From 69669cbdb2a98bcf8c49062b9606e14ce51ecf71 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sat, 19 Sep 2020 11:55:45 +0200
Subject: [PATCH] make IterMut Send/Sync again

---
 library/alloc/src/collections/vec_deque.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/library/alloc/src/collections/vec_deque.rs b/library/alloc/src/collections/vec_deque.rs
index 0f34786b18a..e8e9dae0111 100644
--- a/library/alloc/src/collections/vec_deque.rs
+++ b/library/alloc/src/collections/vec_deque.rs
@@ -2694,6 +2694,13 @@ pub struct IterMut<'a, T: 'a> {
     phantom: PhantomData<&'a mut [T]>,
 }
 
+// SAFETY: we do nothing thread-local and there is no interior mutability,
+// so the usual structural `Send`/`Sync` apply.
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for IterMut<'_, T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for IterMut<'_, T> {}
+
 #[stable(feature = "collection_debug", since = "1.17.0")]
 impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {