[fix,async] exception in async _CancelOnErrorSubscriptionWrapper.onError

[PROGrand]

Patch fixes exception in async (template cast seems to be changed in dart):

Unhandled exception:
type '(Object, StackTrace) => void' is not a subtype of type '(dynamic) => dynamic' in type cast
#0      _CancelOnErrorSubscriptionWrapper.onError.<anonymous closure>.<anonymous closure> (package:async/src/subscription_stream.dart:82:24)
#1      _RootZone.run (dart:async/zone.dart:1670:54)
#2      _FutureListener.handleWhenComplete (dart:async/future_impl.dart:247:18)
#3      Future._propagateToListeners.handleWhenCompleteCallback (dart:async/future_impl.dart:872:39)
#4      Future._propagateToListeners (dart:async/future_impl.dart:928:11)
#5      Future._addListener.<anonymous closure> (dart:async/future_impl.dart:513:9)
#6      _microtaskLoop (dart:async/schedule_microtask.dart:40:21)
#7      _startMicrotaskLoop (dart:async/schedule_microtask.dart:49:5)
#8      _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:118:13)
#9      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:185:5)

[kevmoo]

A test here would be GREAT

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:args	2.6.1-wip	WIP (no publish necessary)
package:async	2.13.0	ready to publish	async-v2.13.0
package:characters	1.4.0	already published at pub.dev
package:collection	1.20.0-wip	WIP (no publish necessary)
package:convert	3.1.2	already published at pub.dev
package:crypto	3.0.6	already published at pub.dev
package:fixnum	1.1.1	already published at pub.dev
package:lints	5.1.1	already published at pub.dev
package:logging	1.3.0	already published at pub.dev
package:os_detect	2.0.3	already published at pub.dev
package:path	1.9.2-wip	WIP (no publish necessary)
package:platform	3.1.6	already published at pub.dev
package:typed_data	1.4.0	already published at pub.dev

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[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
async	None	2.12.0	2.13.0	2.12.0	✔️

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Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

Coverage ✔️

File	Coverage
pkgs/async/lib/src/result/error.dart	💚 88 % ⬆️ 1 %
pkgs/async/lib/src/subscription_stream.dart	💚 100 % ⬆️ 5 %

This check for test coverage is informational (issues shown here will not fail the PR).

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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[PROGrand]

@kevmoo

Passing onError as non-inline callback (example) caused type cast errors. Patch covers this case. Now tests for such callbacks (alongside with inline) are added.

Example:

      void f(Object error, StackTrace stackTrace) {
      }

      subscriptionStream.listen((_) {},
          onError: f,
          cancelOnError: true);

[kevmoo]

@lrhn – thoughts on this?

[PROGrand]

@lrhn
Should Error::handle to be changed also?

core/pkgs/async/lib/src/result/error.dart

Lines 49 to 55 in 3b35aca

	void handle(Function errorHandler) {
	if (errorHandler is ZoneBinaryCallback) {
	errorHandler(error, stackTrace);
	} else {
	(errorHandler as ZoneUnaryCallback)(error);
	}
	}

[lrhn]

That code does look just as wrong. Good catch.
It hasn't been correct since before Dart 2.0 (it actually worked as intended in Dart 1.0).
It's a little scary that nobody has noticed until now. Either nobody types their error handlers (because they rely on inference, which they don't get) or nobody uses the code at all.

[PROGrand]

That code does look just as wrong. Good catch. It hasn't been correct since before Dart 2.0 (it actually worked as intended in Dart 1.0). It's a little scary that nobody has noticed until now. Either nobody types their error handlers (because they rely on inference, which they don't get) or nobody uses the code at all.

Ok, i will change this piece too.