Ensure deps is set, convert BaseSensorOperator to classvar

[uranusjr]

Fix #21807?

This is the easiest way to get mapped operator's deps to work without jumping through too many hoops. This does introduce some potential backward incompatibility for peopel relying on the (internal?) dep class mechanism, but I think it is acceptable.

[uranusjr]

This gets me pass the error, but hits another one:

Traceback (most recent call last):
  File "dags/t.py", line 23, in <module>
    target_time=templates_xcomarg
  File "/opt/airflow/airflow/models/mappedoperator.py", line 215, in apply
    end_date=end_date,
  File "<attrs generated init airflow.models.mappedoperator.MappedOperator>", line 24, in __init__
  File "/opt/airflow/airflow/models/mappedoperator.py", line 259, in __attrs_post_init__
    self._validate_argument_count()
  File "/opt/airflow/airflow/models/mappedoperator.py", line 300, in _validate_argument_count
    op = self._create_unmapped_operator(mapped_kwargs=mocked_mapped_kwargs, real=False)
  File "/opt/airflow/airflow/models/mappedoperator.py", line 453, in _create_unmapped_operator
    **mapped_kwargs,
  File "/opt/airflow/airflow/models/baseoperator.py", line 374, in apply_defaults
    result = func(self, **kwargs, default_args=default_args)
  File "/opt/airflow/airflow/sensors/date_time.py", line 69, in __init__
    f"Expected str or datetime.datetime type for target_time. Got {type(target_time)}"
TypeError: Expected str or datetime.datetime type for target_time. Got <class 'unittest.mock.MagicMock'>

I guess we do need a class-level validate hook on operators.

[ashb]

This fixes the current issue, but may break/not work with customer operators if someone sets deps on an instance level :(

[ashb]

TypeError: Expected str or datetime.datetime type for target_time. Got <class 'unittest.mock.MagicMock'>

I guess we do need a class-level `validate` hook on operators.

We're going to hit this sort of error more and more with other operators. We might need to rethink how we validate the args

[uranusjr]

may break/not work with customer operators if someone sets deps on an instance level :(

Maybe we can detect that (easy enough, simply check the attribute is actually a set/collection on the class level and not a descriptor), and raise an error saying the operator needs to be fixed? This can likely be done on DAG-parsing time.

[ashb]

may break/not work with customer operators if someone sets deps on an instance level :(

Maybe we can detect that (easy enough, simply check the attribute is actually a set/collection on the class level and not a descriptor), and raise an error saying the operator needs to be fixed? This can likely be done on DAG-parsing time.

👍 I think it's unlikely enough to affect many people, so if we put a note in updating about this it should be good enough

@evgenyshulman I remember on the multi-tenancy call that you do this. Would this cause problems for you?

[uranusjr]

Check added.

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.