fix(webpack): ConcatenatedModulePlugin results in an exception.

This happens when an Aurelia module is selected as the root of a concatenated module.

Author: jods4

src/PreserveModuleNamePlugin.ts

@@ -29,23 +29,30 @@ export class PreserveModuleNamePlugin {
         }
 
         for (let module of getPreservedModules(modules)) {
-          let preserve: string | true | undefined = module[preserveModuleName];
+          // Even though it's imported by Aurelia, it's still possible that the module
+          // became the _root_ of a ConcatenatedModule.
+          // We use `constructor.name` rather than `instanceof` for compat. with Webpack 2.
+          let realModule = module;
+          if (module.constructor.name === "ConcatenatedModule")
+            realModule = module["rootModule"];
+
+          let preserve: string | true | undefined = realModule[preserveModuleName];
           let id = typeof preserve === "string" ? preserve : null;
 
           // No absolute request to preserve, we try to normalize the module resource
-          if (!id && module.resource)
-            id = fixNodeModule(module, modulesBeforeConcat) || 
-                 makeModuleRelative(roots, module.resource) ||
-                 aliasRelative(alias, module.resource);
+          if (!id && realModule.resource)
+            id = fixNodeModule(realModule, modulesBeforeConcat) || 
+                 makeModuleRelative(roots, realModule.resource) ||
+                 aliasRelative(alias, realModule.resource);
 
           if (!id)
-            throw new Error(`Can't figure out a normalized module name for ${module.rawRequest}, please call PLATFORM.moduleName() somewhere to help.`);
+            throw new Error(`Can't figure out a normalized module name for ${realModule.rawRequest}, please call PLATFORM.moduleName() somewhere to help.`);
 
           // Remove default extensions 
           normalizers.forEach(n => id = id!.replace(n, ""));
 
           // Keep "async!" in front of code splits proxies, they are used by aurelia-loader
-          if (/^async[?!]/.test(module.rawRequest)) 
+          if (/^async[?!]/.test(realModule.rawRequest)) 
             id = "async!" + id;
 
           id = id.replace(/\\/g, "/");