Convert base config to flat config format

eslint.config.mjs

@@ -1,19 +1,34 @@
 // @ts-check
 
+// @ts-expect-error - `@babel/eslint-parser` doesn't have TypeScript types.
+import babel from '@babel/eslint-parser';
+import baseConfigs from '@metamask/eslint-config';
+
 /**
  * @type {import('eslint').Linter.Config[]}
  */
 const config = [
+  ...baseConfigs,
   // TODO:
   // extends: [
-  //   '@metamask/eslint-config',
   //   '@metamask/eslint-config-nodejs',
   //   '@metamask/eslint-config-jest',
   // ],
 
   {
+    name: 'main',
     languageOptions: {
       ecmaVersion: 2022,
+
+      sourceType: 'module',
+
+      parser: babel,
+      parserOptions: {
+        requireConfigFile: false,
+        babelOptions: {
+          plugins: ['@babel/plugin-syntax-import-attributes'],
+        },
+      },
     },
 
     rules: {
@@ -26,7 +41,7 @@ const config = [
     },
 
     ignores: ['!.eslint.config.mjs'],
-  }
+  },
 ];
 
 export default config;

package.json

@@ -20,7 +20,11 @@
     "test": "jest"
   },
   "devDependencies": {
+    "@babel/core": "^7.25.2",
+    "@babel/eslint-parser": "^7.25.1",
+    "@babel/plugin-syntax-import-attributes": "^7.25.6",
     "@eslint/js": "^9.11.0",
+    "@jest/globals": "^29.7.0",
     "@lavamoat/allow-scripts": "^3.0.4",
     "@metamask/auto-changelog": "^3.4.4",
     "@metamask/eslint-config": "^13.0.0",

packages/base/package.json

@@ -10,8 +10,18 @@
     "type": "git",
     "url": "https://github.com/MetaMask/eslint-config.git"
   },
+  "type": "module",
   "license": "MIT",
-  "main": "src/index.js",
+  "main": "./src/index.mjs",
+  "types": "./src/index.d.mts",
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./src/index.d.mts",
+        "default": "./src/index.mjs"
+      }
+    }
+  },
   "files": [
     "src/",
     "!src/**/*.test.js"
@@ -22,6 +32,7 @@
     "test": "eslint ."
   },
   "devDependencies": {
+    "@jest/globals": "^29.7.0",
     "@metamask/auto-changelog": "^3.4.4",
     "eslint": "^9.11.0",
     "eslint-config-prettier": "^9.1.0",
@@ -46,5 +57,9 @@
   "publishConfig": {
     "access": "public",
     "registry": "https://registry.npmjs.org/"
+  },
+  "dependencies": {
+    "@eslint/js": "^9.11.0",
+    "globals": "^15.9.0"
   }
 }

packages/base/src/index.d.mts

@@ -0,0 +1,6 @@
+declare module '@metamask/eslint-config' {
+  import { Linter } from 'eslint';
+
+  const config: Linter.Config[];
+  export default config;
+}