Remove UsageFunc dispatch from DefaultUsage to fix infinite recursion

run.go

@@ -69,7 +69,12 @@ func ParseAndRun(ctx context.Context, root *Command, args []string, options *Run
 	if err := Parse(root, args); err != nil {
 		if errors.Is(err, ErrHelp) {
 			options = checkAndSetRunOptions(options)
-			_, _ = fmt.Fprintln(options.Stdout, DefaultUsage(root))
+			cmd := root.terminal()
+			if cmd.UsageFunc != nil {
+				_, _ = fmt.Fprintln(options.Stdout, cmd.UsageFunc(cmd))
+			} else {
+				_, _ = fmt.Fprintln(options.Stdout, DefaultUsage(root))
+			}
 			return nil
 		}
 		return err

run_test.go

@@ -228,4 +228,36 @@ func TestRun(t *testing.T) {
 			require.Equal(t, val, GetFlag[string](root.state, "text"))
 		}
 	})
+	t.Run("ParseAndRun uses UsageFunc on help", func(t *testing.T) {
+		t.Parallel()
+
+		root := &Command{
+			Name:      "myapp",
+			ShortHelp: "my application",
+			UsageFunc: func(c *Command) string {
+				return "custom usage output"
+			},
+			Exec: func(ctx context.Context, s *State) error { return nil },
+		}
+
+		stdout := bytes.NewBuffer(nil)
+		err := ParseAndRun(context.Background(), root, []string{"-help"}, &RunOptions{Stdout: stdout})
+		require.NoError(t, err)
+		require.Contains(t, stdout.String(), "custom usage output")
+	})
+	t.Run("ParseAndRun falls back to DefaultUsage without UsageFunc", func(t *testing.T) {
+		t.Parallel()
+
+		root := &Command{
+			Name:      "myapp",
+			ShortHelp: "my application",
+			Exec:      func(ctx context.Context, s *State) error { return nil },
+		}
+
+		stdout := bytes.NewBuffer(nil)
+		err := ParseAndRun(context.Background(), root, []string{"-help"}, &RunOptions{Stdout: stdout})
+		require.NoError(t, err)
+		require.Contains(t, stdout.String(), "my application")
+		require.Contains(t, stdout.String(), "Usage:")
+	})
 }

usage.go

@@ -26,10 +26,6 @@ func DefaultUsage(root *Command) string {
 
 	var b strings.Builder
 
-	if terminalCmd.UsageFunc != nil {
-		return terminalCmd.UsageFunc(terminalCmd)
-	}
-
 	if terminalCmd.ShortHelp != "" {
 		b.WriteString(terminalCmd.ShortHelp)
 		b.WriteString("\n\n")

usage_test.go

@@ -490,3 +490,27 @@ func TestWriteFlagSection(t *testing.T) {
 		require.NotContains(t, output, "Inherited Flags:")
 	})
 }
+
+func TestDefaultUsageComposableFromUsageFunc(t *testing.T) {
+	t.Parallel()
+
+	cmd := &Command{
+		Name:      "myapp",
+		ShortHelp: "my application",
+		Exec:      func(ctx context.Context, s *State) error { return nil },
+	}
+	cmd.UsageFunc = func(c *Command) string {
+		// Calling DefaultUsage from within UsageFunc should not recurse infinitely.
+		s := DefaultUsage(c)
+		return s + "\n\nExamples:\n  myapp --verbose"
+	}
+
+	err := Parse(cmd, []string{})
+	require.NoError(t, err)
+
+	output := cmd.UsageFunc(cmd)
+	require.Contains(t, output, "my application")
+	require.Contains(t, output, "Usage:")
+	require.Contains(t, output, "Examples:")
+	require.Contains(t, output, "myapp --verbose")
+}