code: protected final void warning(Element e, String msg, Object... args) {
          if (messager == null) {
              illegalState();
          }
          messager.printMessage(Diagnostic.Kind.WARNING, String.format(msg, args), e);
      }
docs: Produce a compile warning for the given element and message.
  
  @param e    The element
  @param msg  The message
  @param args The string format args