erroneous complaint that overloaded function implementation does not accept all possible arguments of signature

Bug Report

Erroneous complaint that overloaded function implementation does not accept all possible arguments of signature.

To Reproduce

from datetime import datetime
from typing import overload

class Sample:

    @overload
    @classmethod
    def set(cls, year: int) -> None:
        ...

    @overload
    @classmethod
    def set(cls, instance: datetime, / ) -> None:
        ...

    @classmethod
    def set(cls, *args: datetime | int, **kw: int) -> None:
        pass

Expected Behavior

The above should pass type checking.

Pyright's happy enough:

$ pyright typing_bug.py 
0 errors, 0 warnings, 0 informations 

Actual Behavior

$ mypy typing_bug.py 
typing_bug.py:16: error: Overloaded function implementation does not accept all possible arguments of signature 1  [misc]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.14.1 (compiled: yes)
• Mypy command-line flags: None, see above
• Mypy configuration options from mypy.ini (and other config files): None.
• Python version used: Python 3.12.1

Reproduisez le rapport de typing_bug.py avec mypy 1.14.1 et comparez le résultat avec pyright. Suivez la vérification de compatibilité de l’implémentation de overload pour l’exemple de classmethod ; la tâche est terminée lorsque mypy accepte le code présenté sans le signalement erroné, tout en conservant les diagnostics valides pour les implémentations incompatibles.