#warning "TODO"
    assert(false);

#warning "TODO"
  assert(do_restrict);

  const int gi_regrid_error = CCTK_GroupIndex("CarpetX::regrid_error");
  assert(gi_regrid_error >= 0);
  const int gi_refinement_level = CCTK_GroupIndex("CarpetX::refinement_level");
  assert(gi_refinement_level >= 0);

  for (int gi = 0; gi < numgroups; ++gi) {
    if (CCTK_GroupTypeI(gi) != CCTK_GF)
      continue;
    groups.push_back(gi);

  const auto &leveldata = ghext->leveldata.at(level);
  for (const auto &groupdataptr : leveldata.groupdata) {
    // Restrict only grid functions
    if (groupdataptr) {
      auto &restrict groupdata = *groupdataptr;
      // Restrict only evolved grid functions
      if (groupdata.do_checkpoint)
        groups.push_back(groupdata.groupindex);
    }