Protocol with __call__ method hides type errors #377
Description
Summary
Callable is very restricted in what it can express (no kwargs, no optional arguments, etc) and the official Python typing documentation instructs you to use a Protocol subclass with a __call__ method instead. However with ty this does not work as expected.
Given the following code:
from typing import Protocol
class MyCallable(Protocol):
def __call__(self, arg: int) -> int: ...
def func(mc: MyCallable) -> int:
return mc(1)
# expect to type check
func(lambda n: 1)
# expect to fail check
func(lambda: None)
def x(arg: int) -> int:
return 1
# expect to type check
func(x)
def y(arg: str) -> str:
return "a"
# expect to fail check
func(y)
# expect to type check, but fails with call-non-callable on F
def func2[F: MyCallable](f: F) -> int:
return f(1)Running ty check file.py everything passes but the check on func2, it is happy with all the calls to func even though half the arguments passed in should fail the type check.
Version
ty 0.0.1-alpha.1 (12f466e 2025-05-13)