fn derive_cause<'tcx>(
tcx: TyCtxt<'tcx>,
candidate_kind: ProbeKind<TyCtxt<'tcx>>,
cause: ObligationCause<'tcx>,
idx: usize,
parent_trait_pred: PolyTraitPredicate<'tcx>,
) -> ObligationCause<'tcx>
fn derive_cause<'tcx>(
tcx: TyCtxt<'tcx>,
candidate_kind: ProbeKind<TyCtxt<'tcx>>,
cause: ObligationCause<'tcx>,
idx: usize,
parent_trait_pred: PolyTraitPredicate<'tcx>,
) -> ObligationCause<'tcx>