Rewrite .eslintrc.es5.js to new config format

[MAILPOET-5015]

mailpoet/eslint.config.js

@@ -0,0 +1,11 @@
+const es5Config = require('@mailpoet/eslint-config/eslint-es5.config');
+
+module.exports = [
+  {
+    ignores: ['assets/js/src/vendor/**'],
+  },
+  ...es5Config.map((config) => ({
+    ...config,
+    files: ['assets/js/src/**/*.js'],
+  })),
+];

mailpoet/package.json

@@ -4,11 +4,10 @@
     "extends @wordpress/browserslist-config"
   ],
   "scripts": {
-    "lint": "pnpm run lint6 && pnpm run lint-ts && pnpm run lint5 && pnpm run lint-tests",
+    "lint": "eslint --max-warnings 0 'assets/js/src/**' && pnpm run lint6 && pnpm run lint-ts && pnpm run lint-tests",
-    "lint6": "eslint -c ../packages/js/eslint-config/.eslintrc.es6.js --max-warnings 0 'assets/js/src/**/*.jsx' 'tests/javascript/**/*.js'",
+    "lint6": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.es6.js --max-warnings 0 'assets/js/src/**/*.jsx' 'tests/javascript/**/*.js'",
-    "lint-ts": "eslint -c ../packages/js/eslint-config/.eslintrc.ts.js --max-warnings 0 'assets/js/src/**/*.tsx' 'assets/js/src/**/*.ts'",
+    "lint-ts": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.ts.js --max-warnings 0 'assets/js/src/**/*.tsx' 'assets/js/src/**/*.ts'",
-    "lint5": "eslint -c ../packages/js/eslint-config/.eslintrc.es5.js --max-warnings 0 'assets/js/src/**/*.js' 'webpack.config.js'",
+    "lint-tests": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.tests_newsletter_editor.js --max-warnings 0 'tests/javascript_newsletter_editor'",
-    "lint-tests": "eslint -c ../packages/js/eslint-config/.eslintrc.tests_newsletter_editor.js --max-warnings 0 'tests/javascript_newsletter_editor'",
     "autoprefixer": "postcss assets/dist/css/*.css --use autoprefixer --no-map --replace",
     "scss": "sass assets/css/src/:assets/dist/css/ --style compressed",
     "stylelint": "stylelint --fix",
@@ -22,10 +21,10 @@
   },
   "lint-staged": {
     "*.{scss,css}": "pnpm run stylelint",
-    "!(*spec).js": "eslint -c ../packages/js/eslint-config/.eslintrc.es5.js --max-warnings 0",
+    "!(*spec).js": "eslint --max-warnings 0",
-    "*.jsx": "eslint -c ../packages/js/eslint-config/.eslintrc.es6.js --max-warnings 0",
+    "*.jsx": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.es6.js --max-warnings 0",
-    "*.{tsx,ts}": "eslint -c ../packages/js/eslint-config/.eslintrc.ts.js --max-warnings 0",
+    "*.{tsx,ts}": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.ts.js --max-warnings 0",
-    "**/newsletter_editor/**/*spec.js": "eslint -c ../packages/js/eslint-config/.eslintrc.tests_newsletter_editor.js --max-warnings 0",
+    "**/newsletter_editor/**/*spec.js": "ESLINT_USE_FLAT_CONFIG=false eslint -c ../packages/js/eslint-config/.eslintrc.tests_newsletter_editor.js --max-warnings 0",
     "*.php": [
       "phplint",
       "./do qa:code-sniffer",

packages/js/eslint-config/.eslintrc.es5.js

@@ -1,18 +0,0 @@
-module.exports = {
-  extends: ['airbnb/legacy', 'prettier'],
-  env: {
-    amd: true,
-    browser: true,
-  },
-  plugins: ['eslint-plugin-import'],
-  parser: '@babel/eslint-parser',
-  parserOptions: {
-    ecmaVersion: 6,
-    sourceType: 'module',
-  },
-  rules: {
-    'import/prefer-default-export': 0, // we want to stop using default exports and start using named exports
-    'no-underscore-dangle': 0, // Backbone uses underscores, we cannot remove them
-    'import/no-default-export': 1, // no default exports
-  },
-};

packages/js/eslint-config/eslint-es5.config.js

@@ -0,0 +1,36 @@
+const babelParser = require('@babel/eslint-parser');
+const FlatCompat = require('@eslint/eslintrc').FlatCompat;
+const airbnbLegacyConfig = require('eslint-config-airbnb/legacy');
+const prettierConfig = require('eslint-config-prettier');
+const importPlugin = require('eslint-plugin-import');
+const globals = require('globals');
+
+// compat configs
+const compat = new FlatCompat({ baseDirectory: __dirname });
+const airbnbLegacyCompatConfig = compat.config(airbnbLegacyConfig);
+const prettierCompatConfig = compat.config(prettierConfig);
+
+module.exports = [
+  ...airbnbLegacyCompatConfig,
+  ...prettierCompatConfig,
+  {
+    languageOptions: {
+      parser: babelParser,
+      parserOptions: {
+        ecmaVersion: 6,
+        sourceType: 'module',
+      },
+      globals: {
+        ...globals.browser,
+      },
+    },
+    plugins: {
+      import: importPlugin,
+    },
+    rules: {
+      'import/prefer-default-export': 0, // we want to stop using default exports and start using named exports
+      'no-underscore-dangle': 0, // Backbone uses underscores, we cannot remove them
+      'import/no-default-export': 1, // no default exports
+    },
+  },
+];