Better message for exception for templated base operator fields (apac…

…he#37668)

* Better message for exception for templated base operator fields

* fix test

airflow/serialization/serialized_objects.py

@@ -26,6 +26,7 @@
 import weakref
 from dataclasses import dataclass
 from inspect import signature
+from textwrap import dedent
 from typing import TYPE_CHECKING, Any, Collection, Iterable, Mapping, NamedTuple, Union
 
 import attrs
@@ -912,7 +913,12 @@ def _serialize_node(cls, op: BaseOperator | MappedOperator, include_deps: bool)
         if op.template_fields:
             for template_field in op.template_fields:
                 if template_field in forbidden_fields:
-                    raise AirflowException(f"Cannot template BaseOperator field: {template_field!r}")
+                    raise AirflowException(
+                        dedent(
+                            f"""Cannot template BaseOperator field:
+                        {template_field!r} {op.__class__.__name__=} {op.template_fields=}"""
+                        )
+                    )
                 value = getattr(op, template_field, None)
                 if not cls._is_excluded(value, template_field, op):
                     serialize_op[template_field] = serialize_template_field(value)

tests/serialization/test_dag_serialization.py

@@ -25,9 +25,11 @@
 import multiprocessing
 import os
 import pickle
+import re
 from datetime import datetime, timedelta
 from glob import glob
 from pathlib import Path
+from textwrap import dedent
 from typing import TYPE_CHECKING
 from unittest import mock
 
@@ -2072,7 +2074,15 @@ def execute(self, context: Context):
             task.render_template_fields(context={"test_email_list": ["[email protected]", "[email protected]"]})
             assert task.email == "[email protected],[email protected]"
 
-        with pytest.raises(AirflowException, match="Cannot template BaseOperator field: 'execution_timeout'"):
+        with pytest.raises(
+            AirflowException,
+            match=re.escape(
+                dedent(
+                    """Failed to serialize DAG 'test_dag': Cannot template BaseOperator field:
+                        'execution_timeout' op.__class__.__name__='TestOperator' op.template_fields=('email', 'execution_timeout')"""
+                )
+            ),
+        ):
             SerializedDAG.to_dict(dag)