Invalid Isolate arguments throw uncatchable errors

[nex3]

When you try to send an illegal object across isolate boundaries, Dart currently top-levels an exception. I'd expect it to throw synchronously on the call to SendPort.add(). The current behavior makes it extremely difficult to tell where the illegal object is coming from or to gracefully handle the error.

For example:

import 'dart:async';
import 'dart:isolate';

main() {
  Isolate.spawnUri(new Uri.dataFromString(r"""
    import "dart:isolate";

    void main(_, SendPort port) {
      runZoned(() {
        try {
          port.send([].iterator);
        } catch (error) {
          print("caught sync $error");
        }
      }, onError: (error) {
        print("caught async $error");
      });
    }
  """), [], new ReceivePort());
}

See also #18593.

[floitschG]

Why was this marked as S1?

I can't reproduce.
Once I fixed the code to not fail in the main isolate (by sending new ReceivePort().sendPort), and after I fixed the spawned isolate to also import dart:async (for the runZoned) I correctly get:

caught sync Invalid argument(s): Illegal argument in isolate message : (object is a regular Dart Instance).

Uncaught errors in non-main isolates are not printed in the VM: #26626

Note that the onError argument correctly prints the error.

import 'dart:async';
import 'dart:isolate';

main() {
  var rp = new ReceivePort();
  rp.listen(print);
  Isolate.spawnUri(new Uri.dataFromString(r"""
    import "dart:isolate";
    import "dart:async";

    void main(_, SendPort port) {
      runZoned(() {
        try {
          port.send([].iterator);
        } catch (error) {
          print("caught sync $error");
        }
      }, onError: (error) {
        print("caught async $error");
      });
    }
  """), [], rp.sendPort, onError: rp.sendPort);
}

[kevmoo]

I marked it S1 because I was told it would be difficult to impossible to debug/diagnose

[nex3]

Sorry, my mistake!