Merge pull request #15525 from bangerth/add-indices-dev

Do not remove duplicates before inserting index set elements.

diff --cc include/deal.II/lac/affine_constraints.templates.h
Simple merge

diff --cc include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
index 0307042e620df99b5f35a676b481e23344bdbad0,b936273c7de64f758d0c44bf674e61196aadbf1e..e0589e3989a09c0e86a567f8b94ca51104f875ee
--- 1/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
--- 2/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
+++ b/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
@@@ -762,20 -767,12 +762,17 @@@ namespace interna
                }
            }
  
 -        const int ierr_1 =
 -          MPI_Waitall(requests.size(), requests.data(), MPI_STATUSES_IGNORE);
 -        AssertThrowMPI(ierr_1);
 +        if (!requests.empty())
 +          {
 +            const int ierr_1 = MPI_Waitall(requests.size(),
 +                                           requests.data(),
 +                                           MPI_STATUSES_IGNORE);
 +            AssertThrowMPI(ierr_1);
 +          }
        }
 +#endif
  
        std::sort(ghost_indices.begin(), ghost_indices.end());
-       ghost_indices.erase(std::unique(ghost_indices.begin(),
-                                       ghost_indices.end()),
-                           ghost_indices.end());
  
        this->is_extended_ghosts =
          IndexSet(mg_level_fine == numbers::invalid_unsigned_int ?