Reorganise shared script utils (#52473)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52473

Shared utils that were located in the root of `scripts/` are now colocated closer to their dependencies or moved to `scripts/shared/` — simplifying the root directory layout.

Changelog: [Internal]

Reviewed By: robhogan

Differential Revision: D77873875

fbshipit-source-id: e04dba41a1ef811d32793931033fdfa93afad0cd

scripts/shared/babelRegister.js

@@ -0,0 +1,70 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+const {
+  PACKAGES_DIR,
+  PRIVATE_DIR,
+  RN_INTEGRATION_TESTS_RUNNER_DIR,
+  SCRIPTS_DIR,
+} = require('./consts');
+
+let isRegisteredForMonorepo = false;
+
+/**
+ * Calling this function enables all Node.js packages to run from source when
+ * developing in the React Native repo.
+ *
+ * A call should located in each entry point file in a package (i.e. for all
+ * paths in "exports"), inside a special `if` condition that will be compiled
+ * away on build.
+ *
+ * ```js
+ * // Place in a package entry point
+ * if (!process.env.BUILD_EXCLUDE_BABEL_REGISTER) {
+ *   require('../../../scripts/shared/babelRegister').registerForMonorepo();
+ * }
+ * ```
+ */
+function registerForMonorepo() {
+  if (isRegisteredForMonorepo) {
+    return;
+  }
+
+  if (process.env.FBSOURCE_ENV === '1') {
+    // $FlowExpectedError[cannot-resolve-module] - Won't resolve in OSS
+    require('@fb-tools/babel-register');
+  } else {
+    require('metro-babel-register')([
+      PACKAGES_DIR,
+      PRIVATE_DIR,
+      SCRIPTS_DIR,
+      RN_INTEGRATION_TESTS_RUNNER_DIR,
+    ]);
+  }
+
+  isRegisteredForMonorepo = true;
+}
+
+/**
+ * Calling this function enables entry points under scripts/ to run from source.
+ *
+ * ```js
+ * // Place in a script entry point
+ * require('../shared/babelRegister').registerForScript();
+ * ```
+ */
+function registerForScript() {
+  registerForMonorepo();
+}
+
+module.exports = {
+  registerForMonorepo,
+  registerForScript,
+};