Wrap all non-UMD DEV bundles into a condition (#9969)

* Wrap all non-UMD DEV bundles into a condition

* Update header.js

* Create header.js

scripts/rollup/build.js

@@ -76,36 +76,43 @@ function getHeaderSanityCheck(bundleType, hasteName) {
 
 function getBanner(bundleType, hasteName, filename) {
   switch (bundleType) {
+    // UMDs are not wrapped in conditions.
+    case UMD_DEV:
+    case UMD_PROD:
+      return Header.getUMDHeader(filename, reactVersion);
+    // CommonJS DEV bundle is guarded to help weak dead code elimination.
+    case NODE_DEV:
+      return `'use strict';\n\n\nif (process.env.NODE_ENV !== "production") {\n`;
+    case NODE_PROD:
+      return '';
+    // FB and RN DEV bundles are also guarded.
+    // Additionally, all FB and RN bundles need Haste headers.
     case FB_DEV:
     case FB_PROD:
     case RN_DEV:
     case RN_PROD:
-      let hasteFinalName = hasteName;
-      switch (bundleType) {
-        case FB_DEV:
-        case RN_DEV:
-          hasteFinalName += '-dev';
-          break;
-        case FB_PROD:
-        case RN_PROD:
-          hasteFinalName += '-prod';
-          break;
-      }
-      const fbDevCode = `\n\n'use strict';\n\n` + `\nif (__DEV__) {\n`;
-      return Header.getProvidesHeader(hasteFinalName, bundleType, fbDevCode);
-    case UMD_DEV:
-    case UMD_PROD:
-      return Header.getUMDHeader(filename, reactVersion);
+      const isDev = bundleType === FB_DEV || bundleType === RN_DEV;
+      const hasteFinalName = hasteName + (isDev ? '-dev' : '-prod');
+      return (
+        Header.getProvidesHeader(hasteFinalName) +
+        (isDev ? `\n\n'use strict';\n\n\nif (__DEV__) {\n` : '')
+      );
     default:
-      return '';
+      throw new Error('Unknown type.');
   }
 }
 
 function getFooter(bundleType) {
-  if (bundleType === FB_DEV) {
-    return '\n}\n';
+  // Only need a footer if getBanner() has an opening brace.
+  switch (bundleType) {
+    // Non-UMD DEV bundles need conditions to help weak dead code elimination.
+    case NODE_DEV:
+    case FB_DEV:
+    case RN_DEV:
+      return '\n}\n';
+    default:
+      return '';
   }
-  return '';
 }
 
 function updateBabelConfig(babelOpts, bundleType) {

scripts/rollup/header.js

@@ -1,8 +1,6 @@
-const Bundles = require('./bundles');
+'use strict';
 
-const FB_DEV = Bundles.bundleTypes.FB_DEV;
-
-function getProvidesHeader(hasteFinalName, bundleType, fbDevCode) {
+function getProvidesHeader(hasteFinalName) {
   return `/**
  * Copyright 2013-present, Facebook, Inc.
  * All rights reserved.
@@ -13,7 +11,7 @@ function getProvidesHeader(hasteFinalName, bundleType, fbDevCode) {
  *
  * @noflow
  * @providesModule ${hasteFinalName}
- */${bundleType === FB_DEV ? fbDevCode : ''}
+ */
 `;
 }
 

scripts/rollup/results.json

@@ -1,27 +1,27 @@
 {
   "bundleSizes": {
     "react.development.js (UMD_DEV)": {
-      "size": 71599,
-      "gzip": 18503
+      "size": 71605,
+      "gzip": 18506
     },
     "react.production.min.js (UMD_PROD)": {
       "size": 7585,
       "gzip": 2999
     },
     "react.development.js (NODE_DEV)": {
-      "size": 61813,
-      "gzip": 16088
+      "size": 61884,
+      "gzip": 16131
     },
     "react.production.min.js (NODE_PROD)": {
       "size": 6483,
       "gzip": 2581
     },
     "React-dev.js (FB_DEV)": {
-      "size": 61047,
-      "gzip": 15811
+      "size": 61056,
+      "gzip": 15809
     },
     "React-prod.js (FB_PROD)": {
-      "size": 29022,
+      "size": 29031,
       "gzip": 7690
     },
     "react-dom.development.js (UMD_DEV)": {