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::new(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.