Fix spurious resume when awaiting future in async* code

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
===================================================================
--- runtime/lib/core_patch.dart	(revision 44981)
+++ runtime/lib/core_patch.dart	(working copy)
@@ -36,12 +36,14 @@
   bool isAdding = false;
   bool onListenReceived = false;
   bool isScheduled = false;
+  bool isSuspendedAtYield = false;
   Completer cancellationCompleter = null;
 
   Stream get stream => controller.stream;
 
   void runBody() {
     isScheduled = false;
+    isSuspendedAtYield = false;
     asyncStarBody();
   }
 
@@ -65,12 +67,14 @@
   // if (controller.isCanelled) return;

[Ivan Posva, 2015/04/08 21:49:55]

Cannelloni?

[hausner, 2015/04/08 22:12:44]

Basta.

   bool add(event) {
     if (!onListenReceived) _fatal("yield before stream is listened to!");
+    if (isSuspendedAtYield) _fatal("unexpected yield");
     // If stream is cancelled, tell caller to exit the async generator.
     if (!controller.hasListener) {
       return true;
     }
     controller.add(event);
     scheduleGenerator();
+    isSuspendedAtYield = true;
     return false;
   }
 
@@ -131,7 +135,9 @@
   }
 
   onResume() {
-    scheduleGenerator();
+    if (isSuspendedAtYield) {
+      scheduleGenerator();
+    }
   }
 
   onCancel() {