compiler: replace some mem::forget's with ManuallyDrop

compiler/rustc_lint/src/levels.rs

@@ -529,8 +529,7 @@ impl<'s> LintLevelsBuilder<'s, TopDown> {
 
  /// Called after `push` when the scope of a set of attributes are exited.
  pub(crate) fn pop(&mut self, push: BuilderPush) {
- self.provider.cur = push.prev;
- std::mem::forget(push);
+ self.provider.cur = std::mem::ManuallyDrop(push).prev;
  }
 }
 

compiler/rustc_query_system/src/query/plumbing.rs

@@ -25,7 +25,7 @@ use std::cell::Cell;
 use std::collections::hash_map::Entry;
 use std::fmt::Debug;
 use std::hash::Hash;
-use std::mem;
+use std::mem::ManuallyDrop;
 use thin_vec::ThinVec;
 use tracing::instrument;
 
@@ -169,11 +169,11 @@ where
  where
  C: QueryCache<Key = K>,
  {
- let key = self.key;
- let state = self.state;
-
  // Forget ourself so our destructor won't poison the query
- mem::forget(self);
+ let this = ManuallyDrop::new(self);
+
+ let key = this.key;
+ let state = this.state;
 
  // Mark as complete before we remove the job from the active state
  // so no other thread can re-execute this query.