fn extend_cause_with_original_assoc_item_obligation<'tcx>( tcx: TyCtxt<'tcx>, trait_ref: &TraitRef<'tcx>, item: Option<&Item<'tcx>>, cause: &mut ObligationCause<'tcx>, pred: &Predicate<'tcx>, trait_assoc_items: impl Iterator<Item = &'tcx AssocItem>)