Don't strip stack traces of evaluated webpack bundles (facebook#1050)

* Don't strip stack traces of evaluated webpack code

* Strip stack traces at the end of a string

because the last line doesn't always have a `\n` and `create-react-app` is leaving the last line of the stack traces present in the error messages

* code comment

* code comment

Author: jameslnewell

Diff for: packages/react-dev-utils/formatWebpackMessages.js

@@ -101,9 +101,12 @@ function formatMessage(message) {
 
   // Reassemble the message.
   message = lines.join('\n');
-  // Internal stacks are generally useless so we strip them
+  // Internal stacks are generally useless so we strip them... with the
+  // exception of stacks containing `webpack:` because they're normally
+  // from user code generated by WebPack. For more information see
+  // https://github.com/facebookincubator/create-react-app/pull/1050
   message = message.replace(
-    /^\s*at\s.*:\d+:\d+[\s\)]*\n/gm, ''
+    /^\s*at\s((?!webpack:).)*:\d+:\d+[\s\)]*(\n|$)/gm, ''
   ); // at ... ...:x:y
 
   return message;