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packages/stack_trace/README.md

Index: packages/stack_trace/README.md
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+This library provides the ability to parse, inspect, and manipulate stack traces
+produced by the underlying Dart implementation. It also provides functions to
+produce string representations of stack traces in a more readable format than
+the native [StackTrace] implementation.
+
+`Trace`s can be parsed from native [StackTrace]s using `Trace.from`, or captured
+using `Trace.current`. Native [StackTrace]s can also be directly converted to
+human-readable strings using `Trace.format`.
+
+[StackTrace]: http://api.dartlang.org/docs/releases/latest/dart_core/StackTrace.html
+
+Here's an example native stack trace from debugging this library:
+
+    #0      Object.noSuchMethod (dart:core-patch:1884:25)
+    #1      Trace.terse.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:47:21)
+    #2      IterableMixinWorkaround.reduce (dart:collection:29:29)
+    #3      List.reduce (dart:core-patch:1247:42)
+    #4      Trace.terse (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:40:35)
+    #5      format (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/stack_trace.dart:24:28)
+    #6      main.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/test.dart:21:29)
+    #7      _CatchErrorFuture._sendError (dart:async:525:24)
+    #8      _FutureImpl._setErrorWithoutAsyncTrace (dart:async:393:26)
+    #9      _FutureImpl._setError (dart:async:378:31)
+    #10     _ThenFuture._sendValue (dart:async:490:16)
+    #11     _FutureImpl._handleValue.<anonymous closure> (dart:async:349:28)
+    #12     Timer.run.<anonymous closure> (dart:async:2402:21)
+    #13     Timer.Timer.<anonymous closure> (dart:async-patch:15:15)
+
+and its human-readable representation:
+
+    dart:core-patch                             Object.noSuchMethod
+    pkg/stack_trace/lib/src/trace.dart 47:21    Trace.terse.<fn>
+    dart:collection                             IterableMixinWorkaround.reduce
+    dart:core-patch                             List.reduce
+    pkg/stack_trace/lib/src/trace.dart 40:35    Trace.terse
+    pkg/stack_trace/lib/stack_trace.dart 24:28  format
+    test.dart 21:29                             main.<fn>
+    dart:async                                  _CatchErrorFuture._sendError
+    dart:async                                  _FutureImpl._setErrorWithoutAsyncTrace
+    dart:async                                  _FutureImpl._setError
+    dart:async                                  _ThenFuture._sendValue
+    dart:async                                  _FutureImpl._handleValue.<fn>
+    dart:async                                  Timer.run.<fn>
+    dart:async-patch                            Timer.Timer.<fn>
+
+You can further clean up the stack trace using `Trace.terse`. This folds
+together multiple stack frames from the Dart core libraries, so that only the
+core library method that was directly called from user code is visible. For
+example:
+
+    dart:core                                   Object.noSuchMethod
+    pkg/stack_trace/lib/src/trace.dart 47:21    Trace.terse.<fn>
+    dart:core                                   List.reduce
+    pkg/stack_trace/lib/src/trace.dart 40:35    Trace.terse
+    pkg/stack_trace/lib/stack_trace.dart 24:28  format
+    test.dart 21:29                             main.<fn>
+
+## Stack Chains
+
+This library also provides the ability to capture "stack chains" with the
+`Chain` class. When writing asynchronous code, a single stack trace isn't very
+useful, since the call stack is unwound every time something async happens. A
+stack chain tracks stack traces through asynchronous calls, so that you can see
+the full path from `main` down to the error.
+
+To use stack chains, just wrap the code that you want to track in
+`Chain.capture`. This will create a new [Zone][] in which stack traces are
+recorded and woven into chains every time an asynchronous call occurs. Zones are
+sticky, too, so any asynchronous operations started in the `Chain.capture`
+callback will have their chains tracked, as will asynchronous operations they
+start and so on.
+
+Here's an example of some code that doesn't capture its stack chains:
+
+```dart
+import 'dart:async';
+
+void main() {
+  scheduleAsync();
+}
+
+void scheduleAsync() {
+  return new Future.delayed(new Duration(seconds: 1))
+      .then((_) => runAsync());
+}
+
+void runAsync() {
+  throw 'oh no!';
+}
+```
+
+If we run this, it prints the following:
+
+    Uncaught Error: oh no!
+    Stack Trace: 
+    #0      runAsync (file:///usr/local/google-old/home/goog/dart/dart/test.dart:13:3)
+    #1      scheduleAsync.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/test.dart:9:28)
+    #2      _rootRunUnary (dart:async/zone.dart:717)
+    #3      _RootZone.runUnary (dart:async/zone.dart:854)
+    #4      _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:488)
+    #5      _Future._propagateToListeners (dart:async/future_impl.dart:571)
+    #6      _Future._complete (dart:async/future_impl.dart:317)
+    #7      _SyncCompleter.complete (dart:async/future_impl.dart:44)
+    #8      Future.Future.delayed.<anonymous closure> (dart:async/future.dart:219)
+    #9      _createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:11)
+    #10     _handleTimeout (dart:io/timer_impl.dart:292)
+    #11     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:115)
+
+Notice how there's no mention of `main` in that stack trace. All we know is that
+the error was in `runAsync`; we don't know why `runAsync` was called.
+
+Now let's look at the same code with stack chains captured:
+
+```dart
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+void main() {
+  Chain.capture(() {
+    scheduleAsync();
+  });
+}
+
+void scheduleAsync() {
+  new Future.delayed(new Duration(seconds: 1))
+      .then((_) => runAsync());
+}
+
+void runAsync() {
+  throw 'oh no!';
+}
+```
+
+Now if we run it, it prints this:
+
+    Uncaught Error: oh no!
+    Stack Trace: 
+    test.dart 17:3                                                runAsync
+    test.dart 13:28                                               scheduleAsync.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 129:26  registerUnaryCallback.<fn>.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 174:15  StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 177:7   StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 175:7   StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 129:18  registerUnaryCallback.<fn>
+    dart:async/zone.dart 717                                      _rootRunUnary
+    dart:async/zone.dart 449                                      _ZoneDelegate.runUnary
+    dart:async/zone.dart 654                                      _CustomizedZone.runUnary
+    dart:async/future_impl.dart 488                               _Future._propagateToListeners.handleValueCallback
+    dart:async/future_impl.dart 571                               _Future._propagateToListeners
+    dart:async/future_impl.dart 317                               _Future._complete
+    dart:async/future_impl.dart 44                                _SyncCompleter.complete
+    dart:async/future.dart 219                                    Future.Future.delayed.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 174:15  StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 119:52  registerCallback.<fn>
+    dart:async/zone.dart 706                                      _rootRun
+    dart:async/zone.dart 440                                      _ZoneDelegate.run
+    dart:async/zone.dart 650                                      _CustomizedZone.run
+    dart:async/zone.dart 561                                      _BaseZone.runGuarded
+    dart:async/zone.dart 586                                      _BaseZone.bindCallback.<fn>
+    package:stack_trace/src/stack_zone_specification.dart 174:15  StackZoneSpecification._run
+    package:stack_trace/src/stack_zone_specification.dart 119:52  registerCallback.<fn>
+    dart:async/zone.dart 710                                      _rootRun
+    dart:async/zone.dart 440                                      _ZoneDelegate.run
+    dart:async/zone.dart 650                                      _CustomizedZone.run
+    dart:async/zone.dart 561                                      _BaseZone.runGuarded
+    dart:async/zone.dart 586                                      _BaseZone.bindCallback.<fn>
+    dart:async-patch/timer_patch.dart 11                          _createTimer.<fn>
+    dart:io/timer_impl.dart 292                                   _handleTimeout
+    dart:isolate-patch/isolate_patch.dart 115                     _RawReceivePortImpl._handleMessage
+    ===== asynchronous gap ===========================
+    dart:async/zone.dart 476                                      _ZoneDelegate.registerUnaryCallback
+    dart:async/zone.dart 666                                      _CustomizedZone.registerUnaryCallback
+    dart:async/future_impl.dart 164                               _Future._Future._then
+    dart:async/future_impl.dart 187                               _Future.then
+    test.dart 13:12                                               scheduleAsync
+    test.dart 7:18                                                main.<fn>
+    dart:async/zone.dart 710                                      _rootRun
+    dart:async/zone.dart 440                                      _ZoneDelegate.run
+    dart:async/zone.dart 650                                      _CustomizedZone.run
+    dart:async/zone.dart 944                                      runZoned
+    package:stack_trace/src/chain.dart 93:20                      Chain.capture
+    test.dart 6:16                                                main
+    dart:isolate-patch/isolate_patch.dart 216                     _startIsolate.isolateStartHandler
+    dart:isolate-patch/isolate_patch.dart 115                     _RawReceivePortImpl._handleMessage
+
+That's a lot of text! If you look closely, though, you can see that `main` is
+listed in the first trace in the chain.
+
+Thankfully, you can call `Chain.terse` just like `Trace.terse` to get rid of all
+the frames you don't care about. The terse version of the stack chain above is
+this:
+
+    test.dart 17:3       runAsync
+    test.dart 13:28      scheduleAsync.<fn>
+    ===== asynchronous gap ===========================
+    dart:async           _Future.then
+    test.dart 13:12      scheduleAsync
+    test.dart 7:18       main.<fn>
+    package:stack_trace  Chain.capture
+    test.dart 6:16       main
+
+That's a lot easier to understand!
+
+[Zone]: https://api.dartlang.org/apidocs/channels/stable/#dart-async.Zone