{"ast_node_type":"variable","tokens":[{"end":47,"kind":"keyword","start":0,"text":"let"}]}
        let err_type = Ty::new_error(tcx, err);
        let sig_len = caller_sig.instantiate_identity().skip_binder().inputs().len() + 1;
        return tcx.arena.alloc_from_iter((0..sig_len).map(|_| err_type));