Pyright: List[str] and list[str] results in Union, then becomes Unknown on unpacking.

[nupanick]

I have a conditional in my code which apparently results in a Union[List[str], list[str]]. I would expect the signature to simply be list[str]. Additionally, this union information is lost when used in a comprehension, resulting in a list[Unknown] rather than a list[str].

pairs = [
    s.split(':') if ':' in s else [s, 'null']
    for s in ['foo:bar', 'baz']
]
foo = [p[0] for p in pairs]
bar = [a for [a, b] in pairs]

# (variable) pairs: list[Union[List[str], list[str]]]
# (variable) foo: list[str]
# (variable) bar: list[Unknown]

pyright version: 1.0.81.
VS Code version: 1.39.2.

[nupanick]

Follow-up: I noticed that

bar = [a for a, b in pairs]

correctly flags bar as a list[str]. So maybe I'm just unpacking wrong?

[erictraut]

Thanks for the bug report. Both of these issues will be fixed in the next published version of pyright.

[erictraut]

This is now fixed in 1.0.82, which I just published.