code: private String findCaller(Object factoryInterface) {
      Throwable dummyThrowableForStackTrace = new Throwable();
  
      StackTraceElement[] stackTrace = dummyThrowableForStackTrace.getStackTrace();
  
      for (StackTraceElement element : stackTrace) {
        if (!element.getClassName().equals(GinFactoryModuleBuilder.class.getName())) {
          return element.toString();
        }
      }
  
      return "definition of factory " + factoryInterface;
    }
docs: Find the topmost stack element that's not a method of this class, which is
  presumably the location in a Gin module that invoked build().
  
  @param factoryInterface An object identifying the factory interface; used
  to generate a fallback message if we can't determine the caller.