Eslint keeps requiring overridden parsers when extending config

I am using plugin:typescript/recommended (eslint-plugin-typescript) on top of react-app (eslint-config-react-app) and as I can see from eslint --print-config the parser field is overwritten from babel-eslint to correct /Users/dis/Sites/apple-music/node_modules/eslint-plugin-typescript/parser.js, but for some reason ESLint still tries to resolve the unneeded parser, which is not even in final config.

I’m kinda okay to still install the useless parser, but it is a bit annoying.

Tell us about your environment

• ESLint Version: 5.8.0

Please show your full configuration:

Configuration

{
  "extends": [
    "eslint:recommended",
    "react-app",
    "plugin:typescript/recommended",
    "plugin:import/recommended",
    "plugin:jsx-a11y/recommended",
    "plugin:prettier/recommended"
  ],
  "rules": {
    "no-console": "off",
    "prettier/prettier": "error"
  },
  "env": {
    "browser": true,
    "mocha": true,
    "node": true
  },
  "settings": {
    "import/resolver": {
      "node": {
        "extensions": [
          ".js",
          ".jsx",
          ".ts",
          ".tsx"
        ]
      }
    }
  }
}

eslint --fix src/**/*.ts src/**/*.tsx

What actually happened? Please include the actual, raw output from ESLint.

Error: Cannot find module 'babel-eslint'
Referenced from: /Users/dis/Sites/apple-music/.eslintrc
    at ModuleResolver.resolve (/Users/dis/Sites/apple-music/node_modules/eslint/lib/util/module-resolver.js:72:19)
    at loadFromDisk (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:514:42)
    at load (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:564:20)
    at configExtends.reduceRight (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:430:36)
    at Array.reduceRight (<anonymous>)
    at applyExtends (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:408:26)
    at loadFromDisk (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:528:22)
    at load (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:564:20)
    at configExtends.reduceRight (/Users/dis/Sites/apple-music/node_modules/eslint/lib/config/config-file.js:430:36)
    at Array.reduceRight (<anonymous>)

Are you willing to submit a pull request to fix this bug?

I could if I would know how to fix this…

[bradzacher]

My understanding of the intended use case of peer deps is that you are specifying parent deps, ie my package is run by these packages.

The use of peer dependencies by CRA to attempt to merge or make packages optional seems like an “abuse” (for lack of a better term) of the non-automatic install quality of them…

That said, it’s intentional for us to set the parser to our parser in the new recommended config in 1.0.0.

The question here is that if you’re extending a config that sets a parser, then overriding it in the base config, does it still bug out?

{
  "extends": ["react-app"],
  "parser": "eslint-plugin-typescript/parser"
} 

[not-an-aardvark]

To clarify, if something is a peerDependency of a package, then you always need to install it in order to use that package. This applies to ESLint configs and also everything else.

It’s true that ESLint could probably avoid loading unneeded parsers as a performance optimization, but that is an implementation detail and isn’t defined behavior. If a package is missing its required dependencies or peerDependencies, there are no guarantees about whether it will work.