Add missing AssembleErrorMessage

PiperOrigin-RevId: 721827952
Change-Id: Icb2b07f558b661cad0e7bd9a428e3cb988970d35

Author: timofey-stepanov

koladata/data_slice.cc

@@ -1184,14 +1184,18 @@ absl::StatusOr<DataSlice::AttrNamesSet> DataSlice::GetAttrNames(
     // For entities, just process the schema of the DataSlice.
     return GetAttrsFromSchemaItem(GetSchemaImpl(), db_impl, fallbacks);
   }
-  return VisitImpl(absl::Overload(
+  auto result = VisitImpl(absl::Overload(
       [&](const internal::DataItem& item) {
         return GetAttrsFromDataItem(item, GetSchemaImpl(), db_impl, fallbacks);
       },
       [&](const internal::DataSliceImpl& slice) {
         return GetAttrsFromDataSlice(slice, GetSchemaImpl(), db_impl, fallbacks,
                                      union_object_attrs);
       }));
+  if (!result.ok()) {
+    return AssembleErrorMessage(result.status(), {.ds = *this});
+  }
+  return result;
 }
 
 absl::StatusOr<DataSlice> DataSlice::GetAttr(

py/koladata/types/data_slice_test.py

@@ -997,7 +997,7 @@ def test_get_attr_names_object(self):
     ):
       x.no_bag().get_attr_names(intersection=True)
     with self.assertRaisesRegex(
-        ValueError, 'object.*is missing __schema__ attribute'
+        ValueError, 'object schema is missing for the DataItem'
     ):
       db.new(a=1, b='abc').with_schema(schema_constants.OBJECT).get_attr_names(
           intersection=True