function that returns decorator as class member raises "self-argument missing"

[sanjacob]

Bug Report

Similar to #7778, where having a function that returns a decorator inside a class without a self parameter
is not possible.

To Reproduce
I have this setup to be able to do this inside a class:

@log('hello world')
def method(self):
    ...

from functools import wraps
from typing import Callable

class MyClass:
    def log(text: str):
        def log_decorator(func: Callable) -> Callable:
            @wraps(func)
            def log_wrapper(self):
                func(self)
                print(text) # Passed as param in log
            return log_wrapper
        return log_decorator


    @log('print this')
    def test(self) -> None:
        print('word')

foo = MyClass()
foo.test()

Expected Behavior
mypy should not find any errors with this.

Actual Behavior

mypy test_concept.py
test_concept.py:5: error: Self argument missing for a non-static method (or an invalid type for self)  [misc]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.4.1 (compiled: yes)
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10.0

[rafales]

This is not entirely valid code. MyClass now has an invalid MyClass.log method:

m = MyClass()
m.log()  # doesn't make any sense

[JelleZijlstra]

I'm going to say this is out of scope. This use case is very rare, and any reasonable solution is going to make it a lot harder for mypy to correctly report cases where the user forgot to add self (a common mistake).

[erictraut]

If you mark the method log as a @staticmethod, it will work fine at runtime and type check without errors.

[geipel]

If you mark the method log as a @staticmethod, it will work fine at runtime and type check without errors.

That does run for more recent python, but not 3.8.10 (for example).