Let StreamSubscription.cancel return a Future.

sdk/lib/async/stream_pipe.dart

Index: sdk/lib/async/stream_pipe.dart
diff --git a/sdk/lib/async/stream_pipe.dart b/sdk/lib/async/stream_pipe.dart
index b126747d848bcaa84ebe0315132ecc37ff042330..dde13f82670df2f0a764e7b334304869748dc27d 100644
--- a/sdk/lib/async/stream_pipe.dart
+++ b/sdk/lib/async/stream_pipe.dart
@@ -27,8 +27,23 @@ _runUserCode(userCode(), onSuccess(value), onError(error)) {
 /** Helper function to make an onError argument to [_runUserCode]. */
 _cancelAndError(StreamSubscription subscription, _Future future) =>
   (error) {

[floitsch, 2013/10/12 18:53:57]

You will need to update this for the stack-trace argument.

[Lasse Reichstein Nielsen, 2013/10/14 11:32:33]

And not make it curried.

[Anders Johnsen, 2013/10/16 11:52:21]

Done.

[Anders Johnsen, 2013/10/16 11:52:21]

Done.

-    subscription.cancel();
-    future._completeError(error);
+    var cancelFuture = subscription.cancel();
+    if (cancelFuture != null) {

[floitsch, 2013/10/12 18:53:57]

if (cancelFuture is Future)

Users are used to write: onCancel: () => foo()
If this thing returns something else than a future it should not be an error.

[Anders Johnsen, 2013/10/16 11:52:21]

Done.

+      cancelFuture.whenComplete(() => future._completeError(error));
+    } else {
+      future._completeError(error);
+    }
+  };
+
+/** Helper function to make an onError argument to [_runUserCode]. */
+_cancelAndValue(StreamSubscription subscription, _Future future) =>
+  (value) {
+    var cancelFuture = subscription.cancel();
+    if (cancelFuture != null) {

[floitsch, 2013/10/12 18:53:57]

ditto.

[Anders Johnsen, 2013/10/16 11:52:21]

Done.

+      cancelFuture.whenComplete(() => future._complete(value));
+    } else {
+      future._complete(value);
+    }
   };