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>
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:
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:
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!
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