From 07a804307991dc96613fbf208e91f0ae3cdf318b Mon Sep 17 00:00:00 2001
From: pommicket <pommicket@gmail.com>
Date: Sat, 25 Feb 2023 11:05:21 -0500
Subject: [PATCH] Use checked_add in VecDeque::append for ZSTs to avoid
 overflow

(cherry picked from commit 379b18bb0ab07e8f7ba04ca29ba52a1817cec1ce)
---
 library/alloc/src/collections/vec_deque/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index d4a12509b1cf..8317ac431a5e 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -1924,7 +1924,7 @@ pub fn split_off(&mut self, at: usize) -> Self
     #[stable(feature = "append", since = "1.4.0")]
     pub fn append(&mut self, other: &mut Self) {
         if T::IS_ZST {
-            self.len += other.len;
+            self.len = self.len.checked_add(other.len).expect("capacity overflow");
             other.len = 0;
             other.head = 0;
             return;