Type inference broken with angular inject function + @ngrx/store

[mattlewis92]

Minimal repro (that compiles with typescript 5.8)

import {inject} from '@angular/core';
import {Store} from '@ngrx/store';

const store: Store = inject(Store);

Output with tsgo:

store-generic-inference/index.ts:4:7 - error TS2322: Type 'Store<unknown>' is not assignable to type 'Store<object>'.
  Type 'unknown' is not assignable to type 'object'.

4 const store: Store = inject(Store);
        ~~~~~

Found 1 error in store-generic-inference/index.ts:4

Minimal repro can be run here: https://github.com/mattlewis92/ts-go-issues-repros

[mattlewis92]

Standalone example with no dependencies:

class Store<T = object> {
    select<K>(mapFn: (state: T) => K) {};
}

const store: Store = inject(Store);

function inject<T>(token: ProviderToken<T>): T {
    return {} as T;
}

interface Type<T> extends Function {
    new (...args: any[]): T;
}

type ProviderToken<T> = Type<T> | AbstractType<T>;

interface AbstractType<T> extends Function {
    prototype: T;
}

[ahejlsberg]

Another type ordering issue. When inferring the type argument for the inject(Store) call, two inference candidates are produced: Store<unknown> and Store<any>. Those types are mutual subtypes, so inference picks the first candidate. However, the order of the candidates is determined by the order of the two types in the ProviderToken<T> union type, and that unfortunately differs between the old and the new compiler. You can observe the same error with the old compiler simply by reversing the order of the types in ProviderToken<T>.

Interestingly, when performing subtype reduction on union types, we use the strict subtype relation in which any is a supertype of unknown. We introduced the strict subtype relation specifically to reduce mutual subtype effects, but for some reason we never switched getCommonSupertype to use that relation. If we did, it would fix this issue. I'm running an experiment to see the effects of such a change here.