Runtime Exceptions aren't displayed in the UI console when using DDC/Flutter

[johnpryan]

Exceptions in DDC are reported to the window.onerror callback. Right now, these errors are being reported as "Script error." because the script is being loaded from a different domain. (See this article.) Non-async exceptions are caught by the Flutter framework and printed to the console.

The response headers from the compileDDC endpoint already have an access-control-allow-origin: * header, so setting the crossorigin attribute to anonymous should solve this problem, but doesn't seem to work for me.

We should investigate different options for capturing and reporting errors. For example, the future returned by a module calling main() can be listened to for errors, but won't catch everything:

dartpad_main.main.main().catchError(function (e, st) {
parent.postMessage(
  {'sender': 'frame', 'type': 'stderr', 'message': e + st}, '*');
});

Another option is to use zones, but this requires more investigation

related to #1357

[johnpryan]

Related to flutter/flutter#41878

[parlough]

I'm not sure the full current state of surfacing runtime exceptions, but I'm going to close this in favor of consolidating with the work in #3008. Thanks!