Auto merge of #79273 - Dylan-DPC:rollup-zd10xlt, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - #77844 (clarify rules for ZST Boxes)
 - #79067 (Refactor the abi handling code a bit)
 - #79182 (Fix links to extern types in rustdoc (fixes #78777))
 - #79231 (Exhaustively match in variant count instrinsic)
 - #79238 (Direct RUSTC_LOG (tracing/log) output to stderr instead of stdout.)
 - #79256 (Fix typos)
 - #79264 (Get rid of some doctree items)
 - #79272 (Support building clone shims for arrays with generic size)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 11 insertions, 0 deletions

diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 1512235da6a..b9490c44f4b 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -62,6 +62,13 @@
 //! 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`].
+//!
 //! 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
 //! (i.e. the C type `T*`). This means that if you have extern "C"
@@ -125,6 +132,7 @@
 //! [`Global`]: crate::alloc::Global
 //! [`Layout`]: crate::alloc::Layout
 //! [`Layout::for_value(&*value)`]: crate::alloc::Layout::for_value
+//! [valid]: ptr#safety
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -530,7 +538,10 @@ impl<T: ?Sized> Box<T> {
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same raw pointer.
     ///
+    /// The safety conditions are described in the [memory layout] section.
+    ///
     /// # Examples
+    ///
     /// Recreate a `Box` which was previously converted to a raw pointer
     /// using [`Box::into_raw`]:
     /// ```