Rollup merge of #71256 - cuviper:must_use_replace, r=estebank

Lint must_use on mem::replace

This adds a hint on `mem::replace`, "if you don't need the old value,
you can just assign the new value directly". This is in similar spirit
to the `must_use` on `ManuallyDrop::take`.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
index 29e99c0afd2..094c468a677 100644
--- a/src/libstd/thread/local.rs
+++ b/src/libstd/thread/local.rs
@@ -301,7 +301,7 @@ mod lazy {
             // value (an aliasing violation). To avoid setting the "I'm running a
             // destructor" flag we just use `mem::replace` which should sequence the
             // operations a little differently and make this safe to call.
-            mem::replace(&mut *ptr, Some(value));
+            let _ = mem::replace(&mut *ptr, Some(value));
 
             // After storing `Some` we want to get a reference to the contents of
             // what we just stored. While we could use `unwrap` here and it should