Clear notification in UI when duplicate dag names are present

[TColl]

Description

When using decorators to define dags, e.g. dag_1.py:

from airflow.decorators import dag, task
from airflow.utils.dates import days_ago

DEFAULT_ARGS = {
    "owner": "airflow",
}


@task
def some_task():
    pass


@dag(
    default_args=DEFAULT_ARGS,
    schedule_interval=None,
    start_date=days_ago(2),
)
def my_dag():
    some_task()


DAG_1 = my_dag()

and

dag_2.py:

from airflow.decorators import dag, task
from airflow.utils.dates import days_ago

DEFAULT_ARGS = {
    "owner": "airflow",
}


@task
def some_other_task():
    pass


@dag(
    default_args=DEFAULT_ARGS,
    schedule_interval=None,
    start_date=days_ago(2),
)
def my_dag():
    some_other_task()


DAG_2 = my_dag()

We have two different dags which have been written in isolation, but by sheer bad luck both define my_dag(). This seems fine for each file in isolation, but on the airflow UI, we only end up seeing one entry for my_dag, where it has picked up dag_1.py and ignored dag_2.py.

Use case / motivation

We currently end up with only one DAG showing up on the UI, and no indication as to why the other one hasn't appeared.

Suggestion: popup similar to 'DAG import error' to highlight what needs changing in one of the DAG files in order for both to show up ("DAG import error: duplicate dag names found - please review {duplicate files} and ensure all dag definitions are unique"?)

Are you willing to submit a PR?

No time to spare on this at present

Related Issues

I haven't found any related issues with the search function.

[boring-cyborg]

Thanks for opening your first issue here! Be sure to follow the issue template!

[uranusjr]

I plan to look into this.