`Union[X, NoReturn]` isn't properly narrowed to `X`

[tusharsadhwani]

from typing import Union, NoReturn

def func() -> Union[str, NoReturn]:
    return 'test'

func().lower()

Here, Unoin[str, NoReturn] should effectively be treated as the same as str. But mypy doesn't seem to do that.

$ mypy code.py
code.py:6: error: Item "NoReturn" of "Union[str, NoReturn]" has no attribute "lower"
Found 1 error in 1 file (checked 1 source file)

More information in this discussion page: python/typing#994 (comment)

[gschaffner]

This appears to be fixed as of Mypy 0.940.

[hauntsaninja]

Thanks, this was fixed in #11996