[no-unused-vars] Variables used in an ambient declaration are not detected

[andreubotella]

Repro

{
  "rules": {
    "@typescript-eslint/no-unused-vars": ["error"]
  }
}

import { Octokit } from "@octokit/rest";

declare global {
  namespace Express {
    interface Request {
      githubApi?: Octokit;
    }
  }
}

Expected Result

No ESLint problems are detected.

Actual Result

An error for @typescript-eslint/no-unused-vars shows up: "'Octokit' is defined but never used". If the Octokit type is used elsewhere other than in an ambient declaration, the error goes away.

Additional Info

This might be a case covered in the meta-issue #1856, but I don't know enough about the internals of typescript-eslint to know for sure.

Versions

package	version
@typescript-eslint/eslint-plugin	2.33.0
@typescript-eslint/parser	2.33.0
TypeScript	3.9.2
ESLint	7.0.0
node	12.16.3
npm	6.14.4

[bradzacher]

#1856 will solve it