Fix deep purge of unit when converting units and fix bug where unit was removed if map unit was the same as the project unit

src/ifcopenshell-python/ifcopenshell/util/unit.py

@@ -853,8 +853,9 @@ def convert_file_length_units(ifc_file: ifcopenshell.file, target_units: str = "
             },
         )
 
-    file_patched.remove(old_length)
     unit_assignment = get_unit_assignment(file_patched)
-    unit_assignment.Units = tuple([new_length, *unit_assignment.Units])
+    unit_assignment.Units = [new_length, *(u for u in unit_assignment.Units if u.UnitType != new_length.UnitType)]
+    if not file_patched.get_total_inverses(old_length):
+        ifcopenshell.util.element.remove_deep2(file_patched, old_length)
 
     return file_patched

src/ifcopenshell-python/test/util/test_unit.py

@@ -132,6 +132,24 @@ class TestConvertFileLengthUnits(test.bootstrap.IFC4):
         assert output.by_type("IfcMapConversion")[0].Scale == 1
         assert subject.get_full_unit_name(output.by_type("IfcProjectedCRS")[0].MapUnit) == "METRE"
 
+    def test_preserving_enh_if_there_is_a_map_unit_which_is_also_the_project_default(self):
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject")
+        meter = ifcopenshell.api.unit.add_si_unit(self.file, unit_type="LENGTHUNIT")
+        ifcopenshell.api.context.add_context(self.file, "Model")
+        ifcopenshell.api.georeference.add_georeferencing(self.file)
+        ifcopenshell.api.georeference.edit_georeferencing(
+            self.file, projected_crs={"MapUnit": meter}, coordinate_operation={"Eastings": 10, "Scale": 1}
+        )
+        ifcopenshell.api.unit.assign_unit(self.file, units=[meter])
+        output = subject.convert_file_length_units(self.file, target_units="MILLIMETER")
+        assert subject.get_full_unit_name(subject.get_project_unit(output, "LENGTHUNIT")) == "MILLIMETRE"
+        assert output.by_type("IfcMapConversion")[0].Eastings == 10
+        assert output.by_type("IfcMapConversion")[0].Northings == 0
+        assert output.by_type("IfcMapConversion")[0].Scale == 0.001
+        assert subject.get_full_unit_name(output.by_type("IfcProjectedCRS")[0].MapUnit) == "METRE"
+
+        unit_assignment = subject.get_unit_assignment(output)
+        assert len(unit_assignment.Units) == 1
 
 class TestConvertFileLengthUnitsIFC2X3(test.bootstrap.IFC2X3):
     def test_converting_map_conversion_if_there_is_no_map_unit(self):