Bug: Parse error when using FlatCompat in new flat config

[thepassle]

Environment

Node version: 18.19.0
npm version: 9.5.1
Local ESLint version: 8.56.0
Global ESLint version: n/a
Operating System: macos

What parser are you using?

Default (Espree)

What did you do?

Configuration

import * as url from 'url';
import { FlatCompat } from "@eslint/eslintrc";
const __dirname = url.fileURLToPath(new URL('.', import.meta.url));
const flatCompat = new FlatCompat({
  baseDirectory: __dirname,
});

import airbnb from 'eslint-config-airbnb-base';

export default [
  ...flatCompat.config(airbnb),
];

import foo from './foo.js';

console.log(foo);

What did you expect to happen?

eslint-config-airbnb-base internally uses eslint-plugin-import. When using the FlatCompat utility to use eslint-config-airbnb-base in my new flat config format, I'm getting the following error, which I'm not getting with the old eslint configuration format:

  1:17  error    Parse errors in imported module './foo.js': parserPath or languageOptions.parser is required! (undefined:undefined)  import/no-named-as-default

I found this confusing, because it does work in the old config format. But it seems like with the new config format, each config object that you export in the array thats exported in eslint.config.js, requires their own parserPath or languageOptions.parser, is that assumption correct? Previously we configured the parser in one place, and when extending that, it applied to everything else. (as far as my understanding goes)

I tried to look into the code a little bit to see whats happening, and it seems like the FlatCompat utility creates the following object for eslint-plugin-import specifically:

{
    settings: {
      'import/resolver': [Object],
      'import/extensions': [Array],
      'import/core-modules': [],
      'import/ignore': [Array]
    },
    rules: {
      'import/no-unresolved': [Array],
      'import/named': 'error',
      'import/default': 'off',
      'import/namespace': 'off',
      'import/export': 'error',
      'import/no-named-as-default': 'error',
      'import/no-named-as-default-member': 'error',
      'import/no-deprecated': 'off',
      'import/no-extraneous-dependencies': [Array],
      'import/no-mutable-exports': 'error',
      'import/no-commonjs': 'off',
      'import/no-amd': 'error',
      'import/no-nodejs-modules': 'off',
      'import/first': 'error',
      'import/imports-first': 'off',
      'import/no-duplicates': 'error',
      'import/no-namespace': 'off',
      'import/extensions': [Array],
      'import/order': [Array],
      'import/newline-after-import': 'error',
      'import/prefer-default-export': 'error',
      'import/no-restricted-paths': 'off',
      'import/max-dependencies': [Array],
      'import/no-absolute-path': 'error',
      'import/no-dynamic-require': 'error',
      'import/no-internal-modules': [Array],
      'import/unambiguous': 'off',
      'import/no-webpack-loader-syntax': 'error',
      'import/no-unassigned-import': 'off',
      'import/no-named-default': 'error',
      'import/no-anonymous-default-export': [Array],
      'import/exports-last': 'off',
      'import/group-exports': 'off',
      'import/no-default-export': 'off',
      'import/no-named-export': 'off',
      'import/no-self-import': 'error',
      'import/no-cycle': [Array],
      'import/no-useless-path-segments': [Array],
      'import/dynamic-import-chunkname': [Array],
      'import/no-relative-parent-imports': 'off',
      'import/no-unused-modules': [Array],
      'import/no-import-module-exports': [Array],
      'import/no-relative-packages': 'error'
    },
    languageOptions: { ecmaVersion: 6, sourceType: 'module' },
    plugins: { import: [Object] }
  },

Note that there's no parserPath or languageOptions.parser present. There is a languageOptions.parser present in other objects of the config, however, but as mentioned above, it seems like that's not getting applied to other objects in the exported flat config array.

When I looked into the code, I saw that the error is thrown in eslint-module-utils:

And in the getParserPath I see the following:

Judging on the comment, it seems like it should have defaulted to eslints parser, but that is undefined:

I'm not too familiar with ESLint's internals, but this feels like it could potentially be a bug, so I figured I'd report it.

So two main questions are:

• Is my assumption that parser options are not "inherited" anymore, like was the case in the old config format, and instead now every object in the exported flat config array from eslint.config.js needs to configure their own parser options?
• Is this a bug in ESLint? Or should I report this elsewhere? (like eslint-plugin-import?)

What actually happened?

See explanation above

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-g64xvt?file=eslint.config.js

Participation

• I am willing to submit a pull request for this issue.

Additional comments

Open the stackblitz and run npm run lint in the terminal to see the result:

  1:17  error    Parse errors in imported module './foo.js': parserPath or languageOptions.parser is required! (undefined:undefined)  import/no-named-as-default

[aladdin-add]

it's not eslint's bug - the plugin just has not supported flat configs: import-js/eslint-plugin-import#2943, import-js/eslint-plugin-import#2873

[mdjermanovic]

• Is my assumption that parser options are not "inherited" anymore, like was the case in the old config format, and instead now every object in the exported flat config array from eslint.config.js needs to configure their own parser options?

context.languageOptions.parser is always defined. If languageOptions.parser isn't specified in config objects, then it defaults to Espree which is set in the default config, so when the config objects are merged with the default config the resulting config for a file will have Espree in languageOptions.parser.

[thepassle]

• Is my assumption that parser options are not "inherited" anymore, like was the case in the old config format, and instead now every object in the exported flat config array from eslint.config.js needs to configure their own parser options?

context.languageOptions.parser is always defined. If languageOptions.parser isn't specified in config objects, then it defaults to Espree which is set in the default config, so when the config objects are merged with the default config the resulting config for a file will have Espree in languageOptions.parser.

Okay thanks, so I also just noticed that eslint-module-utils is actually not an official package, but maintained by the same maintainer as eslint-plugin-import, so it seems that this is just a bug on their side then.

Thank you for confirming :) I'll create an issue at eslint-plugin-import

[G-Rath]

@mdjermanovic I've been working on v9 support for eslint-plugin-import and was wondering if you could help clarify something about this for me - a lot of tests are failing due to the error in the original description, seemingly because the parser isn't there.

i.e. if you compare this run using v7 to [this run using v9)[https://github.com/import-js/eslint-plugin-import/actions/runs/8747922114/job/24007140735?pr=2996] - even just glancing through the logs you'll see a lot of parserPath: undefined.

I have a feeling the answer is probably that the defaults you linked to are used for the CLI but not by RuleTester - does that sound right to you?