[flake8-bugbear] Do not raise error if keyword argument is present and target-python version is less or equals than 3.9 (B903)

[guillaumeLepape]

[flake8-bugbear] Do not raise error if keyword argument is present and target-python version is less or equals than 3.9 (B903)

Summary

I have this piece of code in one of my repo

class RuleMetadata:
    def __init__(
        self,
        *,
        function: Union[
            Callable[[Session, UserModel, RuleComputeFinaleFromGroupRank], None],
            Callable[[Session, UserModel, RuleComputePoints], None],
        ],
        attribute: str,
        required_admin: bool = False,
    ) -> None:
        self.function = function
        self.attribute = attribute
        self.required_admin = required_admin

When I did this, I started by using dataclass, although I wanted the 3 arguments of the init function to be keywords only. As dataclass does not support kw_only before python 3.10 (reference https://docs.python.org/3/library/dataclasses.html#module-contents), I ended up writing the init function myself.

With the current implementation of B903, this will raise an error. My suggestion would be not to raise error if an keyword only argument and target-version<=3.9.

Related github issue : #15548

Test Plan

I added a new usecase in class_as_data_structure.py, a class with keyword only.
I tested this file with the target-version = latest python and with python3.9.
With the latest python, I'm expecting error and python3.9 no error should be raised.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+0 -1 violations, +0 -0 fixes in 1 projects; 54 projects unchanged)

apache/airflow (+0 -1 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --no-fix --output-format concise --preview --select ALL

- providers/src/airflow/providers/google/cloud/operators/dataflow.py:64:1: B903 Class could be dataclass or namedtuple

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
B903	1	0	1	0	0

[MichaReiser]

Perfect, and the ecosystem check confirms that this resolves a false positive. Thank you so much!