Inconsistency for `[func-returns-value]`: Error not reported for `staticmethod`s

[harahu]

Bug Report

Static methods decorated with staticmethod that return None do not result in a [func-returns-value] error being reported.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.11&gist=519f480fe4f8840e0043c2555f951f2f

class Example:
    def no_op0(self) -> None:
        return None
        
    @staticmethod
    def no_op0s() -> None:
        return None
        
    def no_op1(self) -> None:
        return
    
    @staticmethod    
    def no_op1s() -> None:
        return
    
ex = Example()

# error: "no_op0" of "Example" does not return a value  [func-returns-value]
assert ex.no_op0() is None

# Decorated version is fine
assert ex.no_op0s() is None

# error: "no_op1" of "Example" does not return a value  [func-returns-value]
assert ex.no_op1() is None

# Decorated version is fine
assert ex.no_op1s() is None

Expected Behavior

A static method is just another callable and it makes sense for the behavior of the [func-returns-value] error to be the same for it as for other callables.

Actual Behavior

The behavior of the [func-returns-value] error for decorated static methods is different from that for other callables. No error is reported.

Your Environment

• Mypy version used: 0.991
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.11

[asottile]

was about to report a similar issue -- it seems this also happens for abstractmethod too! here's a small demo (though looking at the linked PR it seems it's "any decorated function" which I guess makes sense!)

from abc import abstractmethod

class C:
    @abstractmethod
    def returns_none(self) -> None: ...

    def returns_none2(self) -> None: ...


def foo() -> bool:
    return False

def f(c: C, x: int) -> int | None:
    if foo():
        return c.returns_none()  # ok for some reason?
    elif foo():
        return c.returns_none2()  # not ok for some reason?
    elif foo():
        return 5
    else:
        return None  # ok