{"ast_node_type":"variable","tokens":[{"end":75,"kind":"keyword","start":0,"text":"let"}]}
                let index_ty = self.typeck_results.expr_ty_adjusted(index);
            if let ty::Ref(_, base_ty_inner, _) = *base_ty.kind() {
                if self.is_builtin_index(e, base_ty_inner, index_ty) {