Migrate ESLint config to Flat config

CHANGELOG.md

@@ -47,6 +47,7 @@
 * Upgrade development Node.js to v20 LTS ([#359](https://github.com/marp-team/marp-core/pull/359))
 * Upgrade dependent packages to the latest version ([#380](https://github.com/marp-team/marp-core/pull/380))
 * Switch package manager from yarn to npm ([#379](https://github.com/marp-team/marp-core/pull/379))
+* Migrate ESLint config to Flat config ([#385](https://github.com/marp-team/marp-core/pull/385))
 
 ### Fixed
 

eslint.config.mjs

@@ -0,0 +1,60 @@
+import js from '@eslint/js'
+import eslintConfigPrettier from 'eslint-config-prettier'
+import eslintPluginImportX from 'eslint-plugin-import-x'
+import eslintPluginJest from 'eslint-plugin-jest'
+import globals from 'globals'
+import tseslint from 'typescript-eslint'
+
+const tsFiles = ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts']
+const testFiles = ['test/**']
+const forFiles = (files, confs) => confs.map((conf) => ({ ...conf, files }))
+
+export default tseslint.config(
+  js.configs.recommended,
+  eslintPluginImportX.flatConfigs.recommended,
+  ...forFiles(tsFiles, [
+    ...tseslint.configs.recommended,
+    eslintPluginImportX.flatConfigs.typescript,
+    {
+      rules: {
+        '@typescript-eslint/no-explicit-any': 'off',
+        '@typescript-eslint/explicit-function-return-type': 'off',
+        '@typescript-eslint/explicit-module-boundary-types': 'off',
+      },
+    },
+  ]),
+  ...forFiles(testFiles, [
+    eslintPluginJest.configs['flat/recommended'],
+    eslintPluginJest.configs['flat/style'],
+  ]),
+  eslintConfigPrettier,
+  {
+    linterOptions: {
+      reportUnusedDisableDirectives: 'error',
+    },
+    languageOptions: {
+      ecmaVersion: 'latest',
+      globals: {
+        ...globals.node,
+        ...globals.browser,
+      },
+    },
+    rules: {
+      'import-x/order': ['error', { alphabetize: { order: 'asc' } }],
+    },
+    settings: {
+      'import-x/resolver': 'typescript',
+    },
+  },
+  {
+    ignores: [
+      'browser.d.ts',
+      'coverage/**/*',
+      'lib/**/*',
+      'node_modules/**/*',
+      'sandbox/**/*',
+      'tmp/**/*',
+      'types/**/*',
+    ],
+  },
+)