Inline 'testMinificationUsedDCE' and remove unit test for now

What:
- Inlines the 'testMinificationUsedDCE' method into
  'packages/react/index.js'
- Removes unit test for 'testMinififcationUsedDCE'
- Puts dependencies back the way that they were; should remove extra
  dependencies that were added for the unit test.

Why:
- It would add complexity to the build process to add another file to
  the 'build/packages/react/cjs' folder, and that is the only way to
  pull this out and test it. So instead we are inlining this.

package.json

@@ -11,7 +11,6 @@
     "babel-jest": "20.1.0-delta.1",
     "babel-plugin-check-es2015-constants": "^6.5.0",
     "babel-plugin-external-helpers": "^6.22.0",
-    "babel-plugin-minify-dead-code-elimination": "^0.1.7",
     "babel-plugin-syntax-trailing-function-commas": "^6.5.0",
     "babel-plugin-transform-async-to-generator": "^6.22.0",
     "babel-plugin-transform-class-properties": "^6.11.5",
@@ -33,7 +32,6 @@
     "babel-plugin-transform-es3-property-literals": "^6.5.0",
     "babel-plugin-transform-object-rest-spread": "^6.6.5",
     "babel-plugin-transform-react-jsx-source": "^6.8.0",
-    "babel-preset-minify": "0.0.0",
     "babel-preset-react": "^6.5.0",
     "babel-traverse": "^6.9.0",
     "babylon": "6.15.0",
@@ -88,7 +86,7 @@
     "through2": "^2.0.0",
     "tmp": "~0.0.28",
     "typescript": "~1.8.10",
-    "uglify-js": "2.8.29",
+    "uglify-js": "^2.8.29",
     "yargs": "^6.3.0"
   },
   "devEngines": {

packages/react/index.js

@@ -1,9 +1,50 @@
 'use strict';
 
+function testMinificationUsedDCE() {
+  // use scoped variable for our initial test, in case
+  // 'top-level' mangling is not enabled.
+  const source = testMinificationUsedDCE.toString();
+  const longVariableName = source;
+  if (longVariableName && source.match(/longVariableName/g).length === 3) {
+    // We are not minified.
+    // This might be a Node environment where DCE is not expected anyway.
+    return;
+  }
+  if (process.env.NODE_ENV === 'development') {
+    // We expect this method only to be called in production.
+    throw new Error('This is unreachable');
+  }
+  try {
+    if (source.match(/toString/g).length !== 2) {
+      // We always look for two matches:
+      // The actual occurence and then the call to 'match'
+      //
+      // We know for a fact the above line exists so there should be 2
+      // matches.
+      // Therefore the browser gave us invalid source.
+      return;
+    }
+    if (source.match(/unreachable/g).length === 2) {
+      // We always look for two matches:
+      // The actual occurence and then the call to 'match'
+
+      // Dead code elimination would have stripped that branch
+      // because it is impossible to reach in production.
+      setTimeout(function() {
+        // Ensure it gets reported to production logging
+        throw new Error(
+          'React is running in production mode, but dead code ' +
+            'elimination has not been applied. Read how to correctly ' +
+            'configure React for production: ' +
+            'https://fburl.com/react-perf-use-the-production-build'
+        );
+      });
+    }
+  } catch (e) {}
+}
 
 if (process.env.NODE_ENV === 'production') {
-  // TODO: actually update the build process so this works.
-  (require('./cjs/testMinificationUsedDCE.js'))();
+  testMinificationUsedDCE();
   module.exports = require('./cjs/react.production.min.js');
 } else {
   module.exports = require('./cjs/react.development.js');

scripts/rollup/packaging.js

@@ -30,11 +30,6 @@ const reactNativeSrcDependencies = [
   'src/renderers/native/ReactNativeTypes.js',
 ];
 
-// these files need to be copied to the react build
-const reactPackageDependencies = [
-  'src/shared/utils/testMinificationUsedDCE.js',
-];
-
 function getPackageName(name) {
   if (name.indexOf('/') !== -1) {
     return name.split('/')[0];
@@ -104,7 +99,7 @@ function copyBundleIntoNodePackage(packageName, filename, bundleType) {
       from = resolve(`./build/dist/${filename}`);
       to = `${packageDirectory}/umd/${filename}`;
     }
-    const promises = [];
+
     // for NODE bundles we have to move the files into a cjs directory
     // within the package directory. we also need to set the from
     // to be the root build from directory
@@ -115,31 +110,13 @@ function copyBundleIntoNodePackage(packageName, filename, bundleType) {
         fs.mkdirSync(distDirectory);
       }
       to = `${packageDirectory}/cjs/${filename}`;
-      if (packageName === 'react') {
-        // we are building the React package
-        let promises = [];
-        // we also need to copy over some specific files from src
-        // defined in reactPackageDependencies
-        for (const srcDependency of reactPackageDependencies) {
-          // TODO: the srcDependency needs to be processed
-          // before this step.
-          var specificFrom = resolve(srcDependency);
-          var specificTo = resolve(`${distDirectory}/${basename(srcDependency)}`);
-          promises.push(
-            asyncCopyTo(specificFrom, specificTo)
-          );
-        }
-      }
     }
-    promises.push(
-      asyncCopyTo(from, to).then(() => {
-        // delete the old file if this is a not a UMD bundle
-        if (bundleType !== UMD_DEV && bundleType !== UMD_PROD) {
-          fs.unlinkSync(from);
-        }
-      })
-    );
-    return Promise.all(promises);
+    return asyncCopyTo(from, to).then(() => {
+      // delete the old file if this is a not a UMD bundle
+      if (bundleType !== UMD_DEV && bundleType !== UMD_PROD) {
+        fs.unlinkSync(from);
+      }
+    });
   } else {
     return Promise.resolve();
   }