There's a closed pull request on the void-packages repository

glab: add shell completions
https://github.com/void-linux/void-packages/pull/39880

Description:
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#### Testing the changes
- I tested the changes in this PR: **briefly**, but the verdict was that it does not work for me right now on zsh. Not quite sure why, maybe someone else can have a look? The completions are generated, they are written out to the correct place. cc @Gottox 

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