{"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
        let element_tys = tcx.mk_type_list_from_iter(element_tys_iter);
        let element_tys_iter = (0..max_len).map(|_| self.next_ty_var(span));
        let pat_ty = Ty::new_tup(tcx, element_tys);