Add support for CSS Modules with explicit filename (#2285)

* Add css modules with [name].modules.css file convention

* Add e2e for CSS Modules

* Updated based on feedback

* Change css modules class name to be deterministic and fix licences

* Update css modules class naming convention

Author: ro-savage

Diff for: packages/react-scripts/config/webpack.config.dev.js

@@ -30,6 +30,20 @@ const publicUrl = '';
 // Get environment variables to inject into our app.
 const env = getClientEnvironment(publicUrl);
 
+// Options for PostCSS as we reference these options twice
+// Adds vendor prefixing to support IE9 and above
+const postCSSLoaderOptions = {
+  // Necessary for external CSS imports to work
+  // https://github.com/facebookincubator/create-react-app/issues/2677
+  ident: 'postcss',
+  plugins: () => [
+    require('postcss-flexbugs-fixes'),
+    autoprefixer({
+      flexbox: 'no-2009',
+    }),
+  ],
+};
+
 // This is the development configuration.
 // It is focused on developer experience and fast rebuilds.
 // The production configuration is different and lives in a separate file.
@@ -209,8 +223,10 @@ module.exports = {
           // "style" loader turns CSS into JS modules that inject <style> tags.
           // In production, we use a plugin to extract that CSS to a file, but
           // in development "style" loader enables hot editing of CSS.
+          // By default we support CSS Modules with the extension .module.css
           {
             test: /\.css$/,
+            exclude: /\.module\.css$/,
             use: [
               require.resolve('style-loader'),
               {
@@ -221,18 +237,28 @@ module.exports = {
               },
               {
                 loader: require.resolve('postcss-loader'),
+                options: postCSSLoaderOptions,
+              },
+            ],
+          },
+          // Adds support for CSS Modules (https://github.com/css-modules/css-modules)
+          // using the extension .module.css
+          {
+            test: /\.module\.css$/,
+            use: [
+              require.resolve('style-loader'),
+              {
+                loader: require.resolve('css-loader'),
                 options: {
-                  // Necessary for external CSS imports to work
-                  // https://github.com/facebookincubator/create-react-app/issues/2677
-                  ident: 'postcss',
-                  plugins: () => [
-                    require('postcss-flexbugs-fixes'),
-                    autoprefixer({
-                      flexbox: 'no-2009',
-                    }),
-                  ],
+                  importLoaders: 1,
+                  modules: true,
+                  localIdentName: '[path]__[name]___[local]',
                 },
               },
+              {
+                loader: require.resolve('postcss-loader'),
+                options: postCSSLoaderOptions,
+              },
             ],
           },
           // "file" loader makes sure those assets get served by WebpackDevServer.

Diff for: packages/react-scripts/config/webpack.config.prod.js

@@ -55,6 +55,20 @@ const extractTextPluginOptions = shouldUseRelativeAssetPaths
     { publicPath: Array(cssFilename.split('/').length).join('../') }
   : {};
 
+// Options for PostCSS as we reference these options twice
+// Adds vendor prefixing to support IE9 and above
+const postCSSLoaderOptions = {
+  // Necessary for external CSS imports to work
+  // https://github.com/facebookincubator/create-react-app/issues/2677
+  ident: 'postcss',
+  plugins: () => [
+    require('postcss-flexbugs-fixes'),
+    autoprefixer({
+      flexbox: 'no-2009',
+    }),
+  ],
+};
+
 // This is the production configuration.
 // It compiles slowly and is focused on producing a fast and minimal bundle.
 // The development configuration is different and lives in a separate file.
@@ -221,8 +235,10 @@ module.exports = {
           // tags. If you use code splitting, however, any async bundles will still
           // use the "style" loader inside the async code so CSS from them won't be
           // in the main CSS file.
+          // By default we support CSS Modules with the extension .module.css
           {
             test: /\.css$/,
+            exclude: /\.module\.css$/,
             loader: ExtractTextPlugin.extract(
               Object.assign(
                 {
@@ -243,18 +259,43 @@ module.exports = {
                     },
                     {
                       loader: require.resolve('postcss-loader'),
+                      options: postCSSLoaderOptions,
+                    },
+                  ],
+                },
+                extractTextPluginOptions
+              )
+            ),
+            // Note: this won't work without `new ExtractTextPlugin()` in `plugins`.
+          },
+          // Adds support for CSS Modules (https://github.com/css-modules/css-modules)
+          // using the extension .module.css
+          {
+            test: /\.module\.css$/,
+            loader: ExtractTextPlugin.extract(
+              Object.assign(
+                {
+                  fallback: {
+                    loader: require.resolve('style-loader'),
+                    options: {
+                      hmr: false,
+                    },
+                  },
+                  use: [
+                    {
+                      loader: require.resolve('css-loader'),
                       options: {
-                        // Necessary for external CSS imports to work
-                        // https://github.com/facebookincubator/create-react-app/issues/2677
-                        ident: 'postcss',
-                        plugins: () => [
-                          require('postcss-flexbugs-fixes'),
-                          autoprefixer({
-                            flexbox: 'no-2009',
-                          }),
-                        ],
+                        importLoaders: 1,
+                        minimize: true,
+                        sourceMap: shouldUseSourceMap,
+                        modules: true,
+                        localIdentName: '[path]__[name]___[local]',
                       },
                     },
+                    {
+                      loader: require.resolve('postcss-loader'),
+                      options: postCSSLoaderOptions,
+                    },
                   ],
                 },
                 extractTextPluginOptions

Diff for: packages/react-scripts/fixtures/kitchensink/integration/webpack.test.js

@@ -21,6 +21,16 @@ describe('Integration', () => {
       ).to.match(/#feature-css-inclusion\{background:.+;color:.+}/);
     });
 
+    it('css modules inclusion', async () => {
+      const doc = await initDOM('css-modules-inclusion');
+
+      expect(
+        doc.getElementsByTagName('style')[0].textContent.replace(/\s/g, '')
+      ).to.match(
+        /.+__style-module___cssModulesInclusion+\{background:.+;color:.+}/
+      );
+    });
+
     it('image inclusion', async () => {
       const doc = await initDOM('image-inclusion');
 

Diff for: packages/react-scripts/fixtures/kitchensink/src/App.js

@@ -81,6 +81,11 @@ class App extends Component {
           this.setFeature(f.default)
         );
         break;
+      case 'css-modules-inclusion':
+        import(
+          './features/webpack/CssModulesInclusion'
+        ).then(f => this.setFeature(f.default));
+        break;
       case 'custom-interpolation':
         import('./features/syntax/CustomInterpolation').then(f =>
           this.setFeature(f.default)

Diff for: packages/react-scripts/fixtures/kitchensink/src/features/webpack/CssModulesInclusion.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+import styles from './assets/style.module.css';
+
+export default () => (
+  <p className={styles.cssModulesInclusion}>CSS Modules are working!</p>
+);

Diff for: packages/react-scripts/fixtures/kitchensink/src/features/webpack/CssModulesInclusion.test.js

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+import ReactDOM from 'react-dom';
+import CssModulesInclusion from './CssModulesInclusion';
+
+describe('css modules inclusion', () => {
+  it('renders without crashing', () => {
+    const div = document.createElement('div');
+    ReactDOM.render(<CssModulesInclusion />, div);
+  });
+});

Diff for: packages/react-scripts/fixtures/kitchensink/src/features/webpack/assets/style.module.css

@@ -0,0 +1,4 @@
+.cssModulesInclusion {
+  background: darkblue;
+  color: lightblue;
+}

Diff for: packages/react-scripts/package.json

@@ -45,6 +45,7 @@
     "file-loader": "1.1.6",
     "fs-extra": "5.0.0",
     "html-webpack-plugin": "2.30.1",
+    "identity-obj-proxy": "3.0.0",
     "jest": "22.1.1",
     "object-assign": "4.1.1",
     "postcss-flexbugs-fixes": "3.2.0",

Diff for: packages/react-scripts/scripts/utils/createJestConfig.js

@@ -39,9 +39,13 @@ module.exports = (resolve, rootDir, isEjecting) => {
         'config/jest/fileTransform.js'
       ),
     },
-    transformIgnorePatterns: ['[/\\\\]node_modules[/\\\\].+\\.(js|jsx|mjs)$'],
+    transformIgnorePatterns: [
+      '[/\\\\]node_modules[/\\\\].+\\.(js|jsx|mjs)$',
+      '^.+\\.module\\.css$',
+    ],
     moduleNameMapper: {
       '^react-native$': 'react-native-web',
+      '^.+\\.module\\.css$': 'identity-obj-proxy',
     },
     moduleFileExtensions: [
       'web.js',

Diff for: packages/react-scripts/template/README.md

@@ -24,6 +24,7 @@ You can find the most recent version of this guide [here](https://github.com/fac
 - [Importing a Component](#importing-a-component)
 - [Code Splitting](#code-splitting)
 - [Adding a Stylesheet](#adding-a-stylesheet)
+- [Adding a CSS Modules stylesheet](#adding-a-css-modules-stylesheet)
 - [Post-Processing CSS](#post-processing-css)
 - [Adding a CSS Preprocessor (Sass, Less etc.)](#adding-a-css-preprocessor-sass-less-etc)
 - [Adding Images, Fonts, and Files](#adding-images-fonts-and-files)
@@ -513,6 +514,51 @@ In development, expressing dependencies this way allows your styles to be reload
 
 If you are concerned about using Webpack-specific semantics, you can put all your CSS right into `src/index.css`. It would still be imported from `src/index.js`, but you could always remove that import if you later migrate to a different build tool.
 
+## Adding a CSS Modules stylesheet
+
+This project supports [CSS Modules](https://github.com/css-modules/css-modules) alongside regular stylesheets using the **[name].module.css** file naming convention. CSS Modules allows the scoping of CSS by automatically creating a unique classname of the format **[dir]\_\_[filename]___[classname]**.
+
+An advantage of this is the ability to repeat the same classname within many CSS files without worrying about a clash.
+
+### `Button.module.css`
+
+```css
+.button {
+  padding: 20px;
+}
+```
+
+### `another-stylesheet.css`
+
+```css
+.button {
+  color: green;
+}
+```
+
+### `Button.js`
+
+```js
+import React, { Component } from 'react';
+import './another-stylesheet.css'; // Import regular stylesheet
+import styles from './Button.module.css'; // Import css modules stylesheet as styles
+
+class Button extends Component {
+  render() {
+    // You can use them as regular CSS styles
+    return <div className={styles.button} />;
+  }
+}
+```
+### `exported HTML`
+No clashes from other `.button` classnames
+
+```html
+<div class="src__Button-module___button"></div>
+```
+
+**This is an optional feature.** Regular html stylesheets and js imported stylesheets are fully supported. CSS Modules are only added when explictly named as a css module stylesheet using the extension `.module.css`.
+
 ## Post-Processing CSS
 
 This project setup minifies your CSS and adds vendor prefixes to it automatically through [Autoprefixer](https://github.com/postcss/autoprefixer) so you don’t need to worry about it.