Undefined variable false positive with unreachable expression

[hauntsaninja]

• Language Server version: Pylance language server 2020.9.8 (pyright a0620921)
• Python version (& distribution if applicable, e.g. Anaconda): 3.8

Expected behaviour

Pylance just complains about the unreachable (given my Python version) code

Actual behaviour

Pylance complains about message being undefined (in addition to the unreachable code)

Code Snippet / Additional information

import sys

def hello() -> None:
    message = "asdf"
    if sys.version_info < (3, 5) and message:
        print("hi")

[erictraut]

Thanks for the bug report. This was related to reachability analysis. The control flow node represented by message is provably never reachable within the function's body because the first part of the condition expression statically evaluates to False. This caused the analyzer to assume incorrectly that message was unbound.

I've added a fix, and it will be in the next release.

[jakebailey]

This issue has been fixed in version 2020.10.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#2020100-7-october-2020