ashb commented on pull request #8805:
URL: https://github.com/apache/airflow/pull/8805#issuecomment-635400916
> ```python
> with DAG(dag_id='xcomargs_test_3', default_args={"start_date":
datetime.today()}) as dag3:
> op1 = DummyOperator(task_id="op1")
> op2 = CustomOp(task_id="op2", field=op1.output)
>
> assert op1 in op2.upstream_list. # False
> ```
:interrobang:
Fixing that usecase is like 90% of the case I would want to fix with this PR.
Could we use the `__exit__` from the dag to fix this one case (but there are
others that wouldn't be caught by that.
Given how rare metaprogramming is in Python, I think the metaclass approach
gives a more complete solution, it catches all possible ways of assigning deps
between a DAG.
Yes, this is technically a breaking change, but I think it will affect
almost no one. And I think the only "break" would be that using XComArg
wouldn't work with a custom operator, unless your metaclass inherits this new
metaclass. Is that correct? (i.e. the dag would still run, the user's metaclass
would be the one that is used.)
So I'm +1 for metaclass, if I've understood it all correctly.
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