/usr/share/bash-completion/completions/netplan is in netplan.io 0.36.1.
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 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45  | # netplan(1) completion                                       -*- shell-script -*-
_compgen_help()
{
    local options=$1
    shift
    compgen -W '${options} help' $@
}
_netplan()
{
    local cur prev words cword
    _init_completion || return
    case $prev in
        netplan)
            COMPREPLY=( $( _compgen_help 'apply generate ifupdown-migrate ip' "$cur" ) )
            return
            ;;
        apply|generate)
            return
            ;;
        ifupdown-migrate)
            return
            ;;
        ip)
            COMPREPLY=( $( _compgen_help 'leases' -- "$cur" ) )
            return
            ;;
        leases)
            if [ "${COMP_WORDS[COMP_CWORD-2]}" = "ip" ]; then
                _available_interfaces -a
            fi
            return
            ;;
    esac
    if [[ $cur == -* ]]; then
        COMPREPLY=( $( compgen -W '$( _parse_help "$1" )' -- "$cur" ) )
    fi
} &&
complete -F _netplan netplan
# ex: ts=4 sw=4 et filetype=sh
 |