command: filter parse errors

Signed-off-by: Ophestra <cat@gensokyo.uk>

command/command.go

@@ -29,6 +29,11 @@ type (
 
 	Command interface {
 		Parse(arguments []string) error
+
+		// MustParse determines exit outcomes for Parse errors
+		// and calls handleError if [HandlerFunc] returns a non-nil error.
+		MustParse(arguments []string, handleError func(error))
+
 		baseNode[Command]
 	}
 	Node baseNode[Node]

command/parse.go

@@ -3,6 +3,7 @@ package command
 import (
 	"errors"
 	"log"
+	"os"
 )
 
 var (
@@ -78,3 +79,27 @@ func (n *node) printf(format string, a ...any) {
 		n.logf(format, a...)
 	}
 }
+
+func (n *node) MustParse(arguments []string, handleError func(error)) {
+	switch err := n.Parse(arguments); err {
+	case nil:
+		return
+	case ErrHelp:
+		os.Exit(0)
+	case ErrNoMatch:
+		os.Exit(1)
+	case ErrEmptyTree:
+		os.Exit(1)
+	default:
+		var flagError FlagError
+		if !errors.As(err, &flagError) { // returned by HandlerFunc
+			handleError(err)
+			os.Exit(1)
+		}
+
+		if flagError.Success() {
+			os.Exit(0)
+		}
+		os.Exit(1)
+	}
+}