🎨 add first class debugging support

packages/react-scripts/bin/react-scripts.js

@@ -12,18 +12,17 @@
 
 var spawn = require('cross-spawn');
 var script = process.argv[2];
-var args = process.argv.slice(3);
+var getArgs = require('../scripts/utils/getSubscriptArgs');
 
 switch (script) {
   case 'build':
   case 'eject':
   case 'start':
   case 'test':
-    var result = spawn.sync(
-      'node',
-      [require.resolve('../scripts/' + script)].concat(args),
-      { stdio: 'inherit' }
-    );
+    var scriptFilename = require.resolve('../scripts/' + script);
+    var result = spawn.sync('node', getArgs(scriptFilename), {
+      stdio: 'inherit',
+    });
     if (result.signal) {
       if (result.signal === 'SIGKILL') {
         console.log(

packages/react-scripts/config/jest/babelTransform.js

@@ -13,4 +13,5 @@ const babelJest = require('babel-jest');
 module.exports = babelJest.createTransformer({
   presets: [require.resolve('babel-preset-react-app')],
   babelrc: false,
+  sourceMaps: process.env.REACT_APP_DEBUG_JEST ? 'inline' : false,
 });

packages/react-scripts/scripts/test.js

@@ -8,8 +8,16 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 // @remove-on-eject-end
+
+/**
+  * Greetings! If you are here attempting to start a debugging session, please
+  * ensure that your debugger of choice is configured to enable source maps,
+  * otherwise your code may appear mangled by babel!
+  */
 'use strict';
 
+var debugArgs = require('./utils/debugArgs');
+
 process.env.NODE_ENV = 'test';
 process.env.PUBLIC_URL = '';
 
@@ -27,13 +35,23 @@ process.on('unhandledRejection', err => {
 require('dotenv').config({ silent: true });
 
 const jest = require('jest');
-const argv = process.argv.slice(2);
+let argv = process.argv.slice(2);
+const isDebug = !!process.env.REACT_APP_DEBUG_JEST;
+const isRunInBand = argv.indexOf('--runInBand') > -1 || argv.indexOf('-i') > -1;
 
 // Watch unless on CI or in coverage mode
 if (!process.env.CI && argv.indexOf('--coverage') < 0) {
   argv.push('--watch');
 }
 
+// Force debug into single worker
+if (isDebug) {
+  if (!isRunInBand) {
+    argv.push('--runInBand');
+  }
+  argv = debugArgs.removeFrom(argv);
+}
+
 // @remove-on-eject-begin
 // This is not necessary after eject because we embed config into package.json.
 const createJestConfig = require('./utils/createJestConfig');

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

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+const DEBUG_FLAGS = [
+  /^debug$/,
+  /^--debug$/,
+  /^--debug-brk(=\d+)?$/,
+  /^--inspect$/,
+  /^--inspect-brk(=\d+)?$/,
+];
+
+module.exports = {
+  _match: function _matchDebugFlags(args, onMatch) {
+    for (var i in args) {
+      if (args.hasOwnProperty(i)) {
+        for (var j in DEBUG_FLAGS) {
+          if (DEBUG_FLAGS.hasOwnProperty(j)) {
+            if (args[i].match(DEBUG_FLAGS[j])) {
+              onMatch(args[i]);
+            }
+          }
+        }
+      }
+    }
+  },
+  getFrom: function getDebugFlags(args) {
+    var matches = [];
+    this._match(args, function addMatch(arg) {
+      matches.push(arg);
+    });
+    return matches.length ? matches : null;
+  },
+  removeFrom: function removeDebugFlags(args) {
+    var matches = this.getFrom(args) || [];
+    return args.filter(function isNotDebugArg(arg) {
+      return !matches.some(function isPresent(debugArg) {
+        return arg === debugArg;
+      });
+    });
+  },
+};

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

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+var debugArgs = require('../utils/debugArgs');
+
+module.exports = function getSubscriptArgs(scriptFilename) {
+  var args = process.argv.slice(3);
+  var passedDebugArgs;
+  var nonDebugArgs;
+  args.unshift(scriptFilename);
+  passedDebugArgs = debugArgs.getFrom(args);
+  if (passedDebugArgs) {
+    process.env.REACT_APP_DEBUG_JEST = 'true'; // :eyes: side-effect
+    nonDebugArgs = debugArgs.removeFrom(args);
+    args = passedDebugArgs.concat(nonDebugArgs);
+  }
+  return args;
+};