{"ast_node_type":"variable","tokens":[{"end":54,"kind":"keyword","start":0,"text":"let"}]}
            let ocx = ObligationCtxt::new(wfcx.infcx);
        if let Ok(()) = wfcx.infcx.commit_if_ok(|_| {
            ocx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty)?;