{"ast_node_type":"other","tokens":[{"end":100,"kind":"keyword","start":0,"text":"always!(binders.is_empty(Interner));"}]}
                    always!(binders.is_empty(Interner)); // quantified where clauses not yet handled
                        predicate.substitute(Interner, &var_subst).into_value_and_skipped_binders();
                    let var_predicate = self.insert_inference_vars_for_impl_trait(