Types with index signatures lose all attribute signatures when using keyof or Omit

[nuintun]

Bug Report

💻 Code

interface Route {
  name: string;
  path: string;
  href?: string;
  exact?: boolean;
  strict?: boolean;
  [key: string]: string | boolean | undefined | object;
}

type RouteNode = Omit<Route, 'name'>;

const route: RouteNode = {} as RouteNode;

route.p;

🙁 Actual behavior

Lose all attribute signatures

🙂 Expected behavior

Do not lose attribute signatures

[MartinJohns]

This is working as intended.

What search terms did you use to look for existing issues? omit index would already suffice.

[nuintun]

@MartinJohns

I wrote a tool that converts some properties of an object into optional, but it doesn't work.

type PartPartial<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;

interface Route {
  name: string;
  path: string;
  href?: string;
  exact?: boolean;
  strict?: boolean;
  [key: string]: string | boolean | undefined | object;
}

type RouteNode = PartPartial<Route, 'name'>;

And the same PartRequired doesn’t work either.

type PartRequired<T, K extends keyof T> = Omit<T, K> & Required<Pick<T, K>>;

But PartRequired like this is work well.

type PartRequired<T, K extends keyof T> = T & Required<Pick<T, K>>;

[MartinJohns]

See the existing issues: #43139, #40999, etc. Omit<T> is using keyof T, and keyof T for types with indexers always results in string | number, so your individual properties are unavailable. This is working as intended, see #42436.

Issue #41966 mentions a workaround for this behavior (by excluding the index signature from the type).

[nuintun]

@MartinJohns 3Q~