Upgrade to ESLint 9

[IgorKrupenja]

Cannot be upgraded

┌────────────────────────────────────────┬─────────┬────────┬────────────────┐
│ Package                                │ Current │ Latest │ Dependents     │
├────────────────────────────────────────┼─────────┼────────┼────────────────┤
│ @typescript-eslint/eslint-plugin (dev) │ 7.16.1  │ 8.0.0  │ nextjs-starter │
├────────────────────────────────────────┼─────────┼────────┼────────────────┤
│ @typescript-eslint/parser (dev)        │ 7.16.1  │ 8.0.0  │ nextjs-starter │
├────────────────────────────────────────┼─────────┼────────┼────────────────┤
│ eslint (dev)                           │ 8.57.0  │ 9.8.0  │ nextjs-starter │
├────────────────────────────────────────┼─────────┼────────┼────────────────┤
│ eslint-plugin-unused-imports (dev)     │ 3.2.0   │ 4.0.1  │ nextjs-starter │
└────────────────────────────────────────┴─────────┴────────┴────────────────┘

Blockers

• eslint-config-next: next-lint Doesn't Support ESLint 9 vercel/next.js#64409 (comment)
• eslint-plugin-testing-library: Prepare the rules for ESLint v9 testing-library/eslint-plugin-testing-library#899
• eslint-plugin-sort-export-all: Old unpopular plug-in? Necessary? Better alternative?
• eslint-plugin-vitest: Not yet published to npm, workaround OK.
• eslint-plugin-import-x: Overall OK but some dependencies broken.

Info

Track plug in support here eslint/eslint#18391 Some like testing library cannot be upgraded yet.