feat: add flat recommended config

recommended.js is a flat config version of the recommended config.

This diverges from the legacy config version of the recommended config
as it does not automatically configure eslint-config-prettier.

Configs extending other configs is complicated and not transparent. We
should trust the user to configure their configs directly. In a future
major change we should remove eslint-config-prettier from the legacy
config too.

eslint.config.js

@@ -4,7 +4,7 @@ const eslintPluginEslintComments = require('@eslint-community/eslint-plugin-esli
 const eslintPluginEslintPluginRecommended = require('eslint-plugin-eslint-plugin/configs/recommended');
 const eslintPluginMdx = require('eslint-plugin-mdx');
 const eslintConfigPrettier = require('eslint-config-prettier');
-const eslintPluginPrettier = require('./eslint-plugin-prettier');
+const eslintPluginPrettierRecommended = require('./recommended');
 
 module.exports = [
   eslintConfigs.recommended,
@@ -21,11 +21,7 @@ module.exports = [
   eslintPluginMdx.flat,
   eslintPluginMdx.flatCodeBlocks,
   eslintConfigPrettier,
-  // No built-in flat recommended config yet
-  {
-    plugins: { prettier: eslintPluginPrettier },
-    rules: eslintPluginPrettier.configs.recommended.rules,
-  },
+  eslintPluginPrettierRecommended,
   {
     rules: {
       'eslint-plugin/report-message-format': ['error', '^[^a-z].*\\.$'],

package.json

@@ -19,6 +19,8 @@
   "files": [
     "eslint-plugin-prettier.d.ts",
     "eslint-plugin-prettier.js",
+    "recommended.d.ts",
+    "recommended.js",
     "worker.js"
   ],
   "keywords": [

recommended.d.ts

@@ -0,0 +1,5 @@
+import { Linter } from 'eslint';
+
+declare const recommendedConfig: Linter.FlatConfig;
+
+export = recommendedConfig;

recommended.js

@@ -0,0 +1,15 @@
+const eslintPluginPrettier = require('./eslint-plugin-prettier');
+
+// This diverges from the legacy format recommended config, as it does not
+// extend from the `eslint-config-prettier` ruleset. When using the flat config
+// the consumer should add eslint-config-prettier to their own root config.
+module.exports = {
+  plugins: {
+    prettier: eslintPluginPrettier,
+  },
+  rules: {
+    'prettier/prettier': 'error',
+    'arrow-body-style': 'off',
+    'prefer-arrow-callback': 'off',
+  },
+};