/usr/share/bash-completion/completions/patool.bash-completion is in patool 1.12-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19  | # patool completion
have patool &&
_patool()
{
    local cur prev
    COMPREPLY=()
    cur=${COMP_WORDS[COMP_CWORD]}
    prev=${COMP_WORDS[COMP_CWORD-1]}
    if type _argcomplete &> /dev/null; then
        _argcomplete "$@"
    else
        _filedir
    fi
    return 0
}
complete -F _patool $filenames patool
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