feat: use eslint 9

[abrahamguo]

PR Checklist

• Addresses an existing open issue: fixes Repo: Use ESLint v9 for our internal linting  #9082
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

Use eslint@9 internally.

[typescript-eslint]

Thanks for the PR, @abrahamguo!

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 31 targets

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

We should delete this CI job

typescript-eslint/.github/workflows/ci.yml

Lines 137 to 154 in 87a0a48

	eslint_v9_tests:
	name: Run tests on ESLint v9
	needs: [build]
	runs-on: ubuntu-latest
	steps:
	- name: Checkout
	uses: actions/checkout@v4
	- name: Install
	uses: ./.github/actions/prepare-install
	with:
	node-version: ${{ env.PRIMARY_NODE_VERSION }}
	- name: Build
	uses: ./.github/actions/prepare-build
	- run: yarn add eslint@9
	- name: Run tests
	run: yarn test
	env:
	CI: true

have we got an existing integration test to check for regressions on eslint v8?

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converting to draft until CI is passing.

[abrahamguo]

@bradzacher there are currently no integration or CI tests for eslint 8. I can add one if you want, but do you feel that's necessary since we ask for eslint 9 in both our peerDependencies and devDependencies?

Doesn't seem like anything similar was added for eslint 7 when we moved from eslint 7=>8 (#3737)

Also, seems unrelated to this PR since this is about using eslint 9 internally

[bradzacher]

Looks like there's already an integration test for v8 - https://github.com/typescript-eslint/typescript-eslint/tree/main/packages/integration-tests/fixtures/eslint-v8
So nothing to add!

Also, seems unrelated to this PR since this is about using eslint 9 internally

By moving to v9 internally our CI is no longer running against v8 - so we lose the test coverage asserting that we don't regress v8 compat.

But given we have the above integration test - we still have enough coverage.
It's not a super exhaustive test but it'll do (it's the same integration test coverage we maintained when we migrated to v8 internally)

[mattbrannon]

Just wanted to point out that one of your Netlify jobs has been running for nearly a week.
https://github.com/typescript-eslint/typescript-eslint/pull/9119/checks?check_run_id=25428243220

[abrahamguo]

@mattbrannon that's nothing compared to #8673, whose job has been running for 3 weeks 😉

It does seem like that specific job sometimes hangs indefinitely. Not sure why

[abrahamguo]

TODO: looks like this got fixed — try it out