feature #130 Add options callback to Encore.enablePostCssLoader() (Lyrkan)

This PR was merged into the master branch.

Discussion
----------

Add options callback to Encore.enablePostCssLoader()

This PR allows to add a callback as the first argument of `Encore.enablePostCssLoader()` in order to be able to modify the options of the `postcss-loader`.

As an example (fixes #129):

```js
Encore.enablePostCssLoader((options) => {
    options.config = {
        path: 'app/config/postcss.config.js'
    };
});
```

Commits
-------

0999277 Add options callback to Encore.enablePostCssLoader()

Author: weaverryan

index.js

@@ -275,10 +275,20 @@ module.exports = {
      *
      * https://github.com/postcss/postcss-loader
      *
+     *     Encore.enablePostCssLoader();
+     *
+     * Or pass options to the loader
+     *
+     *     Encore.enablePostCssLoader(function(options) {
+     *         // https://github.com/postcss/postcss-loader#options
+     *         // options.config = {...}
+     *     })
+     *
+     * @param {function} postCssLoaderOptionsCallback
      * @return {exports}
      */
-    enablePostCssLoader() {
-        webpackConfig.enablePostCssLoader();
+    enablePostCssLoader(postCssLoaderOptionsCallback = () => {}) {
+        webpackConfig.enablePostCssLoader(postCssLoaderOptionsCallback);
 
         return this;
     },

lib/WebpackConfig.js

@@ -40,6 +40,7 @@ class WebpackConfig {
         this.useVersioning = false;
         this.useSourceMaps = false;
         this.usePostCssLoader = false;
+        this.postCssLoaderOptionsCallback = function() {};
         this.useSassLoader = false;
         this.sassLoaderOptionsCallback = function() {};
         this.sassOptions = {
@@ -198,8 +199,14 @@ class WebpackConfig {
         this.addEntry(name, files);
     }
 
-    enablePostCssLoader() {
+    enablePostCssLoader(postCssLoaderOptionsCallback = () => {}) {
         this.usePostCssLoader = true;
+
+        if (typeof postCssLoaderOptionsCallback !== 'function') {
+            throw new Error('Argument 1 to enablePostCssLoader() must be a callback function.');
+        }
+
+        this.postCssLoaderOptionsCallback = postCssLoaderOptionsCallback;
     }
 
     enableSassLoader(sassLoaderOptionsCallback = () => {}, options = {}) {

lib/loaders/css.js

@@ -38,11 +38,20 @@ module.exports = {
         if (usePostCssLoader) {
             loaderFeatures.ensureLoaderPackagesExist('postcss');
 
+            const postCssLoaderOptions = {
+                sourceMap: webpackConfig.useSourceMaps
+            };
+
+            // allow options to be configured
+            webpackConfig.postCssLoaderOptionsCallback.apply(
+                // use config as the this variable
+                postCssLoaderOptions,
+                [postCssLoaderOptions]
+            );
+
             cssLoaders.push({
                 loader: 'postcss-loader',
-                options: {
-                    sourceMap: webpackConfig.useSourceMaps
-                }
+                options: postCssLoaderOptions
             });
         }
 

test/WebpackConfig.js

@@ -282,6 +282,30 @@ describe('WebpackConfig object', () => {
         });
     });
 
+    describe('enablePostCssLoader', () => {
+        it('Call with no config', () => {
+            const config = createConfig();
+            config.enablePostCssLoader();
+
+            expect(config.usePostCssLoader).to.be.true;
+        });
+
+        it('Pass options callback', () => {
+            const config = createConfig();
+            const callback = () => {};
+            config.enablePostCssLoader(callback);
+
+            expect(config.usePostCssLoader).to.be.true;
+            expect(config.postCssLoaderOptionsCallback).to.equal(callback);
+        });
+
+        it('Pass invalid options callback', () => {
+            const config = createConfig();
+
+            expect(() => config.enablePostCssLoader('FOO')).to.throw('must be a callback function');
+        });
+    });
+
     describe('enableSassLoader', () => {
         it('Call with no config', () => {
             const config = createConfig();

test/loaders/css.js

@@ -44,14 +44,32 @@ describe('loaders/css', () => {
         expect(actualLoaders[0].options.minimize).to.be.true;
     });
 
-    it('getLoaders() with PostCSS', () => {
-        const config = createConfig();
-        config.enableSourceMaps();
-        config.enablePostCssLoader();
+    describe('getLoaders() with PostCSS', () => {
+        it('without options callback', () => {
+            const config = createConfig();
+            config.enableSourceMaps();
+            config.enablePostCssLoader();
 
-        const actualLoaders = cssLoader.getLoaders(config);
-        // css-loader & postcss-loader
-        expect(actualLoaders).to.have.lengthOf(2);
-        expect(actualLoaders[1].options.sourceMap).to.be.true;
+            const actualLoaders = cssLoader.getLoaders(config);
+            // css-loader & postcss-loader
+            expect(actualLoaders).to.have.lengthOf(2);
+            expect(actualLoaders[1].options.sourceMap).to.be.true;
+        });
+
+        it('with options callback', () => {
+            const config = createConfig();
+            config.enableSourceMaps();
+            config.enablePostCssLoader((options) => {
+                options.config = {
+                    path: 'config/postcss.config.js'
+                };
+            });
+
+            const actualLoaders = cssLoader.getLoaders(config);
+            // css-loader & postcss-loader
+            expect(actualLoaders).to.have.lengthOf(2);
+            expect(actualLoaders[1].options.sourceMap).to.be.true;
+            expect(actualLoaders[1].options.config.path).to.equal('config/postcss.config.js');
+        });
     });
 });