`possibly-undefined` false positive when assigning variable for every case in match statement for all possible values

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#16,992 2 comments 5 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
python
Domain
compilers

Research direction

Start by running the minimal Python example in the issue, using the linked mypy playground, and compare the behavior with similar issue #15958. Trace how mypy handles the possibly-undefined check after the exhaustive Literal match; done means the reported error is no longer produced for this example.

Written by the indexing model from the issue text.

Description

bug 
# mypy: enable-error-code=possibly-undefined

from typing import Literal

value: Literal[1, 2]

match value:
    case 1:
        result = 1
    case 2:
        result = 2

result # error: possibly-undefined

playground

similar issue: #15958 (seems it was only fixed when using assert_never at the end)

Dominant language
Python
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Merged PRs (30d)
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