Fix error messages for child compilations

packages/react-dev-utils/README.md

@@ -220,7 +220,7 @@ measureFileSizesBeforeBuild(buildFolder).then(previousFileSizes => {
 });
 ```
 
-#### `formatWebpackMessages({errors: Array<string>, warnings: Array<string>}): {errors: Array<string>, warnings: Array<string>}`
+#### `formatWebpackMessages({errors: Array<string>, warnings: Array<string>, children}): {errors: Array<string>, warnings: Array<string>}`
 
 Extracts and prettifies warning and error messages from webpack [stats](https://github.com/webpack/docs/wiki/node.js-api#stats) object.
 
@@ -236,7 +236,12 @@ compiler.hooks.invalid.tap('invalid', function() {
 });
 
 compiler.hooks.done.tap('done', function(stats) {
-  var rawMessages = stats.toJson({}, true);
+  var rawMessages = stats.toJson({
+    all: false,
+    children: true,
+    warnings: true,
+    errors: true,
+  });
   var messages = formatWebpackMessages(rawMessages);
   if (!messages.errors.length && !messages.warnings.length) {
     console.log('Compiled successfully!');

packages/react-dev-utils/WebpackDevServerUtils.js

@@ -153,7 +153,7 @@ function createCompiler(webpack, config, appName, urls, useYarn) {
     // We only construct the warnings and errors for speed:
     // https://github.com/facebook/create-react-app/issues/4492#issuecomment-421959548
     const messages = formatWebpackMessages(
-      stats.toJson({ all: false, warnings: true, errors: true })
+      stats.toJson({ all: false, children: true, warnings: true, errors: true })
     );
     const isSuccessful = !messages.errors.length && !messages.warnings.length;
     if (isSuccessful) {

packages/react-dev-utils/formatWebpackMessages.js

@@ -109,11 +109,24 @@ function formatMessage(message, isError) {
   return message.trim();
 }
 
+function recursivelyFindMessages(json, property) {
+  let messages = json[property];
+  if (json.children) {
+    json.children.forEach(function(child) {
+      const childMessages = recursivelyFindMessages(child, property);
+      messages = messages.concat(childMessages);
+    });
+  }
+  return messages;
+}
+
 function formatWebpackMessages(json) {
-  const formattedErrors = json.errors.map(function(message) {
+  const errors = recursivelyFindMessages(json, 'errors');
+  const formattedErrors = errors.map(function(message) {
     return formatMessage(message, true);
   });
-  const formattedWarnings = json.warnings.map(function(message) {
+  const warnings = recursivelyFindMessages(json, 'warnings');
+  const formattedWarnings = warnings.map(function(message) {
     return formatMessage(message, false);
   });
   const result = { errors: formattedErrors, warnings: formattedWarnings };

packages/react-scripts/scripts/build.js

@@ -157,7 +157,12 @@ function build(previousFileSizes) {
         });
       } else {
         messages = formatWebpackMessages(
-          stats.toJson({ all: false, warnings: true, errors: true })
+          stats.toJson({
+            all: false,
+            children: true,
+            warnings: true,
+            errors: true,
+          })
         );
       }
       if (messages.errors.length) {