False positive: eslint-config-prettier

[tinymachine]

Bug Description

This might be too much to expect depcheck to handle, but eslint-config-prettier is used by eslint-plugin-prettier when the ESLint config includes{ "extends": ["plugin:prettier/recommended"] }, even though eslint-plugin-prettier's package.json only includes eslint-config-prettier as a dev dependency. (See Prettier's documentation on integrating with ESLint.) When running depcheck --specials=eslint, though, eslint-config-prettier is listed as an unused dev dependency, though it is actually a dev dependency.

(This seems different than #316 where the issue was eslintConfig not being honored in the package.json.)

Code snippets

Where the dependency is used:

// .eslintrc.js
module.exports = {
  "extends": [
    "eslint:recommended",
    "plugin:prettier/recommended"
  ],
  "plugins": [
    "prettier"
  ],
  "env": {
    "browser": true,
    "node": true
  }
}

Where the dependency is listed in package.json:

"devDependencies": {
    "@babel/core": "^7.3.4",
    "@babel/preset-env": "^7.3.4",
    "autoprefixer": "^6.7.7",
    "eslint": "^5.14.1",
    "eslint-config-prettier": "^4.1.0",
    "eslint-plugin-prettier": "^3.0.1",
    "grunt": "^1.0.3",
    "grunt-babel": "^8.0.0",
    "grunt-contrib-nodeunit": "~0.4.1",
    "grunt-contrib-uglify": "^4.0.0",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-reload": "^0.2.0",
    "prettier": "^1.16.4"
}

Versions

• node -v: v8.12.0
• npm -v: 6.4.1
• depcheck --version: 0.7.2

Extra info

Here's the output of depcheck --json --specials=eslint (with the "using" paths obscured):

{"dependencies":[],"devDependencies":["@babel/preset-env","autoprefixer","eslint-config-prettier","grunt-contrib-nodeunit","grunt-reload"],"missing":{},"using":{"eslint-plugin-prettier":[".../.eslintrc.js"],"eslint":[".../.eslintrc.js"],"prettier":[".../.eslintrc.js"],"grunt-babel":[".../gruntfile.js"],"grunt-contrib-watch":[".../gruntfile.js"],"grunt-contrib-uglify":[".../gruntfile.js"],"@babel/core":[".../gruntfile.js"],"grunt":[".../gruntfile.js"]},"invalidFiles":{},"invalidDirs":{}}

Thanks for any help you can provide, and for your work on this package.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[VincentLanglet]

This is still a bug @rumpl, I can't add prettier because of it (#463)