Support setting baseUrl to root directory

packages/react-scripts/config/modules.js

@@ -15,7 +15,7 @@ const chalk = require('react-dev-utils/chalk');
 const resolve = require('resolve');
 
 /**
- * Get the baseUrl of a compilerOptions object.
+ * Get additional module paths based on the baseUrl of a compilerOptions object.
  *
  * @param {Object} options
  */
@@ -46,6 +46,15 @@ function getAdditionalModulePaths(options = {}) {
     return [paths.appSrc];
   }
 
+  // If the path is equal to the root directory we ignore it here.
+  // We don't want to allow importing from the root directly as source files are
+  // not transpiled outside of `src`. We do allow importing them with the
+  // absolute path (e.g. `src/Components/Button.js`) but we set that up with
+  // an alias.
+  if (path.relative(paths.appPath, baseUrlResolved) === '') {
+    return null;
+  }
+
   // Otherwise, throw an error.
   throw new Error(
     chalk.red.bold(
@@ -55,6 +64,48 @@ function getAdditionalModulePaths(options = {}) {
   );
 }
 
+/**
+ * Get webpack aliases based on the baseUrl of a compilerOptions object.
+ *
+ * @param {*} options
+ */
+function getWebpackAliases(options = {}) {
+  const baseUrl = options.baseUrl;
+
+  if (!baseUrl) {
+    return {};
+  }
+
+  const baseUrlResolved = path.resolve(paths.appPath, baseUrl);
+
+  if (path.relative(paths.appPath, baseUrlResolved) === '') {
+    return {
+      src: paths.appSrc,
+    };
+  }
+}
+
+/**
+ * Get jest aliases based on the baseUrl of a compilerOptions object.
+ *
+ * @param {*} options
+ */
+function getJestAliases(options = {}) {
+  const baseUrl = options.baseUrl;
+
+  if (!baseUrl) {
+    return {};
+  }
+
+  const baseUrlResolved = path.resolve(paths.appPath, baseUrl);
+
+  if (path.relative(paths.appPath, baseUrlResolved) === '') {
+    return {
+      'src/(.*)$': '<rootDir>/src/$1',
+    };
+  }
+}
+
 function getModules() {
   // Check if TypeScript is setup
   const hasTsConfig = fs.existsSync(paths.appTsConfig);
@@ -89,6 +140,8 @@ function getModules() {
 
   return {
     additionalModulePaths: additionalModulePaths,
+    webpackAliases: getWebpackAliases(options),
+    jestAliases: getJestAliases(options),
     hasTsConfig,
   };
 }

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

@@ -306,6 +306,7 @@ module.exports = function(webpackEnv) {
         // Support React Native Web
         // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
         'react-native': 'react-native-web',
+        ...(modules.webpackAliases || {}),
       },
       plugins: [
         // Adds support for installing with Plug'n'Play, leading to faster installs and adding
@@ -352,7 +353,9 @@ module.exports = function(webpackEnv) {
                     const eslintCli = new eslint.CLIEngine();
                     let eslintConfig;
                     try {
-                      eslintConfig = eslintCli.getConfigForFile(paths.appIndexJs);
+                      eslintConfig = eslintCli.getConfigForFile(
+                        paths.appIndexJs
+                      );
                     } catch (e) {
                       console.error(e);
                       process.exit(1);

packages/react-scripts/scripts/utils/createJestConfig.js

@@ -56,6 +56,7 @@ module.exports = (resolve, rootDir, isEjecting) => {
     moduleNameMapper: {
       '^react-native$': 'react-native-web',
       '^.+\\.module\\.(css|sass|scss)$': 'identity-obj-proxy',
+      ...(modules.jestAliases || {}),
     },
     moduleFileExtensions: [...paths.moduleFileExtensions, 'node'].filter(
       ext => !ext.includes('mjs')