code: private static long computeMsgId(MsgNode msgNode) {
      return SoyMsgIdComputer.computeMsgId(
          buildMsgParts(msgNode), msgNode.getMeaning(), msgNode.getContentType());
    }
docs: Computes the unique message id for the given MsgNode.
  
  @param msgNode The message parsed from the Soy source.
  @return The message id.