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.
Traces can be parsed from native StackTraces using Trace.from, or captured using Trace.current. Native StackTraces can also be directly converted to human-readable strings using Trace.format.
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 1884:25 Object.noSuchMethod pkg/stack_trace/lib/src/trace.dart 47:21 Trace.terse.<fn> dart:collection 29:29 IterableMixinWorkaround.reduce dart:core-patch 1247:42 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 525:24 _CatchErrorFuture._sendError dart:async 393:26 _FutureImpl._setErrorWithoutAsyncTrace dart:async 378:31 _FutureImpl._setError dart:async 490:16 _ThenFuture._sendValue dart:async 349:28 _FutureImpl._handleValue.<fn> dart:async 2402:21 Timer.run.<fn> dart:async-patch 15:15 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>
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:
import 'dart:async'; void main() { _scheduleAsync(); } void _scheduleAsync() { Future.delayed(Duration(seconds: 1)).then((_) => _runAsync()); } void _runAsync() { throw 'oh no!'; }
If we run this, it prints the following:
Unhandled exception: oh no! #0 _runAsync (file:///Users/kevmoo/github/stack_trace/example/example.dart:12:3) #1 _scheduleAsync.<anonymous closure> (file:///Users/kevmoo/github/stack_trace/example/example.dart:8:52) <asynchronous suspension>
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:
import 'dart:async'; import 'package:stack_trace/stack_trace.dart'; void main() { Chain.capture(_scheduleAsync); } void _scheduleAsync() { Future.delayed(Duration(seconds: 1)).then((_) => _runAsync()); } void _runAsync() { throw 'oh no!'; }
Now if we run it, it prints this:
Unhandled exception: oh no! example/example.dart 14:3 _runAsync example/example.dart 10:52 _scheduleAsync.<fn> package:stack_trace/src/stack_zone_specification.dart 126:26 StackZoneSpecification._registerUnaryCallback.<fn>.<fn> package:stack_trace/src/stack_zone_specification.dart 208:15 StackZoneSpecification._run package:stack_trace/src/stack_zone_specification.dart 126:14 StackZoneSpecification._registerUnaryCallback.<fn> dart:async/zone.dart 1406:47 _rootRunUnary dart:async/zone.dart 1307:19 _CustomZone.runUnary ===== asynchronous gap =========================== dart:async/zone.dart 1328:19 _CustomZone.registerUnaryCallback dart:async/future_impl.dart 315:23 Future.then example/example.dart 10:40 _scheduleAsync package:stack_trace/src/chain.dart 97:24 Chain.capture.<fn> dart:async/zone.dart 1398:13 _rootRun dart:async/zone.dart 1300:19 _CustomZone.run dart:async/zone.dart 1803:10 _runZoned dart:async/zone.dart 1746:10 runZoned package:stack_trace/src/chain.dart 95:12 Chain.capture example/example.dart 6:9 main dart:isolate-patch/isolate_patch.dart 297:19 _delayEntrypointInvocation.<fn> dart:isolate-patch/isolate_patch.dart 192:12 _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!