Add experimental react-refresh support

docusaurus/docs/advanced-configuration.md

@@ -26,4 +26,5 @@ You can adjust various development and production settings by setting environmen
 | INLINE_RUNTIME_CHUNK    | 🚫 Ignored  |  ✅ Used   | By default, Create React App will embed the runtime script into `index.html` during the production build. When set to `false`, the script will not be embedded and will be imported as usual. This is normally required when dealing with CSP.                                                                                                                                                                                                                                                                                                                                                                                                                           |
 | IMAGE_INLINE_SIZE_LIMIT | 🚫 Ignored  |  ✅ Used   | By default, images smaller than 10,000 bytes are encoded as a data URI in base64 and inlined in the CSS or JS build artifact. Set this to control the size limit in bytes. Setting it to 0 will disable the inlining of images.                                                                                                                                                                                                                                                                                                                                                                                                                                          |
 | EXTEND_ESLINT           |   ✅ Used   |  ✅ Used   | When set to `true`, user provided ESLint configs will be used by `eslint-loader`. Note that any rules set to `"error"` will stop the application from building.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
+| FAST_REFRESH            |   ✅ Used   | 🚫 Ignored | When set to `true`, enables experimental support for fast refresh to allow you to tweak your components in real time without reloading the page.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
 | TSC_COMPILE_ON_ERROR    |   ✅ Used   |  ✅ Used   | When set to `true`, you can run and properly build TypeScript projects even if there are TypeScript type check errors. These errors are printed as warnings in the terminal and/or browser console.                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |

packages/react-dev-utils/webpackHotDevClient.js

@@ -243,7 +243,10 @@ function tryApplyUpdates(onHotUpdateSuccess) {
   }
 
   function handleApplyUpdates(err, updatedModules) {
-    if (err || !updatedModules || hadRuntimeError) {
+    const hasReactRefresh = process.env.FAST_REFRESH;
+    const wantsForcedReload = err || !updatedModules || hadRuntimeError;
+    // React refresh can handle hot-reloading over errors.
+    if (!hasReactRefresh && wantsForcedReload) {
       window.location.reload();
       return;
     }

packages/react-scripts/config/env.js

@@ -93,6 +93,11 @@ function getClientEnvironment(publicUrl) {
         WDS_SOCKET_HOST: process.env.WDS_SOCKET_HOST,
         WDS_SOCKET_PATH: process.env.WDS_SOCKET_PATH,
         WDS_SOCKET_PORT: process.env.WDS_SOCKET_PORT,
+        // Whether or not react-refresh is enabled.
+        // react-refresh is not 100% stable at this time,
+        // which is why it's disabled by default.
+        // It is defined here so it is available in the webpackHotDevClient.
+        FAST_REFRESH: process.env.FAST_REFRESH || false,
       }
     );
   // Stringify all values so we can feed into webpack DefinePlugin

packages/react-scripts/config/hotRefreshOverlayModuleStub.js

@@ -0,0 +1,22 @@
+/**
+ * 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.
+ */
+
+// This file is currently required because the error overlay has a bug preventing the its outright disabling.
+
+'use strict';
+
+function handleRuntimeError() {
+  // Stubbed out due to a bug.
+}
+function clearRuntimeErrors() {
+  // Stubbed out due to a bug.
+}
+
+module.exports = {
+  handleRuntimeError,
+  clearRuntimeErrors,
+};

packages/react-scripts/config/webpack.config.js

@@ -32,6 +32,7 @@ const getClientEnvironment = require('./env');
 const ModuleNotFoundPlugin = require('react-dev-utils/ModuleNotFoundPlugin');
 const ForkTsCheckerWebpackPlugin = require('react-dev-utils/ForkTsCheckerWebpackPlugin');
 const typescriptFormatter = require('react-dev-utils/typescriptFormatter');
+const ReactRefreshWebpackPlugin = require('@pmmmwh/react-refresh-webpack-plugin');
 // @remove-on-eject-begin
 const getCacheIdentifier = require('react-dev-utils/getCacheIdentifier');
 // @remove-on-eject-end
@@ -41,6 +42,11 @@ const appPackageJson = require(paths.appPackageJson);
 
 // Source maps are resource heavy and can cause out of memory issue for large source files.
 const shouldUseSourceMap = process.env.GENERATE_SOURCEMAP !== 'false';
+
+const webpackDevClientEntry = require.resolve(
+  'react-dev-utils/webpackHotDevClient'
+);
+
 // Some apps do not need the benefits of saving a web request, so not inlining the chunk
 // makes for a smoother build process.
 const shouldInlineRuntimeChunk = process.env.INLINE_RUNTIME_CHUNK !== 'false';
@@ -77,6 +83,8 @@ module.exports = function(webpackEnv) {
   // Get environment variables to inject into our app.
   const env = getClientEnvironment(paths.publicUrlOrPath.slice(0, -1));
 
+  const shouldUseReactRefresh = env.raw.FAST_REFRESH;
+
   // common function to get style loaders
   const getStyleLoaders = (cssOptions, preProcessor) => {
     const loaders = [
@@ -158,10 +166,13 @@ module.exports = function(webpackEnv) {
       // Note: instead of the default WebpackDevServer client, we use a custom one
       // to bring better experience for Create React App users. You can replace
       // the line below with these two lines if you prefer the stock client:
+      //
       // require.resolve('webpack-dev-server/client') + '?/',
       // require.resolve('webpack/hot/dev-server'),
-      isEnvDevelopment &&
-        require.resolve('react-dev-utils/webpackHotDevClient'),
+      //
+      // When using the experimental react-refresh integration,
+      // the webpack plugin takes care of injecting the dev client for us.
+      isEnvDevelopment && !shouldUseReactRefresh && webpackDevClientEntry,
       // Finally, this is your app's code:
       paths.appIndexJs,
       // We include the app code last so that if there is a runtime error during
@@ -419,7 +430,10 @@ module.exports = function(webpackEnv) {
                         },
                       },
                     },
-                  ],
+                    isEnvDevelopment &&
+                      shouldUseReactRefresh &&
+                      require.resolve('react-refresh/babel'),
+                  ].filter(Boolean),
                 ],
                 // This is a feature of `babel-loader` for webpack (not Babel itself).
                 // It enables caching results in ./node_modules/.cache/babel-loader/
@@ -607,6 +621,17 @@ module.exports = function(webpackEnv) {
       new webpack.DefinePlugin(env.stringified),
       // This is necessary to emit hot updates (currently CSS only):
       isEnvDevelopment && new webpack.HotModuleReplacementPlugin(),
+      // Experimental hot reloading for React .
+      // https://github.com/facebook/react/tree/master/packages/react-refresh
+      isEnvDevelopment &&
+        shouldUseReactRefresh &&
+        new ReactRefreshWebpackPlugin({
+          overlay: {
+            entry: webpackDevClientEntry,
+            // TODO: This is just a stub module. Clean this up if possible.
+            module: require.resolve('./hotRefreshOverlayModuleStub'),
+          },
+        }),
       // Watcher doesn't work well if you mistype casing in a path so we use
       // a plugin that prints an error when you attempt to do this.
       // See https://github.com/facebook/create-react-app/issues/240

packages/react-scripts/package.json

@@ -29,6 +29,7 @@
   "types": "./lib/react-app.d.ts",
   "dependencies": {
     "@babel/core": "7.9.0",
+    "@pmmmwh/react-refresh-webpack-plugin": "0.3.0-beta.1",
     "@svgr/webpack": "4.3.3",
     "@typescript-eslint/eslint-plugin": "^2.10.0",
     "@typescript-eslint/parser": "^2.10.0",
@@ -68,6 +69,7 @@
     "postcss-safe-parser": "4.0.1",
     "react-app-polyfill": "^1.0.6",
     "react-dev-utils": "^10.2.1",
+    "react-refresh": "^0.8.1",
     "resolve": "1.15.0",
     "resolve-url-loader": "3.1.1",
     "sass-loader": "8.0.2",