Install plugins from lessLoader option

Author: mfellner

README.md

@@ -53,6 +53,26 @@ module.exports = {
 
 See the [LESS documentation](http://lesscss.org/usage/#command-line-usage-options) for all available options. LESS translates dash-case to camelCase.
 
+### LESS plugins
+
+In order to use [plugins](http://lesscss.org/usage/#plugins), simply define
+the `lessLoader.lessPlugins` option. You can also change the options key
+with a query parameter: `"style!css!less?config=lessLoaderCustom"`.
+
+``` javascript
+var LessPluginCleanCSS = require('less-plugin-clean-css');
+
+module.exports = {
+  module: {
+    loaders: [...]
+  },
+  lessLoader:
+    lessPlugins: [
+      new LessPluginCleanCSS({advanced: true})
+    ]
+};
+```
+
 ## Note on imports
 
 webpack provides an [advanced mechanism to resolve files](http://webpack.github.io/docs/resolving.html). The less-loader stubs less' `fileLoader` and passes all queries to the webpack resolving engine. Thus you can import your less-modules from `node_modules` or `bower_components`. Just prepend them with a `~` which tells webpack to look-up the [`modulesDirectories`](http://webpack.github.io/docs/configuration.html#resolve-modulesdirectories)

index.js

@@ -18,6 +18,7 @@ module.exports = function(source) {
 	var cb = this.async();
 	var isSync = typeof cb !== "function";
 	var finalCb = cb || this.callback;
+	var configKey = query.config || 'lessLoader';
 	var config = {
 		filename: this.resource,
 		paths: [],
@@ -44,6 +45,11 @@ module.exports = function(source) {
 	config.plugins = config.plugins || [];
 	config.plugins.push(webpackPlugin);
 
+	// If present, add custom LESS plugins.
+	if (this.options[configKey]) {
+		config.plugins = config.plugins.concat(this.options[configKey].lessPlugins || []);
+	}
+
 	// not using the `this.sourceMap` flag because css source maps are different
 	// @see https://github.com/webpack/css-loader/pull/40
 	if (query.sourceMap) {

test/index.test.js

@@ -36,6 +36,15 @@ describe("less-loader", function() {
 		query: "?sourceMap",
 		devtool: "source-map"
 	});
+	test("should install plugins", "url-path", {
+		query: "?config=lessLoaderTest",
+		lessPlugins: [
+			{ wasCalled: false, install: function() {this.wasCalled = true;} }
+		],
+		after: function(testVariables) {
+			this.lessPlugins[0].wasCalled.should.be.true;
+		}
+	});
 	it("should report error correctly", function(done) {
 		webpack({
 			entry: path.resolve(__dirname, "../index.js") + "!" +
@@ -109,6 +118,9 @@ function test(name, id, testOptions) {
 				path: __dirname + "/output",
 				filename: "bundle.js",
 				libraryTarget: "commonjs2"
+			},
+			lessLoaderTest: {
+				lessPlugins: testOptions.lessPlugins || []
 			}
 		}, function onCompilationFinished(err, stats) {
 			var actualMap;