@task_group returns int, but it appears in @task as TaskGroup

[MatrixManAtYrService]

Apache Airflow version

13faa69

Environment

• Configuration: Local Executor
• OS (e.g. from /etc/os-release): Mac OS 11.3
• Kernel: Darwin Kernel Version 20.4.0
• Install tools: pip install -e .

The DAG

@task
def one():
    return 1

@task_group
def trivial_group(inval):

    @task
    def add_one(i):
        return i + 1

    outval = add_one(inval)
    return outval

@task
def print_it(inval):
    print(inval)

@dag(schedule_interval=None, start_date=days_ago(1), default_args={"owner": "airflow"})
def wrap():

    x = one()
    y = trivial_group(x)
    z = print_it(y)

wrap_dag = wrap()

What happened:
print_it had no predecessors and receives <airflow.utils.task_group.TaskGroup object at 0x128921940>

What you expected to happen:
print_it comes after trivial_group.add_one and receives 2

The caller ends up with the task group itself, equivalent in the traditional api to tg_ref in:

with TaskGroup("trivial_group") tg_ref:
    pass

This interrupts the ability to continue using the Task Flow api because passing it into a function annotated with @task fails to register the dependency with whatever magic gets it out of xcom and adds edges to the dag.

To Replicate

 $ airflow dags test wrap $(date "+%Y-%m-%d")

[boring-cyborg]

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[MatrixManAtYrService]

FYI @ashb, @dimberman

[ashb]

Hmmm I wonder if we can do this without breaking existing DAGs? (It's possible someone is using the fact that the decorated fn returns the TG object?

(Or have we not released this yet and can change it. It's to early and I can't remember.)

[MatrixManAtYrService]

@ashb the @task_group decorator was merged here: #15034 (Apr 1).

I think that means that it's not in any released packages. DAG's using it would have opted in to the bleeding edge by cloning master instead of waiting for a release. Seems reasonable to fix it directly.

[ashb]

Yeah, not released yet. (Sorry, I checked before adding the high priority label but forgot to comment)

We'll change this before 2.1 is cut