@task and chain() don't play well together

Apache Airflow version

main (development)

What happened

I’ve been told that the current community preference is to use an @task decorated method instead of the Python Operator when possible, but the chain() method does not support that yet. ci_install_and_test_provider_packages.sh will fail with the following message:

File "/usr/local/lib/python3.7/site-packages/airflow/models/baseoperator.py", line 1578, in chain 
up_type=type(up_task), down_type=type(down_task)

TypeError: Chain not supported between instances of <class 'airflow.models.xcom_arg.XComArg'> 
and <class 'airflow.models.xcom_arg.XComArg'>

What you think should happen instead

Might be as simple as adding the Typing to the chain() signature?

How to reproduce

see this example DAG

In case that isn’t persistent, this should do it as well:

from datetime import datetime

from airflow import DAG
from airflow.decorators import task
from airflow.models.baseoperator import chain


@task
def echo1():
    print('hello')


@task
def echo2():
    print('world')


with DAG(
    dag_id='example_dag',
    schedule_interval=None,
    start_date=datetime(2021, 1, 1),
    tags=['example'],
    catchup=False,
) as dag:
    
    chain(echo1(), echo2())

Operating System

linux

Versions of Apache Airflow Providers

No response

Deployment

Docker-Compose

Deployment details

I am running it in an updated Breeze environment and it passes all test there; this does not fail until the CI tests on github run /opt/airflow/scripts/in_container/run_install_and_test_provider_packages.sh

Anything else

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project’s Code of Conduct

[potiuk]

Assigned you 😃 in the meantime

[ferruzzi]

Alright, after a chat with Jarek, this is a non-issue. The part I was missing was that chain() currently supports @task but did not in 2.1; providers require 2.1 compatibility so the CI testing failed on the backward compatibility checks.