lattwood opened a new pull request #11016:
URL: https://github.com/apache/airflow/pull/11016
This can have *extremely* bad consequences. After this change, a jinja2
template like the one below will cause the task instance to fail, if the DAG
being executed is not a sub-DAG. This may also display an error on the Rendered
tab of the Task Instance page.
`task_instance.xcom_pull('z', key='return_value',
dag_id=dag.parent_dag.dag_id)`
Prior to the change in this commit, the above template would pull the latest
value for task_id 'z', for the given execution_date, from *any DAG*. If your
task_ids between DAGs are all unique, or if DAGs using the same task_id always
have different execution_date values, this will appear to act like dag_id=None.
Our current theory is SQLAlchemy/Python doesn't behave as expected when
comparing `jinja2.Undefined` to `None`.
Admittedly this issue boils down to PEBKAC, but this is also a case of
Airflow not doing the (perceived) right thing in the face of ambiguity, and
this PR fixes that up.
I did find this note about why it was only set to `jinja2.Undefined`, but
given the way this can fail (and the difficulty in tracking down the root
cause), I strongly feel this warrants breaking backwards compatibility with
DAGs/task instances that are attempting to erroneously use undefined variables.
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