Auto merge of #3044 - rust-lang:rustup-2023-08-31, r=RalfJung

Automatic sync from rustc

1 files changed, 51 insertions, 0 deletions

diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index e45ddc7896b..ae7bac0c85f 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -1218,6 +1218,15 @@ impl<T, A: Allocator> Vec<T, A> {
     /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
     /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
     ///
+    /// 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`].
+    /// 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.
+    /// See the second example below for how this guarantee can be used.
+    ///
+    ///
     /// # Examples
     ///
     /// ```
@@ -1231,7 +1240,23 @@ impl<T, A: Allocator> Vec<T, A> {
     /// }
     /// ```
     ///
+    /// Due to the aliasing guarantee, the following code is legal:
+    ///
+    /// ```rust
+    /// unsafe {
+    ///     let mut v = vec![0, 1, 2];
+    ///     let ptr1 = v.as_ptr();
+    ///     let _ = ptr1.read();
+    ///     let ptr2 = v.as_mut_ptr().offset(2);
+    ///     ptr2.write(2);
+    ///     // Notably, the write to `ptr2` did *not* invalidate `ptr1`
+    ///     // because it mutated a different element:
+    ///     let _ = ptr1.read();
+    /// }
+    /// ```
+    ///
     /// [`as_mut_ptr`]: Vec::as_mut_ptr
+    /// [`as_ptr`]: Vec::as_ptr
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
     #[inline]
     pub fn as_ptr(&self) -> *const T {
@@ -1248,6 +1273,15 @@ impl<T, A: Allocator> Vec<T, A> {
     /// 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`] and [`as_mut_ptr`].
+    /// 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
     ///
     /// ```
@@ -1265,6 +1299,23 @@ impl<T, A: Allocator> Vec<T, A> {
     /// }
     /// assert_eq!(&*x, &[0, 1, 2, 3]);
     /// ```
+    ///
+    /// Due to the aliasing guarantee, the following code is legal:
+    ///
+    /// ```rust
+    /// unsafe {
+    ///     let mut v = vec![0];
+    ///     let ptr1 = v.as_mut_ptr();
+    ///     ptr1.write(1);
+    ///     let ptr2 = v.as_mut_ptr();
+    ///     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
     #[stable(feature = "vec_as_ptr", since = "1.37.0")]
     #[inline]
     pub fn as_mut_ptr(&mut self) -> *mut T {