/usr/share/fish/completions/aunpack.fish is in fish-common 2.4.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | complete -c aunpack -w atool
complete -c aunpack -a '(__fish_complete_atool_archive_contents)' -d 'Archive content'
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