rustc_errors: take self by value in DiagnosticBuilder::cancel.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1962,7 +1962,9 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
             // Avoid complaining about other inference issues for expressions like
             // `42 >> 1`, where the types are still `{integer}`, but we want to
             // Do we need `trait_ref.skip_binder().self_ty().is_numeric() &&` too?
-            err.cancel();
+            // NOTE(eddyb) this was `.cancel()`, but `err`
+            // is borrowed, so we can't fully defuse it.
+            err.downgrade_to_delayed_bug();
             return;
         }
         let post = if post.len() > 4 {

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -2114,7 +2114,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
                 let ty = parent_trait_ref.skip_binder().self_ty();
                 if parent_trait_ref.references_error() {
-                    err.cancel();
+                    // NOTE(eddyb) this was `.cancel()`, but `err`
+                    // is borrowed, so we can't fully defuse it.
+                    err.downgrade_to_delayed_bug();
                     return;
                 }