Chaining custom signal store features with input declared as functions fails about platform

[skovalyov]

I looked more into tests such as https://github.com/ngrx/platform/blob/main/modules/signals/spec/types/signal-store.types.spec.ts, and it turned out that this syntax would work, i.e. with <_> in function declaration:

const withFooFeature = <_>() =>
  signalStoreFeature(
    {
      state: type<{ foo: number }>()
    },
    withState({})
  );

const withBarFeature = <_>() =>
  signalStoreFeature(
    {
      state: type<{ bar: number }>()
    },
    withState({})
  );

export const FooBarStore = signalStore(
  withState({
    foo: 10,
    bar: 20
  }),
  withComputed(store => ({
    foofoo: computed(() => store.foo() * store.foo()),
    barbar: computed(() => store.bar() * store.bar())
  })),
  withFooFeature(),
  withBarFeature()
);

It is not very intuitive, so I think documentation update would make sense.

[markostanimirovic]

Correct, it can be fixed with unused generic. And I agree with you, this is unintuitive TypeScript behavior.

Once we change SignalStore types to disable property/method overriding, the type implementation will be simpler, so this issue may disappear. Let's see.