Move `buildRegExps` from `react-native` to `metro-babel-register`

Summary: Moves the `buildRegExps` function from `react-native` to `metro-babel-register`. This way, it is easier to reuse, and we can remove FB-specific logic from React Native.

Reviewed By: jeanlauliac, mjesun

Differential Revision: D7727483

fbshipit-source-id: 0f7773ff044033c465f0712c523a0aef61bf8444

packages/metro-babel-register/babel-register.js

@@ -8,6 +8,8 @@
  */
 'use strict';
 
+const escapeRegExp = require('escape-string-regexp');
+const path = require('path');
 require('./node-polyfills');
 
 var _only = [];
@@ -34,14 +36,41 @@ function registerOnly(onlyList) {
 function config(onlyList) {
   _only = _only.concat(onlyList);
   return {
-    presets: [],
-    plugins: PLUGINS,
+    babelrc: false,
+    ignore: null,
     only: _only,
+    plugins: PLUGINS,
+    presets: [],
     retainLines: true,
     sourceMaps: 'inline',
-    babelrc: false,
   };
 }
 
+/**
+ * We use absolute paths for matching only the top-level folders reliably. For
+ * example, we would not want to match some deeply nested forder that happens to
+ * have the same name as one of `BABEL_ENABLED_PATHS`.
+ */
+function buildRegExps(basePath, dirPaths) {
+  return dirPaths.map(
+    folderPath =>
+      // Babel `only` option works with forward slashes in the RegExp so replace
+      // backslashes for Windows.
+      folderPath instanceof RegExp
+        ? new RegExp(
+            `^${escapeRegExp(
+              path.resolve(basePath, '.').replace(/\\/g, '/'),
+            )}/${folderPath.source}`,
+            folderPath.flags,
+          )
+        : new RegExp(
+            `^${escapeRegExp(
+              path.resolve(basePath, folderPath).replace(/\\/g, '/'),
+            )}`,
+          ),
+  );
+}
+
 module.exports = registerOnly;
 module.exports.config = config;
+module.exports.buildRegExps = buildRegExps;

packages/metro-babel-register/package.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.34.1",
+  "version": "0.34.2",
   "name": "metro-babel-register",
   "description": "🚇 babel/register configuration for Metro.",
   "main": "babel-register.js",
@@ -14,6 +14,7 @@
     "@babel/plugin-transform-flow-strip-types": "7.0.0-beta.40",
     "@babel/plugin-transform-modules-commonjs": "7.0.0-beta.40",
     "@babel/register": "7.0.0-beta.40",
-    "core-js": "^2.2.2"
+    "core-js": "^2.2.2",
+    "escape-string-regexp": "^1.0.5"
   }
 }

packages/metro/package.json

@@ -78,7 +78,7 @@
     "merge-stream": "^1.0.1",
     "metro-babel7-plugin-react-transform": "0.34.0",
     "metro-babylon7": "0.34.0",
-    "metro-babel-register": "0.34.1",
+    "metro-babel-register": "0.34.2",
     "metro-cache": "0.34.0",
     "metro-core": "0.34.0",
     "metro-minify-uglify": "0.34.0",