Auto merge of #34756 - habnabit:mutex-refunwindsafe, r=alexcrichton

Mutex and RwLock need RefUnwindSafe too

Incomplete, because I don't know what the appropriate stability annotation is here, but this is an attempt to bring the documentation for `std::panic` in line with reality. Right now, it says:

>Types like `&Mutex<T>`, however, are unwind safe because they implement poisoning by default.

But only `Mutex<T>`, not `&Mutex<T>`, is unwind-safe.

Author: bors

src/libstd/panic.rs

@@ -227,6 +227,11 @@ impl<T: ?Sized> !RefUnwindSafe for UnsafeCell<T> {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T> RefUnwindSafe for AssertUnwindSafe<T> {}
 
+#[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")]
+impl<T: ?Sized> RefUnwindSafe for Mutex<T> {}
+#[stable(feature = "unwind_safe_lock_refs", since = "1.12.0")]
+impl<T: ?Sized> RefUnwindSafe for RwLock<T> {}
+
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T> Deref for AssertUnwindSafe<T> {
     type Target = T;

src/test/run-pass/panic-safe.rs

@@ -36,6 +36,8 @@ fn main() {
     assert::<Box<i32>>();
     assert::<Mutex<i32>>();
     assert::<RwLock<i32>>();
+    assert::<&Mutex<i32>>();
+    assert::<&RwLock<i32>>();
     assert::<Rc<i32>>();
     assert::<Arc<i32>>();