Function items_of_instance 

fn items_of_instance<'tcx>(
    tcx: TyCtxt<'tcx>,
    (instance, mode): (Instance<'tcx>, CollectionMode),
) -> Result<(&'tcx [Spanned<MonoItem<'tcx>>], &'tcx [Spanned<MonoItem<'tcx>>]), NormalizationErrorInMono>