There is no telling what will happen.这句的句中成分怎么划分?有的说There is

There is no telling what will happen.这句的句中成分怎么划分?有的说There is no telling是固定用法,那就是what will happen 是主语.那这句就是what will happen is no telling ；有的又说telling what will happen动名词短语作主语,到底哪个对啊?