/usr/share/fish/completions/apt-setup.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 3 | #apt-setup
complete -c apt-setup -a probe --description "Probe a CD"
complete -c apt-setup -s N --description "Run in non-interactive mode"
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