vuex模块化之后如何提交子模块的方法？

版本

• vue3
• vuex4.x
• javascript

代码

user.js

export default createStore({
  state: () => ({
    username: 'nihao',
    password: ''
  }),
  mutations: {
    setUsername: (state, username) => {
      state.username = username
    }
  },
  actions: {
  },
  modules: {
  }
})

index.js

import user from './modules/user'
export default createStore({
  state: {
  },
  mutations: {
  },
  actions: {
  },
  getters: {
  },
  modules: {
    user: user
  }
})

调用的方法

const store = useStore()
store.commit('setUsername', 'xxx')
store.commit('user/setUsername', 'xxx')

无论是加了namespaced: true还是不加，上面的两句话都不行。