Never is inferred in combination with generics and partial

[rggjan]

Not sure if this is related / the same issue as #16522, but the following code doesn't work in mypy 1.7.0:

from functools import partial
from typing import TypeVar, Optional


E = TypeVar("E")


def foo(x: E, y: E) -> Optional[E]:
    print(x)
    return y


bar = partial(foo, 3) # error: Argument 1 to "partial" has incompatible type "Callable[[E, E], Optional[E]]"; expected "Callable[..., Never]"  [arg-type]
print(bar(4))

whereas it worked fine in mypy 1.4.1.

I believe the code and typing are correct, though?

It also works fine when returning E instead of Optional[E] in both versions.

[ilevkivskyi]

This is fixed on master.