fix comment

Author: MingyuChen1

compiler/rustc_error_messages/locales/en-US/middle.ftl

@@ -1,6 +1,6 @@
 middle_drop_check_overflow =
     overflow while adding drop-check rules for {$ty}
-    .note = {$note}
+    .note = overflowed on {$overflow_ty}
 
 middle_opaque_hidden_type_mismatch =
     concrete type differs from previous defining opaque type use

compiler/rustc_middle/src/error.rs

@@ -10,7 +10,7 @@ pub struct DropCheckOverflow<'tcx> {
     #[primary_span]
     pub span: Span,
     pub ty: Ty<'tcx>,
-    pub note: String,
+    pub overflow_ty: Ty<'tcx>,
 }
 
 #[derive(SessionDiagnostic)]

compiler/rustc_middle/src/traits/query.rs

@@ -117,8 +117,7 @@ pub struct DropckOutlivesResult<'tcx> {
 impl<'tcx> DropckOutlivesResult<'tcx> {
     pub fn report_overflows(&self, tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
         if let Some(overflow_ty) = self.overflows.get(0) {
-            let note = format!("overflowed on {}", overflow_ty);
-            tcx.sess.emit_err(DropCheckOverflow { span, ty, note });
+            tcx.sess.emit_err(DropCheckOverflow { span, ty, overflow_ty: *overflow_ty });
         }
     }