The following code will result in a confusing runtime error (myPanel is a com.google.gwt.user.client.ui.Panel or a subclass of it): So, add an inspection that reports panels added to themselves. A generalization of this is detecting more complicated cycles (e.g. panel A added to B, B added to C, C added to A). Implement this also if it doesn't take a long time to implement. If it does, then this time could probably be spend on more important things.