Function with decorator + required kwargs is not type checked properly

[dekim24]

Bug Report

If you wrap a function containing required keyword arguments with a decorator, type checking doesn't behave as one might expect - if you call the function and it's missing those kwargs (and/or contains unexpected kwargs), the mypy type check succeeds.

To Reproduce

from functools import lru_cache

@lru_cache(maxsize=128)
def my_function(required_param: str) -> None:
    pass

my_function(color="blue", speed="fast")

Run mypy <filename> - observe that it succeeds
Run python <filename> - observe error

Note that the actual code I was testing in our codebase uses a different decorator. I just picked a random one that is publicly available

Expected Behavior

mypy returns a typecheck error because required_param is not set

Actual Behavior

Success: no issues found in 1 source file

if I try to execute this code, python raises the expected TypeError: my_function() got an unexpected keyword argument 'color'

if I remove the decorator mypy correctly raises a typecheck error.

Your Environment

• Mypy version used: 1.7.1 (latest)
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None that would impact this case
• Python version used: 3.11.6

[erictraut]

This is a duplicate of #16261. For additional details, see #5107 (comment).

This isn't a problem with decorators in general. It's specific to lru_cache, and it's because of the way lru_cache is defined in the typeshed stubs.

[dekim24]

This is a duplicate of #16261. For additional details, see #5107 (comment).

This isn't a problem with decorators in general. It's specific to lru_cache, and it's because of the way lru_cache is defined in the typeshed stubs.

I agree it's not a mypy bug, so closing the issue is fine - but as I mentioned in the issue description, the actual decorator we implemented in our code is not lru_cache. I did some more research and the underlying issue is that while our function is type hinted, the decorator we wrote was not type hinted.