From 3d16d4b1007fbee2f48e823d08f2ae0ab29aea73 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <mail@jshimwell.com>
Date: Thu, 19 Jun 2025 22:43:45 +0200
Subject: [PATCH] Adding checks to geometry.plot to avoid material name
 overlaps (#3458)

Co-authored-by: Patrick Shriwise <pshriwise@gmail.com>
---
 openmc/geometry.py                  | 30 +++++++++++++++++++++--------
 tests/unit_tests/dagmc/test_plot.py | 11 +++++++++--
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/openmc/geometry.py b/openmc/geometry.py
index 9b2af7b4a..f56b9b6fe 100644
--- a/openmc/geometry.py
+++ b/openmc/geometry.py
@@ -758,13 +758,27 @@ class Geometry:
         model.geometry = self
         model.materials = self.get_all_materials().values()
 
-        # Add placeholder materials for DAGMCUniverses
-        universes = self.get_all_universes()
-        for universe in universes.values():
-            if isinstance(universe, openmc.DAGMCUniverse):
-                for name in universe.material_names:
-                    mat_dag = openmc.Material(name=name)
-                    mat_dag.add_nuclide('H1', 1.0)
-                    model.materials.append(mat_dag)
+        # collect all the material names from the geometry
+        all_material_names = {m.name for m in model.materials if m.name is not None}
+
+        # makes a placeholder material for each material name if it isn't
+        # already present on the model. These materials are otherwise missing
+        # from the geometry and are needed for plotting.
+        for universe in model.geometry.get_all_universes().values():
+            if not isinstance(universe, openmc.DAGMCUniverse):
+                continue
+            for name in universe.material_names:
+                # if this name is already present in the model, skip it
+                # (this can happen if the same material name is used in multiple
+                # universes)
+                if name in all_material_names:
+                    continue
+                # if the material name is not present on the model,
+                # create a placeholder material with the same name
+                # and add it to the model
+                mat_dag = openmc.Material(name=name)
+                mat_dag.add_nuclide('H1', 1.0)
+                model.materials.append(mat_dag)
+                all_material_names.add(name)
 
         return model.plot(*args, **kwargs)
diff --git a/tests/unit_tests/dagmc/test_plot.py b/tests/unit_tests/dagmc/test_plot.py
index afc2c395e..62022b258 100644
--- a/tests/unit_tests/dagmc/test_plot.py
+++ b/tests/unit_tests/dagmc/test_plot.py
@@ -48,14 +48,21 @@ def test_plotting_geometry_filled_with_dagmc_universe(request):
     dag_universe = openmc.DAGMCUniverse(request.path.parent / 'dagmc.h5m', auto_geom_ids=True)
 
     sphere1 = openmc.Sphere(r=50.0)
-    sphere2 = openmc.Sphere(r=60.0, boundary_type='vacuum')
+    sphere2 = openmc.Sphere(r=60.0)
+    sphere2 = openmc.Sphere(r=70.0, boundary_type='vacuum')
 
-    # Adding a material to the CSG Universe to check all materials are accounted for
+    # Adding a material to the CSG Universe to check universe materials are accounted for
     csg_material = openmc.Material(name='csg_material')
     csg_material.add_nuclide("H1", 1.0)
 
+    # Adding a material with the same name as a dagmc material to check that
+    # the plot can handel two materials with the same name from different universes
+    csg_material = openmc.Material(name=dag_universe.material_names[0])
+    csg_material.add_nuclide("H1", 1.0)
+
     cell1 = openmc.Cell(fill=dag_universe, region=-sphere1)
     cell2 = openmc.Cell(fill=csg_material, region=+sphere1 & -sphere2)
 
     geometry = openmc.Geometry([cell1, cell2])
+
     geometry.plot()