ifcdiff: fix crash when exporting property diffs to JSON

DeepDiff's dictionary_item_added/set_item_added results are a
deepdiff.helper.SetOrdered instance, which subclasses orderly_set's
StableSetEq rather than the OrderedSet class json_dump_default checked
for, so the property relationship check always crashed export() with
"Object of type SetOrdered is not JSON serializable". Check against
StableSet, the common base class shared by every orderly_set set
flavour, instead.

Fixes #8905

Generated with the assistance of an AI coding tool.

src/ifcdiff/ifcdiff.py

@@ -36,7 +36,7 @@ import ifcopenshell.util.representation
 import ifcopenshell.util.selector
 import numpy as np
 from deepdiff import DeepDiff
-from orderly_set import OrderedSet
+from orderly_set import StableSet
 
 __version__ = version = "0.0.0"
 
@@ -257,7 +257,7 @@ class IfcDiff:
 
     def json_dump_default(self, obj):
         # result of DeepDiff may contain ordered sets
-        if isinstance(obj, (OrderedSet, set)):
+        if isinstance(obj, (StableSet, set)):
             return list(obj)
         return json.JSONEncoder.default(None, obj)
 

src/ifcdiff/test.py

@@ -16,9 +16,14 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
+import json
+import os
+import tempfile
+
 import ifcopenshell
 import ifcopenshell.api.context
 import ifcopenshell.api.geometry
+import ifcopenshell.api.pset
 import ifcopenshell.api.root
 import ifcopenshell.api.unit
 import ifcopenshell.util.representation
@@ -94,6 +99,29 @@ class TestIfcDiff:
         assert ifc_diff.deleted_elements == set()
         assert ifc_diff.change_register == {wall.GlobalId: {"attributes_changed": True}}
 
+    def test_property_diff_exports_to_json(self):
+        # Regression test for #8905: comparing "property" relationships makes
+        # DeepDiff report a dictionary_item_added as a SetOrdered, which
+        # json.dump couldn't serialise, crashing export() with no results.
+        ifc_file = setup_project()
+        wall = ifcopenshell.api.root.create_entity(ifc_file, ifc_class="IfcWall", name="Foo")
+
+        new_file = ifc_file.from_string(ifc_file.to_string())
+        wall_new = new_file.by_id(wall.id())
+        pset = ifcopenshell.api.pset.add_pset(new_file, product=wall_new, name="Pset_WallCommon")
+        ifcopenshell.api.pset.edit_pset(new_file, pset=pset, properties={"FireRating": "2HR"})
+
+        ifc_diff = ifcdiff.IfcDiff(ifc_file, new_file, relationships=["property"])
+        ifc_diff.diff()
+        assert ifc_diff.change_register[wall.GlobalId]["properties_changed"]
+
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            output = os.path.join(tmp_dir, "diff.json")
+            ifc_diff.export(output)
+            with open(output) as f:
+                results = json.load(f)
+            assert "Pset_WallCommon" in str(results["changed"][wall.GlobalId]["properties_changed"])
+
     def test_changed_geometry(self):
         ifc_file = setup_project()
         wall = ifcopenshell.api.root.create_entity(ifc_file, ifc_class="IfcWall", name="Foo")