Change and documentat how completer handles futures.

sdk/lib/async/future_impl.dart

Index: sdk/lib/async/future_impl.dart
diff --git a/sdk/lib/async/future_impl.dart b/sdk/lib/async/future_impl.dart
index 178445838e37bb7e1445cb5435e6eed2f228a763..9540da4f81a2818b467c9d6e6a0721fe51ca43db 100644
--- a/sdk/lib/async/future_impl.dart
+++ b/sdk/lib/async/future_impl.dart
@@ -14,7 +14,7 @@ typedef _FutureAction();
 abstract class _Completer<T> implements Completer<T> {
   final _Future<T> future = new _Future<T>();
 
-  void complete([T value]);
+  void complete([value]);
 
   void completeError(Object error, [StackTrace stackTrace]);
 
@@ -25,12 +25,17 @@ abstract class _Completer<T> implements Completer<T> {
 
 class _AsyncCompleter<T> extends _Completer<T> {
 
-  void complete([T value]) {
+  void complete([value]) {
     if (!future._mayComplete) throw new StateError("Future already completed");
     future._asyncComplete(value);
   }
 
   void completeError(Object error, [StackTrace stackTrace]) {
+    if (error is Future) {

[floitsch, 2013/10/29 18:13:35]

ditto. I don't think this restriction is necessary.

[Lasse Reichstein Nielsen, 2013/10/30 09:22:17]

Removing.

+      throw new ArgumentError("Cannot use completeError with a future - "
+                              "use complete instead");
+    }
+    if (error == null) throw new ArgumentError("Error must not be null");
     if (!future._mayComplete) throw new StateError("Future already completed");
     future._asyncCompleteError(error, stackTrace);
   }
@@ -38,12 +43,16 @@ class _AsyncCompleter<T> extends _Completer<T> {
 
 class _SyncCompleter<T> extends _Completer<T> {
 
-  void complete([T value]) {
+  void complete([value]) {
     if (!future._mayComplete) throw new StateError("Future already completed");
     future._complete(value);
   }
 
   void completeError(Object error, [StackTrace stackTrace]) {
+    if (error is Future) {

[floitsch, 2013/10/29 18:13:35]

ditto

[Lasse Reichstein Nielsen, 2013/10/30 09:22:17]

ditto too.

+      throw new ArgumentError("Cannot use completeError with a future. "
+                              "Use complete instead.");
+    }
     if (!future._mayComplete) throw new StateError("Future already completed");
     future._completeError(error, stackTrace);
   }
@@ -231,6 +240,7 @@ class _Future<T> implements Future<T> {
 
   void _addListener(_Future listener) {
     assert(listener._nextListener == null);
+    _Future target = this;

[floitsch, 2013/10/29 18:13:35]

spurious change?

[Lasse Reichstein Nielsen, 2013/10/30 09:22:17]

ack, yes. Left over from debugging.
Removed.

     if (_isComplete) {
       // Handle late listeners asynchronously.
       _zone.scheduleMicrotask(() {
@@ -314,7 +324,7 @@ class _Future<T> implements Future<T> {
       _attachStackTrace(error, stackTrace);
     }
 
-    _Future listeners = _isChained ? null : _removeListeners();
+    _Future listeners = _removeListeners();
     _setError(error, stackTrace);
     _propagateToListeners(this, listeners);
   }