From 595ce4ce987f73b521d2fb8c4b69ccdd554bede8 Mon Sep 17 00:00:00 2001
From: Max Dexheimer <maxdexh03@gmail.com>
Date: Thu, 20 Aug 2026 23:22:32 +0200
Subject: [PATCH] Tighten allocator `Send` and `Sync` bounds on `Arc`

---
 library/alloc/src/rc.rs   | 5 +----
 library/alloc/src/sync.rs | 6 +++---
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 3655ee327bec2..48c489cc8fa5e 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -344,10 +344,7 @@ impl<T: ?Sized, A: Allocator> !Sync for Rc<T, A> {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe + RefUnwindSafe> UnwindSafe for Rc<T, A> {}
 #[stable(feature = "rc_ref_unwind_safe", since = "1.58.0")]
-impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe + RefUnwindSafe> RefUnwindSafe
-    for Rc<T, A>
-{
-}
+impl<T: RefUnwindSafe + ?Sized, A: Allocator + RefUnwindSafe> RefUnwindSafe for Rc<T, A> {}
 
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Rc<U, A>> for Rc<T, A> {}
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 8ff3927aabf5e..b944da8ed47eb 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -283,7 +283,7 @@ pub struct Arc<
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Send for Arc<T, A> {}
 #[stable(feature = "rust1", since = "1.0.0")]
-unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Sync> Sync for Arc<T, A> {}
+unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Sync for Arc<T, A> {}
 
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe + RefUnwindSafe> UnwindSafe
@@ -369,7 +369,7 @@ pub struct Weak<
 #[stable(feature = "arc_weak", since = "1.4.0")]
 unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Send for Weak<T, A> {}
 #[stable(feature = "arc_weak", since = "1.4.0")]
-unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Sync> Sync for Weak<T, A> {}
+unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Sync for Weak<T, A> {}
 
 #[unstable(feature = "coerce_unsized", issue = "18598")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<Weak<U, A>> for Weak<T, A> {}
@@ -4429,7 +4429,7 @@ pub struct UniqueArc<
 unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Send for UniqueArc<T, A> {}
 
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
-unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Sync> Sync for UniqueArc<T, A> {}
+unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send + Sync> Sync for UniqueArc<T, A> {}
 
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
 // #[unstable(feature = "coerce_unsized", issue = "18598")]