Forward decorated function type to provide_session reusult

[uranusjr]

Now that we have NEW_SESSION, we don’t really need any more special hacks to make provide_session-decorated functions be type-checked. This is enough to type check the following:

from sqlalchemy.orm import Session
from airflow.utils.session import NEW_SESSION, provide_session

@provide_session
def foo(x: int, *, session: Session = NEW_SESSION) -> str:
    return str(x)

foo(x="a")
foo(y=1)

and emit

Run mypy.................................................................Failed
- hook id: mypy
- exit code: 1

No need to rebuild the image: none of the important files changed

airflow/play.py:8: error: Argument "x" to "foo" has incompatible type "str";
expected "int"
    foo(x="a")
          ^
airflow/play.py:9: error: Unexpected keyword argument "y" for "foo"
    foo(y=1)
    ^
Found 2 errors in 1 file (checked 2 source files)

ERROR: The previous step completed with error. Please take a look at output above

For some reason, this does not type check session—I can pass literally anything to it (e.g. session=object()) and Mypy would let it pass. Not sure why, maybe because SQLAlchemy is not well-typed? But this is still very useful.

[potiuk]

Interesting, but indeed helpful :)

[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.

[ashb]

For some reason, this does not type check session—I can pass literally anything to it (e.g. session=object()) and Mypy would let it pass. Not sure why, maybe because SQLAlchemy is not well-typed?

Correct. It's because our version of SQLA isn't currently typed (1.4 is) and we have ignore_missing_imports I think -- so Session is treated as Any, as I understand it.