Disable attrs state management on MappedOperator (#24772)

(cherry picked from commit 6fd06fa)

airflow/models/mappedoperator.py

@@ -239,7 +239,17 @@ def _expand(self, **mapped_kwargs: "Mappable") -> "MappedOperator":
         return op
 
 
-@attr.define(kw_only=True)
+@attr.define(
+    kw_only=True,
+    # Disable custom __getstate__ and __setstate__ generation since it interacts
+    # badly with Airflow's DAG serialization and pickling. When a mapped task is
+    # deserialized, subclasses are coerced into MappedOperator, but when it goes
+    # through DAG pickling, all attributes defined in the subclasses are dropped
+    # by attrs's custom state management. Since attrs does not do anything too
+    # special here (the logic is only important for slots=True), we use Python's
+    # built-in implementation, which works (as proven by good old BaseOperator).
+    getstate_setstate=False,
+)
 class MappedOperator(AbstractOperator):
     """Object representing a mapped operator in a DAG."""
 

tests/serialization/test_dag_serialization.py

@@ -24,6 +24,7 @@
 import json
 import multiprocessing
 import os
+import pickle
 from datetime import datetime, timedelta
 from glob import glob
 from unittest import mock
@@ -1890,6 +1891,21 @@ def x(arg1, arg2, arg3):
         "retry_delay": timedelta(seconds=30),
     }
 
+    # Ensure the serialized operator can also be correctly pickled, to ensure
+    # correct interaction between DAG pickling and serialization. This is done
+    # here so we don't need to duplicate tests between pickled and non-pickled
+    # DAGs everywhere else.
+    pickled = pickle.loads(pickle.dumps(deserialized))
+    assert pickled.mapped_op_kwargs == {
+        "arg2": {"a": 1, "b": 2},
+        "arg3": _XComRef("op1", XCOM_RETURN_KEY),
+    }
+    assert pickled.partial_kwargs == {
+        "op_args": [],
+        "op_kwargs": {"arg1": [1, 2, {"a": "b"}]},
+        "retry_delay": timedelta(seconds=30),
+    }
+
 
 @pytest.mark.filterwarnings("ignore::DeprecationWarning")
 @pytest.mark.parametrize(