Fix caching source-less modules (#279)

* chore: Add failing prefetch test

PrefetchPlugin can build modules that are then not included in the output
chunks, leaving them without rendered source. hard-source must cache module's
that do not have a source.

* chore: Fix caching source-less modules

* chore: Extend base-es2015 and plugin-concatenated test trees

Author: mzgoddard

lib/util/serial.js

@@ -101,13 +101,19 @@ const assigned = exports.assigned = (members) => ({
 
 const created = exports.created = (members) => ({
   freeze(arg, module, extra, methods) {
+    if (!arg) {
+      return null;
+    }
     const out = {};
     for (const key in members) {
       out[key] = members[key].freeze(arg[key], module, extra, methods);
     }
     return out;
   },
   thaw(arg, frozen, extra, methods) {
+    if (!arg) {
+      return null;
+    }
     const out = {};
     for (const key in members) {
       out[key] = members[key].thaw(arg[key], frozen, extra, methods);

tests/fixtures/base-es2015-module/a.js

@@ -0,0 +1,2 @@
+import b from './b';
+export {b};

tests/fixtures/base-es2015-module/b.js

@@ -0,0 +1 @@
+export default 'key';

tests/fixtures/base-es2015-module/obj.js

@@ -1,3 +1,3 @@
 import fib from './fib';
-let key = 'obj';
+import {b as key} from './a';
 export {key, fib};

tests/fixtures/plugin-concatenated-module/a.js

@@ -0,0 +1,2 @@
+import b from './b';
+export {b};

tests/fixtures/plugin-concatenated-module/b.js

@@ -0,0 +1 @@
+export default 'a key';

tests/fixtures/plugin-concatenated-module/obj.js

@@ -1,4 +1,3 @@
 import fib from './fib';
-import {b} from './a'
-let key = b;
+import {b as key} from './a';
 export {key, fib};

tests/fixtures/plugin-prefetch-es2015/a.js

@@ -0,0 +1,2 @@
+import b from './b';
+export {b};

tests/fixtures/plugin-prefetch-es2015/b.js

@@ -0,0 +1 @@
+export default 'key';

tests/fixtures/plugin-prefetch-es2015/fib.js

@@ -0,0 +1,3 @@
+export default function(n) {
+  return n + (n > 0 ? n - 1 : 0);
+};

tests/fixtures/plugin-prefetch-es2015/index.js

@@ -0,0 +1,3 @@
+import {key} from './obj';
+
+console.log(key);

tests/fixtures/plugin-prefetch-es2015/obj.js

@@ -0,0 +1,3 @@
+import fib from './fib';
+import {b as key} from './a';
+export {key, fib};

tests/fixtures/plugin-prefetch-es2015/unused.js

@@ -0,0 +1,2 @@
+import b from './b';
+export {b};

tests/fixtures/plugin-prefetch-es2015/webpack.config.js

@@ -0,0 +1,20 @@
+var webpack = require('webpack');
+var HardSourceWebpackPlugin = require('../../..');
+
+module.exports = {
+  context: __dirname,
+  entry: './index.js',
+  output: {
+    path: __dirname + '/tmp',
+    filename: 'main.js',
+  },
+  plugins: [
+    new webpack.PrefetchPlugin('./unused.js'),
+    new HardSourceWebpackPlugin({
+      cacheDirectory: 'cache',
+      environmentHash: {
+        root: __dirname + '/../../..',
+      },
+    }),
+  ],
+};

tests/plugins-webpack-1.js

@@ -37,12 +37,15 @@ describe('plugin webpack use', function() {
   itCompilesTwice('plugin-source-map-1dep');
   itCompilesTwice.skipIf([c.uglify])('plugin-uglify-devtool-source-map');
   itCompilesTwice.skipIf([c.uglify])('plugin-uglify-devtool-source-map', {exportStats: true});
+  itCompilesTwice('plugin-prefetch-es2015');
+  itCompilesTwice('plugin-prefetch-es2015', {exportStats: true});
 
   itCompilesHardModules('plugin-dll', ['./fib.js']);
   itCompilesHardModules('plugin-dll-reference', ['./index.js']);
   itCompilesHardModules('plugin-dll-reference-scope', ['./index.js']);
   itCompilesHardModules.skipIf([c.html])('plugin-html-lodash', [/lodash\/lodash\.js$/, /\!\.\/index\.html$/]);
   itCompilesHardModules('plugin-serializer-json-base-1dep', ['./fib.js', './index.js']);
+  itCompilesHardModules('plugin-prefetch-es2015', ['./unused.js']);
 
 });
 

tests/plugins-webpack-3.js

@@ -14,7 +14,7 @@ describeWP(3)('plugin webpack 3 use', function() {
   itCompilesHardModules('plugin-concatenated-module', function(out) {
     out.run2.compilation.modules.forEach(function(module) {
       if (module.modules) {
-        expect(module.modules.length).to.equal(2);
+        expect(module.modules.length).to.equal(4);
         module.modules.forEach(function(usedModule) {
           expect(usedModule.cacheItem).to.be.ok;
         });