Re-adding the traditional createSharedEntry functionality

Author: weaverryan

CHANGELOG.md

@@ -2,9 +2,13 @@
 
 ## 0.21.0 Webpack 4 Upgrade
 
- * Webpack was upgraded to version 4. This includes a number of major
+ * [BC BREAK] Webpack was upgraded to version 4. This includes a number of major
    and minor changes. The changes are listed below.
 
+ * [BC BREAK] If you're using `createSharedEntry()`, the name of the
+   `manifest.js` file is now `runtime.js`. You will need to update
+   your `<script>` tag to point to the new `runtime.js`.
+
  * The NamedModulesPlugin was removed.
 
  * The `babel-preset-env` package (which was at version ^1.2.2) was

lib/config-generator.js

@@ -321,6 +321,27 @@ class ConfigGenerator {
             optimization.namedModules = true;
         }
 
+        if (this.webpackConfig.sharedCommonsEntryName) {
+            const cacheGroups = {};
+            cacheGroups[this.webpackConfig.sharedCommonsEntryName] = {
+                chunks: 'initial',
+                name: this.webpackConfig.sharedCommonsEntryName,
+                // important: setting this to the entry name means that
+                // all modules included by that entry go into this cache group
+                test: this.webpackConfig.sharedCommonsEntryName,
+                // seems to default the rest of the options (like minSize)
+                // to settings so that modules matched by "test" are
+                // *definitely* included.
+                enforce: true,
+            };
+
+            optimization.splitChunks = {
+                cacheGroups: cacheGroups
+            };
+            // causes a runtime.js to be emitted with the Webpack runtime
+            optimization.runtimeChunk = 'single';
+        }
+
         return optimization;
     }