Don't super-fold types when we hit the recursion limit

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -230,17 +230,14 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                     Reveal::All => {
                         let args = data.args.try_fold_with(self)?;
                         let recursion_limit = self.interner().recursion_limit();
+
                         if !recursion_limit.value_within_limit(self.anon_depth) {
-                            // A closure or coroutine may have itself as in its upvars.
-                            // This should be checked handled by the recursion check for opaque
-                            // types, but we may end up here before that check can happen.
-                            // In that case, we delay a bug to mark the trip, and continue without
-                            // revealing the opaque.
-                            self.infcx
+                            let guar = self
+                                .infcx
                                 .err_ctxt()
                                 .build_overflow_error(&ty, self.cause.span, true)
                                 .delay_as_bug();
-                            return ty.try_super_fold_with(self);
+                            return Ok(Ty::new_error(self.interner(), guar));
                         }
 
                         let generic_ty = self.interner().type_of(data.def_id);

tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs

@@ -0,0 +1,8 @@
+#![feature(type_alias_impl_trait)]
+
+type T = impl Copy;
+//~^ ERROR cannot resolve opaque type
+
+static STATIC: T = None::<&'static T>;
+
+fn main() {}

tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr

@@ -0,0 +1,9 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/infinite-cycle-involving-weak.rs:3:10
+   |
+LL | type T = impl Copy;
+   |          ^^^^^^^^^ cannot resolve opaque type
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0720`.