Polish webpack message output (#5174)

* Only install react-scripts in CI mode

* Link locally

* Re-enable all output tests

* 💄 Polish webpack output

* Test sass support message

* Add more tests, but disabled

* Format missing default export error

* Format aliased import

* Why was node-sass required? Odd

* Format webpack rejection error

* Re-enable unknown package test

* Format file not found error and catch module scope plugin error

* Re-disable case sensitive paths

* Intercept and format case sensitive path errors

* Test out of scope message formatting

* Run behavior on macOS

* Run behavior on Node 8 and 10, only Node 8 for macOS

* Add some debugging

* Update matcher

* Only check stderr

* Remove old snapshot

* More debug

* Remove debug

* Add new debug

* Disable test on linux

* Add comment for future

packages/react-scripts/scripts/build.js

@@ -141,12 +141,20 @@ function build(previousFileSizes) {
   let compiler = webpack(config);
   return new Promise((resolve, reject) => {
     compiler.run((err, stats) => {
+      let messages;
       if (err) {
-        return reject(err);
+        if (!err.message) {
+          return reject(err);
+        }
+        messages = formatWebpackMessages({
+          errors: [err.message],
+          warnings: [],
+        });
+      } else {
+        messages = formatWebpackMessages(
+          stats.toJson({ all: false, warnings: true, errors: true })
+        );
       }
-      const messages = formatWebpackMessages(
-        stats.toJson({ all: false, warnings: true, errors: true })
-      );
       if (messages.errors.length) {
         // Only keep the first error. Others are often indicative
         // of the same problem, but confuse the reader with noise.