Set up a monorepo with Lerna

packages/react-scripts/scripts/utils/checkRequiredFiles.js

@@ -0,0 +1,33 @@
+// @remove-on-eject-begin
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+// @remove-on-eject-end
+
+const fs = require('fs');
+const path = require('path');
+const chalk = require('chalk');
+const paths = require('../../config/paths');
+
+function checkRequiredFiles() {
+  const filesPathToCheck = [paths.appHtml, paths.appIndexJs];
+  filesPathToCheck.forEach(filePath => {
+    try {
+      fs.accessSync(filePath, fs.F_OK);
+    } catch (err) {
+      const dirName = path.dirname(filePath);
+      const fileName = path.basename(filePath);
+      console.log(chalk.red('Could not find a required file.'));
+      console.log(chalk.red('  Name: ') + chalk.cyan(fileName));
+      console.log(chalk.red('  Searched in: ') + chalk.cyan(dirName));
+      process.exit(1);
+    }
+  });
+}
+
+module.exports = checkRequiredFiles;