Research Spike: ESLint 9 compatibility

[ChristianMurphy]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Problem

ESLint 9 is changing the plugin API: https://eslint.org/blog/2023/09/preparing-custom-rules-eslint-v9/
There may be changes needed in ESLint-MDX

Solution

Check to see if any changed/removed APIs are used, migrate if needed.

Alternatives

• No change may be needed
• We could remain on eslint 8 for a while if the migration is challenging

[JounQin]

I don't see how to test eslint@9 at this point.

[ChristianMurphy]

https://github.com/eslint/eslint/releases/tag/v9.0.0-alpha.0

[remcohaszing]

Since the new flat config no longer resolves files, and supports eslint.config.mjs, I think ESLint MDX integrations can switch to ESM.

[JounQin]

Since the new flat config no longer resolves files, and supports eslint.config.mjs, I think ESLint MDX integrations can switch to ESM.

I'd like to keep dual. Legacy .eslintrc configs are still supported.

[ChristianMurphy]

Legacy configuration are deprecated https://eslint.org/blog/2023/12/eslint-v9.0.0-alpha.0-released/

There are far less quirks and hacks packaging as pure ESM, rather than dealing with dual packaging limitations.

[JounQin]

#496

@ChristianMurphy

worker.mts will bypass all the limitations.

They're deprecated but still supported. I don't want to break anyone's current workflow before they're ready including myself.

For example, compatibility with other plugins.

import-js/eslint-plugin-import#2948 (comment)

[tianyingchun]

What's the plan?

[karlhorky]

If you don't use Markdown, then the current version eslint-plugin-mdx@3.1.5 appears to work in ESLint v9 by copying the flat config which is exported:

eslint.config.js or eslint.config.mjs

import eslintMdx from 'eslint-mdx';
import mdx from 'eslint-plugin-mdx';

/** @type {import('eslint').Linter.FlatConfig} */
const config = [
  {
    files: ['**/*.mdx'],
    languageOptions: {
      sourceType: 'module',
      ecmaVersion: 'latest',
      parser: eslintMdx,
      globals: {
        React: false,
      },
    },
    plugins: {
      mdx,
    },
    rules: {
      'mdx/remark': 'warn',
      'no-unused-expressions': 'error',
      'react/react-in-jsx-scope': 0,
    },
  },
];

export default config;

[tianyingchun]

i have integrating mdx into a plugin it can works fine for eslint V9
https://github.com/hyperse-io/eslint-config-hyperse

[tianyingchun]

what's plan for ESLint V9, i used it in local, it seems that everything works fine except we need to bump eslint-plugin-markdown to latest version (5.1.0) for now it used "eslint-plugin-markdown": "^3.0.1"?

[reduckted]

ESLint v8 is EOL in one month (https://eslint.org/version-support/). Would you consider dropping v8 support to make it easier to migrate this plugin to v9?

If anyone really needs v8 support, they can continue to use the current version of this plugin.

[remcohaszing]

@eslint/markdown (formerly eslint-plugin-markdown 6.0.0 is ESM only. I think it’s fair to drop CJS support in other ESLint plugins as well.

[tianyingchun]

it's time to drop cjs +1 :)

[terrymun]

I'm wondering what's the state of adding eslint 9 (and @eslint/markdown) compatibility? AFAIK @eslint/markdown is already at version 6 and the one used by eslint-mdx is three major versions behind.