static new ThreadLocal<Bool> addMenu_addIfEmpty; // defaults to true

static JMenu addMenu(final Component c, fS menuName, fO... items) {
  final RootPaneContainer frame = getPossiblyInternalFrame(c);
  ret (JMenu) swing(func {
    JMenuBar bar = addMenuBar((Component) frame);
    Pair<S, Int> p = jmenu_autoMnemonic(menuName);
    JMenu menu = getMenuNamed(bar, p.a);
    bool isNew = menu == null;
    ifdef addMenu_debug
      print("addMenu " + menuName + " " + isNew);
    endifdef
    if (isNew)
      menu = new JMenu(p.a);
    else
      menu.removeAll();
    menu.setMnemonic(p.b);
    fillJMenu(menu, items);
    if (isNew) {
      if (!isFalse(addMenu_addIfEmpty!) || menuItemCount(menu) > 0) {
        bar.add(menu);
        revalidate((Component) frame);
      }
    }
    ret menu;
  });
}