$ git clone -q https://github.com/biox/pa.git
$ cd pa/contrib
$ ls -1 -p
pa-bemenu
pa-completion.bash
pa-completion.fish
pa-dmenu
pa-fuzzel
pa-pass
pa-rekey
pa-rofi
pa-ssg
pa-urn
pa-wmenu
$ nl -b a -s ' ' -w 3 pa-completion.fish

  1
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  8

function __fish_complete_pa -d 'Complete pa'
    set -l cmd (commandline -opc)
    test (count $cmd) -eq 2; and string match -q -r $argv[1] $cmd[2]
end

complete -c pa -f
complete -c pa -n "__fish_complete_pa ^[des]" -a "(pa l)"
complete -c pa -n "__fish_complete_pa ^l" -a "(pa l | sed 's/[^/]\+\$//' | grep '/\$' | sort -u)"