zsh/completion: put compdef on first line

[bryango]

Motivation

Some zsh setups (including mine) do not load the completion if #compdef is not on the first line. So we move the # shellcheck comment to the second line to avoid this issue.

Context

The # shellcheck comment is introduced in 8839bab so cc @fzakaria for comments and review!

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[fzakaria]

Is there a comment or rationale explaining why "some" don't work but others do ?
Might be good to then include as a comment as to why it's not the first line.

[fzakaria]

Ultimately the file is disabled for shellcheck so I don't think it really matters but I personally dislike making changes without knowing why :P

[xokdvium]

Thank you. I was wondering why zsh completions broke

[internal-nix-ci]

Successfully created backport PR for 2.32-maintenance:

• [Backport 2.32-maintenance] zsh/completion: put compdef on first line #14413

[bryango]

Some zsh setups (including mine) do not load the completion if #compdef is not on the first line.

Is there a comment or rationale explaining why "some" don't work but others do ?

I am just saying that at least it broke on my system. Maybe it breaks on everyone else's as well, or maybe it doesn't 😆 It is very hard to track down all the zsh config files (system / user level, .profile or .zshrc etc) that might change how zsh behaves¹... And surely I have no understanding of its completion system... Though after some searches I found this in their doc which seems to suggest that it might have been breaking everyone's setup:

When compinit is run, it searches all such files accessible via fpath/FPATH and reads the first line of each of them. This line should contain one of the tags described below. Files whose first line does not start with one of these tags are not considered to be part of the completion system and will not be treated specially.

The tags are:

#compdef ...

https://zsh.sourceforge.io/Doc/Release/Completion-System.html#Autoloaded-files

Footnotes

1. This can be mitigated by migrating all zsh config to a NixOS/nix-darwin/home-manager module but due to the sheer amout of work, I still haven't done it even after using Nix for several years 😢 my bad ↩