[flake8-unused-arguments] Mark **kwargs in TypeVar as used (ARG001)

[ValdonVitija]

Summary

Fixes false positive in ARG001 when **kwargs is passed to typing.TypeVar

Closes #22178

When **kwargs is used in a typing.TypeVar call, the checker was not recognizing it as a usage, leading to false positive "unused function argument" warnings.

Root Cause

In the AST, keyword arguments are represented by the Keyword struct with an arg field of type Option<Identifier>:

• Named keywords like bound=int have arg = Some("bound")
• Dictionary unpacking like **kwargs has arg = None

The existing code only handled the Some(id) case, never visiting the expression when arg was None, so **kwargs was never marked as used.

Changes

Added an else branch to handle **kwargs unpacking by calling visit_non_type_definition(value) when arg is None. This ensures the kwargs variable is properly visited and marked as used by the semantic model.

Test Plan

Tested with the following code:

import typing

def f(
    *args: object,
    default: object = None,
    **kwargs: object,
) -> None:
    typing.TypeVar(*args, **kwargs)

Before :

ARG001 Unused function argument: kwargs

After :

All checks passed!

Run the example with the following command(from the root of ruff and please change the path to the module that contains the code example):

cargo run -p ruff -- check /path/to/file.py --isolated --select=ARG --no-cache

[astral-sh-bot]

ruff-ecosystem results

Linter (stable)

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

scikit-build/scikit-build-core (+1 -0 violations, +0 -0 fixes)

+ src/scikit_build_core/_compat/typing.py:36:32: RUF100 [*] Unused `noqa` directive (unused: `ARG001`)

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
RUF100	1	1	0	0	0

Linter (preview)

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

scikit-build/scikit-build-core (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --no-fix --output-format concise --preview

+ src/scikit_build_core/_compat/typing.py:36:32: RUF100 [*] Unused `noqa` directive (unused: `ARG001`)

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
RUF100	1	1	0	0	0

[ntBre]

Thank you! This is exactly the fix I had in mind.

Could you add your manual test case from the PR summary as a new ARG001 case just to prevent future regressions?

You could add it at the bottom of this file:

ruff/crates/ruff_linter/resources/test/fixtures/flake8_unused_arguments/ARG.py

Lines 254 to 258 in fbb5c8a

	class C:
	def f(self, x, y):
	"""Docstring."""
	msg = t"{x}..."
	raise NotImplementedError(msg)

[ntBre]

I'm not sure we need the first part of this comment, but I like the example.

Suggested change

	// The only case when a keyword argument is None is when using **kwargs, since there is no explicit 'arg' name for it.
	// Ex: typing.TypeVar(*args, **kwargs)
	// Ex: typing.TypeVar(**kwargs)

I just removed the *args to make it even more clear which part is relevant.

[ValdonVitija]

@ntBre Added the required test case & removed the first part of the comment.

Thank you!

[ntBre]

Thank you!