Continue ESLint upgrade to V9

.changeset/sweet-tables-worry.md

@@ -0,0 +1,10 @@
+---
+'eslint-plugin-primer-react': minor
+---
+
+Add support for ESLint v9
+
+- Adds flat config support
+- Adds meta information to config object
+- Backwards compatibility with v8
+- Updates README with usage example for flat config

.markdownlint-cli2.cjs

@@ -16,11 +16,11 @@ const options = githubMarkdownOpinions.init({
   'no-hard-tabs': false,
   'first-line-heading': false,
   'no-space-in-emphasis': false,
-  'blanks-around-fences': false
+  'blanks-around-fences': false,
 })
 
 module.exports = {
   config: options,
   customRules: ['@github/markdownlint-github'],
-  outputFormatters: [['markdownlint-cli2-formatter-pretty', {appendLink: true}]]
+  outputFormatters: [['markdownlint-cli2-formatter-pretty', {appendLink: true}]],
 }

README.md

@@ -6,28 +6,48 @@ ESLint rules for Primer React
 
 ## Installation
 
-1. Assuming you already have [ESLint](https://www.npmjs.com/package/eslint) and
-   [Primer React](https://github.com/primer/react) installed, run:
+Assuming you already have [ESLint](https://www.npmjs.com/package/eslint) and [Primer React](https://github.com/primer/react) installed, run:
 
-   ```shell
-   npm install --save-dev eslint-plugin-primer-react
+```shell
+npm install --save-dev eslint-plugin-primer-react
 
-   # or
+# or
 
-   yarn add --dev eslint-plugin-primer-react
-   ```
+yarn add --dev eslint-plugin-primer-react
+```
 
-2. In your [ESLint configuration file](https://eslint.org/docs/user-guide/configuring/configuration-files), extend the
-   recommended Primer React ESLint config:
+## Setup
 
-   ```js
-   {
-     "extends": [
-       // ...
-       "plugin:primer-react/recommended"
-     ]
-   }
-   ```
+### Flat Configuration (`eslint.config.js`)
+
+In your [`eslint.config`](https://eslint.org/docs/user-guide/configuring/configuration-files) file, import `eslint-plugin-primer-react` and extend the recommended configuration using `getFlatConfigs()`:
+
+```js
+import pluginPrimerReact from 'eslint-plugin-primer-react'
+
+export default [
+  pluginPrimerReact.getFlatConfigs().recommended,
+  {
+    rules: {
+      'primer-react/no-system-props': 'error',
+      // other custom rules...
+    },
+  },
+]
+```
+
+### Legacy Configuration (`.eslintrc.js`)
+
+In your [`.eslintrc`](https://eslint.org/docs/latest/use/configure/configuration-files-deprecated) file, extend the recommended Primer React ESLint config:
+
+```js
+{
+  "extends": [
+    // ...
+    "plugin:primer-react/recommended"
+  ]
+}
+```
 
 ## Rules
 

eslint.config.js

@@ -0,0 +1,48 @@
+const eslintJs = require('@eslint/js')
+const github = require('eslint-plugin-github')
+const globals = require('globals')
+const pluginJest = require('eslint-plugin-jest')
+
+module.exports = [
+  github.getFlatConfigs().recommended,
+  eslintJs.configs.recommended,
+  {
+    languageOptions: {
+      parserOptions: {
+        ecmaVersion: 'latest',
+      },
+      globals: {
+        ...globals.commonjs,
+        ...globals.node,
+      },
+    },
+    rules: {
+      'import/no-commonjs': 'off',
+      'no-shadow': 'off',
+      'no-unused-vars': [
+        'error',
+        {
+          varsIgnorePattern: '^_',
+        },
+      ],
+    },
+    ignores: ['**/dist/**', '**/node_modules/**'],
+  },
+  {
+    files: ['**/*.test.js'],
+    languageOptions: {
+      globals: {
+        ...pluginJest.environments.globals.globals,
+      },
+    },
+    rules: {
+      'i18n-text/no-en': 'off',
+    },
+  },
+  {
+    files: ['.markdownlint-cli2.cjs'],
+    rules: {
+      'github/filenames-match-regex': 'off',
+    },
+  },
+]