Error propagation doesn't work correctly in combination with async/await

[Noobware1]

here I am trying to catch the error thrown by loadMediaDetails but I am unable to do so.

import 'dart:io';
import 'package:meiyou_extenstions/meiyou_extenstions.dart';

import 'build.dart';

void main(List<String> args) async {
  final file = File(args[0]).readAsStringSync();
  final query = args[1];

  final packages = {
    'meiyou': {'main.dart': fixImports(file), ...getAllExtractors(file, {})}
  };

  final compiled = ExtenstionComplier().compilePackages(packages);

  final pluginApi = ExtenstionLoader()
      .runtimeEval(compiled)
      .executeLib('package:meiyou/main.dart', 'main') as $BasePluginApi;

  print('Starting loadMediaDetails for $query');
  try {
    final media = await pluginApi.loadMediaDetails(
        SearchResponse(title: '', url: '', poster: '', type: ShowType.Movie));
    print(media);
  } catch (e) {
    print('Caught error');
  }

}

I mean it should print Caught error but instead it prints this

Starting loadMediaDetails for oppenheimer
Unhandled exception:
dart_eval runtime exception: type 'Null' is not a subtype of type 'String'
#0      $AppUtils.$parseHtml (package:meiyou_extenstions/src/bridge_models/utils_models/app_utils.dart:327:56)
#1      InvokeExternal.run (package:dart_eval/src/eval/runtime/ops/bridge.dart:107:44)
#2      Runtime.bridgeCall (package:dart_eval/src/eval/runtime/runtime.dart:847:12)
at <asynchronous gap>

RUNTIME STATE
=============
Program offset: 1090
Stack sample: [L0: Instance of '$BasePluginApi', L1: $"", L2: Instance of '$Completer<dynamic>', L3: Instance of '$JsonCodec', L4: $"", L5: $"https://aniwatch.to", L6: $"https://aniwatch.to", L7: $"/ajax/v2/episode/list/", L8: $"https://aniwatch.to/ajax/v2/episode/list/", L9: $"https://aniwatch.to/ajax/v2/episode/list/"]
Args sample: []
Call stack: [0, -1]
TRACE:
1084: PushConstant (C78)
1085: BoxString (L19)
1086: PushArg (L19)
1087: InvokeDynamic (L18.C79)
1088: PushReturnValue ()
1089: PushArg (L20)
1090: InvokeExternal (Ex#159)  <<< EXCEPTION
1091: PushReturnValue ()
1092: PushConstant (C97)
1093: BoxString (L22)

#0      Runtime.bridgeCall (package:dart_eval/src/eval/runtime/runtime.dart:857:7)
#1      Await._suspend (package:dart_eval/src/eval/runtime/ops/bridge.dart:169:13)
<asynchronous suspension>

[ethanblake4]

I think this is primarily caused because error handling isn't really implemented yet in combination with async/await, so I'll rename this issue to reflect that. In the meantime you might be able to make this work by replacing async/await stuff with Future.then() etc in the affected codepath.

[Noobware1]

It's ok I can wait that'll be more easier.

[Noobware1]

But I am confused about one thing this code is not eval code this is real dart code so error handling is done in actually dart, so it should fine right?

[ethanblake4]

Well it appears that the loadMediaDetails() eval code implementation contains an await in it or calls a function that uses await.

[Noobware1]

So the error thrown in loadMediaDetails should catched by above catch block but It doesn't?

[ethanblake4]

Yeah. Because loadMediaDetails has an await somewhere in it, that currently breaks its ability to throw exceptions across the bridge.

[Noobware1]

Ic, Thanks for the explanation.

[Noobware1]

If this issue gets resolved will I be able to bridge these type of functions and not get any error?

T? trySync<T>(T Function() fun) {
  try {
    return fun();
  } catch (e) {
    return null;
  }
}

Future<T?> tryAsync<T>(Future<T> Function() fun) async {
  try {
    return await fun();
  } catch (e) {
    return null;
  }
}

[ethanblake4]

The first function trySync should already work, no? But yeah once I get around to fixing this you'd probably be able to use tryAsync too either as a bridge or eval function.

[Noobware1]

yeah, it works.

test('trySync', () {
      final value = compiler.compileWriteAndLoad({
        'example': {
          'main.dart': '''
          import 'package:meiyou_extensions_lib/meiyou_extensions_lib.dart';

          int? main() {
            return AppUtils.trySync<int>(() => StringUtils.toInt('this is not a number'));
          }
          '''
        }
      }).executeLib('package:example/main.dart', 'main');
      expect((value as $Value).$value, null);
    });

[Noobware1]

Any update on this?

[ethanblake4]

This is a complicated issue to solve with a lot of edge cases, it's not going to be done that soon unfortunately.

[Noobware1]

Is there any way I can help cause I need this fix bad but I also understand where you coming from so it's ok if it can't be done right now

[ethanblake4]

Alright, I figured out a temporary change I could do to allow errors to propagate through an await to the top-level. This isn't really correct since try/catch blocks inside dart_eval still won't work at all, but at least it should let a try/catch in real Dart that surrounds it function for the most part. Released in v0.7.3, don't close this though since it's not actually fixed in a correct way

[Noobware1]

Thanks a lot man

[Noobware1]

Alright, I figured out a temporary change I could do to allow errors to propagate through an await to the top-level. This isn't really correct since try/catch blocks inside dart_eval still won't work at all, but at least it should let a try/catch in real Dart that surrounds it function for the most part. Released in v0.7.3, don't close this though since it's not actually fixed in a correct way

try catch in real dart still isn't able to catch it sadly.

[ethanblake4]

Can you give more info on the error you get? I have tested it and this test passes successfully:

test('Exception bubbles through asynchronous gap', () {
      final runtime = compiler.compileWriteAndLoad({
        'example': {
          'main.dart': '''
            import 'dart:async';

            void main() async {
              await Future.delayed(const Duration(milliseconds: 10));
              throw 'error';
            }
          '''
        }
      });
      expect(() => runtime.executeLib('package:example/main.dart', 'main'),
          throwsA($String('error')));
    });