Recursive reverse mapped types don't work well with mixed object and tuple structures

[Andarist]

🔎 Search Terms

inference recursive reverse mapped type tuples arrays

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBAygxgCwgWwIZQLxQEoTgewCcATAHgGdhCBLAOwHMAaKAV1oGtb8B3WgPigAfKIQipi+WgBsQrDl14BtALoBuAFDrQkKABEIAMzrVg1SaQAqArAG91UKIoDSUOlHYQQ+A1AvKAXFAAFEEAlJgCFs7K4cL6RrQmZrSW0XwaAL4a6sR4UqiiUAZscKaSUHCiqMAQllAQAB41tMTksIgoqHxBuQlJkoHxxmUpVqGBFtkEtJQiEOQsUsCYFVU1QXYOqIFhEVAAjIz2UABGgZsOFTvhGAIARHdHDhlHGaHZAPQfUMAI1G2SaCJOAQGSuWgGCCENoAAxsUG2UFoLGQJyhqlO5yuUEoNAYUAyBJh6lECyWGi+UAAegB+TTTWakxbAABMK0qYnWil2twOzG5N3ud2UMU+31+-yggPBkOhUBhyNRUJUMNOLGWJhxCHwi2IMqh8sUirRhH5uLo9BFxKZSxZFO+tPpkkZ82ZAGZ2WsIBtjoieQJDsczo5-VAHspXu9NJSJQDaNA6LLYfDEcaocxg+aGCoiWqNctyNrdfrCPKU4E06bMY4s5aiSTXUs3fbqTSgA

💻 Code

type Schema = Record<string, unknown> | readonly unknown[];

type Definition<T> = {
  [K in keyof T]: (() => T[K]) | Definition<T[K]>;
};

declare function create<T extends Schema>(definition: Definition<T>): T;

const result = create({
  a: () => 1,
  b: {
    c: () => "",
  },
});

// this one nicely infers `{ a: number; b: { c: string } }`
result;
// ^?

const result2 = create([() => 1, [() => ""]]);

// this one infers `number[]` but it should infer `[number, [string]]`
result2;
// ^?

const result3 = create({
  a: () => 1,
  b: [() => ""],
});

// this one infers `{ a: number, b: string[] }` but it should infer `{ a: number, b: [string] }`
result3;
// ^?

🙁 Actual behavior

tuples can't be inferred recursively here

🙂 Expected behavior

tuples are inferred as arrays

Additional information about the issue

I understand that I need some tuple context to actually infer tuples but I've tried a couple of ways to add it and I just can't make it work. It would be much simpler if TS would just infer tuples here with the original code.

1. an attempt with const type parameter: TS playground
2. an attempt with adding a constraint to Definition: TS playground
3. "routing"/resolving the T[K]'s constraint using a conditional type to satisfy the Definition's constraint: TS playground
4. an attempt with changing Schema to use any over unknown to fix the recursive constraint problem: TS playground
5. an attempt with a separate mapped type for the array constraint and routing to it: TS playground

[andreaTarascioSophany]

Hi! I would be excited to contributing fixing this issue