type config struct {
   Field1 string `flagarize:"name=case9|help=help|hidden=true|required=true|default=some|envvar=LOL|short=z|placeholder=<something2>"`
}

func main() {
	// Create new kingpin app as usual.
	a := kingpin.New(filepath.Base(os.Args[0]), "<Your CLI description>")

	// Define you own config.
    type ComponentAOptions struct {
	    Field1 []string `flagarize:"name=a.flag1|help=Help for field 1 in nested struct for component A."`
    }
	type ConfigForCLI struct {
		Field1     string                   `flagarize:"name=flag1|help=Help for field 1.|default=something"`
		Field2     *url.URL                 `flagarize:"name=flag2|help=Help for field 2.|placeholder=<URL>"`
		Field3     int                      `flagarize:"name=flag3|help=Help for field 3.|default=2144"`
		Field4     flagarize.TimeOrDuration `flagarize:"name=flag4|help=Help for field 4.|default=1m|placeholder=<time or duration>"`
		ComponentA ComponentAOptions

		NotFromFlags int
	}

	// You can define some fields as usual as well.
	var notInConfigField time.Duration
	a.Flag("some-field10", "Help for some help which is defined outside of ConfigForCLI struct.").
		DurationVar(&notInConfigField)

	// Create new config.
	cfg := &ConfigForCLI{}

	// Flagarize your config! (Register flags from config). Parse the flags afterwards.
	if err := flagarize.Flagarize(a, cfg); err != nil {
		log.Fatal(err)
	}
	if _, err := a.Parse(os.Args[1:]); err != nil {
		log.Fatal(err)
	}

	// Config is filled with values from flags!
	_ = cfg.Field1

    // Run your command...
}

cfg := struct {
    configFile string

    localStoragePath    string
    notifier            notifier.Options
    notifierTimeout     model.Duration
    forGracePeriod      model.Duration
    outageTolerance     model.Duration
    resendDelay         model.Duration
    web                 web.Options
    tsdb                tsdbOptions
    lookbackDelta       model.Duration
    webTimeout          model.Duration
    queryTimeout        model.Duration
    queryConcurrency    int
    queryMaxSamples     int
    RemoteFlushDeadline model.Duration

    prometheusURL   string
    corsRegexString string

    promlogConfig promlog.Config
}{}

a := kingpin.New(filepath.Base(os.Args[0]), "The Prometheus monitoring server")
a.Version(version.Print("prometheus"))
a.HelpFlag.Short('h')

a.Flag("config.file", "Prometheus configuration file path.").
    Default("prometheus.yml").StringVar(&cfg.configFile)

a.Flag("web.listen-address", "Address to listen on for UI, API, and telemetry.").
    Default("0.0.0.0:9090").StringVar(&cfg.web.ListenAddress)

a.Flag("web.read-timeout",
    "Maximum duration before timing out read of the request, and closing idle connections.").
    Default("5m").SetValue(&cfg.webTimeout)

a.Flag("web.max-connections", "Maximum number of simultaneous connections.").
    Default("512").IntVar(&cfg.web.MaxConnections)

a.Flag("web.external-url",
    "The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically.").
    PlaceHolder("<URL>").StringVar(&cfg.prometheusURL)

a.Flag("web.route-prefix",
    "Prefix for the internal routes of web endpoints. Defaults to path of --web.external-url.").
    PlaceHolder("<path>").StringVar(&cfg.web.RoutePrefix)

a.Flag("web.user-assets", "Path to static asset directory, available at /user.").
    PlaceHolder("<path>").StringVar(&cfg.web.UserAssetsPath)

a.Flag("web.enable-lifecycle", "Enable shutdown and reload via HTTP request.").
    Default("false").BoolVar(&cfg.web.EnableLifecycle)

a.Flag("web.enable-admin-api", "Enable API endpoints for admin control actions.").
    Default("false").BoolVar(&cfg.web.EnableAdminAPI)

a.Flag("web.console.templates", "Path to the console template directory, available at /consoles.").
    Default("consoles").StringVar(&cfg.web.ConsoleTemplatesPath)

//... Thousands more of that.

if _, err := a.Parse(os.Args[1:]); err != nil {
    fmt.Fprintln(os.Stderr, errors.Wrapf(err, "Error parsing commandline arguments"))
    a.Usage(os.Args[1:])
    os.Exit(2)
}

cfg := struct {
    ConfigFile           string         `flagarize:"name=config.file|help=Prometheus configuration file path.|default=prometheus.yml"`
    ExternalURL          string         `flagarize:"name=web.external-url|help=The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically.|placeholder=<URL>"`
    StoragePath          string         `flagarize:"name=storage.tsdb.path|help=Base path for metrics storage.|default=data/"`
    RemoteFlushDeadline  model.Duration `flagarize:"name=storage.remote.flush-deadline|help=How long to wait flushing sample on shutdown or config reload.|default=1m|placeholder=<duration>"`
    RulesOutageTolerance model.Duration `flagarize:"name=rules.alert.for-outage-tolerance|help=Max time to tolerate prometheus outage for restoring \"for\" state of alert.|default=1h"`
    RulesForGracePeriod  model.Duration `flagarize:"name=rules.alert.for-grace-period|help=Minimum duration between alert and restored \"for\" state. This is maintained only for alerts with configured \"for\" time greater than grace period.|default=10m"`
    RulesResendDelay     model.Duration `flagarize:"name=rules.alert.resend-delay|help=Minimum amount of time to wait before resending an alert to Alertmanager.|default=1m"`
    LookbackDelta        model.Duration `flagarize:"name=query.lookback-delta|help=The maximum lookback duration for retrieving metrics during expression evaluations and federation.|default=5m"`
    QueryTimeout         model.Duration `flagarize:"name=query.timeout|help=Maximum time a query may take before being aborted.|default=2m"`
    QueryConcurrency     int            `flagarize:"name=query.max-concurrency|help=Maximum number of queries executed concurrently.|default=20"`
    QueryMaxSamples      int            `flagarize:"name=query.max-samples|help=Maximum number of samples a single query can load into memory. Note that queries will fail if they try to load more samples than this into memory, so this also limits the number of samples a query can return.|default=50000000"`

    Web      web.Options
    Notifier notifier.Options
    TSDB     tsdbOptions
    PromLog  promlog.Config
}{}

a := kingpin.New(filepath.Base(os.Args[0]), "The Prometheus monitoring server")
a.Version(version.Print("prometheus"))
a.HelpFlag.Short('h')

if err := flagarize.Flagarize(a, &cfg); err != nil {
    fmt.Fprintln(os.Stderr, err)
    os.Exit(2)
}

if _, err := a.Parse(os.Args[1:]); err != nil {
    fmt.Fprintln(os.Stderr, errors.Wrapf(err, "Error parsing commandline arguments"))
    a.Usage(os.Args[1:])
    os.Exit(2)
}

// Done!

// ValueFlagarizer is the simplest way to extend flagarize to parse your custom type.
// If any field has `flagarize:` struct tag and it implements the ValueFlagarizer, this will be
// used by kingping to parse the flag value.
//
// For an example see: `./timeduration.go` or `./regexp.go`
type ValueFlagarizer interface {
	// FlagarizeSetValue is invoked on kinpgin.Parse with the flag value passed as string.
	// It is expected from this method to parse the string to the underlying type.
	// This method has to be a pointer receiver for the method to take effect.
	// Flagarize will return error otherwise.
	Set(s string) error
}

// Flagarizer is more advanced way to extend flagarize to parse a type. It allows to register
// more than one flag or register them in a custom way. It's ok for a method to register nothing.
// If any field implements `Flagarizer` this method will be invoked even if field does not
// have `flagarize:` struct tag.
//
// If the field implements both ValueFlagarizer and Flagarizer, only Flagarizer will be used.
//
// For an example usage see: `./pathorcontent.go`
type Flagarizer interface {
	// Flagarize is invoked on Flagarize. If field type does not implement custom Flagarizer
	// default one will be used.
	// Tag argument is nil if no `flagarize` struct tag was specified. Otherwise it has parsed
	//`flagarize` struct tag.
	// The ptr argument is an address of the already allocated type, that can be used
	// by FlagRegisterer kingping *Var methods.
	Flagarize(r FlagRegisterer, tag *Tag, ptr unsafe.Pointer) error
}