{"ast_node_type":"variable","tokens":[{"end":88,"kind":"keyword","start":0,"text":"let"}]}
    let (infcx, param_env) = cx.tcx.infer_ctxt().build_with_typing_env(cx.typing_env());
    let ty = args.type_at(0);
    let ocx = ObligationCtxt::new(&infcx);