Google Cloud Providers - Fix _MethodDefault deepcopy failure (#29518)

This is the attempt to fix #28751 by setting a memo to the same instance of DEFAULT,
which is the stub for a Literal value type introduced to support Python 3.7 with mypy
in Google's API core Python client.

Without this any operator that has the parameter set to DEFAULT constant
(which is often the default value for retry parameters) will throw the
error in mini-scheduler after execution as the attemt to deepcopy this
project would fail.

Co-authored-by: Igor Kholopov <[email protected]>

airflow/providers/google/cloud/operators/cloud_base.py

@@ -18,6 +18,8 @@
 """This module contains a Google API base operator."""
 from __future__ import annotations
 
+from google.api_core.gapic_v1.method import DEFAULT
+
 from airflow.models import BaseOperator
 
 
@@ -27,4 +29,11 @@ class GoogleCloudBaseOperator(BaseOperator):
     on top of Google API client libraries.
     """
 
-    pass
+    def __deepcopy__(self, memo):
+        """
+        Updating the memo to fix the non-copyable global constant.
+        This constant can be specified in operator parameters as a retry configuration to indicate a default.
+        See https://github.com/apache/airflow/issues/28751 for details.
+        """
+        memo[id(DEFAULT)] = DEFAULT
+        return super().__deepcopy__(memo)

tests/providers/google/cloud/operators/test_cloud_base.py

@@ -0,0 +1,56 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from __future__ import annotations
+
+import copy
+import unittest
+
+from google.api_core.gapic_v1.method import DEFAULT, _MethodDefault
+from google.api_core.retry import Retry
+
+from airflow.providers.google.cloud.operators.cloud_base import GoogleCloudBaseOperator
+
+TASK_ID = "task-id"
+
+
+class GoogleSampleOperator(GoogleCloudBaseOperator):
+    def __init__(
+        self,
+        retry: Retry | _MethodDefault = DEFAULT,
+        config: dict | None = None,
+        **kwargs,
+    ) -> None:
+        super().__init__(**kwargs)
+        self.retry = retry
+        self.config = config
+
+
+class TestGoogleCloudBaseOperator(unittest.TestCase):
+    def test_handles_deepcopy_with_method_default(self):
+        op = GoogleSampleOperator(task_id=TASK_ID)
+        copied_op = copy.deepcopy(op)
+
+        self.assertEqual(copied_op.retry, DEFAULT)
+        self.assertEqual(copied_op.config, None)
+
+    def test_handles_deepcopy_with_non_default_retry(self):
+        op = GoogleSampleOperator(task_id=TASK_ID, retry=Retry(deadline=30), config={"config": "value"})
+        copied_op = copy.deepcopy(op)
+
+        self.assertEqual(copied_op.retry.deadline, 30)
+        self.assertEqual(copied_op.config, {"config": "value"})