From c3f0577002b5c158c63dab92476d94af954086f1 Mon Sep 17 00:00:00 2001
From: John Kugelman <john@kugelman.name>
Date: Mon, 11 Oct 2021 20:40:03 -0400
Subject: Add #[must_use] to non-mutating verb methods

---
 library/alloc/src/rc.rs   | 2 ++
 library/alloc/src/sync.rs | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

(limited to 'library/alloc')

diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 2f4a131136e..4023d7b21ed 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -2229,6 +2229,8 @@ impl<T: ?Sized> Weak<T> {
     ///
     /// assert!(weak_five.upgrade().is_none());
     /// ```
+    #[must_use = "this returns a new `Rc`, \
+                  without modifying the original weak pointer"]
     #[stable(feature = "rc_weak", since = "1.4.0")]
     pub fn upgrade(&self) -> Option<Rc<T>> {
         let inner = self.inner()?;
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 1d4216d7d57..905e3d72a45 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -146,7 +146,7 @@ macro_rules! acquire {
 /// use std::sync::Arc;
 ///
 /// let my_arc = Arc::new(());
-/// Arc::downgrade(&my_arc);
+/// let my_weak = Arc::downgrade(&my_arc);
 /// ```
 ///
 /// `Arc<T>`'s implementations of traits like `Clone` may also be called using
@@ -897,6 +897,8 @@ impl<T: ?Sized> Arc<T> {
     ///
     /// let weak_five = Arc::downgrade(&five);
     /// ```
+    #[must_use = "this returns a new `Weak` pointer, \
+                  without modifying the original `Arc`"]
     #[stable(feature = "arc_weak", since = "1.4.0")]
     pub fn downgrade(this: &Self) -> Weak<T> {
         // This Relaxed is OK because we're checking the value in the CAS
@@ -1861,6 +1863,8 @@ impl<T: ?Sized> Weak<T> {
     ///
     /// assert!(weak_five.upgrade().is_none());
     /// ```
+    #[must_use = "this returns a new `Arc`, \
+                  without modifying the original weak pointer"]
     #[stable(feature = "arc_weak", since = "1.4.0")]
     pub fn upgrade(&self) -> Option<Arc<T>> {
         // We use a CAS loop to increment the strong count instead of a
-- 
cgit 1.4.1-3-g733a5