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

package.json

@@ -167,7 +167,7 @@
     "inquirer": "^3.0.6",
     "lodash": "^4.17.5",
     "metro": "^0.34.0",
-    "metro-babel-register": "^0.34.1",
+    "metro-babel-register": "^0.34.2",
     "metro-core": "^0.34.0",
     "mime": "^1.3.4",
     "minimist": "^1.2.0",

setupBabel.js

@@ -8,43 +8,8 @@
 'use strict';
 
 const babelRegisterOnly = require('metro-babel-register');
-const escapeRegExp = require('lodash/escapeRegExp');
-const path = require('path');
 
-const BABEL_ENABLED_PATHS = ['local-cli', 'metro'];
+const BABEL_ENABLED_PATHS = ['local-cli'];
-
-/**
- * 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 =>
-      folderPath === 'metro'
-        // metro uses flow (for example) which needs to be stripped out w/babel.
-        // it'll resolve to .../metro/src/index.js we want root
-        ? path.resolve(require.resolve('metro'), '..')
-        // 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, '/')
-              )}`
-            )
-  );
-}
-
-function getOnlyList() {
-  return buildRegExps(__dirname, BABEL_ENABLED_PATHS);
-}
 
 /**
  * Centralized place to register all the directories that need a Babel
@@ -52,9 +17,7 @@ function getOnlyList() {
  * support Flow type annotations.
  */
 function setupBabel() {
-  babelRegisterOnly(getOnlyList());
+  babelRegisterOnly(babelRegisterOnly.buildRegExps(__dirname, BABEL_ENABLED_PATHS));
 }
 
-setupBabel.buildRegExps = buildRegExps;
-setupBabel.getOnlyList = getOnlyList;
 module.exports = setupBabel;