Summary

Wasn't able to find this, but apologies if it's already been brought up in another issue, but this is more or less a rehash of python/mypy#17421 for Ty.

In effect Ty doesn't raise a warning if you pass in an class implementation that enforces positional arguments on a method, for a protocol that does not.

Take this example, which should raise a warning but doesn't:

from typing import Protocol


class Readable(Protocol):
    def read(self, n: int = -1) -> bytes: ...

class ActualReadable:
    def read(self, n: int = -1, /) -> bytes:
        return b""


def foo(readable: Readable) -> None:
    readable.read(n=1)


foo(ActualReadable())

This can lead to a runtime error if the protocol implementation is called using a key-word argument.

Ty Playground

If this is simply the result of support for protocols not being finalized, feel free to close this.