From 9cf2516251c5379d3e8429342e8a392df81b9aaa Mon Sep 17 00:00:00 2001
From: William Woodruff <william@trailofbits.com>
Date: Thu, 10 Dec 2020 17:47:28 -0500
Subject: [PATCH 1/2] doc(array,vec): add notes about side effects when
 empty-initializing

---
 library/alloc/src/macros.rs       | 3 +++
 library/std/src/primitive_docs.rs | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
index a992d768d6314..bbff1d3dc4d2e 100644
--- a/library/alloc/src/macros.rs
+++ b/library/alloc/src/macros.rs
@@ -29,6 +29,9 @@
 /// to the same boxed integer value, not five references pointing to independently
 /// boxed integers.
 ///
+/// Also, note that `[T; 0]` is a valid initializer. This will initialize (or call)
+/// `T` but not populate the vector with it, so be mindful of side effects.
+///
 /// [`Vec`]: crate::vec::Vec
 #[cfg(not(test))]
 #[macro_export]
diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs
index 55171ef2292d7..b22adbbe3d356 100644
--- a/library/std/src/primitive_docs.rs
+++ b/library/std/src/primitive_docs.rs
@@ -489,6 +489,9 @@ mod prim_pointer {}
 /// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.
 ///   The type of `x` must be [`Copy`].
 ///
+/// Note that `[x; 0]` is a valid repeat expression. This will produce an empty array
+/// but will also initialize (or call) `x`, which may produce side effects.
+///
 /// Arrays of *any* size implement the following traits if the element type allows it:
 ///
 /// - [`Copy`]

From d986924eb13a103fc79c474eded47a663c91bb7f Mon Sep 17 00:00:00 2001
From: William Woodruff <william@trailofbits.com>
Date: Fri, 11 Dec 2020 10:09:40 -0500
Subject: [PATCH 2/2] doc: apply suggestions

---
 library/alloc/src/macros.rs       | 5 +++--
 library/std/src/primitive_docs.rs | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/library/alloc/src/macros.rs b/library/alloc/src/macros.rs
index bbff1d3dc4d2e..7d4eff6185dbe 100644
--- a/library/alloc/src/macros.rs
+++ b/library/alloc/src/macros.rs
@@ -29,8 +29,9 @@
 /// to the same boxed integer value, not five references pointing to independently
 /// boxed integers.
 ///
-/// Also, note that `[T; 0]` is a valid initializer. This will initialize (or call)
-/// `T` but not populate the vector with it, so be mindful of side effects.
+/// Also, note that `vec![expr; 0]` is allowed, and produces an empty vector.
+/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
+/// be mindful of side effects.
 ///
 /// [`Vec`]: crate::vec::Vec
 #[cfg(not(test))]
diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs
index b22adbbe3d356..7aca5451ebc20 100644
--- a/library/std/src/primitive_docs.rs
+++ b/library/std/src/primitive_docs.rs
@@ -489,8 +489,9 @@ mod prim_pointer {}
 /// * A repeat expression `[x; N]`, which produces an array with `N` copies of `x`.
 ///   The type of `x` must be [`Copy`].
 ///
-/// Note that `[x; 0]` is a valid repeat expression. This will produce an empty array
-/// but will also initialize (or call) `x`, which may produce side effects.
+/// Note that `[expr; 0]` is allowed, and produces an empty array.
+/// This will still evaluate `expr`, however, and immediately drop the resulting value, so
+/// be mindful of side effects.
 ///
 /// Arrays of *any* size implement the following traits if the element type allows it:
 ///