Missing type inference using TypeScript and Immer following example from Readme

[Duckling92]

Bug Description

Description

When using Immer with Zustand, TypeScript does not catch type errors when setting nested state. The code follows the example from the Zustand documentation, but TypeScript doesn’t detect the type mismatch (state becomes any).

import { produce } from 'immer'
import { create } from 'zustand'

interface MyStore {
  aNumber: number
  setNumber: () => void
}
const useStore = create<MyStore>()((set) => ({
  aNumber: 0,
  setNumber: () => set(
    produce((state) => {
      state.aNumber = "not a number"
    }),
  ),    
}))

Steps to Reproduce

1. Clone this minimally working example
2. run npm install
3. run npm typecheck

Expected behaviour

TypeScript should detect that "not a number" is a string and raise a type error since the aNumber property is typed as a number.

Actual behaviour

TypeScript does not raise any errors, allowing the assignment of a string to a number field without warnings.

Is this intended behaviour?

Reproduction Link

https://github.com/Duckling92/zustand-immer-ts-bug

[dbritto-dev]

@Duckling92 you are using produce from immer directly so you need to take care of typing produce, that's not zustand issue

import { produce } from 'immer'
import { create } from 'zustand'

interface MyStore {
  aNumber: number
  setNumber: () => void
}
const useStore = create<MyStore>()((set, get) => ({
  aNumber: 0,
  setNumber: () => set(
    produce<ReturnType<typeof get>>((state) => {
      state.aNumber = "not a number"
    }),
  ),
}))

[Duckling92]

Of course, that makes perfect sense. Thank you.