please include function componentPopupMenu.

static JPopupMenu showInternalFramePopupMenu(final JInternalFrame f) {
  ret f == null ? null : swing(func -> JPopupMenu {
    componentPopupMenu_init();
    L maker = cast _get(findComponentPopupMenuListener_gen(f), 'maker);
    if (empty(maker)) null;

    new JPopupMenu menu;
    int emptyCount = menu.getComponentCount();
    componentPopupMenu_mouseEvent.set(new MouseEvent
      (f, MouseEvent.MOUSE_PRESSED, now(), 0, 30, 15, 1, true));
    
    for (O menuMaker : maker)
      pcallF(menuMaker, menu);
      
    // show menu if any items in it
    if (menu.getComponentCount() == emptyCount) null;
    
    menu.show(f, 30, 15); // ?
    ret menu;
  });
}