Changing arguments to position only on an override should be incompatible

[hackaugusto]

Bug Report

To Reproduce

B.f below should be incompatible with A.f:

class A:
    def f(self, a: int) -> None:
        pass


class B(A):
    def f(self, a: int, /) -> None:
        pass

because the following fails:

def t(a: A) -> None:
    a.f(a=1)


t(B())

Expected Behavior

The signature of B.f should cause an error

Actual Behavior

No errors are reported

Your Environment

• Mypy version used: mypy 0.961 (compiled: no) and mypy 0.980+dev.64a40e8487f591d57576396baaafae9e3a618555 (compiled: no)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: Python 3.8.9
• Operating system and version: macOS Monterey 12.4

[hauntsaninja]

Agreed that this is unsound, but it's a place where mypy has chosen to be pragmatic. It's not just positional-only args, the same sort of thing also applies to argument name changes:

class A:
    def f(self, a: int) -> None: ...

class B(A):
    def f(self, b: int) -> None: ...

Linking #1013