no-unused-variable: false positive for exported function return type

[msklvsk]

Bug Report

• TSLint version: 3.8.0
• TypeScript version: 1.8.10
• Running TSLint via: gulp-tslint

TypeScript code being linted

import {Server, createServer} from 'http';
// unused variable: 'Server' (while it is used as return type)

export function getServer() {
  return createServer();
}

with tslint.json:

{
  "rules": {
    "no-unused-variable": true
  }
}

Actual behavior

An error unused variable: 'Server' is reported, but it is used as a return type and removing Server from imports causes a native typescript error: Return type of exported function has or is using name 'Server' from external module "http" but cannot be named

Expected behavior

no tslint error is reported

[adidahiya]

Hm, this is an interesting problem with implicit typedefs that hasn't really come up before. Not sure if we'll be able to identify Server as an implicitly-used type, especially without full type checker info (#680). For now I would suggest adding an explicit return type to getServer (IMO it's good practice to do so for exported APIs anyway).

[andy-hanson]

This is handled in #2235. Although it should be fixed in TypeScript itself, for which the issue is microsoft/TypeScript#9944 or microsoft/TypeScript#13694.