Add options callback to Encore.enableLessLoader()

index.js

@@ -330,10 +330,21 @@ module.exports = {
     /**
      * Call this if you plan on loading less files.
      *
+     *     Encore.enableLessLoader();
+     *
+     * Or pass options to the loader
+     *
+     *     Encore.enableLessLoader(function(options) {
+     *         // https://github.com/webpack-contrib/less-loader#examples
+     *         // http://lesscss.org/usage/#command-line-usage-options
+     *         // options.relativeUrls = false;
+     *     });
+     *
+     * @param {function} lessLoaderOptionsCallback
      * @return {exports}
      */
-    enableLessLoader() {
-        webpackConfig.enableLessLoader();
+    enableLessLoader(lessLoaderOptionsCallback = () => {}) {
+        webpackConfig.enableLessLoader(lessLoaderOptionsCallback);
 
         return this;
     },

lib/WebpackConfig.js

@@ -47,6 +47,7 @@ class WebpackConfig {
             resolve_url_loader: true
         };
         this.useLessLoader = false;
+        this.lessLoaderOptionsCallback = function() {};
         this.cleanupOutput = false;
         this.sharedCommonsEntryName = null;
         this.providedVariables = {};
@@ -231,8 +232,14 @@ class WebpackConfig {
         }
     }
 
-    enableLessLoader() {
+    enableLessLoader(lessLoaderOptionsCallback = () => {}) {
         this.useLessLoader = true;
+
+        if (typeof lessLoaderOptionsCallback !== 'function') {
+            throw new Error('Argument 1 to enableLessLoader() must be a callback function.');
+        }
+
+        this.lessLoaderOptionsCallback = lessLoaderOptionsCallback;
     }
 
     enableReactPreset() {

lib/loaders/less.js

@@ -21,13 +21,22 @@ module.exports = {
     getLoaders(webpackConfig, ignorePostCssLoader = false) {
         loaderFeatures.ensureLoaderPackagesExist('less');
 
+        const config = {
+            sourceMap: webpackConfig.useSourceMaps
+        };
+
+        // allow options to be configured
+        webpackConfig.lessLoaderOptionsCallback.apply(
+            // use config as the this variable
+            config,
+            [config]
+        );
+
         return [
             ...cssLoader.getLoaders(webpackConfig, ignorePostCssLoader),
             {
                 loader: 'less-loader',
-                options: {
-                    sourceMap: webpackConfig.useSourceMaps
-                }
+                options: config
             },
         ];
     }

test/WebpackConfig.js

@@ -339,6 +339,31 @@ describe('WebpackConfig object', () => {
         });
     });
 
+    describe('enableLessLoader', () => {
+        it('Calling method sets it', () => {
+            const config = createConfig();
+            config.enableLessLoader();
+
+            expect(config.useLessLoader).to.be.true;
+        });
+
+        it('Calling with callback', () => {
+            const config = createConfig();
+            const callback = (lessOptions) => {};
+            config.enableLessLoader(callback);
+
+            expect(config.lessLoaderOptionsCallback).to.equal(callback);
+        });
+
+        it('Calling with non-callback throws an error', () => {
+            const config = createConfig();
+
+            expect(() => {
+                config.enableLessLoader('FOO');
+            }).to.throw('must be a callback function');
+        });
+    });
+
     describe('enableTypeScriptLoader', () => {
         it('Calling method sets it', () => {
             const config = createConfig();

test/loaders/less.js

@@ -39,4 +39,26 @@ describe('loaders/less', () => {
 
         cssLoader.getLoaders.restore();
     });
+
+    it('getLoaders() with options callback', () => {
+        const config = createConfig();
+        config.enableSourceMaps(true);
+
+        // make the cssLoader return nothing
+        sinon.stub(cssLoader, 'getLoaders')
+            .callsFake(() => []);
+
+        config.enableLessLoader(function(lessOptions) {
+            lessOptions.custom_option = 'foo';
+            lessOptions.other_option = true;
+        });
+
+        const actualLoaders = lessLoader.getLoaders(config);
+        expect(actualLoaders[0].options).to.deep.equals({
+            sourceMap: true,
+            custom_option: 'foo',
+            other_option: true
+        });
+        cssLoader.getLoaders.restore();
+    });
 });