static <A extends JComponent> A onFirstComponentShow(final A component, final Runnable onShow) {
  swing {
    component.addAncestorListener(new AncestorListener {
      public void ancestorAdded(AncestorEvent event) {
        component.removeAncestorListener(this);
        pcallF(onShow);
      }
      public void ancestorRemoved(AncestorEvent event) {}
      public void ancestorMoved(AncestorEvent event) {}
    });
  }
  ret component;
}

Began life as a copy of #1003557