Don't zone-register async callbacks for every await call in the VM.

tests/lib/async/async_await_zones_test.dart

Index: tests/lib/async/async_await_zones_test.dart
diff --git a/tests/lib/async/async_await_zones_test.dart b/tests/lib/async/async_await_zones_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..dc29823f493ed71a5b67fe158ac624085de51878
--- /dev/null
+++ b/tests/lib/async/async_await_zones_test.dart
@@ -0,0 +1,134 @@
+// 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:async';
+import 'package:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
+

[hausner, 2015/08/11 21:22:07]

Maybe a sentence or two to document what this test does?

[floitsch, 2015/08/12 15:03:14]

Done.

+gee(i) async {
+  return await i;
+}
+
+bar() async* {
+  var i = 0;
+  while (true) yield await gee(i++);
+}
+
+
+awaitForTest() async {
+  var sum = 0;
+  await for (var x in bar().take(100)) {
+    sum += x;
+  }
+  Expect.equals(4950, sum);
+}
+
+awaitTest() async {
+  await(null);

[hausner, 2015/08/11 21:22:07]

Curious: why use await like a function call here? Why not await null; ?

[floitsch, 2015/08/12 15:03:14]

My mistake...
done.

+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  await(null);
+  return await 499;
+}
+
+runTests() async {
+  await awaitTest();
+  await awaitForTest();
+}
+
+var depth = 0;
+
+var depthIncreases = 0;
+
+increaseDepth() {
+  depthIncreases++;
+  depth++;
+  // The async/await code should not register callbacks recursively in the
+  // then-calls. As such the depth should never grow too much. We don't want
+  // to commit to a specific value, since implementations still have some
+  // room in how async/await is implemented, but 20 should be safe.
+  Expect.isTrue(depth < 20);
+}
+
+registerCallback(Zone self, ZoneDelegate parent, Zone zone, f) {
+  var oldDepth = depth;
+  increaseDepth();
+  return parent.registerCallback(zone, () {
+    depth = oldDepth;
+    return f();
+  });
+}
+registerUnaryCallback(Zone self, ZoneDelegate parent, Zone zone, f) {
+  var oldDepth = depth;
+  increaseDepth();
+  return parent.registerUnaryCallback(zone, (x) {
+    depth = oldDepth;
+    return f(x);
+  });
+}
+registerBinaryCallback(Zone self, ZoneDelegate parent, Zone zone, f) {
+  var oldDepth = depth;
+  increaseDepth();
+  return parent.registerBinaryCallback(zone, (x, y) {
+    depth = oldDepth;
+    return f(x, y);
+  });
+}
+
+sm(Zone self, ZoneDelegate parent, Zone zone, f) {
+  var oldDepth = depth;
+  increaseDepth();
+  return parent.scheduleMicrotask(zone, () {
+    depth = oldDepth;
+    return f();
+  });
+}
+
+main() {
+  asyncStart();
+  var desc = new ZoneSpecification(
+      registerCallback: registerCallback,
+      registerUnaryCallback: registerUnaryCallback,
+      registerBinaryCallback: registerBinaryCallback,
+      scheduleMicrotask: sm
+      );
+  var future = runZoned(runTests, zoneSpecification: desc);
+  future.then((_) => asyncEnd());
+}