State argument on createSlice is no longer inferred with typescript beta 4.8 and they do not plan to fix it

[lukeapage]

See the bug on the typescript repo: https://github.com/microsoft/TypeScript/issues/49307#issuecomment-1195031370

It seems the typescript team will not fix this. Maybe the redux-toolkit types can be fixed to be compatible and still infer? else the examples and documentation need changing to say that the state argument will not be inferred and need to be explicitly provided.

cc/ @markerikson

[markerikson]

Hmm. @phryneas , you know way more about the createSlice types than I do - any ideas?

[lukeapage]

In trying to fix this, I've discovered that even in strict mode, nothing enforces that the payload argument of a slice is typed - and it defaults to any. And in trying to fix that, even on 4.7, it ends up requiring the user to type not just the action parameter but the state one too.

[phryneas]

Essentially, it breaks ValidateSliceCaseReducers. That's not gonna be fun.

[phryneas]

For historical context why that type is there: https://github.com/reduxjs/redux-toolkit/pull/149#issuecomment-515787522

[lukeapage]

btw I worked out how to enforce a payload type is always provided:

export type ValidateSliceCaseReducers<S, ACR extends SliceCaseReducers<S>> = ACR & {
    [T in keyof ACR]: ACR[T] extends {
        reducer(s: S, action?: infer A): any;
    }
        ? A extends PayloadAction<any>
            ? CaseReducerWithPrepare<S, A>
            : never
        : ACR[T] extends CaseReducer<S, PayloadAction<EmptyObject>>
        ? (state: S) => S
        : CaseReducer<S, PayloadAction<any>>;

For ts 4.7, I think it does the same enforcement that prepare actions match, it does not require a typed state argument and it enforces that the payload can never be any, unknown or a empty object (but the argument can be missing).

Since it forces typing actions on everyone using typescript, I don't know if you want to include it.

Unfortunately though, it does not help with the infer of the state argument in 4.8.

[markerikson]

Either we fixed this or it isn't enough of an issue that people are complaining :)