Intersected type variable with a recursive constraint fails to infer

🔎 Search Terms

intersection type variable parameter inference recursive constraint

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20230906#code/C4TwDgpgBAysCGwIGED2A7AZgSwOYB4AVAQQGNhsMoIAPJdAEwGcongAnbdXAPigF4oAbwBQUaug4gA-AC4oJcpXRjWCJEzlQAShFKp2DfG07cANLHUoMOAoooYePANwiAvq5GhIlxBBikABYQALbwAsKqbH6a8rr6hsYcXLgWcH4BwWEu7p4MegA28OzQmACu6EpUpCV+ALLwQVwQ+Kr2ytR0EIwsJilmbWhYeJ30zL5ImaHwAzwAFPrDuPKEQ7ZQAGQT1ktEZA7oPACU8gDa7RgWqzZ4ALqei2xQXJgQ7CUMAArF8CEsgjUIPVGoFmnNROJulJ5AAiTCoVAwgbiaIaeQQ8RQeDo1SYiTQqAwgBGxSRuKgbmRFIGbiOnhebw+33YvyYrgA9OyoAA9aQiIA

💻 Code

type StateConfig<TAction extends string> = {
  entry?: TAction
  states?: Record<string, StateConfig<TAction>>;
};

type StateSchema = {
  states?: Record<string, StateSchema>;
};

declare function createMachine<
  TAction extends string,
  TConfig extends StateSchema,
>(config: TConfig & StateConfig<TAction>): [TAction, TConfig];

const inferredParams = createMachine({
  entry: "foo",
  states: {
    a: {
      entry: "bar",
    },
  },
});

inferredParams; // ["foo" | "bar", StateSchema]

🙁 Actual behavior

TConfig gets inferred as its constraint

🙂 Expected behavior

I'd expect TConfig to infer successfully

Additional information about the issue

This is very related to the other issue I just created (see here). The underlying problem of this particular example is the same. The inferredType for TConfig fails the compareTypes check in getInferredType here. This time there is no excess property errors apparent to the user because the excess properties are satisfied through the intersection.

Despite the problem having the same root cause I think it's worth discussing this separately. The other issue could be closed as design limitation/working as intended but this one feels to me a lot closer to being an actual bug that would be worth fixing.

Reproduce the inference result from the provided TypeScript Playground link, then read src/compiler/checker.ts around getInferredType and its compareTypes check. Trace why the intersected recursive constraint causes TConfig to fall back to StateSchema; done means the example infers the configuration successfully without regressing related inference behavior.