Types like "keyof interface" should not be expanded when compiled due to declaration merging

[shigma]

TypeScript Version: 3.9.6

Search Terms: keyof declaration merging ts2339

Code

// module-A
interface Data {
  foo: string
}

export const keys = new Set<keyof Data>(['foo'])

Expected behavior:

// emitted module-A/index.d.ts
export interface Data {
    foo: string;
}
export declare const keys: Set<keyof Data>;

Actual behavior:

// emitted module-A/index.d.ts
export interface Data {
    foo: string;
}
export declare const keys: Set<"foo">;

// module-B
declare module 'module-A' {
  interface Data {
    bar: number
  }
}

keys.add('bar') // error here (ts2339)

Playground Link:

Related Issues:

[weswigham]

Dupe #17294, which I've had #20838 open in the past for.

[Val-istar-Guo]

TypeScript Version: 4.0.3

This bug is fixed???

// moduleA
export interface DefaultAlias {
}

// module B

declare module 'moduleA'  {
  export interface DefaultAlias {
    'case': string
  }
}

// module C

declare module 'moduleA'  {
  export interface DefaultAlias {
    'plan': string
  }
}

Expected behavior:

type AliasKey = keyof DefaultAlias
const a: AliasKey = 'case'
const b: AliasKey = 'plan'

Actual behavior:

type AliasKey = keyof DefaultAlias
const a: AliasKey = 'case'
const b: AliasKey = 'plan' // throw error

In vs code: