Add ChangeToFlag to allow changing the current working directory.

util_test.go

@@ -3,6 +3,7 @@ package kong
 import (
 	"io/ioutil"
 	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -42,3 +43,24 @@ func TestVersionFlag(t *testing.T) {
 	require.Equal(t, "0.1.1", strings.TrimSpace(w.String()))
 	require.Equal(t, 0, called)
 }
+
+func TestChangeDirFlag(t *testing.T) {
+	cwd, err := os.Getwd()
+	require.NoError(t, err)
+	defer os.Chdir(cwd) // nolint: errcheck
+
+	dir := t.TempDir()
+	file := filepath.Join(dir, "out.txt")
+	err = os.WriteFile(file, []byte("foobar"), 0o600)
+	require.NoError(t, err)
+
+	var cli struct {
+		ChangeDir ChangeDirFlag `short:"C"`
+		Path      string        `arg:"" type:"existingfile"`
+	}
+
+	p := Must(&cli)
+	_, err = p.Parse([]string{"-C", dir, "out.txt"})
+	require.NoError(t, err)
+	require.Equal(t, file, cli.Path)
+}