From 5a8cf3362c29cbc503d9ea1ec8c119578da38fc7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Se=C3=A1n=20de=20B=C3=BArca?= <sdeburca@fastmail.net>
Date: Fri, 7 Nov 2025 09:47:55 -0800
Subject: [PATCH] alloc: Document panics when allocations will exceed max

---
 library/alloc/src/string.rs  | 21 +++++++++++++++++----
 library/alloc/src/vec/mod.rs |  9 +++++++--
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 4a2689e01ff17..f5ba71c288334 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -454,6 +454,10 @@ impl String {
     ///
     /// [`new`]: String::new
     ///
+    /// # Panics
+    ///
+    /// Panics if the capacity exceeds `isize::MAX` _bytes_.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1079,6 +1083,10 @@ impl String {
 
     /// Appends a given string slice onto the end of this `String`.
     ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
+    ///
     /// # Examples
     ///
     /// ```
@@ -1101,8 +1109,9 @@ impl String {
     ///
     /// # Panics
     ///
-    /// Panics if the range has `start_bound > end_bound`, or, if the range is
-    /// bounded on either end and does not lie on a [`char`] boundary.
+    /// Panics if the range has `start_bound > end_bound`, if the range is
+    /// bounded on either end and does not lie on a [`char`] boundary, or if the
+    /// new capacity exceeds `isize::MAX` bytes.
     ///
     /// # Examples
     ///
@@ -1158,7 +1167,7 @@ impl String {
     ///
     /// # Panics
     ///
-    /// Panics if the new capacity overflows [`usize`].
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
     ///
     /// # Examples
     ///
@@ -1208,7 +1217,7 @@ impl String {
     ///
     /// # Panics
     ///
-    /// Panics if the new capacity overflows [`usize`].
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
     ///
     /// # Examples
     ///
@@ -1372,6 +1381,10 @@ impl String {
 
     /// Appends the given [`char`] to the end of this `String`.
     ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
+    ///
     /// # Examples
     ///
     /// ```
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 13d38d3c9609a..0c485ed31912a 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -3338,6 +3338,10 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
     /// except that it also works with slice elements that are Clone but not Copy.
     /// If Rust gets specialization this function may be deprecated.
     ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
+    ///
     /// # Examples
     ///
     /// ```
@@ -3359,8 +3363,9 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
     ///
     /// # Panics
     ///
-    /// Panics if starting index is greater than the end index
-    /// or if the index is greater than the length of the vector.
+    /// Panics if starting index is greater than the end index, if the index is
+    /// greater than the length of the vector, or if the new capacity exceeds
+    /// `isize::MAX` _bytes_.
     ///
     /// # Examples
     ///