reportUnusedVariable false positives when used with an Unknown list

[Avasam]

Note: if you are reporting a wrong signature of a function or a class in the standard library, then the typeshed tracker is better suited for this report: https://github.com/python/typeshed/issues.

Describe the bug
In the example below, read is unknown. So image is unknown as well. Pyright doesn't see that I do use the variable x to slice or access the image. Note this doesn't happen at the top level, it has to be inside of a function.

To Reproduce
See minimal repro below

Expected behavior
No errors

Screenshots or Code
If applicable, add screenshots or the text of the code (surrounded by triple back ticks) to help explain your problem.

import cv2


def __example(capture_device: cv2.VideoCapture):
    _, image = capture_device.read()
    x = 1
    image[x]

C:\Users\Avasam\Documents\Git\Auto-Split\src\region_capture.py
C:\Users\Avasam\Documents\Git\Auto-Split\src\region_capture.py:139:5 - error: Variable "y" is not accessed (reportUnusedVariable)
C:\Users\Avasam\Documents\Git\Auto-Split\src\region_capture.py:140:5 - error: Variable "x" is not accessed (reportUnusedVariable)

I don't think it's specific to cv2, but I'm using the types bundled with microsoft/python-type-stubs

VS Code extension or command-line
[email protected]

[erictraut]

Thanks for the bug report. This will be addressed in the next release. It stems from a bug in the type stubs where VideoCapture is declared in a circular fashion.

VideoCapture = _mod_cv2.VideoCapture

Since _mod_cv2 refers back to the same type stub, this is effectively the same as

VideoCapture = VideoCapture

Pyright detects this case and reports an error, but it didn't properly handle the resulting type, and this propagated up to eventually cause the problem you observed.

[erictraut]

I've also filed this bug to report the circular type aliases in the stub.

[erictraut]

This is addressed in pyright 1.1.253, which I just published. It will also be included in the next release of pylance.