GCG: Warn properly for HTG inputs

Filters/Parallel/vtkHyperTreeGridGhostCellsGenerator.cxx

@@ -33,6 +33,7 @@ void vtkHyperTreeGridGhostCellsGenerator::PrintSelf(ostream& os, vtkIndent inden
 int vtkHyperTreeGridGhostCellsGenerator::FillOutputPortInformation(int, vtkInformation* info)
 {
   info->Set(vtkDataObject::DATA_TYPE_NAME(), "vtkHyperTreeGrid");
+  info->Set(vtkDataObject::DATA_TYPE_NAME(), "vtkPartitionedDataSet");
   return 1;
 }
 

Filters/ParallelDIY2/vtkGhostCellsGenerator.cxx

@@ -190,8 +190,14 @@ int vtkGhostCellsGenerator::GenerateGhostCells(
       error = true;
     }
 
-    if (vtkHyperTreeGrid::SafeDownCast(inputPartition) ||
-      vtkExplicitStructuredGrid::SafeDownCast(inputPartition))
+    if (vtkHyperTreeGrid::SafeDownCast(inputPartition))
+    {
+      error = true;
+      vtkErrorMacro(<< "vtkHyperTreeGrid is not supported by this filter. Please use the "
+                       "appropriate vtkHyperTreeGridGhostCellsGenerator filter instead.");
+    }
+
+    if (vtkExplicitStructuredGrid::SafeDownCast(inputPartition))
     {
       error = true;
       vtkErrorMacro(<< "Input data set type " << inputPartition->GetClassName()