Bonsai: refuse class-mismatched type assignment

Schema-illegal IfcDoor->IfcWallType pairings parse cleanly but propagate
into operators that fan out by type and eventually crash the wrapper.
Block the pairing at its source: API guard in ifcopenshell.api.type.
assign_type, per-object partition in BIM_OT_assign_type + DuplicateType,
new tool.Type.is_relating_type_compatible helper, AST forward-compat
guard. Files in the wild are still loaded unchanged.

Generated with the assistance of an AI coding tool.

src/ifcopenshell-python/ifcopenshell/api/type/assign_type.py

@@ -24,6 +24,7 @@ import ifcopenshell.api.owner
 import ifcopenshell.api.type
 import ifcopenshell.guid
 import ifcopenshell.util.element
+import ifcopenshell.util.type
 
 
 def assign_type(
@@ -189,6 +190,20 @@ class Usecase:
         if not related_objects:
             return
 
+        # The EXPRESS schema has no WHERE rule pairing RelatingType /
+        # RelatedObjects classes; the canonical class pairing per schema
+        # is a buildingSMART implementer agreement, enforced here.
+        allowed_occurrences = ifcopenshell.util.type.get_applicable_entities(
+            relating_type.is_a(), schema=self.file.schema
+        )
+        mismatched_classes = sorted({o.is_a() for o in related_objects if o.is_a() not in allowed_occurrences})
+        if mismatched_classes:
+            raise TypeError(
+                f"{relating_type.is_a()} cannot type {', '.join(mismatched_classes)} "
+                f"in schema {self.file.schema} (allowed occurrence classes: "
+                f"{allowed_occurrences or '<none>'})"
+            )
+
         ifc2x3 = self.file.schema == "IFC2X3"
         related_objects_set = set(related_objects)
         if ifc2x3:

src/ifcopenshell-python/test/api/type/test_assign_type.py

@@ -183,6 +183,39 @@ class TestAssignType(test.bootstrap.IFC4):
             assert element.PredefinedType == "USERDEFINED"
         assert element.ObjectType == "Test"
 
+    def test_class_mismatched_pair_raises(self):
+        door = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcDoor")
+        wall_type = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWallType")
+        with pytest.raises(TypeError, match=r"IfcWallType cannot type IfcDoor"):
+            ifcopenshell.api.type.assign_type(self.file, related_objects=[door], relating_type=wall_type)
+        assert ifcopenshell.util.element.get_type(door) is None
+
+    def test_class_mismatched_pair_does_not_mutate(self):
+        door = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcDoor")
+        wall_type = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWallType")
+        rels_before = self.file.by_type("IfcRelDefinesByType")
+        with pytest.raises(TypeError):
+            ifcopenshell.api.type.assign_type(self.file, related_objects=[door], relating_type=wall_type)
+        rels_after = self.file.by_type("IfcRelDefinesByType")
+        assert rels_after == rels_before
+
+    def test_partial_mismatch_in_selection_rejects_whole_call(self):
+        door = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcDoor")
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        wall_type = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWallType")
+        with pytest.raises(TypeError):
+            ifcopenshell.api.type.assign_type(self.file, related_objects=[door, wall], relating_type=wall_type)
+        # The good occurrence must NOT have been typed — partial mutation is the
+        # bug class this guard exists to prevent.
+        assert ifcopenshell.util.element.get_type(wall) is None
+        assert ifcopenshell.util.element.get_type(door) is None
+
+    def test_untypable_occurrence_rejected(self):
+        opening = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcOpeningElement")
+        any_type = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWallType")
+        with pytest.raises(TypeError):
+            ifcopenshell.api.type.assign_type(self.file, related_objects=[opening], relating_type=any_type)
+
 
 class TestAssignTypeIFC2X3(test.bootstrap.IFC2X3, TestAssignType):
     pass