of<'a>(self, haystack: &'a str) -> Option<&str>
+    fn strip_suffix_of<'a>(self, haystack: &'a str) -> Option<&'a str>
     where
         Self::Searcher<'a>: core::str::pattern::ReverseSearcher<'a>,
     {
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 024a794f17b..50886244d58 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -17,7 +17,7 @@ use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
 use core::marker::{PhantomData, Unsize};
-use core::mem::{self, align_of_val_raw, ManuallyDrop};
+use core::mem::{self, ManuallyDrop, align_of_val_raw};
 use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, Receiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 use core::pin::{Pin, PinCoerceUnsized};
@@ -450,54 +450,7 @@ impl<T> Arc<T> {
     where
         F: FnOnce(&Weak<T>) -> T,
     {
-        // Construct the inner in the "uninitialized" state with a single
-        // weak reference.
-        let uninit_ptr: NonNull<_> = Box::leak(Box::new(ArcInner {
-            strong: atomic::AtomicUsize::new(0),
-            weak: atomic::AtomicUsize::new(1),
-            data: mem::MaybeUninit::<T>::uninit(),
-        }))
-        .into();
-        let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast();
-
-        let weak = Weak { ptr: init_ptr, alloc: Global };
-
-        // It's important we don't give up ownership of the weak pointer, or
-        // else the memory might be freed by the time `data_fn` returns. If
-        // we really wanted to pass ownership, we could create an additional
-        // weak pointer for ourselves, but this would result in additional
-        // updates to the weak reference count which might not be necessary
-        // otherwise.
-        let data = data_fn(&weak);
-
-        // Now we can properly initialize the inner value and turn our weak
-        // reference into a strong reference.
-        let strong = unsafe {
-            let inner = init_ptr.as_ptr();
-            ptr::write(ptr::addr_of_mut!((*inner).data), data);
-
-            // The above write to the data field must be visible to any threads which
-            // observe a non-zero strong count. Therefore we need at least "Release" ordering
-            // in order to synchronize with the `compare_exchange_weak` in `Weak::upgrade`.
-            //
-            // "Acquire" ordering is not required. When considering the possible behaviours
-            // of `data_fn` we only need to look at what it could do with a reference to a
-            // non-upgradeable `Weak`:
-            // - It can *clone* the `Weak`, increasing the weak reference count.
-            // - It can drop those clones, decreasing the weak reference count (but never to zero).
-            //
-            // These side effects do not impact us in any way, and no other side effects are
-            // possible with safe code alone.
-            let prev_value = (*inner).strong.fetch_add(1, Release);
-            debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
-
-            Arc::from_inner(init_ptr)
-        };
-
-        // Strong references should collectively own a shared weak reference,
-        // so don't run the destructor for our old weak reference.
-        mem::forget(weak);
-        strong
+        Self::new_cyclic_in(data_fn, Global)
     }
 
     /// Constructs a new `Arc` with uninitialized contents.
@@ -520,7 +473,7 @@ impl<T> Arc<T> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> {
         unsafe {
@@ -781,6 +734,98 @@ impl<T, A: Allocator> Arc<T, A> {
         }
     }
 
+    /// Constructs a new `Arc<T, A>` in the given allocator while giving you a `Weak<T, A>` to the allocation,
+    /// to allow you to construct a `T` which holds a weak pointer to itself.
+    ///
+    /// Generally, a structure circularly referencing itself, either directly or
+    /// indirectly, should not hold a strong reference to itself to prevent a memory leak.
+    /// Using this function, you get access to the weak pointer during the
+    /// initialization of `T`, before the `Arc<T, A>` is created, such that you can
+    /// clone and store it inside the `T`.
+    ///
+    /// `new_cyclic_in` first allocates the managed allocation for the `Arc<T, A>`,
+    /// then calls your closure, giving it a `Weak<T, A>` to this allocation,
+    /// and only afterwards completes the construction of the `Arc<T, A>` by placing
+    /// the `T` returned from your closure into the allocation.
+    ///
+    /// Since the new `Arc<T, A>` is not fully-constructed until `Arc<T, A>::new_cyclic_in`
+    /// returns, calling [`upgrade`] on the weak reference inside your closure will
+    /// fail and result in a `None` value.
+    ///
+    /// # Panics
+    ///
+    /// If `data_fn` panics, the panic is propagated to the caller, and the
+    /// temporary [`Weak<T>`] is dropped normally.
+    ///
+    /// # Example
+    ///
+    /// See [`new_cyclic`]
+    ///
+    /// [`new_cyclic`]: Arc::new_cyclic
+    /// [`upgrade`]: Weak::upgrade
+    #[cfg(not(no_global_oom_handling))]
+    #[inline]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    pub fn new_cyclic_in<F>(data_fn: F, alloc: A) -> Arc<T, A>
+    where
+        F: FnOnce(&Weak<T, A>) -> T,
+    {
+        // Construct the inner in the "uninitialized" state with a single
+        // weak reference.
+        let (uninit_raw_ptr, alloc) = Box::into_raw_with_allocator(Box::new_in(
+            ArcInner {
+                strong: atomic::AtomicUsize::new(0),
+                weak: atomic::AtomicUsize::new(1),
+                data: mem::MaybeUninit::<T>::uninit(),
+            },
+            alloc,
+        ));
+        let uninit_ptr: NonNull<_> = (unsafe { &mut *uninit_raw_ptr }).into();
+        let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast();
+
+        let weak = Weak { ptr: init_ptr, alloc: alloc };
+
+        // It's important we don't give up ownership of the weak pointer, or
+        // else the memory might be freed by the time `data_fn` returns. If
+        // we really wanted to pass ownership, we could create an additional
+        // weak pointer for ourselves, but this would result in additional
+        // updates to the weak reference count which might not be necessary
+        // otherwise.
+        let data = data_fn(&weak);
+
+        // Now we can properly initialize the inner value and turn our weak
+        // reference into a strong reference.
+        let strong = unsafe {
+            let inner = init_ptr.as_ptr();
+            ptr::write(ptr::addr_of_mut!((*inner).data), data);
+
+            // The above write to the data field must be visible to any threads which
+            // observe a non-zero strong count. Therefore we need at least "Release" ordering
+            // in order to synchronize with the `compare_exchange_weak` in `Weak::upgrade`.
+            //
+            // "Acquire" ordering is not required. When considering the possible behaviours
+            // of `data_fn` we only need to look at what it could do with a reference to a
+            // non-upgradeable `Weak`:
+            // - It can *clone* the `Weak`, increasing the weak reference count.
+            // - It can drop those clones, decreasing the weak reference count (but never to zero).
+            //
+            // These side effects do not impact us in any way, and no other side effects are
+            // possible with safe code alone.
+            let prev_value = (*inner).strong.fetch_add(1, Release);
+            debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
+
+            // Strong references should collectively own a shared weak reference,
+            // so don't run the destructor for our old weak reference.
+            // Calling into_raw_with_allocator has the double effect of giving us back the allocator,
+            // and forgetting the weak reference.
+            let alloc = weak.into_raw_with_allocator().1;
+
+            Arc::from_inner_in(init_ptr, alloc)
+        };
+
+        strong
+    }
+
     /// Constructs a new `Pin<Arc<T, A>>` in the provided allocator. If `T` does not implement `Unpin`,
     /// then `data` will be pinned in memory and unable to be moved.
     #[cfg(not(no_global_oom_handling))]
@@ -1115,7 +1160,7 @@ impl<T> Arc<[T]> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use]
     pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
         unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) }
@@ -1262,7 +1307,7 @@ impl<T, A: Allocator> Arc<mem::MaybeUninit<T>, A> {
     ///
     /// assert_eq!(*five, 5)
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
     pub unsafe fn assume_init(self) -> Arc<T, A> {
@@ -1303,7 +1348,7 @@ impl<T, A: Allocator> Arc<[mem::MaybeUninit<T>], A> {
     ///
     /// assert_eq!(*values, [1, 2, 3])
     /// ```
-    #[stable(feature = "new_uninit", since = "CURRENT_RUSTC_VERSION")]
+    #[stable(feature = "new_uninit", since = "1.82.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
     pub unsafe fn assume_init(self) -> Arc<[T], A> {
diff --git a/library/alloc/src/sync/tests.rs b/library/alloc/src/sync/tests.rs
index d6b3de87577..3f66c889923 100644
--- a/library/alloc/src/sync/tests.rs
+++ b/library/alloc/src/sync/tests.rs
@@ -1,10 +1,10 @@
 use std::clone::Clone;
 use std::mem::MaybeUninit;
 use std::option::Option::None;
+use std::sync::Mutex;
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering::SeqCst;
 use std::sync::mpsc::channel;
-use std::sync::Mutex;
 use std::thread;
 
 use super::*;
diff --git a/library/alloc/src/vec/in_place_collect.rs b/library/alloc/src/vec/in_place_collect.rs
index d119e6ca397..fd94bbbdeb1 100644
--- a/library/alloc/src/vec/in_place_collect.rs
+++ b/library/alloc/src/vec/in_place_collect.rs
@@ -163,7 +163,7 @@ use core::num::NonZero;
 use core::ptr;
 
 use super::{InPlaceDrop, InPlaceDstDataSrcBufDrop, SpecFromIter, SpecFromIterNested, Vec};
-use crate::alloc::{handle_alloc_error, Global};
+use crate::alloc::{Global, handle_alloc_error};
 
 const fn in_place_collectible<DEST, SRC>(
     step_merge: Option<NonZero<usize>>,
@@ -191,7 +191,7 @@ const fn in_place_collectible<DEST, SRC>(
 
 const fn needs_realloc<SRC, DEST>(src_cap: usize, dst_cap: usize) -> bool {
     if const { mem::align_of::<SRC>() != mem::align_of::<DEST>() } {
-        // FIXME: use unreachable! once that works in const
+        // FIXME(const-hack): use unreachable! once that works in const
         panic!("in_place_collectible() prevents this");
     }
 
@@ -208,7 +208,7 @@ const fn needs_realloc<SRC, DEST>(src_cap: usize, dst_cap: usize) -> bool {
 
     // type layouts don't guarantee a fit, so do a runtime check to see if
     // the allocations happen to match
-    return src_cap > 0 && src_cap * mem::size_of::<SRC>() != dst_cap * mem::size_of::<DEST>();
+    src_cap > 0 && src_cap * mem::size_of::<SRC>() != dst_cap * mem::size_of::<DEST>()
 }
 
 /// This provides a shorthand for the source type since local type aliases aren't a thing.
@@ -328,7 +328,7 @@ where
 
     mem::forget(dst_guard);
 
-    let vec = unsafe { Vec::from_nonnull(dst_buf, len, dst_cap) };
+    let vec = unsafe { Vec::from_parts(dst_buf, len, dst_cap) };
 
     vec
 }
diff --git a/library/alloc/src/vec/in_place_drop.rs b/library/alloc/src/vec/in_place_drop.rs
index 27f75979310..4d5b4e47d39 100644
--- a/library/alloc/src/vec/in_place_drop.rs
+++ b/library/alloc/src/vec/in_place_drop.rs
@@ -1,5 +1,5 @@
 use core::marker::PhantomData;
-use core::ptr::{self, drop_in_place, NonNull};
+use core::ptr::{self, NonNull, drop_in_place};
 use core::slice::{self};
 
 use crate::alloc::Global;
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index fad8abad493..f7aad56695d 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -142,7 +142,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
         // struct and then overwriting &mut self.
         // this creates less assembly
         self.cap = 0;
-        self.buf = RawVec::NEW.non_null();
+        self.buf = RawVec::new().non_null();
         self.ptr = self.buf;
         self.end = self.buf.as_ptr();
 
@@ -288,11 +288,11 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
 
         // Safety: `len` is larger than the array size. Copy a fixed amount here to fully initialize
         // the array.
-        return unsafe {
+        unsafe {
             ptr::copy_nonoverlapping(self.ptr.as_ptr(), raw_ary.as_mut_ptr() as *mut T, N);
             self.ptr = self.ptr.add(N);
             Ok(raw_ary.transpose().assume_init())
-        };
+        }
     }
 
     fn fold<B, F>(mut self, mut accum: B, mut f: F) -> B
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index cfd2e4a1512..1984cfeefc1 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -416,10 +416,11 @@ impl<T> Vec<T> {
     /// ```
     #[inline]
     #[rustc_const_stable(feature = "const_vec_new", since = "1.39.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_new")]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
     pub const fn new() -> Self {
-        Vec { buf: RawVec::NEW, len: 0 }
+        Vec { buf: RawVec::new(), len: 0 }
     }
 
     /// Constructs a new, empty `Vec<T>` with at least the specified capacity.
@@ -476,6 +477,7 @@ impl<T> Vec<T> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_with_capacity")]
     pub fn with_capacity(capacity: usize) -> Self {
         Self::with_capacity_in(capacity, Global)
     }
@@ -603,15 +605,116 @@ impl<T> Vec<T> {
         unsafe { Self::from_raw_parts_in(ptr, length, capacity, Global) }
     }
 
-    /// A convenience method for hoisting the non-null precondition out of [`Vec::from_raw_parts`].
+    #[doc(alias = "from_non_null_parts")]
+    /// Creates a `Vec<T>` directly from a `NonNull` pointer, a length, and a capacity.
     ///
     /// # Safety
     ///
-    /// See [`Vec::from_raw_parts`].
+    /// This is highly unsafe, due to the number of invariants that aren't
+    /// checked:
+    ///
+    /// * `ptr` must have been allocated using the global allocator, such as via
+    ///   the [`alloc::alloc`] function.
+    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
+    ///   (`T` having a less strict alignment is not sufficient, the alignment really
+    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
+    ///   allocated and deallocated with the same layout.)
+    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+    ///   to be the same size as the pointer was allocated with. (Because similar to
+    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
+    /// * `length` needs to be less than or equal to `capacity`.
+    /// * The first `length` values must be properly initialized values of type `T`.
+    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    /// * The allocated size in bytes must be no larger than `isize::MAX`.
+    ///   See the safety documentation of [`pointer::offset`].
+    ///
+    /// These requirements are always upheld by any `ptr` that has been allocated
+    /// via `Vec<T>`. Other allocation sources are allowed if the invariants are
+    /// upheld.
+    ///
+    /// Violating these may cause problems like corrupting the allocator's
+    /// internal data structures. For example it is normally **not** safe
+    /// to build a `Vec<u8>` from a pointer to a C `char` array with length
+    /// `size_t`, doing so is only safe if the array was initially allocated by
+    /// a `Vec` or `String`.
+    /// It's also not safe to build one from a `Vec<u16>` and its length, because
+    /// the allocator cares about the alignment, and these two types have different
+    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
+    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1. To avoid
+    /// these issues, it is often preferable to do casting/transmuting using
+    /// [`NonNull::slice_from_raw_parts`] instead.
+    ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
+    /// [`String`]: crate::string::String
+    /// [`alloc::alloc`]: crate::alloc::alloc
+    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// use std::ptr::NonNull;
+    /// use std::mem;
+    ///
+    /// let v = vec![1, 2, 3];
+    ///
+    // FIXME Update this when vec_into_raw_parts is stabilized
+    /// // Prevent running `v`'s destructor so we are in complete control
+    /// // of the allocation.
+    /// let mut v = mem::ManuallyDrop::new(v);
+    ///
+    /// // Pull out the various important pieces of information about `v`
+    /// let p = unsafe { NonNull::new_unchecked(v.as_mut_ptr()) };
+    /// let len = v.len();
+    /// let cap = v.capacity();
+    ///
+    /// unsafe {
+    ///     // Overwrite memory with 4, 5, 6
+    ///     for i in 0..len {
+    ///         p.add(i).write(4 + i);
+    ///     }
+    ///
+    ///     // Put everything back together into a Vec
+    ///     let rebuilt = Vec::from_parts(p, len, cap);
+    ///     assert_eq!(rebuilt, [4, 5, 6]);
+    /// }
+    /// ```
+    ///
+    /// Using memory that was allocated elsewhere:
+    ///
+    /// ```rust
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// use std::alloc::{alloc, Layout};
+    /// use std::ptr::NonNull;
+    ///
+    /// fn main() {
+    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
+    ///     let vec = unsafe {
+    ///         let Some(mem) = NonNull::new(alloc(layout).cast::<u32>()) else {
+    ///             return;
+    ///         };
+    ///
+    ///         mem.write(1_000_000);
+    ///
+    ///         Vec::from_parts(mem, 1, 16)
+    ///     };
+    ///
+    ///     assert_eq!(vec, &[1_000_000]);
+    ///     assert_eq!(vec.capacity(), 16);
+    /// }
+    /// ```
     #[inline]
-    #[cfg(not(no_global_oom_handling))] // required by tests/run-make/alloc-no-oom-handling
-    pub(crate) unsafe fn from_nonnull(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
-        unsafe { Self::from_nonnull_in(ptr, length, capacity, Global) }
+    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    pub unsafe fn from_parts(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
+        unsafe { Self::from_parts_in(ptr, length, capacity, Global) }
     }
 }
 
@@ -830,19 +933,119 @@ impl<T, A: Allocator> Vec<T, A> {
         unsafe { Vec { buf: RawVec::from_raw_parts_in(ptr, capacity, alloc), len: length } }
     }
 
-    /// A convenience method for hoisting the non-null precondition out of [`Vec::from_raw_parts_in`].
+    #[doc(alias = "from_non_null_parts_in")]
+    /// Creates a `Vec<T, A>` directly from a `NonNull` pointer, a length, a capacity,
+    /// and an allocator.
     ///
     /// # Safety
     ///
-    /// See [`Vec::from_raw_parts_in`].
+    /// This is highly unsafe, due to the number of invariants that aren't
+    /// checked:
+    ///
+    /// * `ptr` must be [*currently allocated*] via the given allocator `alloc`.
+    /// * `T` needs to have the same alignment as what `ptr` was allocated with.
+    ///   (`T` having a less strict alignment is not sufficient, the alignment really
+    ///   needs to be equal to satisfy the [`dealloc`] requirement that memory must be
+    ///   allocated and deallocated with the same layout.)
+    /// * The size of `T` times the `capacity` (ie. the allocated size in bytes) needs
+    ///   to be the same size as the pointer was allocated with. (Because similar to
+    ///   alignment, [`dealloc`] must be called with the same layout `size`.)
+    /// * `length` needs to be less than or equal to `capacity`.
+    /// * The first `length` values must be properly initialized values of type `T`.
+    /// * `capacity` needs to [*fit*] the layout size that the pointer was allocated with.
+    /// * The allocated size in bytes must be no larger than `isize::MAX`.
+    ///   See the safety documentation of [`pointer::offset`].
+    ///
+    /// These requirements are always upheld by any `ptr` that has been allocated
+    /// via `Vec<T, A>`. Other allocation sources are allowed if the invariants are
+    /// upheld.
+    ///
+    /// Violating these may cause problems like corrupting the allocator's
+    /// internal data structures. For example it is **not** safe
+    /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
+    /// It's also not safe to build one from a `Vec<u16>` and its length, because
+    /// the allocator cares about the alignment, and these two types have different
+    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
+    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
+    ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
+    /// [`String`]: crate::string::String
+    /// [`dealloc`]: crate::alloc::GlobalAlloc::dealloc
+    /// [*currently allocated*]: crate::alloc::Allocator#currently-allocated-memory
+    /// [*fit*]: crate::alloc::Allocator#memory-fitting
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(allocator_api, box_vec_non_null)]
+    ///
+    /// use std::alloc::System;
+    ///
+    /// use std::ptr::NonNull;
+    /// use std::mem;
+    ///
+    /// let mut v = Vec::with_capacity_in(3, System);
+    /// v.push(1);
+    /// v.push(2);
+    /// v.push(3);
+    ///
+    // FIXME Update this when vec_into_raw_parts is stabilized
+    /// // Prevent running `v`'s destructor so we are in complete control
+    /// // of the allocation.
+    /// let mut v = mem::ManuallyDrop::new(v);
+    ///
+    /// // Pull out the various important pieces of information about `v`
+    /// let p = unsafe { NonNull::new_unchecked(v.as_mut_ptr()) };
+    /// let len = v.len();
+    /// let cap = v.capacity();
+    /// let alloc = v.allocator();
+    ///
+    /// unsafe {
+    ///     // Overwrite memory with 4, 5, 6
+    ///     for i in 0..len {
+    ///         p.add(i).write(4 + i);
+    ///     }
+    ///
+    ///     // Put everything back together into a Vec
+    ///     let rebuilt = Vec::from_parts_in(p, len, cap, alloc.clone());
+    ///     assert_eq!(rebuilt, [4, 5, 6]);
+    /// }
+    /// ```
+    ///
+    /// Using memory that was allocated elsewhere:
+    ///
+    /// ```rust
+    /// #![feature(allocator_api, box_vec_non_null)]
+    ///
+    /// use std::alloc::{AllocError, Allocator, Global, Layout};
+    ///
+    /// fn main() {
+    ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
+    ///     let vec = unsafe {
+    ///         let mem = match Global.allocate(layout) {
+    ///             Ok(mem) => mem.cast::<u32>(),
+    ///             Err(AllocError) => return,
+    ///         };
+    ///
+    ///         mem.write(1_000_000);
+    ///
+    ///         Vec::from_parts_in(mem, 1, 16, Global)
+    ///     };
+    ///
+    ///     assert_eq!(vec, &[1_000_000]);
+    ///     assert_eq!(vec.capacity(), 16);
+    /// }
+    /// ```
     #[inline]
-    #[cfg(not(no_global_oom_handling))] // required by tests/run-make/alloc-no-oom-handling
-    pub(crate) unsafe fn from_nonnull_in(
-        ptr: NonNull<T>,
-        length: usize,
-        capacity: usize,
-        alloc: A,
-    ) -> Self {
+    #[unstable(feature = "allocator_api", reason = "new API", issue = "32838")]
+    // #[unstable(feature = "box_vec_non_null", issue = "130364")]
+    pub unsafe fn from_parts_in(ptr: NonNull<T>, length: usize, capacity: usize, alloc: A) -> Self {
         unsafe { Vec { buf: RawVec::from_nonnull_in(ptr, capacity, alloc), len: length } }
     }
 
@@ -885,6 +1088,49 @@ impl<T, A: Allocator> Vec<T, A> {
         (me.as_mut_ptr(), me.len(), me.capacity())
     }
 
+    #[doc(alias = "into_non_null_parts")]
+    /// Decomposes a `Vec<T>` into its raw components: `(NonNull pointer, length, capacity)`.
+    ///
+    /// Returns the `NonNull` pointer to the underlying data, the length of
+    /// the vector (in elements), and the allocated capacity of the
+    /// data (in elements). These are the same arguments in the same
+    /// order as the arguments to [`from_parts`].
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// memory previously managed by the `Vec`. The only way to do
+    /// this is to convert the `NonNull` pointer, length, and capacity back
+    /// into a `Vec` with the [`from_parts`] function, allowing
+    /// the destructor to perform the cleanup.
+    ///
+    /// [`from_parts`]: Vec::from_parts
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(vec_into_raw_parts, box_vec_non_null)]
+    ///
+    /// let v: Vec<i32> = vec![-1, 0, 1];
+    ///
+    /// let (ptr, len, cap) = v.into_parts();
+    ///
+    /// let rebuilt = unsafe {
+    ///     // We can now make changes to the components, such as
+    ///     // transmuting the raw pointer to a compatible type.
+    ///     let ptr = ptr.cast::<u32>();
+    ///
+    ///     Vec::from_parts(ptr, len, cap)
+    /// };
+    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
+    /// ```
+    #[must_use = "losing the pointer will leak memory"]
+    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
+    pub fn into_parts(self) -> (NonNull<T>, usize, usize) {
+        let (ptr, len, capacity) = self.into_raw_parts();
+        // SAFETY: A `Vec` always has a non-null pointer.
+        (unsafe { NonNull::new_unchecked(ptr) }, len, capacity)
+    }
+
     /// Decomposes a `Vec<T>` into its raw components: `(pointer, length, capacity, allocator)`.
     ///
     /// Returns the raw pointer to the underlying data, the length of the vector (in elements),
@@ -934,6 +1180,54 @@ impl<T, A: Allocator> Vec<T, A> {
         (ptr, len, capacity, alloc)
     }
 
+    #[doc(alias = "into_non_null_parts_with_alloc")]
+    /// Decomposes a `Vec<T>` into its raw components: `(NonNull pointer, length, capacity, allocator)`.
+    ///
+    /// Returns the `NonNull` pointer to the underlying data, the length of the vector (in elements),
+    /// the allocated capacity of the data (in elements), and the allocator. These are the same
+    /// arguments in the same order as the arguments to [`from_parts_in`].
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// memory previously managed by the `Vec`. The only way to do
+    /// this is to convert the `NonNull` pointer, length, and capacity back
+    /// into a `Vec` with the [`from_parts_in`] function, allowing
+    /// the destructor to perform the cleanup.
+    ///
+    /// [`from_parts_in`]: Vec::from_parts_in
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(allocator_api, vec_into_raw_parts, box_vec_non_null)]
+    ///
+    /// use std::alloc::System;
+    ///
+    /// let mut v: Vec<i32, System> = Vec::new_in(System);
+    /// v.push(-1);
+    /// v.push(0);
+    /// v.push(1);
+    ///
+    /// let (ptr, len, cap, alloc) = v.into_parts_with_alloc();
+    ///
+    /// let rebuilt = unsafe {
+    ///     // We can now make changes to the components, such as
+    ///     // transmuting the raw pointer to a compatible type.
+    ///     let ptr = ptr.cast::<u32>();
+    ///
+    ///     Vec::from_parts_in(ptr, len, cap, alloc)
+    /// };
+    /// assert_eq!(rebuilt, [4294967295, 0, 1]);
+    /// ```
+    #[must_use = "losing the pointer will leak memory"]
+    #[unstable(feature = "allocator_api", issue = "32838")]
+    // #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
+    pub fn into_parts_with_alloc(self) -> (NonNull<T>, usize, usize, A) {
+        let (ptr, len, capacity, alloc) = self.into_raw_parts_with_alloc();
+        // SAFETY: A `Vec` always has a non-null pointer.
+        (unsafe { NonNull::new_unchecked(ptr) }, len, capacity, alloc)
+    }
+
     /// Returns the total number of elements the vector can hold without
     /// reallocating.
     ///
@@ -1253,6 +1547,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     #[inline]
     #[stable(feature = "vec_as_slice", since = "1.7.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_as_slice")]
     pub fn as_slice(&self) -> &[T] {
         self
     }
@@ -1270,6 +1565,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     #[inline]
     #[stable(feature = "vec_as_slice", since = "1.7.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_as_mut_slice")]
     pub fn as_mut_slice(&mut self) -> &mut [T] {
         self
     }
@@ -1288,7 +1584,8 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// This method guarantees that for the purpose of the aliasing model, this method
     /// does not materialize a reference to the underlying slice, and thus the returned pointer
-    /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
+    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
+    /// and [`as_non_null`].
     /// Note that calling other methods that materialize mutable references to the slice,
     /// or mutable references to specific elements you are planning on accessing through this pointer,
     /// as well as writing to those elements, may still invalidate this pointer.
@@ -1325,6 +1622,7 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
     /// [`as_ptr`]: Vec::as_ptr
+    /// [`as_non_null`]: Vec::as_non_null
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
     #[rustc_never_returns_null_ptr]
     #[inline]
@@ -1344,7 +1642,8 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// This method guarantees that for the purpose of the aliasing model, this method
     /// does not materialize a reference to the underlying slice, and thus the returned pointer
-    /// will remain valid when mixed with other calls to [`as_ptr`] and [`as_mut_ptr`].
+    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
+    /// and [`as_non_null`].
     /// Note that calling other methods that materialize references to the slice,
     /// or references to specific elements you are planning on accessing through this pointer,
     /// may still invalidate this pointer.
@@ -1384,6 +1683,7 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
     /// [`as_ptr`]: Vec::as_ptr
+    /// [`as_non_null`]: Vec::as_non_null
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
     #[rustc_never_returns_null_ptr]
     #[inline]
@@ -1393,6 +1693,69 @@ impl<T, A: Allocator> Vec<T, A> {
         self.buf.ptr()
     }
 
+    /// Returns a `NonNull` pointer to the vector's buffer, or a dangling
+    /// `NonNull` pointer valid for zero sized reads if the vector didn't allocate.
+    ///
+    /// The caller must ensure that the vector outlives the pointer this
+    /// function returns, or else it will end up dangling.
+    /// Modifying the vector may cause its buffer to be reallocated,
+    /// which would also make any pointers to it invalid.
+    ///
+    /// This method guarantees that for the purpose of the aliasing model, this method
+    /// does not materialize a reference to the underlying slice, and thus the returned pointer
+    /// will remain valid when mixed with other calls to [`as_ptr`], [`as_mut_ptr`],
+    /// and [`as_non_null`].
+    /// Note that calling other methods that materialize references to the slice,
+    /// or references to specific elements you are planning on accessing through this pointer,
+    /// may still invalidate this pointer.
+    /// See the second example below for how this guarantee can be used.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// // Allocate vector big enough for 4 elements.
+    /// let size = 4;
+    /// let mut x: Vec<i32> = Vec::with_capacity(size);
+    /// let x_ptr = x.as_non_null();
+    ///
+    /// // Initialize elements via raw pointer writes, then set length.
+    /// unsafe {
+    ///     for i in 0..size {
+    ///         x_ptr.add(i).write(i as i32);
+    ///     }
+    ///     x.set_len(size);
+    /// }
+    /// assert_eq!(&*x, &[0, 1, 2, 3]);
+    /// ```
+    ///
+    /// Due to the aliasing guarantee, the following code is legal:
+    ///
+    /// ```rust
+    /// #![feature(box_vec_non_null)]
+    ///
+    /// unsafe {
+    ///     let mut v = vec![0];
+    ///     let ptr1 = v.as_non_null();
+    ///     ptr1.write(1);
+    ///     let ptr2 = v.as_non_null();
+    ///     ptr2.write(2);
+    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`:
+    ///     ptr1.write(3);
+    /// }
+    /// ```
+    ///
+    /// [`as_mut_ptr`]: Vec::as_mut_ptr
+    /// [`as_ptr`]: Vec::as_ptr
+    /// [`as_non_null`]: Vec::as_non_null
+    #[unstable(feature = "box_vec_non_null", reason = "new API", issue = "130364")]
+    #[inline]
+    pub fn as_non_null(&mut self) -> NonNull<T> {
+        // SAFETY: A `Vec` always has a non-null pointer.
+        unsafe { NonNull::new_unchecked(self.as_mut_ptr()) }
+    }
+
     /// Returns a reference to the underlying allocator.
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
@@ -1519,6 +1882,7 @@ impl<T, A: Allocator> Vec<T, A> {
         #[cold]
         #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
         #[track_caller]
+        #[optimize(size)]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("swap_remove index (is {index}) should be < len (is {len})");
         }
@@ -1567,6 +1931,7 @@ impl<T, A: Allocator> Vec<T, A> {
         #[cold]
         #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
         #[track_caller]
+        #[optimize(size)]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("insertion index (is {index}) should be <= len (is {len})");
         }
@@ -1629,6 +1994,7 @@ impl<T, A: Allocator> Vec<T, A> {
         #[cold]
         #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
         #[track_caller]
+        #[optimize(size)]
         fn assert_failed(index: usize, len: usize) -> ! {
             panic!("removal index (is {index}) should be < len (is {len})");
         }
@@ -2085,6 +2451,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Takes *O*(1) time.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_pop")]
     pub fn pop(&mut self) -> Option<T> {
         if self.len == 0 {
             None
@@ -2278,6 +2645,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// assert!(!v.is_empty());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "vec_is_empty")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }
@@ -2317,6 +2685,7 @@ impl<T, A: Allocator> Vec<T, A> {
         #[cold]
         #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
         #[track_caller]
+        #[optimize(size)]
         fn assert_failed(at: usize, len: usize) -> ! {
             panic!("`at` split index (is {at}) should be <= len (is {len})");
         }
@@ -2748,6 +3117,7 @@ impl<T: PartialEq, A: Allocator> Vec<T, A> {
 #[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "vec_from_elem")]
 pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
     <T as SpecFromElem>::from_elem(elem, n, Global)
 }
diff --git a/library/alloc/src/vec/spec_from_iter.rs b/library/alloc/src/vec/spec_from_iter.rs
index 6646ae7bccb..e1f0b639bdf 100644
--- a/library/alloc/src/vec/spec_from_iter.rs
+++ b/library/alloc/src/vec/spec_from_iter.rs
@@ -51,7 +51,7 @@ impl<T> SpecFromIter<T, IntoIter<T>> for Vec<T> {
                 if has_advanced {
                     ptr::copy(it.ptr.as_ptr(), it.buf.as_ptr(), it.len());
                 }
-                return Vec::from_nonnull(it.buf, it.len(), it.cap);
+                return Vec::from_parts(it.buf, it.len(), it.cap);
             }
         }