{"ast_node_type":"other","tokens":[{"end":54,"kind":"keyword","start":0,"text":"CanonicalizeMode::Response"}]}
                CanonicalizeMode::Response { .. } => {
                CanonicalizeMode::Input(_) => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
                    panic!("unexpected region in response: {r:?}")