/usr/share/bash-completion/completions/linkchecker-completion is in linkchecker 9.3-4.
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 20 | # Install this file into directory /etc/bash_completion.d/ on a
# Debian Linux system. For other system read the documentation that
# comes with the bash-completion package.
have linkchecker &&
_linkcheck() {
    local cur prev
    COMPREPLY=()
    cur=${COMP_WORDS[COMP_CWORD]}
    prev=${COMP_WORDS[COMP_CWORD-1]}
    if type _argcomplete &> /dev/null; then
        _argcomplete "$@"
    else
        _filedir
    fi
    return 0
}
[ "$have" ] && complete $filenames -F _linkcheck linkchecker
 |