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?