{"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
            let ocx = ObligationCtxt::new(&infcx);
            let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
            let assumed_wf_tys = ocx.assumed_wf_types(param_env, parent_def_id).unwrap_or_default();