From 30c9d9e9f7a6ae36586fb41edafea9dcbb4b2282 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Szabo?= <tomas.szabo@deftomat.com>
Date: Fri, 8 Feb 2019 04:34:52 +0100
Subject: [PATCH] Speed up TypeScript projects (#5903)

As a lot of [people](https://hackernoon.com/why-i-no-longer-use-typescript-with-react-and-why-you-shouldnt-either-e744d27452b4) is complaining about TypeScript performance in CRA, I decided to enable `async` mode in TypeScript checker.

These changes basically brings the JS compilation times to TS projects. So, recompilation took less than 1 second instead of 3 seconds in medium size project.

The problem with async mode is that type-errors are reported after Webpack ends up recompilation as TypeScript could be slower than Babel. PR allows to emit files compiled by Babel immediately and then wait for TS and show type errors in terminal later. Also, if there was no compilation errors and any type error occurs, we trigger a hot-reload with new errors to show error overlay in browser.

Also, I wanted to start a discussion about `skipLibCheck: false` option in default `tsconfig.json`. This makes recompilations really slow and we should consider to set it to `true` or at least give users a big warning to let them know that it could be really slow.

The following video is showing the updated workflow with a forced 2.5 second delay for type-check to give you an idea how it works.

![nov-26-2018 15-47-01](https://user-images.githubusercontent.com/5549148/49021284-9446fe80-f192-11e8-952b-8f83d77d5fbc.gif)


I'm pretty sure that PR needs some polishing and improvements but it should works as it is. Especially a "hack" with reloading the browser after type-check looks ugly to me.

cc @brunolemos as he is an initiator of an original TypeScript PR.

Should fix https://github.com/facebook/create-react-app/issues/5820
---
 config/webpack.config.js | 16 +++++-----------
 package.json             |  2 +-
 scripts/start.js         | 17 ++++++++++++++++-
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/config/webpack.config.js b/config/webpack.config.js
index 942c22a2cc7..1e304d76046 100644
--- a/config/webpack.config.js
+++ b/config/webpack.config.js
@@ -29,7 +29,7 @@ const getCSSModuleLocalIdent = require('react-dev-utils/getCSSModuleLocalIdent')
 const paths = require('./paths');
 const getClientEnvironment = require('./env');
 const ModuleNotFoundPlugin = require('react-dev-utils/ModuleNotFoundPlugin');
-const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin-alt');
+const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');
 const typescriptFormatter = require('react-dev-utils/typescriptFormatter');
 // @remove-on-eject-begin
 const getCacheIdentifier = require('react-dev-utils/getCacheIdentifier');
@@ -617,17 +617,10 @@ module.exports = function(webpackEnv) {
           typescript: resolve.sync('typescript', {
             basedir: paths.appNodeModules,
           }),
-          async: false,
+          async: isEnvDevelopment,
+          useTypescriptIncrementalApi: true,
           checkSyntacticErrors: true,
           tsconfig: paths.appTsConfig,
-          compilerOptions: {
-            module: 'esnext',
-            moduleResolution: 'node',
-            resolveJsonModule: true,
-            isolatedModules: true,
-            noEmit: true,
-            jsx: 'preserve',
-          },
           reportFiles: [
             '**',
             '!**/*.json',
@@ -638,7 +631,8 @@ module.exports = function(webpackEnv) {
           ],
           watch: paths.appSrc,
           silent: true,
-          formatter: typescriptFormatter,
+          // The formatter is invoked directly in WebpackDevServerUtils during development
+          formatter: isEnvProduction ? typescriptFormatter : undefined,
         }),
     ].filter(Boolean),
     // Some libraries import Node modules but don't use them in the browser.
diff --git a/package.json b/package.json
index a9ed5e4c835..d393b73190b 100644
--- a/package.json
+++ b/package.json
@@ -45,7 +45,7 @@
     "eslint-plugin-jsx-a11y": "6.1.2",
     "eslint-plugin-react": "7.12.3",
     "file-loader": "2.0.0",
-    "fork-ts-checker-webpack-plugin-alt": "0.4.14",
+    "fork-ts-checker-webpack-plugin": "1.0.0-alpha.6",
     "fs-extra": "7.0.1",
     "html-webpack-plugin": "4.0.0-alpha.2",
     "identity-obj-proxy": "3.0.0",
diff --git a/scripts/start.js b/scripts/start.js
index 852e6b8fb44..6ad020c9d46 100644
--- a/scripts/start.js
+++ b/scripts/start.js
@@ -94,9 +94,24 @@ checkBrowsers(paths.appPath, isInteractive)
     const config = configFactory('development');
     const protocol = process.env.HTTPS === 'true' ? 'https' : 'http';
     const appName = require(paths.appPackageJson).name;
+    const useTypeScript = fs.existsSync(paths.appTsConfig);
     const urls = prepareUrls(protocol, HOST, port);
+    const devSocket = {
+      warnings: warnings =>
+        devServer.sockWrite(devServer.sockets, 'warnings', warnings),
+      errors: errors =>
+        devServer.sockWrite(devServer.sockets, 'errors', errors),
+    };
     // Create a webpack compiler that is configured with custom messages.
-    const compiler = createCompiler(webpack, config, appName, urls, useYarn);
+    const compiler = createCompiler(
+      webpack,
+      config,
+      appName,
+      urls,
+      useYarn,
+      useTypeScript,
+      devSocket
+    );
     // Load proxy config
     const proxySetting = require(paths.appPackageJson).proxy;
     const proxyConfig = prepareProxy(proxySetting, paths.appPublic);