Move the new plugin to its own file

scripts/rollup/build.js

@@ -16,6 +16,7 @@ const argv = require('minimist')(process.argv.slice(2));
 const Modules = require('./modules');
 const Bundles = require('./bundles');
 const sizes = require('./plugins/sizes-plugin');
+const useForks = require('./plugins/use-forks-plugin');
 const Stats = require('./stats');
 const extractErrorCodes = require('../error-codes/extract-errors');
 const syncReactDom = require('./sync').syncReactDom;
@@ -208,44 +209,6 @@ function isProductionBundleType(bundleType) {
   }
 }
 
-let resolveCache = new Map();
-function useForks(forks) {
-  let resolvedForks = {};
-  Object.keys(forks).forEach(srcModule => {
-    const targetModule = forks[srcModule];
-    resolvedForks[require.resolve(srcModule)] = require.resolve(targetModule);
-  });
-  return {
-    resolveId(importee, importer) {
-      if (!importer || !importee) {
-        return null;
-      }
-      let resolvedImportee = null;
-      let cacheKey = `${importer}:::${importee}`;
-      if (resolveCache.has(cacheKey)) {
-        // Avoid hitting file system if possible.
-        resolvedImportee = resolveCache.get(cacheKey);
-      } else {
-        try {
-          resolvedImportee = require.resolve(importee, {
-            paths: [path.dirname(importer)],
-          });
-        } catch (err) {
-          // Not our fault, let Rollup fail later.
-        }
-        if (resolvedImportee) {
-          resolveCache.set(cacheKey, resolvedImportee);
-        }
-      }
-      if (resolvedImportee && resolvedForks.hasOwnProperty(resolvedImportee)) {
-        // We found a fork!
-        return resolvedForks[resolvedImportee];
-      }
-      return null;
-    },
-  };
-}
-
 function getPlugins(
   entry,
   externals,

scripts/rollup/plugins/sizes-plugin.js

@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
 const gzip = require('gzip-size');
 
 module.exports = function sizes(options) {

scripts/rollup/plugins/use-forks-plugin.js

@@ -0,0 +1,47 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
+let resolveCache = new Map();
+function useForks(forks) {
+  let resolvedForks = {};
+  Object.keys(forks).forEach(srcModule => {
+    const targetModule = forks[srcModule];
+    resolvedForks[require.resolve(srcModule)] = require.resolve(targetModule);
+  });
+  return {
+    resolveId(importee, importer) {
+      if (!importer || !importee) {
+        return null;
+      }
+      let resolvedImportee = null;
+      let cacheKey = `${importer}:::${importee}`;
+      if (resolveCache.has(cacheKey)) {
+        // Avoid hitting file system if possible.
+        resolvedImportee = resolveCache.get(cacheKey);
+      } else {
+        try {
+          resolvedImportee = require.resolve(importee, {
+            paths: [path.dirname(importer)],
+          });
+        } catch (err) {
+          // Not our fault, let Rollup fail later.
+        }
+        if (resolvedImportee) {
+          resolveCache.set(cacheKey, resolvedImportee);
+        }
+      }
+      if (resolvedImportee && resolvedForks.hasOwnProperty(resolvedImportee)) {
+        // We found a fork!
+        return resolvedForks[resolvedImportee];
+      }
+      return null;
+    },
+  };
+}
+
+module.exports = useForks;