feat!: support ESLint 9 flat config

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 package-lock.json
+dist

.prettierrc.json

@@ -0,0 +1,5 @@
+{
+  "semi": false,
+  "singleQuote": true,
+  "arrowParens": "avoid"
+}

README.md

@@ -1,75 +1,120 @@
 # @vue/eslint-config-typescript
 
-> eslint-config-typescript for Vue
+ESLint configuration for Vue 3 + TypeScript projects.
 
 See [@typescript-eslint/eslint-plugin](https://typescript-eslint.io/rules/) for available rules.
 
-This config is specifically designed to be used by `@vue/cli` & `create-vue` setups
+This config is specifically designed to be used by `create-vue` setups
 and is not meant for outside use (it can be used but some adaptations
 on the user side might be needed - for details see the config file).
 
 A part of its design is that this config may implicitly depend on
-other parts of `@vue/cli`/`create-vue` setups, such as `eslint-plugin-vue` being
+other parts of `create-vue` setups, such as `eslint-plugin-vue` being
 extended in the same resulting config.
 
-## Installation
+> [!NOTE]
+> The current version doesn't support the legacy `.eslintrc*` configuraion format. For that you need to use version 13 or earlier. See the [corresponding README](https://www.npmjs.com/package/@vue/eslint-config-typescript/v/legacy-eslintrc) for more usage instructions.
 
-In order to work around [a known limitation in ESLint](https://github.com/eslint/eslint/issues/3458), we recommend you to use this package alongside `@rushstack/eslint-patch`, so that you don't have to install too many dependencies:
+## Installation
 
 ```sh
-npm add --dev @vue/eslint-config-typescript @rushstack/eslint-patch
+npm add --dev @vue/eslint-config-typescript
 ```
 
-## Usage
+Please also make sure that you have `typescript` and `eslint` installed.
 
-This package comes with 2 rulesets.
-
-### `@vue/eslint-config-typescript`
+## Usage
 
-This ruleset is the base configuration for Vue-TypeScript projects.
-Besides setting the parser and plugin options, it also turns off several conflicting rules in the `eslint:recommended` ruleset.
-So when used alongside other sharable configs, this config should be placed at the end of the `extends` array.
+Because of the complexity of this config, it is exported as a factory function that takes an options object and returns an ESLint configuration object.
 
-An example `.eslintrc.cjs`:
+### Minimal Setup
 
 ```js
-/* eslint-env node */
-require("@rushstack/eslint-patch/modern-module-resolution")
-
-module.exports = {
-  extends: [
-    'eslint:recommended',
-    'plugin:vue/vue3-essential',
-    '@vue/eslint-config-typescript'
-  ]
-}
+// eslint.config.mjs
+import pluginVue from "eslint-plugin-vue";
+import vueTsEslintConfig from "@vue/eslint-config-typescript";
+
+export default [
+  ...pluginVue.configs["flat/essential"],
+  ...vueTsEslintConfig(),
+]
 ```
 
-### `@vue/eslint-config-typescript/recommended`
+The above configuration enables [the essential rules for Vue 3](https://eslint.vuejs.org/rules/#priority-a-essential-error-prevention) and [the recommended rules for TypeScript](https://typescript-eslint.io/rules/?=recommended).
 
-This is extended from the `@typescript-eslint/recommended` ruleset, which is an **_opinionated_** ruleset.
-See the [original documentation](https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/eslint-plugin/src/configs#recommended) for more information.
+All the `<script>` blocks in `.vue` files *MUST* be written in TypeScript (should be either `<script setup lang="ts">` or `<script lang="ts">`).
 
-Some of its rules, however, might conflict with `prettier`.
-So when used alongside other sharable configs, this config should be placed after all other configs except for the one from `@vue/eslint-config-prettier` or `eslint-plugin-prettier` in the `extends` array.
-
-An example `.eslintrc.cjs`:
+### Advanced Setup
 
 ```js
-/* eslint-env node */
-require("@rushstack/eslint-patch/modern-module-resolution")
-
-module.exports = {
-  extends: [
-    'plugin:vue/vue3-essential',
-    '@vue/eslint-config-typescript/recommended',
-    '@vue/eslint-config-prettier'
-  ]
-}
+// eslint.config.mjs
+import pluginVue from "eslint-plugin-vue";
+import vueTsEslintConfig from "@vue/eslint-config-typescript";
+
+export default [
+  ...pluginVue.configs["flat/essential"],
+
+  ...vueTsEslintConfig({
+    // Optional: extend additional configurations from `typescript-eslint`.
+    // Supports all the configurations in https://typescript-eslint.io/users/configs#recommended-configurations
+    extends: [
+      // By default, only the recommended rules are enabled.
+      "recommended",
+      // You can also manually enable the stylistic rules.
+      // "stylistic",
+
+      // [!NOTE] The ones with `-type-checked` are not yet tested.
+
+      // Other utility configurations, such as `eslint-recommended`,
+      // are also extendable here. But we don't recommend using them directly.
+    ],
+
+    // Optional: specify the script langs in `.vue` files
+    // Defaults to `{ ts: true, js: false, tsx: false, jsx: false }`
+    supportedScriptLangs: {
+      ts: true,
+
+      // [!DISCOURAGED]
+      // Set to `true` to allow plain `<script>` or `<script setup>` blocks.
+      // This might result-in false positive or negatives in some rules for `.vue` files.
+      // Note you also need to configure `allowJs: true` and `checkJs: true`
+      // in corresponding `tsconfig.json` files.
+      js: false,
+
+      // [!STRONGLY DISCOURAGED]
+      // Set to `true` to allow `<script lang="tsx">` blocks.
+      // This would be in conflict with all type-aware rules.
+      tsx: false,
+
+      // [!STRONGLY DISCOURAGED]
+      // Set to `true` to allow `<script lang="jsx">` blocks.
+      // This would be in conflict with all type-aware rules and may result in false positives.
+      jsx: false,
+    },
+
+    // [!NOT YET IMPLEMENTED]
+    // <https://github.com/vuejs/eslint-plugin-vue/issues/1910#issuecomment-1819993961>
+    // Optional: the root directory to resolve the `.vue` files, defaults to `process.cwd()`.
+    // 
+    // This is useful when you allow any other languages than `ts` in `.vue` files.
+    // Our config helper would resolve and parse all the `.vue` files under `rootDir`,
+    // and only apply the loosened rules to the files that do need them.
+    // 
+    // rootDir: __dirname,
+  })
+]
 ```
 
+## Further Reading
+
+TODO
+
 ### With Other Community Configs
 
 Work-In-Progress.
 
 ~~If you are following the [`standard`](https://standardjs.com/) or [`airbnb`](https://github.com/airbnb/javascript/) style guides, don't manually extend from this package. Please use `@vue/eslint-config-standard-with-typescript` or `@vue/eslint-config-airbnb-with-typescript` instead.~~
+
+## Migrating from `.eslintrc.cjs`
+
+TODO

examples/allow-js/.gitignore

@@ -0,0 +1,30 @@
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+node_modules
+.DS_Store
+dist
+dist-ssr
+coverage
+*.local
+
+/cypress/videos/
+/cypress/screenshots/
+
+# Editor directories and files
+.vscode/*
+!.vscode/extensions.json
+.idea
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?
+
+*.tsbuildinfo

examples/allow-js/.vscode/extensions.json

@@ -0,0 +1,6 @@
+{
+  "recommendations": [
+    "Vue.volar",
+    "dbaeumer.vscode-eslint"
+  ]
+}

examples/allow-js/README.md

@@ -0,0 +1,39 @@
+# allow-js
+
+This template should help get you started developing with Vue 3 in Vite.
+
+## Recommended IDE Setup
+
+[VSCode](https://code.visualstudio.com/) + [Volar](https://marketplace.visualstudio.com/items?itemName=Vue.volar) (and disable Vetur).
+
+## Type Support for `.vue` Imports in TS
+
+TypeScript cannot handle type information for `.vue` imports by default, so we replace the `tsc` CLI with `vue-tsc` for type checking. In editors, we need [Volar](https://marketplace.visualstudio.com/items?itemName=Vue.volar) to make the TypeScript language service aware of `.vue` types.
+
+## Customize configuration
+
+See [Vite Configuration Reference](https://vitejs.dev/config/).
+
+## Project Setup
+
+```sh
+npm install
+```
+
+### Compile and Hot-Reload for Development
+
+```sh
+npm run dev
+```
+
+### Type-Check, Compile and Minify for Production
+
+```sh
+npm run build
+```
+
+### Lint with [ESLint](https://eslint.org/)
+
+```sh
+npm run lint
+```

examples/allow-js/env.d.ts

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+/// <reference types="vite/client" />

examples/allow-js/eslint.config.js

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+import pluginVue from "eslint-plugin-vue";
+import vueTsEslintConfig from "@vue/eslint-config-typescript";
+
+export default [
+  {
+    name: 'app/files-to-lint',
+    files: ['**/*.js', '**/*.mjs', '**/*.ts', '**/*.mts', '**/*.vue'],
+    ignores: ['**/dist/**'],
+  },
+
+  ...pluginVue.configs["flat/essential"],
+  ...vueTsEslintConfig({
+    supportedScriptLangs: {
+      ts: true,
+      js: true
+    }
+  }),
+]

examples/allow-js/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8">
+    <link rel="icon" href="/favicon.ico">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Vite App</title>
+  </head>
+  <body>
+    <div id="app"></div>
+    <script type="module" src="/src/main.ts"></script>
+  </body>
+</html>

examples/allow-js/package.json

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+{
+  "name": "allow-js",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "run-p type-check \"build-only {@}\" --",
+    "preview": "vite preview",
+    "build-only": "vite build",
+    "type-check": "vue-tsc --build --force",
+    "lint": "eslint . --fix"
+  },
+  "dependencies": {
+    "vue": "^3.5.6"
+  },
+  "devDependencies": {
+    "@tsconfig/node20": "^20.1.4",
+    "@types/node": "^20.16.5",
+    "@vitejs/plugin-vue": "^5.1.4",
+    "@vue/eslint-config-typescript": "workspace:*",
+    "@vue/tsconfig": "^0.5.1",
+    "eslint": "^9.10.0",
+    "eslint-plugin-vue": "^9.28.0",
+    "npm-run-all2": "^6.2.3",
+    "typescript": "~5.5.4",
+    "vite": "^5.4.6",
+    "vue-tsc": "^2.1.6"
+  }
+}

examples/allow-js/src/App.vue

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+<script setup>
+import HelloWorld from './components/HelloWorld.vue'
+import TheWelcome from './components/TheWelcome.vue'
+
+</script>
+
+<template>
+  <header>
+    <img alt="Vue logo" class="logo" src="./assets/logo.svg" width="125" height="125" />
+
+    <div class="wrapper">
+      <HelloWorld msg="You did it!" />
+    </div>
+  </header>
+
+  <main>
+    <TheWelcome />
+  </main>
+</template>
+
+<style scoped>
+header {
+  line-height: 1.5;
+}
+
+.logo {
+  display: block;
+  margin: 0 auto 2rem;
+}
+
+@media (min-width: 1024px) {
+  header {
+    display: flex;
+    place-items: center;
+    padding-right: calc(var(--section-gap) / 2);
+  }
+
+  .logo {
+    margin: 0 2rem 0 0;
+  }
+
+  header .wrapper {
+    display: flex;
+    place-items: flex-start;
+    flex-wrap: wrap;
+  }
+}
+</style>