`extension FutureIterable<T>.wait` does not work properly in Dart/Flutter

extension FutureIterable<T>.wait does not work properly

from the documentation:

/// Similar to [Future.wait], but reports errors using a
/// [ParallelWaitError], which allows the caller to
/// handle errors and dispose successful results if necessary.

The following code:

Future<int> main() async {
  await process([1, 2, 3, 4, 5]);
  return 0;
}

Future<void> process(Iterable<int> messages) async {
  print("len: ${messages.length}");
  Iterable<Future<int>> futures = messages.map((message) {
    return fibo(message);
  });
  assert(messages.length == futures.length);
  try {
    print("before big wait");
    await futures.wait;
    print("after big wait");
  } catch (e) {
    print(e.runtimeType);
    print("$e from the end");
  }
  print("stop!");
}

Future<int> fibo(int message) {
  throw "Test error handling";
}

output:

flutter: len: 5
flutter: before big wait
flutter: String
flutter: Test error handling from the end
flutter: stop!

I don’t see any sign of ParallelWaitError, as the documentation mentions. And the future returns an error at the first exception.

What do I miss?

>Solution :

Instead of using throw, try using Future.error to return an error from your function:

Future<int> fibo(int message) {
  return Future.error("Test error handling");
}

The result will show the ParallelWaitError as you expect:

len: 5
before big wait
ParallelWaitError<List<int?>, List<AsyncError?>>
ParallelWaitError(5 errors): Test error handling from the end
stop!