systemd-stable/shell-completion/zsh/_hostnamectl

#compdef hostnamectl

_hostnamectl_command() {
    local -a _hostnamectl_cmds
    _hostnamectl_cmds=(
        "status:Show current hostname settings"
        "set-hostname:Set system hostname"
        "set-icon-name:Set icon name for host"
    )
    if (( CURRENT == 1 )); then
        _describe -t commands 'hostnamectl commands' _hostnamectl_cmds || compadd "$@"
    else
        local curcontext="$curcontext"
        cmd="${${_hostnamectl_cmds[(r)$words[1]:*]%%:*}}"
        if (( $#cmd )); then
            [[ $cmd == status ]] && msg="no options" || msg="options for $cmd"
            _message "$msg"
        else
            _message "unknown hostnamectl command: $words[1]"
        fi
    fi
}

_arguments -s \
    {-h,--help}'[Show this help]' \
    '--version[Show package version]' \
    '--transient[Only set transient hostname]' \
    '--static[Only set static hostname]' \
    '--pretty[Only set pretty hostname]' \
    '--no-ask-password[Do not prompt for password]' \
    {-H+,--host=}'[Operate on remote host]:userathost:_sd_hosts_or_user_at_host' \
    '*::hostnamectl commands:_hostnamectl_command'