Allow to use extra postcss plugins after css-modules related plugins

Author: Strate

README.md

@@ -254,6 +254,34 @@ Usage:
 require('file.css').className
 ```
 
+### Use extra postcss plugins
+
+You can add your own [postcss](http://postcss.org/) plugins into this loader pipeline.
+It could be better for performance than using extra `postcss-loader`, because plugin will be called in the chain with other
+plugins used by `css-loader`, without extra parsing of css.
+
+Usage:
+```js
+// webpack.config.js
+var autoprefixer = require("autoprefixer")
+module.exports = {
+  modules: [
+    {
+      test: /\.css$/,
+      loader: [
+        "style",
+        "css?modules&afterModules=autoprefixer"
+      ]
+    }
+  ]
+  cssLoader: {
+    autoprefixer: function(pipeline) {
+      pipeline.use(autoprefixer)
+    }
+  }
+}
+```
+
 ## License
 
 MIT (http://www.opensource.org/licenses/mit-license.php)

lib/processCss.js

@@ -176,6 +176,14 @@ module.exports = function processCss(inputSource, inputMap, options, callback) {
 		parserPlugin(parserOptions)
 	]);
 
+	if (
+		query.afterModules &&
+		options.loaderContext.options.cssLoader &&
+		typeof options.loaderContext.options.cssLoader[query.afterModules] === "function"
+	) {
+		options.loaderContext.options.cssLoader[query.afterModules](pipeline)
+	}
+
 	if(minimize) {
 		var minimizeOptions = assign({}, query);
 		["zindex", "normalizeUrl", "discardUnused", "mergeIdents", "reduceIdents"].forEach(function(name) {