Unexpected immer middlerware behavior on delete key at root of state

[simlmx]

This test cases sums it up:

describe('test immer delete root key', () => {
  const store = createStore<State>()(immer(() => ({})))

  // State starts empty.
  expect(store.getState()).toEqual({})

  // Set some field.
  store.setState((state) => {
    state.x = 3
  })
  
  expect(store.getState()).toEqual({ x: 3 })

  // Delete field.
  store.setState((state) => {
    delete state.x
  })
  
  // The field should be gone.
  expect(store.getState()).toEqual({}) // <- THIS FAILS and is still equal to {x: 3}
})

The last expect fails.

If I understand correctly, what is happening is that the two states are merged together; when using immer, shouldn't we always set replace=true, since immer takes care of merging the states.

Indeed if I modify the immer middleware plugin and hardcode replace=true, the problem goes away.

[dai-shi]

since immer takes care of merging the states.

Yeah, if that's the case, replace=true sounds reasonable.
Would you mind opening a PR. A test case would be good to add.

[dbritto-dev]

@simlmx ping me if you need some help with the PR