Merge ref '3507a749b365' from rust-lang/rust

Pull recent changes from https://github.com/rust-lang/rust via Josh.

Upstream ref: 3507a74
Filtered ref: 67f9124a1e199effc310447c1c1f9548093bd8f9

This merge was created using https://github.com/rust-lang/josh-sync.

Author: The Miri Cronjob Bot

alloc/src/lib.rs

@@ -102,6 +102,7 @@
 #![feature(async_iterator)]
 #![feature(bstr)]
 #![feature(bstr_internals)]
+#![feature(cast_maybe_uninit)]
 #![feature(char_internals)]
 #![feature(char_max_len)]
 #![feature(clone_to_uninit)]

alloc/src/vec/mod.rs

@@ -3176,7 +3176,7 @@ impl<T, A: Allocator> Vec<T, A> {
         // - but the allocation extends out to `self.buf.capacity()` elements, possibly
         // uninitialized
         let spare_ptr = unsafe { ptr.add(self.len) };
-        let spare_ptr = spare_ptr.cast::<MaybeUninit<T>>();
+        let spare_ptr = spare_ptr.cast_uninit();
         let spare_len = self.buf.capacity() - self.len;
 
         // SAFETY:

core/src/alloc/layout.rs

@@ -226,10 +226,10 @@ impl Layout {
 
     /// Creates a `NonNull` that is dangling, but well-aligned for this Layout.
     ///
-    /// Note that the pointer value may potentially represent a valid pointer,
-    /// which means this must not be used as a "not yet initialized"
-    /// sentinel value. Types that lazily allocate must track initialization by
-    /// some other means.
+    /// Note that the address of the returned pointer may potentially
+    /// be that of a valid pointer, which means this must not be used
+    /// as a "not yet initialized" sentinel value.
+    /// Types that lazily allocate must track initialization by some other means.
     #[unstable(feature = "alloc_layout_extra", issue = "55724")]
     #[must_use]
     #[inline]