"Arguments for ParamSpec are missing" error

[srittau]

Describe the bug

Please have a look at python/typeshed#15597. In this PR, I try to change operator.methodcaller to use a ParamSpec with defaults:

_P = ParamSpec("_P", default=...)
_R = TypeVar("_R", default=Any)

@final
class methodcaller(Generic[_P, _R]):
    def __new__(cls, name: str, /, *args: _P.args, **kwargs: _P.kwargs) -> methodcaller[_P, Any]: ...
    def __call__(self, obj: Any) -> _R: ...

Unfortunately, the following test cases then fail:

m1 = methodcaller("foo")  # Arguments for ParamSpec "_P@methodcaller" are missing (reportCallIssue)
assert_type(m1, methodcaller[[], Any])  #  "assert_type" mismatch: expected "methodcaller[(), Any]" but received "methodcaller[..., Any]"
m2 = methodcaller("foo", 42, bar="")  # Arguments for ParamSpec "_P@methodcaller" are missing (reportCallIssue)

I'm unsure what there problem here seems to be.

From the CI environment:

pyright 1.1.408, node v24.14.0, pyright-action 3.0.2