{"ast_node_type":"impl","tokens":[{"end":82,"kind":"keyword","start":0,"text":"variant:"}]}
        variant: impl FnOnce(DerivedHostCause<'tcx>) -> ObligationCauseCode<'tcx>,
        parent_host_pred: ty::Binder<'tcx, ty::HostEffectPredicate<'tcx>>,
    ) -> ObligationCause<'tcx> {