Repro

{
  "rules": {
    "@typescript-eslint/no-empty-interface": "error"
  }
}

import { tokens } from './theme.treat';

declare module 'treat/theme' {
  type Tokens = typeof tokens;
  // eslint-disable-next-line @typescript-eslint/no-empty-interface
  export interface Theme extends Tokens {}
}

The code above can be found here, along with the referenced theme.treat.ts file in the same directory.

Expected Result

No errors should be thrown, as the Theme interface of module 'treat/theme' is being augmented.

Actual Result

An interface declaring no members is equivalent to its supertype.

(As thrown by @typescript-eslint/no-empty-interface.)

Additional Info

The code above gets auto-fixed to:

import { tokens } from './theme.treat';

declare module 'treat/theme' {
  type Tokens = typeof tokens;
  export type Theme = Tokens;
}

Which throws a TypeScript error ts(2300):

Duplicate identifier 'Theme'.

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