@babel/eslint-parser false positive for no-unused-vars rule with TypeScript types

Bug Report

• I would like to work on a fix!

Current behavior @babel/eslint-parser gives false positive (shows error) for no-unused-vars rule with TypeScript types:

error  'Rubik' is defined but never used  no-unused-vars

Input Code

import Rubik from './Rubik';

export default class Arranger {
  private readonly rubik: Rubik;
}

Expected behavior When run eslint, no errors/warnings should arise.

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)

• Filename: babel.config.js

{
  "presets": [
    "@babel/preset-env",
    "@babel/preset-typescript"
  ],
  "plugins": [
    "@babel/proposal-class-properties"
  ]
}

• Filename: .eslintrc.json

{
  "parser": "@babel/eslint-parser",
  "rules": {
    "no-unused-vars": ["error"]
  }
}

Environment

  System:
    OS: Linux 4.19 Alpine Linux
  Binaries:
    Node: 12.18.3 - /usr/bin/node
    Yarn: 1.22.4 - /usr/bin/yarn
  npmPackages:
    @babel/core: ^7.10.2 => 7.11.4
    @babel/eslint-parser: ^7.11.4 => 7.11.4
    @babel/eslint-plugin: ^7.11.3 => 7.11.3
    @babel/plugin-proposal-class-properties: ^7.8.3 => 7.10.4
    @babel/preset-env: ^7.10.2 => 7.11.0
    @babel/preset-typescript: ^7.9.0 => 7.10.4
    eslint: 7.2.* => 7.2.0
    webpack: ^4.43.0 => 4.44.1

Note This issue already existed before switching to Babel monorepo (in babel/babel-eslint) so the switch is not the cause.

[taylankasap]

In that case it’s all good.

Maybe this part can be mentioned in readme or docs:

We’ve left linting TypeScript to @typescript-eslint due to all the duplicated work and lack of type information

Anyway, thanks for the info.

[kaicataldo]

@taylankasap That’s a good idea!

@prateekbh That’s right!