Potential bug: Never as invariant type-var

[Azureblade3808]

Look at this --

from typing import Any, Generic, Never, TypeVar

T = TypeVar("T")

class C(Generic[T]): ...

def f(cond: Any, c_never: C[Never], c_object: C[object], c_int: C[int]):
    if cond:
        c_never = c_object
    elif cond:
        c_never = c_int
    elif cond:
        c_object = c_never  # Not reported.
    elif cond:
        c_object = c_int
    elif cond:
        c_int = c_never  # Not reported.
    elif cond:
        c_int = c_object

It is expected that every assignment in f gets reported as T is invariant and Never is a different type from object or int. Mypy is giving a correct result: https://mypy-play.net/?mypy=latest&python=3.12&gist=f14c91ed1eb6b2bbf31153ccf8fd0d45 .

If the type-var is changed into co-variant or contra-variant, the result will be correct accordingly.

I haven't thought of a practical case affected by this yet, but maybe it's worth some check.

[erictraut]

Thanks, I agree this is a bug. It will be addressed in the next release.