Missing argument (`cls`) error when `classmethod` is mixed with other decorators

[AA-Turner]

Summary

I couldn't find an existing issue for this. Error is new in alpha 32, no problems reported in alpha 31.

error[missing-argument]: No argument provided for required parameter `cls`
   --> tests\test_intl\test_intl.py:880:10
    |
879 |     # see: https://github.com/pytest-dev/pytest/issues/363
880 |     with pytest.MonkeyPatch.context() as mock:
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
881 |         clock: _MockClock
882 |         if os.name == 'posix':
    |
info: Union variant `(cls) -> _GeneratorContextManager[Unknown, None, None]` is incompatible with this call site
info: Attempted to call union type `((cls) -> _GeneratorContextManager[Unknown, None, None]) | ((cls) -> _GeneratorContextManager[Unknown, None, None])`
info: rule `missing-argument` is enabled by default

Minimal reproducer (playground):

from collections.abc import Generator
from contextlib import contextmanager

class Spam:
    @contextmanager
    @classmethod
    def context(cls) -> Generator[None]:
        yield None


def func():
    with Spam.context() as ctx:  # No argument provided for required parameter `cls` (missing-argument) [Ln 12, Col 10]
        print("blah")

I imagine this is a bad interaction between the classmethod decorator and other decorators?

A

Version

ty 0.0.1-alpha.32 (84a1881 2025-12-05)

[carljm]

Looks like we need to bind cls on classmethods when solving a paramspec.

[dhruvmanila]

I think this requires astral-sh/ruff#21685, I tried the minimal reproducer on that branch and the diagnostics goes away.

[aidandj]

I'm guessing this is the same/similar issue. If not I can open a new issue.

from typing import overload, Type, Dict, TypeVar, Iterator, Tuple, Union, Set
from contextlib import contextmanager

class Base: ...


class Child(Base): ...


T = TypeVar("T", bound=Base)

@contextmanager
def cm(
    d: Dict[Type[T], int] | Dict[str, int],
):
    yield ({},)


with cm({Child: 1}) as (): # Argument is incorrect: Expected `dict[type[T@cm], int] | dict[str, int]`, found `dict[Unknown | <class 'Child'>, Unknown | int]` (invalid-argument-type) [Ln 19, Col 9]
    pass

[dhruvmanila]

I'm guessing this is the same/similar issue. If not I can open a new issue.

No, this is related to #1729

[carljm]

@dhruvmanila astral-sh/ruff#21685 has landed, but the reproducer here still errors.

[dhruvmanila]

I don't think this is related to ParamSpec as the issue exists on main as well https://play.ty.dev/939b003c-20bd-4aeb-b607-54d4113d6221:

from collections.abc import Callable
from typing import Any


def decorator(fn: Callable[[Any], None]) -> Callable[[Any], None]:
    return fn


class Foo:
	@decorator
    @classmethod
    def context(cls) -> None:
        return None

# ty: No argument provided for required parameter 1 [missing-argument]
Foo.context()

I think I know where the issue is -- in Type::bindings the type of Foo.context is not BoundMethod but CallableType which is why there's no "bound" type argument that's being added to the CallableBinding here which is required to get an accurate CallArguments here.