Not valid when inferring return value types from function parameters of nested array types

[fxioi]

Bug Report

A function that passes in a custom schema that constrains the values of the properties of the returned object.

But when the parameters are nested arrays, the type constraint does not take effect.

🔎 Search Terms

nested array, nested tuple, type Inference, type constraints

🕗 Version & Regression Information

v4.6.4

⏯ Playground Link

Playground link with relevant code

💻 Code

function pickFunc<T extends DemoO, U extends ToSchemaType<T>>(
  obj: T,
  schema: U
): PickBySchema<T, U> {
  throw "not yet implemented";
}

const res = pickFunc(post, ["id", "body"]);
res.id;
// The message "title does not exist" was successfully displayed
res.title;
res.body;

// When using nested schema, the type constraint does not take effect
const res = pickFunc(post, ["id", ["tags", ["name"]]]);
res.id;
// Expect an error message
res.title;
// Expect an error message
res.tags[0].id
res.tags[0].name

I created the PickBySchema type to generate attribute field constraints for the object.

It is effective when used alone.

type PickBySchema<T extends DemoO, U extends ToSchemaType<T>> = {
  [K in U extends (infer U1)[]
    ? U1 extends string
      ? U1
      : U1 extends [infer U2, SelectSchemaType]
      ? U2 extends string
        ? U2
        : never
      : never
    : never]: T[K] extends string
    ? T[K]
    : T[K] extends (infer O)[]
    ? O extends DemoO
      ? PickBySchema<O, GetNestedSchema<U, K>>[]
      : never
    : never;
};

type PostOnlyId = PickBySchema<Post, ["id", ["tags", ["id", "name"]]]>;

🙁 Actual behavior

When passing nested arrays in function parameters, the return value does not get the expected type constraints

🙂 Expected behavior

When passing a one-dimensional array or a nested array as a function parameter, the return value is expected to be bound by the specified field

[jcalz]

That's quite a long reproduction; could you demonstrate the issue with less code?

I think this might be related to #30680; the compiler is inferring wider array/string types than you want.

[RyanCavanaugh]

This repro is long enough that it's unlikely to represent a bug in TypeScript. If you can provide a shorter one (5-10 lines is sufficient to reproduce almost any defect) we can investigate, but we don't have the resources to dig in to things this large.

[fxioi]

First of all, thank you very much for your replies, and I apologize for providing a slightly longer reproduction. Since this problem was discovered during debugging nested arrays, I'll close the issue before I provide a parsimonious reproduction.