Sane asynchronous debugging and stack traces

runtime/lib/async_patch.dart

Index: runtime/lib/async_patch.dart
diff --git a/runtime/lib/async_patch.dart b/runtime/lib/async_patch.dart
index 3e22fb044545fef55933c31361b6ea48c946e976..3db2220ae47f38a6fe7a3ef144d285e230763223 100644
--- a/runtime/lib/async_patch.dart
+++ b/runtime/lib/async_patch.dart
@@ -42,7 +42,10 @@ Function _asyncErrorWrapperHelper(continuation) {
 ///
 /// Returns the result of registering with `.then`.
 Future _awaitHelper(
-    var object, Function thenCallback, Function errorCallback) {
+    var object,
+    Function thenCallback,
+    Function errorCallback,
+    var awaiter) {
   if (object is! Future) {
     object = new _Future().._setValue(object);
   } else if (object is! _Future) {
@@ -56,9 +59,33 @@ Future _awaitHelper(
   //
   // We can only do this for our internal futures (the default implementation of
   // all futures that are constructed by the `dart:async` library).
+  object._awaiter = awaiter;
   return object._thenNoZoneRegistration(thenCallback, errorCallback);
 }
 
+// Called as part of the 'await for (...)' construct.
+void _asyncStarListenHelper(var object,
+                            var awaiter) {
+  if (object is! _StreamImpl) {
+    return;
+  }
+  // `object` is a `_StreamImpl`.
+  object._awaiter = awaiter;
+}
+
+// Called after the
+void _asyncStarMoveNextHelper(var object) {
+  if (object is! _StreamImpl) {
+    return;
+  }
+  // `object` is a `_StreamImpl`.
+  if (object._generator == null) {
+    // No generator registered, this isn't an async* Stream.
+    return;
+  }
+  _moveNextDebuggerStepCheck(object._generator);
+}
+
 // _AsyncStarStreamController is used by the compiler to implement
 // async* generator functions.
 class _AsyncStarStreamController {
@@ -70,7 +97,11 @@ class _AsyncStarStreamController {
   bool isSuspendedAtYield = false;
   Completer cancellationCompleter = null;
 
-  Stream get stream => controller.stream;
+  Stream get stream {
+    Stream local = controller.stream;
+    local._generator = asyncStarBody;
+    return local;
+  }
 
   void runBody() {
     isScheduled = false;
@@ -190,3 +221,30 @@ class _AsyncStarStreamController {
 }
 
 @patch void _rethrow(Object error, StackTrace stackTrace) native "Async_rethrow";
+
+@patch class _Future<T> {
+  Object _awaiter;
+}
+
+@patch class _StreamImpl<T> {
+  Object _awaiter;
+  Object _generator;
+}
+
+void _completeOnAsyncReturn(Object completer, [value]) {
+  completer.complete(value);
+}
+
+/// Returns a [StackTrace] object containing the synchronous prefix for this
+/// asynchronous method.
+Object _asyncStackTraceHelper(Object closure)
+    native "StackTrace_forAsyncMethod";
+
+void _clearAsyncThreadStackTrace()
+    native "StackTrace_clearAsyncThreadStackTrace";
+
+void _setAsyncThreadStackTrace(StackTrace stackTrace) native
+    "StackTrace_setAsyncThreadStackTrace";
+
+void _moveNextDebuggerStepCheck(async_op)
+    native "AsyncStarMoveNext_debuggerStepCheck";