use.future inside a RearchConsumer possible issue

[busslina]

I have a Scrollable widget whose children are disposed if they are not visible. One of the children is _AsyncImage, a RearchConsumer that uses the future side effect to precache the image (from the Internet) and show a loading spinner while loading. So the problem came when I scroll quickly enough to get this widget created and disposed before the image get loaded. I got a Stream error which I'm 99% sure it is related to use.future. Do you have a solution for this scenario?

Widget:

class _AsyncImage extends RearchConsumer {
  const _AsyncImage(this.image);

  final Image image;

  @override
  Widget build(BuildContext context, WidgetHandle use) {
    final precacheValue = use.future(
      use.memo(
        () => image.precache(context),
        [image],
      ),
    );

    switch (precacheValue) {
      case AsyncLoading():
        return const CircularProgressIndicator().centered();

      case AsyncError():
        return const Label.error('Precaching image');

      case AsyncValue():
        return image.rounded(radius: 25);
    }
  }
}

Error stack trace (on the web):

Error
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/err
ors.dart 296:3  throw_
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/err
ors.dart 29:3   assertFailed
packages/flutter/src/widgets/framework.dart 5018:49
markNeedsBuild
packages/flutter_rearch/src/widgets/consumer.dart 150:5
rebuild
packages/rearch/src/side_effects.dart 71:12
setter
packages/rearch/src/side_effects.dart 331:29
<fn>
dart-sdk/lib/async/zone.dart 1594:9
runUnaryGuarded
dart-sdk/lib/async/stream_impl.dart 365:5
[_sendData]
dart-sdk/lib/async/stream_impl.dart 297:7
[_add]
dart-sdk/lib/async/stream_controller.dart 784:5
[_sendData]
dart-sdk/lib/async/stream_controller.dart 658:7
[_add]
dart-sdk/lib/async/stream.dart 250:17
<fn>
dart-sdk/lib/async/zone.dart 1661:54
runUnary
dart-sdk/lib/async/future_impl.dart 163:18
handleValue
dart-sdk/lib/async/future_impl.dart 847:44
handleValueCallback
dart-sdk/lib/async/future_impl.dart 876:13
_propagateToListeners
dart-sdk/lib/async/future_impl.dart 652:5
[_completeWithValue]
dart-sdk/lib/async/future_impl.dart 722:7
callback
dart-sdk/lib/async/schedule_microtask.dart 40:11
_microtaskLoop
dart-sdk/lib/async/schedule_microtask.dart 49:5
_startMicrotaskLoop
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart
181:7           <fn>
Error
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/err
ors.dart 296:3  throw_
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/err
ors.dart 29:3   assertFailed
packages/flutter/src/widgets/framework.dart 5018:49
markNeedsBuild
packages/flutter_rearch/src/widgets/consumer.dart 150:5
rebuild
packages/rearch/src/side_effects.dart 71:12
setter
packages/rearch/src/side_effects.dart 331:29
<fn>
dart-sdk/lib/async/zone.dart 1594:9
runUnaryGuarded
dart-sdk/lib/async/stream_impl.dart 365:5
[_sendData]
dart-sdk/lib/async/stream_impl.dart 297:7
[_add]
dart-sdk/lib/async/stream_controller.dart 784:5
[_sendData]
dart-sdk/lib/async/stream_controller.dart 658:7
[_add]
dart-sdk/lib/async/stream.dart 250:17
<fn>
dart-sdk/lib/async/zone.dart 1661:54
runUnary
dart-sdk/lib/async/future_impl.dart 163:18
handleValue
dart-sdk/lib/async/future_impl.dart 847:44
handleValueCallback
dart-sdk/lib/async/future_impl.dart 876:13
_propagateToListeners
dart-sdk/lib/async/future_impl.dart 652:5
[_completeWithValue]
dart-sdk/lib/async/future_impl.dart 722:7
callback
dart-sdk/lib/async/schedule_microtask.dart 40:11
_microtaskLoop
dart-sdk/lib/async/schedule_microtask.dart 49:5
_startMicrotaskLoop
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart
181:7           <fn>

[busslina]

This packages/rearch/src/side_effects.dart 331:29 points to (data) => setValue(AsyncData(data)) here:

AsyncValue<T>? nullableStream<T>(Stream<T>? stream) {
    final (getValue, setValue) = use.data<AsyncValue<T>>(
      AsyncLoading<T>(None<T>()),
    );

    final (getSubscription, setSubscription) =
        use.data<StreamSubscription<T>?>(null);
    use.effect(() => getSubscription()?.cancel, [getSubscription()]);

    final oldStream = use.previous(stream);
    final needToInitializeState = stream != oldStream;

    if (needToInitializeState) {
      setValue(AsyncLoading(getValue().data));
      setSubscription(
        stream?.listen(
          (data) => setValue(AsyncData(data)),
          onError: (Object error, StackTrace trace) =>
              setValue(AsyncError(error, trace, getValue().data)),
          cancelOnError: false,
        ),
      );
    }

    return stream == null ? null : getValue();
  }

[GregoryConrad]

Taking a look. This means that canceling the subscription on the stream like is being done now isn't being done in time, which is annoying. Will have to update the rebuild call to ignore rebuilds done after dispose. This isn't really a ReArch issue per say, but I suppose I can add a workaround in.

[busslina]

Okay, if there were not a workaround I still could use CancelableOperation in order to bypass it.

Also, don't you think that it could be a future side effect that doesn't use Stream, and use Completer instead? I think this problem will not be present in this case. Or even using CancelableOperation: then you could cancel it on capsule dispose

[GregoryConrad]

Or even using CancelableOperation: then you could cancel it on capsule dispose

I almost did back when I was first creating ReArch, but I didn't want to add another dependency, and I still don't really want to. That's why use.future uses use.stream, since it appeared I could cancel a subscription that way.

I could rewrite it to use Completer, since I think that is in dart:async and thus wouldn't need another dependency. Since my other option would be a somewhat hacky workaround, I might try that first.

[busslina]

I could rewrite it to use Completer.

Yeah, it's in the Dart SDK.

[GregoryConrad]

Tracking this bug in #195