Overriding callable attribute with method not caught by [mutable-override]

[brianschubert]

Bug Report

Follows from #12569, #3208

Mypy has an optional error code mutable-override that checks for unsafe overrides of mutable attributes:

class Parent:
    x: float

class Child(Parent):
    x: int  # E: Covariant override of a mutable attribute (base class "Parent" defined the type as "float", expression has type "int")  [mutable-override]

However, this error isn't emitted when overriding a callable attribute with a method:

from typing import Callable

class Parent:
    func: Callable[[str], None]

class Child(Parent):
    def func(self, x: object) -> None: pass  # no error

This allows dubious code like the following to pass type checking:

def foo(x: str) -> None:
    assert isinstance(x, str)
    
def modify_parent(x: Parent) -> None:
    x.func = foo 
    
c = Child()
modify_parent(c)
c.func(1)  # boom!

Your Environment

• Mypy version used: master (1.14.0+dev.2b033cbd7)
• Mypy command-line flags: --strict --enable-error-code=mutable-override
• Mypy configuration options from mypy.ini (and other config files): N/A (empty)
• Python version used: 3.12.7