Add flag to disable capturing stack traces.

pkg/scheduled_test/lib/src/task.dart

 // Copyright (c) 2013, 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.
 
 library task;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:stack_trace/stack_trace.dart';
 
+import '../scheduled_test.dart' show captureStackTraces;
 import 'future_group.dart';
 import 'schedule.dart';
 import 'utils.dart';
 
 typedef Future TaskBody();
 
 /// A single task to be run as part of a [TaskQueue].
 ///
 /// There are two levels of tasks. **Top-level tasks** are created by calling
 /// [TaskQueue.schedule] before the queue in question is running. They're run in
@@ skipping 32 matching lines @@
   /// task within [queue]; for nested tasks, this is the index within
   /// [parent.children]. It's used for debugging when [description] isn't
   /// provided.
   int _id;
 
   /// A Future that will complete to the return value of [fn] once this task
   /// finishes running.
   Future get result => _resultCompleter.future;
   final _resultCompleter = new Completer();
 
-  final stackTrace = new Trace.current();
+  final stackTrace = captureStackTraces ? new Trace.current() : null;
 
   Task(fn(), String description, TaskQueue queue)
     : this._(fn, description, queue, null, queue.contents.length);
 
   Task._child(fn(), String description, Task parent)
     : this._(fn, description, parent.queue, parent, parent.children.length);
 
   Task._(fn(), this.description, this.queue, this.parent, this._id) {
     this.fn = () {
       if (state != TaskState.WAITING) {
@@ skipping 39 matching lines @@
     // Ignore errors in the FutureGroup; they'll get picked up via wrapFuture,
     // and we don't want them to short-circuit the other Futures.
     _childGroup.add(task.result.catchError((_) {}));
     task.fn();
     return task.result;
   }
 
   String toString() => description == null ? "#$_id" : description;
 
   String toStringWithStackTrace() {
-    var stackString = prefixLines(terseTraceString(stackTrace));
-    return "$this\n\nStack trace:\n$stackString";
+    var result = "$this";

[nweiz, 2013/04/09 21:25:58]

I think I prefer `this.toString()` here.

[Bob Nystrom, 2013/04/10 21:52:00]

Done.

+    if (stackTrace != null) {
+      var stackString = prefixLines(terseTraceString(stackTrace));
+      result += "\n\nStack trace:\n$stackString";
+    }
+    return result;
   }
 
   /// Returns a detailed representation of [queue] with this task highlighted.
   String generateTree() => queue.generateTree(this);
 }
 
 /// An enum of states for a [Task].
 class TaskState {
   /// The task is waiting to be run.
   static const WAITING = const TaskState._("WAITING");
@@ skipping 11 matching lines @@
   final String name;
 
   /// Whether the state indicates that the task has finished running. This is
   /// true for both the [SUCCESS] and [ERROR] states.
   bool get isDone => this == SUCCESS || this == ERROR;
 
   const TaskState._(this.name);
 
   String toString() => name;
 }