feat: support ESLint v9

[JoshuaKGoldberg]

👉 NOTE: This is into our v8 branch. Once it's merged, it'll only be included in our v8 versions.

PR Checklist

• Addresses an existing open issue: fixes ESLint v9 Support #8211
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

Keeps us on ESLint v8 internally, but adds v9 to the supported version ranges. Adds a CI check that yarn add eslint@9; yarn test passes.

[typescript-eslint]

Thanks for the PR, @JoshuaKGoldberg!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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✅ Successfully ran 32 targets

• nx test eslint-plugin --coverage=false
• nx run-many --target=test --parallel --exclude integration-tests --exclude website --exclude website-eslint
• nx test eslint-plugin
• nx test typescript-estree --coverage=false
• nx test repo-tools --coverage=false
• nx run types:build
• nx test scope-manager --coverage=false
• nx run repo-tools:postinstall-script
• nx test type-utils --coverage=false
• nx test typescript-eslint --coverage=false
• nx test rule-schema-to-typescript-types --coverage=false
• nx test visitor-keys --coverage=false
• nx test utils --coverage=false
• nx test parser --coverage=false
• nx test eslint-plugin-internal --coverage=false
• nx run-many --target=lint --parallel --exclude eslint-plugin
• nx run-many --target=build --parallel --exclude=website --exclude=website-eslint
• nx test ast-spec --coverage=false
• nx test typescript-estree
• nx test visitor-keys
• nx test utils
• nx test scope-manager
• nx test type-utils
• nx test typescript-eslint
• nx test eslint-plugin-internal
• nx test repo-tools
• nx test parser
• nx test ast-spec
• nx test rule-schema-to-typescript-types
• nx run integration-tests:test
• nx run-many --target=typecheck --parallel
• nx run repo-tools:generate-configs

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[auvred]

Awesome! LGTM 🏆

[bradzacher]

question: do we really want to do the bump to v9 if it completely breaks our lint setup like this?
would we be better served by instead just adding a decent integration test which runs against v9, and leaving our setup on v8 for now?

[JoshuaKGoldberg]

I ran yarn dedupe to trim this file down a bit. Then I reverted the tmp upgrades as they cause a few odd CI failures. #8589

[JoshuaKGoldberg]

Now that this is merged, the v8 versions of typescript-eslint starting with v8.0.0-alpha.10 now support ESLint v9. Hooray! 🙌

If you still have problems with typescript-eslint and ESLint v9:

1. Please make sure you're using [email protected] or newer
2. Go through our issue chooser to file a new issue reporting your problems
   • That issue template includes searching for existing issues matching your problem - please do not file duplicate issues

Note that we do not plan on backporting ESLint v9 support to v7 versions of typescript-eslint. There are a lot of breaking changes inherent to our ESLint v9 support.

If any enterprising individual wants to try onboarding us in typescript-eslint to ESLint v9, #9082 tracks that as a followup.