chore: use eslint v9 with flat config

eslint.config.mjs

@@ -0,0 +1,30 @@
+import eslint from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import prettierPluginRecommended from 'eslint-plugin-prettier/recommended'
+
+export default [
+  {
+    ignores: ['docs/.vitepress', 'coverage', 'dist']
+  },
+  ...tseslint.config({
+    extends: [
+      eslint.configs.recommended,
+      ...tseslint.configs.recommended,
+      prettierPluginRecommended
+    ],
+    rules: {
+      'prettier/prettier': ['error'],
+      'no-restricted-imports': [
+        'error',
+        {
+          patterns: ['src/*']
+        }
+      ],
+
+      // Currently, disabled to avoid a lot of changes during migration
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unused-vars': 'off',
+      '@typescript-eslint/ban-ts-comment': 'off'
+    }
+  })
+]

examples/TodoApp.spec.js

@@ -4,6 +4,7 @@
  * yarn build. Then you can run this with `yarn test examples`
  */
 import { mount } from '../dist/vue-test-utils.cjs.js'
+import { test, expect } from 'vitest'
 
 import TodoApp from './TodoApp.vue'
 

package.json

@@ -41,7 +41,7 @@
     "@vue/compiler-dom": "3.4.35",
     "@vue/compiler-sfc": "3.4.35",
     "@vue/server-renderer": "3.4.35",
-    "eslint": "8.57.0",
+    "eslint": "9.8.0",
     "eslint-config-prettier": "9.1.0",
     "eslint-plugin-prettier": "5.2.1",
     "husky": "9.1.4",
@@ -77,7 +77,7 @@
     "tsd": "tsc -p test-dts/tsconfig.tsd.json",
     "build": "rollup -c rollup.config.ts --bundleConfigAsCjs",
     "prepare": "rollup -c rollup.config.ts --bundleConfigAsCjs",
-    "lint": "eslint --ext .ts src/ tests/",
+    "lint": "eslint .",
     "lint:fix": "pnpm run lint --fix",
     "docs:dev": "vitepress dev docs",
     "docs:build": "vitepress build docs",