[BREAKING] Support ESLint v9 in plugin, config and next lint

.gitignore

@@ -5,7 +5,7 @@ dist
 target
 packages/next/wasm/@next
 tarballs/
-packages/next/*.tgz
+packages/**/*.tgz
 
 # dependencies
 node_modules

packages/eslint-config-next/package.json

@@ -11,18 +11,18 @@
   "homepage": "https://nextjs.org/docs/app/building-your-application/configuring/eslint#eslint-config",
   "dependencies": {
     "@next/eslint-plugin-next": "15.0.0-canary.188",
-    "@rushstack/eslint-patch": "^1.3.3",
+    "@rushstack/eslint-patch": "^1.10.3",
     "@typescript-eslint/eslint-plugin": "^5.4.2 || ^6.0.0 || ^7.0.0 || ^8.0.0",
     "@typescript-eslint/parser": "^5.4.2 || ^6.0.0 || ^7.0.0 || ^8.0.0",
     "eslint-import-resolver-node": "^0.3.6",
     "eslint-import-resolver-typescript": "^3.5.2",
-    "eslint-plugin-import": "^2.28.1",
-    "eslint-plugin-jsx-a11y": "^6.7.1",
-    "eslint-plugin-react": "^7.33.2",
-    "eslint-plugin-react-hooks": "^4.5.0 || 5.0.0-canary-7118f5dd7-20230705"
+    "eslint-plugin-import": "^2.31.0",
+    "eslint-plugin-jsx-a11y": "^6.10.0",
+    "eslint-plugin-react": "^7.35.0",
+    "eslint-plugin-react-hooks": "^4.5.0 || ^5.0.0"
   },
   "peerDependencies": {
-    "eslint": "^7.23.0 || ^8.0.0",
+    "eslint": "^7.23.0 || ^8.0.0 || ^9.0.0",
     "typescript": ">=3.3.1"
   },
   "peerDependenciesMeta": {

packages/next/src/cli/next-lint.ts

@@ -23,21 +23,23 @@ export type NextLintOptions = {
   config?: string
   dir?: string[]
   errorOnUnmatchedPattern?: boolean
-  ext: string[]
   file?: string[]
   fix?: boolean
   fixType?: string
   format?: string
   ignore: boolean
-  ignorePath?: string
-  inlineConfig: boolean
-  maxWarnings: number
   outputFile?: string
   quiet?: boolean
+  strict?: boolean
+  // TODO(jiwon): ESLint v9 unsupported options
+  // we currently delete them at `runLintCheck` when used in v9
+  ext: string[]
+  ignorePath?: string
   reportUnusedDisableDirectivesSeverity: 'error' | 'off' | 'warn'
   resolvePluginsRelativeTo?: string
   rulesdir?: string
-  strict?: boolean
+  inlineConfig: boolean
+  maxWarnings: number
 }
 
 const eslintOptions = (

packages/next/src/lib/eslint/runLintCheck.ts

@@ -155,6 +155,23 @@ async function lint(
       ...eslintOptions,
     }
 
+    if (semver.gte(eslintVersion, '9.0.0')) {
+      for (const option of [
+        'useEslintrc',
+        'extensions',
+        'ignorePath',
+        'reportUnusedDisableDirectives',
+        'resolvePluginsRelativeTo',
+        'rulePaths',
+        'inlineConfig',
+        'maxWarnings',
+      ]) {
+        if (option in options) {
+          delete options[option]
+        }
+      }
+    }
+
     let eslint = new ESLint(options)
 
     let nextEslintPluginIsEnabled = false
@@ -163,10 +180,20 @@ async function lint(
     for (const configFile of [eslintrcFile, pkgJsonPath]) {
       if (!configFile) continue
 
-      const completeConfig: Config =
+      const completeConfig: Config | undefined =
         await eslint.calculateConfigForFile(configFile)
+      if (!completeConfig) continue
+
+      const plugins = completeConfig.plugins
+
+      const hasNextPlugin =
+        // in ESLint < 9, `plugins` value is string[]
+        Array.isArray(plugins)
+          ? plugins.includes('@next/next')
+          : // in ESLint >= 9, `plugins` value is Record<string, unknown>
+            '@next/next' in plugins
 
-      if (completeConfig.plugins?.includes('@next/next')) {
+      if (hasNextPlugin) {
         nextEslintPluginIsEnabled = true
         for (const [name, [severity]] of Object.entries(completeConfig.rules)) {
           if (!name.startsWith('@next/next/')) {
@@ -309,6 +336,17 @@ export async function runLintCheck(
     const eslintrcFile =
       (await findUp(
         [
+          // eslint v9
+          'eslint.config.js',
+          'eslint.config.mjs',
+          'eslint.config.cjs',
+          // TODO(jiwon): Support when it's stable.
+          // TS extensions are experimental and requires to install another package `jiti`.
+          // https://eslint.org/docs/latest/use/configure/configuration-files#typescript-configuration-files
+          // 'eslint.config.ts',
+          // 'eslint.config.mts',
+          // 'eslint.config.cts',
+          // eslint <= v8
           '.eslintrc.js',
           '.eslintrc.cjs',
           '.eslintrc.yaml',