Fix conversion 3to4 of name/identifier when identifier is empty

imas/ids_convert.py

@@ -456,6 +456,8 @@ def _apply_3to4_conversion(self, old: Element, new: Element) -> None:
             # Map DD3 name -> DD4 description
             if name_path not in self.old_to_new.path:
                 self._add_rename(name_path, desc_path)
+                # GH#114: Also preserve name in DD4 name when identifier is empty
+                self.old_to_new.type_change[name_path] = _name_identifier_3to4
 
             # Map DD3 identifier -> DD4 name
             if id_path in self.old_to_new.path:
@@ -1154,6 +1156,19 @@ def _circuit_connections_4to3(node: IDSPrimitive) -> None:
     node.value = new_value
 
 
+def _name_identifier_3to4(source_name: IDSBase, target_description: IDSBase) -> None:
+    """Preserve name when identifier is empty, see GH#114."""
+    # Always copy DD3 name -> DD4 description
+    target_description.value = source_name.value
+
+    # When DD3 identifier is empty, also preserve name in DD4 name
+    source_parent = source_name._parent
+    source_identifier = getattr(source_parent, "identifier", None)
+    if source_identifier is None or not source_identifier.value:
+        target_parent = target_description._parent
+        target_parent.name = source_name.value
+
+
 def _ids_properties_source(source: IDSString0D, provenance: IDSStructure) -> None:
     """Handle DD3to4 migration of ids_properties/source to ids_properties/provenance."""
     if len(provenance.node) > 0:

imas/test/test_ids_convert.py

@@ -575,6 +575,29 @@ def test_4to3_name_identifier_mapping_magnetics():
     assert dst.b_field_pol_probe[0].identifier == "TEST_NAME"
 
 
+def test_3to4_name_identifier_empty_identifier():
+    """GH#114: name must be preserved when identifier is empty."""
+    factory = IDSFactory("3.40.1")
+
+    src = factory.pf_active()
+    src.ids_properties.homogeneous_time = IDS_TIME_MODE_HOMOGENEOUS
+    src.coil.resize(2)
+    # Case 1: name populated, identifier empty
+    src.coil[0].name = "TEST_NAME"
+    src.coil[0].identifier = ""
+    # Case 2: name populated, identifier not set at all
+    src.coil[1].name = "TEST_NAME2"
+
+    dst = convert_ids(src, "4.0.0")
+
+    # name must be preserved in DD4 name (not overwritten by empty identifier)
+    assert dst.coil[0].name == "TEST_NAME"
+    assert dst.coil[0].description == "TEST_NAME"
+
+    assert dst.coil[1].name == "TEST_NAME2"
+    assert dst.coil[1].description == "TEST_NAME2"
+
+
 def test_3to4_cocos_hardcoded_paths():
     # Check for existence in 3.42.0
     factory = IDSFactory("3.42.0")