no error issued when calling a decorated function with the wrong argument type

[clo-vis]

To Reproduce

Run mypy on this code and then run the code

import functools

@functools.cache
def factorial(n: int) -> int:
    return n * factorial(n-1) if n else 1    

def identity(n: int) -> int:        
    return n

if __name__ == '__main__':
    print(factorial.__name__, factorial.__annotations__)
    print(identity.__name__, identity.__annotations__)
    factorial("")
    identity("")

The output of the program is:

factorial {'n': <class 'int'>, 'return': <class 'int'>}
identity {'n': <class 'int'>, 'return': <class 'int'>}

so type information is available.

Expected Behavior

The lines
factorial("")
and
identity("")
should be both flagged as wrong because the function is called with an incompatible type

Actual Behavior

An error is issued for
identity("")
but not for
factorial("")

As a side note, mypy issues an error

_lru_cache_wrapper[int]" has no attribute "name" for _print(factorial.name, ...)

but this is another issue.

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.9.5
• Operating system and version: Windows 10

[erictraut]

This appears to be a deficiency in the functools.pyi type stub. It defines _lru_cache_wrapper and cache as follows:

class _lru_cache_wrapper(Generic[_T]):
    __wrapped__: Callable[..., _T]
    def __call__(self, *args: Hashable, **kwargs: Hashable) -> _T: ...

def cache(__user_function: Callable[..., _T]) -> _lru_cache_wrapper[_T]: ...

Now that typeshed stubs are starting to incorporate PEP 612 (ParamSpec) support, it could be updated to the following:

_P = ParamSpec("_P")

class _lru_cache_wrapper(Generic[_P, _T]):
    __wrapped__: Callable[_P, _T]
    def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _T: ...

def cache(__user_function: Callable[_P, _T]) -> _lru_cache_wrapper[_P, _T]: ...

Mypy doesn't currently have full support for ParamSpec (see this tracking issue), but once that support is added, this should address the issue you've reported. I confirmed that it works with pyright.

[hauntsaninja]

Closing, since the change to typeshed is being tracked in typeshed (any blocking mypy issues should be tracked in a more specific issue than this one).