Prevent cyclic references when assigning nesting or aggregation

Walk up the full hierarchy via get_parent() in can_nest() and
can_aggregate() to reject assignments that would create a cycle.
Also reject self-assignment.

Fix #7248

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/bonsai/bonsai/tool/aggregate.py

@@ -49,21 +49,40 @@ class Aggregate(bonsai.core.tool.Aggregate):
         related_object = tool.Ifc.get_entity(related_obj)
         if not relating_object or not related_object:
             return False
+        if relating_object == related_object:
+            return False
+
+        is_compatible_class = False
         if (relating_object.is_a("IfcElement") or relating_object.is_a("IfcElementType")) and related_object.is_a(
             "IfcElement"
         ):
-            return True
-        if tool.Ifc.get_schema() == "IFC2X3":
+            is_compatible_class = True
+        elif tool.Ifc.get_schema() == "IFC2X3":
             if relating_object.is_a("IfcSpatialStructureElement") and related_object.is_a("IfcSpatialStructureElement"):
-                return True
-            if relating_object.is_a("IfcProject") and related_object.is_a("IfcSpatialStructureElement"):
-                return True
+                is_compatible_class = True
+            elif relating_object.is_a("IfcProject") and related_object.is_a("IfcSpatialStructureElement"):
+                is_compatible_class = True
         else:
             if relating_object.is_a("IfcSpatialElement") and related_object.is_a("IfcSpatialElement"):
-                return True
-            if relating_object.is_a("IfcProject") and related_object.is_a("IfcSpatialElement"):
-                return True
-        return False
+                is_compatible_class = True
+            elif relating_object.is_a("IfcProject") and related_object.is_a("IfcSpatialElement"):
+                is_compatible_class = True
+
+        if not is_compatible_class:
+            return False
+
+        # Prevent cyclic references: walk up the full hierarchy from the
+        # proposed parent and reject if we encounter the proposed child.
+        ancestor = ifcopenshell.util.element.get_parent(relating_object)
+        seen = {relating_object}
+        while ancestor:
+            if ancestor == related_object:
+                return False
+            if ancestor in seen:
+                break
+            seen.add(ancestor)
+            ancestor = ifcopenshell.util.element.get_parent(ancestor)
+        return True
 
     @classmethod
     def has_physical_body_representation(cls, element: ifcopenshell.entity_instance) -> bool:

src/bonsai/bonsai/tool/nest.py

@@ -45,9 +45,23 @@ class Nest(bonsai.core.tool.Nest):
         related_object = tool.Ifc.get_entity(related_obj)
         if not relating_object or not related_object:
             return False
-        if relating_object.is_a("IfcElement") and related_object.is_a("IfcElement"):
-            return True
-        return False
+        if relating_object == related_object:
+            return False
+        is_compatible_class = relating_object.is_a("IfcElement") and related_object.is_a("IfcElement")
+        if not is_compatible_class:
+            return False
+        # Prevent cyclic references: walk up the full hierarchy from the
+        # proposed parent and reject if we encounter the proposed child.
+        ancestor = ifcopenshell.util.element.get_parent(relating_object)
+        seen = {relating_object}
+        while ancestor:
+            if ancestor == related_object:
+                return False
+            if ancestor in seen:
+                break
+            seen.add(ancestor)
+            ancestor = ifcopenshell.util.element.get_parent(ancestor)
+        return True
 
     @classmethod
     def disable_editing(cls, obj: bpy.types.Object) -> None:

src/bonsai/test/tool/test_aggregate.py

@@ -18,6 +18,7 @@
 
 import bpy
 import ifcopenshell
+import ifcopenshell.api.aggregate
 import ifcopenshell.api.context
 import ifcopenshell.api.geometry
 import ifcopenshell.api.root
@@ -99,6 +100,42 @@ class TestCanAggregate(NewFile):
         subelement_obj = bpy.data.objects.new("Object", None)
         assert subject.can_aggregate(element_obj, subelement_obj) is False
 
+    def test_element_cannot_aggregate_to_itself(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        element = ifc.createIfcElementAssembly()
+        element_obj = bpy.data.objects.new("Object", None)
+        tool.Ifc.link(element, element_obj)
+        assert subject.can_aggregate(element_obj, element_obj) is False
+
+    def test_cyclic_aggregation_is_prevented(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        assembly_a = ifc.createIfcElementAssembly()
+        assembly_a_obj = bpy.data.objects.new("AssemblyA", None)
+        tool.Ifc.link(assembly_a, assembly_a_obj)
+        beam = ifc.createIfcBeam()
+        beam_obj = bpy.data.objects.new("Beam", None)
+        tool.Ifc.link(beam, beam_obj)
+        ifcopenshell.api.aggregate.assign_object(ifc, products=[beam], relating_object=assembly_a)
+        assert subject.can_aggregate(beam_obj, assembly_a_obj) is False
+
+    def test_deep_cyclic_aggregation_is_prevented(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        assembly_a = ifc.createIfcElementAssembly()
+        assembly_a_obj = bpy.data.objects.new("AssemblyA", None)
+        tool.Ifc.link(assembly_a, assembly_a_obj)
+        assembly_b = ifc.createIfcElementAssembly()
+        assembly_b_obj = bpy.data.objects.new("AssemblyB", None)
+        tool.Ifc.link(assembly_b, assembly_b_obj)
+        beam = ifc.createIfcBeam()
+        beam_obj = bpy.data.objects.new("Beam", None)
+        tool.Ifc.link(beam, beam_obj)
+        ifcopenshell.api.aggregate.assign_object(ifc, products=[assembly_b], relating_object=assembly_a)
+        ifcopenshell.api.aggregate.assign_object(ifc, products=[beam], relating_object=assembly_b)
+        assert subject.can_aggregate(beam_obj, assembly_a_obj) is False
+
 
 class TestHasPhysicalBodyRepresentation(NewFile):
     def test_run(self):

src/bonsai/test/tool/test_nest.py

@@ -19,6 +19,7 @@
 import bpy
 import ifcopenshell
 import ifcopenshell.api
+import ifcopenshell.api.nest
 import ifcopenshell.api.spatial
 
 import bonsai.core.tool
@@ -51,6 +52,42 @@ class TestCanNest(NewFile):
         subelement_obj = bpy.data.objects.new("Object", None)
         assert subject.can_nest(element_obj, subelement_obj) is False
 
+    def test_element_cannot_nest_to_itself(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        element = ifc.createIfcWall()
+        element_obj = bpy.data.objects.new("Object", None)
+        tool.Ifc.link(element, element_obj)
+        assert subject.can_nest(element_obj, element_obj) is False
+
+    def test_cyclic_nesting_is_prevented(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        wall_a = ifc.createIfcWall()
+        wall_a_obj = bpy.data.objects.new("WallA", None)
+        tool.Ifc.link(wall_a, wall_a_obj)
+        wall_b = ifc.createIfcWall()
+        wall_b_obj = bpy.data.objects.new("WallB", None)
+        tool.Ifc.link(wall_b, wall_b_obj)
+        ifcopenshell.api.nest.assign_object(ifc, related_objects=[wall_b], relating_object=wall_a)
+        assert subject.can_nest(wall_b_obj, wall_a_obj) is False
+
+    def test_deep_cyclic_nesting_is_prevented(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        wall_a = ifc.createIfcWall()
+        wall_a_obj = bpy.data.objects.new("WallA", None)
+        tool.Ifc.link(wall_a, wall_a_obj)
+        wall_b = ifc.createIfcWall()
+        wall_b_obj = bpy.data.objects.new("WallB", None)
+        tool.Ifc.link(wall_b, wall_b_obj)
+        wall_c = ifc.createIfcWall()
+        wall_c_obj = bpy.data.objects.new("WallC", None)
+        tool.Ifc.link(wall_c, wall_c_obj)
+        ifcopenshell.api.nest.assign_object(ifc, related_objects=[wall_b], relating_object=wall_a)
+        ifcopenshell.api.nest.assign_object(ifc, related_objects=[wall_c], relating_object=wall_b)
+        assert subject.can_nest(wall_c_obj, wall_a_obj) is False
+
 
 class TestDisableEditing(NewFile):
     def test_run(self):