Upgrade eslint to version 9.0.0

[timvandermeij]

We should upgrade to ESLint 9 now that it's officially released. The changelog, including the breaking changes that should be audited, can be found at https://github.com/eslint/eslint/releases/tag/v9.0.0. Note that this upgrade is currently blocked on the ESLint plugins that we use indicating support for ESLint 9 in their package.json ranges first, so this is mostly a tracking issue at the moment.

[wojtekmaj]

Let's make it a tracking issue then :D

Plugins

Plugin name	Update status	Development status	Issue	Comments
eslint-plugin-import	✅ 78bf528	✅ Implemented	import-js/eslint-plugin-import#2948	Worth considering a switch to eslint-plugin-import-x, much more reasonably maintained alternative
eslint-plugin-jasmine	✅ 764e67e	✅ Implemented	tlvince/eslint-plugin-jasmine@f9e0798
eslint-plugin-json		✅ Implemented	azeemba/eslint-plugin-json#80	Update blocked by eslint-plugin-mozilla support for v4.0.0
eslint-plugin-no-unsanitized	✅ ae13b4a	✅ Implemented	mozilla/eslint-plugin-no-unsanitized#234	Released in v4.1.0
eslint-plugin-sort-exports		❓ Unknown	n/a
eslint-plugin-unicorn	✅ d7f2bc0	✅ Implemented	sindresorhus/eslint-plugin-unicorn#2250

[timvandermeij]

In commit d7f2bc0 eslint-plugin-unicorn got upgraded to version 53.0.0 which contains support for ESLint 9, so we can cross that one off the list.

[nicolo-ribaudo]

If you haven't already seen https://eslint.org/blog/2024/05/eslint-compatibility-utilities/, it might be useful for this. It provides wrappers to run ESLint 8 plugins in ESLint 9.

[mozfreddyb]

I can comment for eslint-plugin-no-unsanitized: It's planned but blocked on dependencies (heh)
mozilla/eslint-plugin-no-unsanitized#241

[timvandermeij]

eslint-plugin-json 4.0.0 is now released and contains ESLint 9 support (see azeemba/eslint-plugin-json@0ff302c), but we can't update to it yet because eslint-plugin-mozilla has not indicated support for version 4.0.0 in package.json yet:

npm error While resolving: [email protected]
npm error Found: [email protected]
npm error node_modules/eslint-plugin-json
npm error   dev eslint-plugin-json@"^4.0.0" from the root project
npm error
npm error Could not resolve dependency:
npm error peer eslint-plugin-json@"^3.1.0" from [email protected]
npm error node_modules/eslint-plugin-mozilla
npm error   dev eslint-plugin-mozilla@"^3.7.4" from the root project
npm error
npm error Conflicting peer dependency: [email protected]
npm error node_modules/eslint-plugin-json
npm error   peer eslint-plugin-json@"^3.1.0" from [email protected]
npm error   node_modules/eslint-plugin-mozilla
npm error     dev eslint-plugin-mozilla@"^3.7.4" from the root project

[timvandermeij]

In commit c77dbe0 eslint-plugin-jasmine got updated to version 4.2.0 which contains support for ESLint 9, so we can cross that one off the list.

[timvandermeij]

In PR #18571 the idea came up of trying to remove eslint-plugin-mozilla given that we only used three rules from it and after that PR we are down to two: one at https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/.eslintrc#L19 and one at https://github.com/mozilla/pdf.js/blob/master/.eslintrc#L47. The latter is already covered by an existing unicorn rule, and the former may be removed in favor of explicitly documenting the remaining globals we have left. Note that when eslint-plugin-mozilla was introduced in 2e9ae50 there were more occurrences than nowadays, mainly because we don't have Firefox extension files in this repository anymore and we eliminated most globals usage.

We should check if this is possible since it would unblock the eslint-plugin-json update and that combined with the removal of eslint-plugin-mozilla would bring us two steps closer to ESLint 9. Note that we can't actually upgrade eslint-plugin-json yet because that version only supports ESLint 9 and isn't backwards compatible with ESLint 8, but it would remove the blocker.

[timvandermeij]

In commit be93d53 eslint-plugin-mozilla got removed, so we also can cross that one off the list.

[mozfreddyb]

no-unsanitized now supports eslint 9. We just released a new version earlier in the week.

[timvandermeij]

In commit ae13b4a eslint-plugin-no-unsanitized got updated to version 4.1.0 which contains support for ESLint 9, so we can cross that one off the list.

[timvandermeij]

In commit 78bf528 eslint-plugin-import got updated to version 2.31.0 which contains support for ESLint 9, so we can cross that one off the list.

[timvandermeij]

In the PRs above we removed obsolete plugins and replaced eslint-plugin-sort-exports, which should have removed the final blocker for the upgrade here.

[nicolo-ribaudo]

It seems like now just bumping the version in package.json works, but I haven't had time to test deeply.