Sane asynchronous debugging and stack traces

runtime/lib/async_patch.dart

 // Copyright (c) 2015, 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.
 
 import "dart:_internal";
 
 // We need to pass the value as first argument and leave the second and third
 // arguments empty (used for error handling).
 // See vm/ast_transformer.cc for usage.
 Function _asyncThenWrapperHelper(continuation) {
@@ skipping 24 matching lines @@
   if (Zone.current == Zone.ROOT) return errorCallback;
   return Zone.current.registerBinaryCallback(errorCallback);
 }
 
 /// Registers the [thenCallback] and [errorCallback] on the given [object].
 ///
 /// If [object] is not a future, then it is wrapped into one.
 ///
 /// 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) {
     return object.then(thenCallback, onError: errorCallback);
   }
   // `object` is a `_Future`.
   //
   // Since the callbacks have been registered in the current zone (see
   // [_asyncThenWrapperHelper] and [_asyncErrorWrapperHelper]), we can avoid
   // another registration and directly invoke the no-zone-registration `.then`.
   //
   // 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 {
   StreamController controller;
   Function asyncStarBody;
   bool isAdding = false;
   bool onListenReceived = false;
   bool isScheduled = false;
   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;
     isSuspendedAtYield = false;
     asyncStarBody();
   }
 
   void scheduleGenerator() {
     if (isScheduled || controller.isPaused || isAdding) {
       return;
@@ skipping 99 matching lines @@
       // suspended at an await.
       if (isSuspendedAtYield) {
         scheduleGenerator();
       }
     }
     return cancellationCompleter.future;
   }
 }
 
 @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";