Rollup merge of rust-lang#89833 - jkugelman:must-use-rc-downgrade, r=joshtriplett

matthiaskrgr · web-flow · commit b30d41df9a50 · 2021-10-31T03:14:33.000+01:00
Add #[must_use] to Rc::downgrade Missed this in previous PR rust-lang#89796 (comment) Parent issue: rust-lang#89692 r? ``@joshtriplett``
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
@@ -41,7 +41,7 @@
 //! use std::rc::Rc;
 //!
 //! let my_rc = Rc::new(());
-//! Rc::downgrade(&my_rc);
+//! let my_weak = Rc::downgrade(&my_rc);
 //! ```
 //!
 //! `Rc<T>`'s implementations of traits like `Clone` may also be called using
@@ -889,6 +889,8 @@ impl<T: ?Sized> Rc<T> {
     ///
     /// let weak_five = Rc::downgrade(&five);
     /// ```
+    #[must_use = "this returns a new `Weak` pointer, \
+                  without modifying the original `Rc`"]
     #[stable(feature = "rc_weak", since = "1.4.0")]
     pub fn downgrade(this: &Self) -> Weak<T> {
         this.inner().inc_weak();
