Add hook support.

_examples/shell/main.go

@@ -3,25 +3,29 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"os"
 
 	"github.com/alecthomas/kong"
 )
 
 var CLI struct {
-	Rm struct {
+	Help bool `kong:"help='Display help.'"`
+	Rm   struct {
 		Force     bool `kong:"help='Force removal.'"`
 		Recursive bool `kong:"help='Recursively remove files.'"`
 
-		Paths []string `kong:"help='Paths to remove.',type='path'"`
-	} `kong:"help='Remove files.'"`
+		Paths []string `kong:"arg,help='Paths to remove.',type='path'"`
+	} `kong:"cmd,help='Remove files.'"`
 
 	Ls struct {
 		Paths []string `kong:"help='Paths to list.',type='path'"`
-	} `kong:"help='List paths.'"`
+	} `kong:"cmd,help='List paths.'"`
 }
 
 func main() {
-	cmd := kong.Parse(&CLI)
+	app := kong.Must(&CLI).Hook(&CLI.Help, kong.Help(nil, nil))
+	cmd, err := app.Parse(os.Args[1:])
+	app.FatalIfErrorf(err)
 	s, _ := json.Marshal(&CLI)
 	fmt.Println(cmd)
 	fmt.Println(string(s))