Signal Store: Custom Store Feature requires withEntities from feature-using store

[ChristopherAdamINF]

I am trying to seperate my entity signal store into reusable parts.
I have a main store file, that defines which entities are used and the an initial state, and then a number of features that add functionality and more fields to the state.
Basically I want to type the store within the feature in a way, that enforces that it already has withEntities.

This problem is very similar to #4767, however in his final solution Donnerstagnacht did not use any of the entity management functions like addEntity, which are causing my problems.

I also tried the suggestion from this comment: #4767 (comment) which does work, but causes ngrx to throw warnings at runtime which I don't want.

@ngrx/signals: SignalStore members cannot be overridden. Trying to override: entities

I'll add a simple example using the similar code as the documentation: https://ngrx.io/guide/signals/signal-store/custom-store-features#creating-a-custom-feature-with-input

My main store

type BaseState = { someField: number };

export const BooksStore = signalStore(
  {providedIn: "root"},
  withState<BaseState>({someField: 2}),
  withEntities<Book>(),
  withAddBooks()
);

My feature

type WithAddBookSubState = { booksAddedCount: number };

export function withAddBooks() {
  return signalStoreFeature(
    {
      state: type<EntityState<Book>>(),
    },
    // withEntities<Book>(), ===> this works but throws a warning at runtime
    withState<WithAddBookSubState>({booksAddedCount: 0}),
    withMethods(store => ({
     // here the type mismatch happens
      addBook(newBook: Book): void {
        patchState(store, addEntity(newBook));
      },
    }))
  );
}

The type mismatch

TS2345: Argument of type PartialStateUpdater<EntityState<Book>> is not assignable to parameter of type
Partial<NoInfer<{
    ids: string[] | number[];
    entities: Dictionary<Book>;
    booksAddedCount: number;
}>> | PartialStateUpdater<NoInfer<{
    ids: string[] | number[];
    entities: Dictionary<Book>;
    booksAddedCount: number;
}>>
Type PartialStateUpdater<EntityState<Book>> is not assignable to type
PartialStateUpdater<NoInfer<{
    ids: string[] | number[];
    entities: Dictionary<Book>;
    booksAddedCount: number;
}>>
Types of parameters state and state are incompatible.
Property entityMap is missing in type
{
    ids: string[] | number[];
    entities: Dictionary<Book>;
    booksAddedCount: number;
}
but required in type EntityState<Book>

While this might look like unneccesary seperating, my actual project has multiple generically typed features that multiple large stores use like modular building blocks. This is just a small example to highlight the issue.

Looking forward to help and suggestions!