Remove and fix useless drop of reference

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -828,7 +828,7 @@ fn tys(&mut self, a: Ty<'tcx>, _: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
                 } else {
                     match variables.probe(vid) {
                         TypeVariableValue::Known { value: u } => {
-                            drop(variables);
+                            drop(inner);
                             self.relate(u, u)
                         }
                         TypeVariableValue::Unknown { universe: _universe } => {

compiler/rustc_middle/src/mir/visit.rs

@@ -880,12 +880,11 @@ fn super_constant(
             ) {
                 let Constant {
                     span,
-                    user_ty,
+                    user_ty: _, // no visit method for this
                     literal,
                 } = constant;
 
                 self.visit_span($(& $mutability)? *span);
-                drop(user_ty); // no visit method for this
                 match literal {
                     ConstantKind::Ty(ct) => self.visit_ty_const($(&$mutability)? *ct, location),
                     ConstantKind::Val(_, ty) => self.visit_ty($(& $mutability)? *ty, TyContext::Location(location)),

library/std/src/sys/sgx/waitqueue/mod.rs

@@ -207,7 +207,7 @@ pub fn notify_one<T>(
                 let mut entry_guard = entry.lock();
                 let tcs = entry_guard.tcs;
                 entry_guard.wake = true;
-                drop(entry);
+                drop(entry_guard);
                 Ok(WaitGuard { mutex_guard: Some(guard), notified_tcs: NotifiedTcs::Single(tcs) })
             } else {
                 Err(guard)

library/std/src/sys/unix/fs.rs

@@ -1210,7 +1210,7 @@ pub fn set_times(&self, times: FileTimes) -> io::Result<()> {
                 // Redox doesn't appear to support `UTIME_OMIT`.
                 // ESP-IDF and HorizonOS do not support `futimens` at all and the behavior for those OS is therefore
                 // the same as for Redox.
-                drop(times);
+                let _ = times;
                 Err(io::const_io_error!(
                     io::ErrorKind::Unsupported,
                     "setting file times not supported",

library/std/src/thread/tests.rs

@@ -375,7 +375,9 @@ fn test_scoped_threads_nll() {
     // this is mostly a *compilation test* for this exact function:
     fn foo(x: &u8) {
         thread::scope(|s| {
-            s.spawn(|| drop(x));
+            s.spawn(|| match x {
+                _ => (),
+            });
         });
     }
     // let's also run it for good measure