feat: add support for Flat Config

This change adds support for ESLint's new Flat config system.  It maintains backwards compatibility with eslintrc
style configs as well.

To achieve this, we're now dynamically creating flat configs on a new `flatConfigs` export.

Usage

```js
import importPlugin from 'eslint-plugin-import';
import js from '@eslint/js';
import tsParser from '@typescript-eslint/parser';

export default [
  js.configs.recommended,
  importPlugin.flatConfigs.recommended,
  importPlugin.flatConfigs.react,
  importPlugin.flatConfigs.typescript,
  {
    files: ['**/*.{js,mjs,cjs,jsx,mjsx,ts,tsx,mtsx}'],
    languageOptions: {
      parser: tsParser,
      ecmaVersion: 'latest',
      sourceType: 'module',
    },
    ignores: ['eslint.config.js'],
    rules: {
      'no-unused-vars': 'off',
      'import/no-dynamic-require': 'warn',
      'import/no-nodejs-modules': 'warn',
    },
  },
];
```

Author: michaelfaith

.editorconfig

@@ -7,3 +7,4 @@ insert_final_newline = true
 indent_style = space
 indent_size = 2
 end_of_line = lf
+quote_type = single

README.md

@@ -106,6 +106,8 @@ The maintainers of `eslint-plugin-import` and thousands of other packages are wo
 npm install eslint-plugin-import --save-dev
 ```
 
+### Config - Legacy (`.eslintrc`)
+
 All rules are off by default. However, you may configure them manually
 in your `.eslintrc.(yml|json|js)`, or extend one of the canned configs:
 
@@ -123,14 +125,41 @@ plugins:
   - import
 
 rules:
-  import/no-unresolved: [2, {commonjs: true, amd: true}]
+  import/no-unresolved: [2, { commonjs: true, amd: true }]
   import/named: 2
   import/namespace: 2
   import/default: 2
   import/export: 2
   # etc...
 ```
 
+### Config - Flat (`eslint.config.js`)
+
+All rules are off by default. However, you may configure them manually
+in your `eslint.config.(js|cjs|mjs)`, or extend one of the canned configs:
+
+```js
+import importPlugin from 'eslint-plugin-import';
+import js from '@eslint/js';
+
+export default [
+  js.configs.recommended,
+  importPlugin.flatConfigs.recommended,
+  {
+    files: ['**/*.{js,mjs,cjs}'],
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+    },
+    rules: {
+      'no-unused-vars': 'off',
+      'import/no-dynamic-require': 'warn',
+      'import/no-nodejs-modules': 'warn',
+    },
+  },
+];
+```
+
 ## TypeScript
 
 You may use the following snippet or assemble your own config using the granular settings described below it.

config/flat/errors.js

@@ -0,0 +1,14 @@
+/**
+ * unopinionated config. just the things that are necessarily runtime errors
+ * waiting to happen.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    'import/no-unresolved': 2,
+    'import/named': 2,
+    'import/namespace': 2,
+    'import/default': 2,
+    'import/export': 2,
+  },
+};

config/flat/react.js

@@ -0,0 +1,19 @@
+/**
+ * Adds `.jsx` as an extension, and enables JSX parsing.
+ *
+ * Even if _you_ aren't using JSX (or .jsx) directly, if your dependencies
+ * define jsnext:main and have JSX internally, you may run into problems
+ * if you don't enable these settings at the top level.
+ */
+module.exports = {
+  settings: {
+    'import/extensions': ['.js', '.jsx'],
+  },
+  languageOptions: {
+    parserOptions: {
+      ecmaFeatures: {
+        jsx: true,
+      },
+    },
+  },
+};

config/flat/recommended.js

@@ -0,0 +1,26 @@
+/**
+ * The basics.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    // analysis/correctness
+    'import/no-unresolved': 'error',
+    'import/named': 'error',
+    'import/namespace': 'error',
+    'import/default': 'error',
+    'import/export': 'error',
+
+    // red flags (thus, warnings)
+    'import/no-named-as-default': 'warn',
+    'import/no-named-as-default-member': 'warn',
+    'import/no-duplicates': 'warn',
+  },
+
+  // need all these for parsing dependencies (even if _your_ code doesn't need
+  // all of them)
+  languageOptions: {
+    ecmaVersion: 2018,
+    sourceType: 'module',
+  },
+};

config/flat/stage-0.js

@@ -0,0 +1,11 @@
+/**
+ * Rules in progress.
+ *
+ * Do not expect these to adhere to semver across releases.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    'import/no-deprecated': 1,
+  },
+};

config/flat/warnings.js

@@ -0,0 +1,11 @@
+/**
+ * more opinionated config.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    'import/no-named-as-default': 1,
+    'import/no-named-as-default-member': 1,
+    'import/no-duplicates': 1,
+  },
+};

examples/flat/eslint.config.mjs

@@ -0,0 +1,24 @@
+import importPlugin from 'eslint-plugin-import';
+import js from '@eslint/js';
+import tsParser from '@typescript-eslint/parser';
+
+export default [
+  js.configs.recommended,
+  importPlugin.flatConfigs.recommended,
+  importPlugin.flatConfigs.react,
+  importPlugin.flatConfigs.typescript,
+  {
+    files: ['**/*.{js,mjs,cjs,jsx,mjsx,ts,tsx,mtsx}'],
+    languageOptions: {
+      parser: tsParser,
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+    },
+    ignores: ['eslint.config.js'],
+    rules: {
+      'no-unused-vars': 'off',
+      'import/no-dynamic-require': 'warn',
+      'import/no-nodejs-modules': 'warn',
+    },
+  },
+];

examples/flat/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "flat",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "lint": "cross-env ESLINT_USE_FLAT_CONFIG=true eslint src --report-unused-disable-directives"
+  },
+  "devDependencies": {
+    "@eslint/js": "^9.5.0",
+    "@types/node": "^20.14.5",
+    "@typescript-eslint/parser": "^7.13.1",
+    "cross-env": "^7.0.3",
+    "eslint": "^8.57.0",
+    "eslint-plugin-import": "file:../..",
+    "typescript": "^5.4.5"
+  }
+}

examples/flat/src/exports.ts

@@ -0,0 +1,12 @@
+export type ScalarType = string | number;
+export type ObjType = {
+  a: ScalarType;
+  b: ScalarType;
+};
+
+export const a = 13;
+export const b = 18;
+
+const defaultExport: ObjType = { a, b };
+
+export default defaultExport;