$ 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.bash

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_pa() {
    [[ $COMP_CWORD -eq 2 ]] && case "${COMP_WORDS[1]}" in [des]*)
        names=()

        # Escape all password names so compgen doesn't break.
        while read -r name; do names+=("${name@Q}"); done < <(pa l)

        mapfile -t COMPREPLY < <(compgen -W "${names[*]}" -- "${COMP_WORDS[2]}")
        ;;
    esac
}

complete -o filenames -F _pa pa