[`flake8-unused-arguments`] Mark `**kwargs` in `TypeVar` as used (`ARG001`) (#22214)
## 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:
```python
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`
ruff
77c2f4c6 - [`flake8-unused-arguments`] Mark `**kwargs` in `TypeVar` as used (`ARG001`) (#22214)
