bug in not-None inference for list items

[davidszotten]

Apologies if this is already reported, it's hard to know what words to look for

I think this is a bug in the "not None inference"

source:

from typing import List, Optional

idx = 0
lst: List[Optional[int]] = []

lst[0] is not None and reveal_type(lst[0])
lst[idx] is not None and reveal_type(lst[idx])

$ mypy foo.py
foo.py:6: note: Revealed type is 'builtins.int'
foo.py:7: note: Revealed type is 'Union[builtins.int, None]'

i would have expected mypy to also tell that the index lookup is identical when it's using a var idx and infer the type to be not-None

$ mypy --version
mypy 0.790+dev.fbc45aabdf46c820e81e3fc85e3d50b3ebf28ad0

[JukkaL]

Closing as duplicate of #2199.