Recursive use

[bard]

🐛 Bug Report

I've read through #100 and #225 but I'm still not sure whether what I'm looking for is supposed to work or not. So this may not be a bug report at all, just a request for clarification.

Given the following:

import produce from 'immer'

const reducer = (state, action) => produce(state, (draft) => {
    switch (action.type) {
        case 'INCREMENT':
            draft.counter++
            return
        case 'DOUBLE_THEN_INCREMENT':
            draft.counter *= 2;
            reducer(draft, { type: 'INCREMENT' })
            return
    }
})
const state = { counter: 2 }
const newState = reducer(state, { type: 'DOUBLE_THEN_INCREMENT' })
console.log(newState.counter)

I would expect the last line to print 5, instead it prints 4.

It's easy enough to work around it with a manual check to see if the passed state is already a draft, in which case I skip produce, like this:

const producer = (draft, action) => {
    switch (action.type) {
        case 'INCREMENT':
            draft.counter++
            return
        case 'DOUBLE_THEN_INCREMENT':
            draft.counter *= 2
            reducer(draft, { type: 'INCREMENT' })
            return
    }
}
const reducer = (stateOrDraft, action) => isDraft(stateOrDraft)
    ? producer(stateOrDraft, action)
    : produce(stateOrDraft, (draft) => producer(draft, action))

Link to repro

https://codesandbox.io/s/m506x7pwx8

Environment

• Immer version: 3.1.1
• Occurs with setUseProxies(true)
• Occurs with setUseProxies(false) (ES5 only)

[bard]

On second look, I see that I'm overloading the concept of reducer and a return-less call like:

            reducer(draft, { type: 'INCREMENT' })

Doesn't really make sense. Sorry for the noise, closing as wontmakesense.

[aleclarson]

Note: You can still do return reducer(draft, { ... }) and it should work

[bard]

That is only if the draft is unmodified, no? In other words, just return reducer(draft, { ... }) would work, but draft.counter *= 2; return reducer(draft, { ... }) wouldn't.

[aleclarson]

@bard No, any draft that is passed into produce is wrapped with another draft that reflects any current changes.

edit: Oh, I forgot about the error that's thrown when a producer both modifies its draft and returns a new value. So yes, you're right about that.