fix splitChunks support

Author: sokra

src/index.js

@@ -52,6 +52,13 @@ class CssModule extends webpack.Module {
     return `css ${requestShortener.shorten(this._identifier)}${this._identifierIndex ? ` (${this._identifierIndex})` : ''}`;
   }
 
+  nameForCondition() {
+    const resource = this._identifier.split('!').pop();
+    const idx = resource.indexOf('?');
+    if (idx >= 0) return resource.substr(0, idx);
+    return resource;
+  }
+
   build(options, compilation, resolver, fileSystem, callback) {
     this.buildInfo = {};
     this.buildMeta = {};

test/cases/split-chunks/expected/main.css

@@ -0,0 +1,2 @@
+body { background: red; }
+

test/cases/split-chunks/expected/vendors~main.css

@@ -0,0 +1,5 @@
+/* This could be bootstrap.css */
+body {
+  background: green;
+}
+

test/cases/split-chunks/index.js

@@ -0,0 +1,2 @@
+import 'bootstrap.css';
+import './style.css';

test/cases/split-chunks/node_modules/bootstrap.css

@@ -0,0 +1 @@
+body { background: red; }

test/cases/split-chunks/style.css

@@ -0,0 +1,32 @@
+const Self = require('../../../');
+
+module.exports = {
+  entry: './index.js',
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          Self.loader,
+          'css-loader',
+        ],
+      },
+    ],
+  },
+  optimization: {
+    splitChunks: {
+      chunks: 'all',
+      cacheGroups: {
+        vendors: {
+          test: /node_modules/,
+          enforce: true
+        }
+      }
+    }
+  },
+  plugins: [
+    new Self({
+      filename: '[name].css',
+    }),
+  ],
+};