Always capture stack traces when running pub tests.

pkg/scheduled_test/lib/src/schedule.dart

Index: pkg/scheduled_test/lib/src/schedule.dart
diff --git a/pkg/scheduled_test/lib/src/schedule.dart b/pkg/scheduled_test/lib/src/schedule.dart
index d5eb9af41929f55e15741b14f3eecabd02325740..1dfb6106d93cba63650ce32e32d0f374b1f7a539 100644
--- a/pkg/scheduled_test/lib/src/schedule.dart
+++ b/pkg/scheduled_test/lib/src/schedule.dart
@@ -379,9 +379,9 @@ class TaskQueue {
 
   /// The descriptions of all callbacks that are blocking the completion of
   /// [this].
-  List<String> get pendingCallbacks =>
-      new UnmodifiableListView<String>(_pendingCallbacks);
-  final _pendingCallbacks = new Queue<String>();
+  List<PendingCallback> get pendingCallbacks =>
+      new UnmodifiableListView<PendingCallback>(_pendingCallbacks);
+  final _pendingCallbacks = new Queue<PendingCallback>();
 
   /// A completer that will be completed once [_pendingCallbacks] becomes empty
   /// after the queue finishes running its tasks.
@@ -505,18 +505,21 @@ class TaskQueue {
     bool _timedOut() =>
       _schedule.currentQueue != this || pendingCallbacks.isEmpty;
 
-    if (description == null) {
-      description = "Out-of-band operation #${_totalCallbacks}";
-    }
-
-    if (captureStackTraces) {
-      var stackString = prefixLines(terseTraceString(new Trace.current()));
-      description += "\n\nStack trace:\n$stackString";
-    }
-
     _totalCallbacks++;
+    var trace = captureStackTraces ? new Trace.current() : null;
+    var pendingCallback = new PendingCallback._(() {
+      var fullDescription = description;
+      if (fullDescription == null) {
+        fullDescription = "Out-of-band operation #${_totalCallbacks}";
+      }
+
+      if (captureStackTraces) {

[Bob Nystrom, 2013/04/30 23:05:36]

If capturing stack traces is fast enough now, how about removing this flag
entirely?

[nweiz, 2013/04/30 23:13:14]

Done.

+        var stackString = prefixLines(terseTraceString(trace));
+        fullDescription += "\n\nStack trace:\n$stackString";
+      }
+    });
+    _pendingCallbacks.add(pendingCallback);
 
-    _pendingCallbacks.add(description);
     return (arg) {
       try {
         return fn(arg);
@@ -531,7 +534,7 @@ class TaskQueue {
       } finally {
         if (_timedOut()) return;
 
-        _pendingCallbacks.remove(description);
+        _pendingCallbacks.remove(pendingCallback);
         if (_pendingCallbacks.isEmpty && !isRunningTasks) {
           _noPendingCallbacksCompleter.complete();
         }
@@ -605,3 +608,22 @@ class TaskQueue {
     }).join("\n");
   }
 }
+
+/// A thunk for lazily resolving the description of a [PendingCallback].
+typedef String _DescriptionThunk();

[Bob Nystrom, 2013/04/30 23:05:36]

Oh Dart and your awful function type syntax. You could just stick:

typedef T Fn<T>();

Somewhere in utils and be done with it. :)

[nweiz, 2013/04/30 23:13:14]

Currently we're using this once each in several different packages, so that
wouldn't save us anything.

+
+/// An identifier for an out-of-band callback running during a schedule.
+class PendingCallback {

[Bob Nystrom, 2013/04/30 23:05:36]

The fact that it's for an out-of-band callback isn't really relevant to the
class itself, is it? How about "Description" and then in the body document that
the class exists to lazily calculate the description for perf and stack trace
reasons?

[nweiz, 2013/04/30 23:13:14]

I'm more interested in being able to add more pending-callback-related
information here than I am in using it in other places that would require a lazy
description.

[Bob Nystrom, 2013/05/01 00:02:25]

In that case, keep the name of this type, but update the doc comments above to
remove "The descriptions of".

[nweiz, 2013/05/01 00:33:44]

That's specifically referring to the string, not the [PendingCallback] object.

+  final _DescriptionThunk _thunk;
+  String _description;
+
+  /// The string description of the callback.
+  String get description {
+    if (_description == null) _description = _thunk();
+    return _description;
+  }
+
+  String toString() => description;
+
+  PendingCallback._(this._thunk);
+}