Upgrade to ESlint 9 (#16470)

Closes https://github.com/astral-sh/ruff/issues/12723

.github/renovate.json5

@@ -101,14 +101,7 @@
       matchManagers: ["cargo"],
       matchPackageNames: ["strum"],
       description: "Weekly update of strum dependencies",
-    },
+    }
-    {
-      groupName: "ESLint",
-      matchManagers: ["npm"],
-      matchPackageNames: ["eslint"],
-      allowedVersions: "<9",
-      description: "Constraint ESLint to version 8 until TypeScript-eslint supports ESLint 9", // https://github.com/typescript-eslint/typescript-eslint/issues/8211
-    },
   ],
   vulnerabilityAlerts: {
     commitMessageSuffix: "",

playground/.eslintrc

@@ -1,24 +0,0 @@
-{
-  "parser": "@typescript-eslint/parser",
-  "plugins": ["@typescript-eslint"],
-  "extends": [
-    "eslint:recommended",
-    "plugin:@typescript-eslint/eslint-recommended",
-    "plugin:@typescript-eslint/recommended",
-    "plugin:react/recommended",
-    "plugin:react/jsx-runtime",
-    "plugin:react-hooks/recommended",
-    "plugin:import/recommended",
-    "plugin:import/typescript"
-  ],
-  "rules": {
-    // Disable some recommended rules that we don't want to enforce.
-    "@typescript-eslint/no-explicit-any": "off",
-    "eqeqeq": ["error","always", { "null":  "never"}]
-  },
-  "settings": {
-    "react": {
-      "version": "detect"
-    }
-  }
-}

playground/eslint.config.mjs

@@ -0,0 +1,35 @@
+import react from "eslint-plugin-react";
+import tseslint from "typescript-eslint";
+import reactHooks from "eslint-plugin-react-hooks";
+import importPlugin from "eslint-plugin-import";
+
+export default tseslint.config(
+  tseslint.configs.eslintRecommended,
+  tseslint.configs.recommended,
+  reactHooks.configs["recommended-latest"],
+  importPlugin.flatConfigs.recommended,
+  importPlugin.flatConfigs.typescript,
+  {
+    ...react.configs.flat.recommended,
+    ...react.configs.flat["jsx-runtime"],
+    files: ["**/*.{js,mjs,cjs,jsx,mjsx,ts,tsx,mtsx}"],
+    languageOptions: {
+      ...react.configs.flat.recommended.languageOptions,
+      ecmaVersion: "latest",
+      sourceType: "module",
+    },
+    rules: {
+      eqeqeq: [
+        "error",
+        "always",
+        {
+          null: "never",
+        },
+      ],
+      "@typescript-eslint/no-explicit-any": "off",
+    },
+  },
+  {
+    ignores: ["src/pkg/**"],
+  },
+);

playground/package.json

@@ -25,20 +25,20 @@
     "smol-toml": "^1.3.0"
   },
   "devDependencies": {
+    "@eslint/js": "^9.21.0",
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
-    "@typescript-eslint/eslint-plugin": "^8.0.0",
-    "@typescript-eslint/parser": "^8.0.0",
     "@vitejs/plugin-react-swc": "^3.0.0",
     "autoprefixer": "^10.4.13",
-    "eslint": "^8.30.0",
+    "eslint": "^9.0.0",
-    "eslint-plugin-import": "^2.29.1",
+    "eslint-plugin-import": "^2.31.0",
     "eslint-plugin-react": "^7.31.11",
-    "eslint-plugin-react-hooks": "^5.0.0",
+    "eslint-plugin-react-hooks": "^5.2.0",
     "postcss": "^8.4.20",
     "prettier": "^3.0.0",
     "tailwindcss": "^3.2.4",
     "typescript": "^5.1.6",
+    "typescript-eslint": "^8.25.0",
     "vite": "^6.0.0"
   },
   "overrides": {