170 lines
7.9 KiB
Markdown
170 lines
7.9 KiB
Markdown
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[](https://github.com/dart-lang/tools/actions/workflows/stack_trace.yaml)
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[](https://pub.dev/packages/stack_trace)
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[](https://pub.dev/packages/stack_trace/publisher)
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This library provides the ability to parse, inspect, and manipulate stack traces
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produced by the underlying Dart implementation. It also provides functions to
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produce string representations of stack traces in a more readable format than
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the native [StackTrace] implementation.
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`Trace`s can be parsed from native [StackTrace]s using `Trace.from`, or captured
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using `Trace.current`. Native [StackTrace]s can also be directly converted to
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human-readable strings using `Trace.format`.
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[StackTrace]: https://api.dart.dev/stable/dart-core/StackTrace-class.html
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Here's an example native stack trace from debugging this library:
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#0 Object.noSuchMethod (dart:core-patch:1884:25)
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#1 Trace.terse.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:47:21)
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#2 IterableMixinWorkaround.reduce (dart:collection:29:29)
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#3 List.reduce (dart:core-patch:1247:42)
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#4 Trace.terse (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/src/trace.dart:40:35)
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#5 format (file:///usr/local/google-old/home/goog/dart/dart/pkg/stack_trace/lib/stack_trace.dart:24:28)
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#6 main.<anonymous closure> (file:///usr/local/google-old/home/goog/dart/dart/test.dart:21:29)
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#7 _CatchErrorFuture._sendError (dart:async:525:24)
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#8 _FutureImpl._setErrorWithoutAsyncTrace (dart:async:393:26)
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#9 _FutureImpl._setError (dart:async:378:31)
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#10 _ThenFuture._sendValue (dart:async:490:16)
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#11 _FutureImpl._handleValue.<anonymous closure> (dart:async:349:28)
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#12 Timer.run.<anonymous closure> (dart:async:2402:21)
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#13 Timer.Timer.<anonymous closure> (dart:async-patch:15:15)
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and its human-readable representation:
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dart:core-patch 1884:25 Object.noSuchMethod
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pkg/stack_trace/lib/src/trace.dart 47:21 Trace.terse.<fn>
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dart:collection 29:29 IterableMixinWorkaround.reduce
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dart:core-patch 1247:42 List.reduce
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pkg/stack_trace/lib/src/trace.dart 40:35 Trace.terse
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pkg/stack_trace/lib/stack_trace.dart 24:28 format
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test.dart 21:29 main.<fn>
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dart:async 525:24 _CatchErrorFuture._sendError
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dart:async 393:26 _FutureImpl._setErrorWithoutAsyncTrace
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dart:async 378:31 _FutureImpl._setError
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dart:async 490:16 _ThenFuture._sendValue
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dart:async 349:28 _FutureImpl._handleValue.<fn>
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dart:async 2402:21 Timer.run.<fn>
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dart:async-patch 15:15 Timer.Timer.<fn>
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You can further clean up the stack trace using `Trace.terse`. This folds
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together multiple stack frames from the Dart core libraries, so that only the
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core library method that was directly called from user code is visible. For
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example:
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dart:core Object.noSuchMethod
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pkg/stack_trace/lib/src/trace.dart 47:21 Trace.terse.<fn>
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dart:core List.reduce
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pkg/stack_trace/lib/src/trace.dart 40:35 Trace.terse
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pkg/stack_trace/lib/stack_trace.dart 24:28 format
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test.dart 21:29 main.<fn>
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## Stack Chains
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This library also provides the ability to capture "stack chains" with the
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`Chain` class. When writing asynchronous code, a single stack trace isn't very
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useful, since the call stack is unwound every time something async happens. A
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stack chain tracks stack traces through asynchronous calls, so that you can see
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the full path from `main` down to the error.
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To use stack chains, just wrap the code that you want to track in
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`Chain.capture`. This will create a new [Zone][] in which stack traces are
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recorded and woven into chains every time an asynchronous call occurs. Zones are
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sticky, too, so any asynchronous operations started in the `Chain.capture`
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callback will have their chains tracked, as will asynchronous operations they
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start and so on.
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Here's an example of some code that doesn't capture its stack chains:
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```dart
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import 'dart:async';
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void main() {
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_scheduleAsync();
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}
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void _scheduleAsync() {
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Future.delayed(Duration(seconds: 1)).then((_) => _runAsync());
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}
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void _runAsync() {
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throw 'oh no!';
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}
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```
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If we run this, it prints the following:
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Unhandled exception:
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oh no!
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#0 _runAsync (file:///Users/kevmoo/github/stack_trace/example/example.dart:12:3)
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#1 _scheduleAsync.<anonymous closure> (file:///Users/kevmoo/github/stack_trace/example/example.dart:8:52)
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<asynchronous suspension>
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Notice how there's no mention of `main` in that stack trace. All we know is that
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the error was in `runAsync`; we don't know why `runAsync` was called.
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Now let's look at the same code with stack chains captured:
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```dart
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import 'dart:async';
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import 'package:stack_trace/stack_trace.dart';
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void main() {
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Chain.capture(_scheduleAsync);
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}
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void _scheduleAsync() {
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Future.delayed(Duration(seconds: 1)).then((_) => _runAsync());
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}
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void _runAsync() {
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throw 'oh no!';
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}
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```
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Now if we run it, it prints this:
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Unhandled exception:
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oh no!
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example/example.dart 14:3 _runAsync
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example/example.dart 10:52 _scheduleAsync.<fn>
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package:stack_trace/src/stack_zone_specification.dart 126:26 StackZoneSpecification._registerUnaryCallback.<fn>.<fn>
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package:stack_trace/src/stack_zone_specification.dart 208:15 StackZoneSpecification._run
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package:stack_trace/src/stack_zone_specification.dart 126:14 StackZoneSpecification._registerUnaryCallback.<fn>
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dart:async/zone.dart 1406:47 _rootRunUnary
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dart:async/zone.dart 1307:19 _CustomZone.runUnary
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===== asynchronous gap ===========================
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dart:async/zone.dart 1328:19 _CustomZone.registerUnaryCallback
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dart:async/future_impl.dart 315:23 Future.then
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example/example.dart 10:40 _scheduleAsync
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package:stack_trace/src/chain.dart 97:24 Chain.capture.<fn>
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dart:async/zone.dart 1398:13 _rootRun
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dart:async/zone.dart 1300:19 _CustomZone.run
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dart:async/zone.dart 1803:10 _runZoned
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dart:async/zone.dart 1746:10 runZoned
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package:stack_trace/src/chain.dart 95:12 Chain.capture
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example/example.dart 6:9 main
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dart:isolate-patch/isolate_patch.dart 297:19 _delayEntrypointInvocation.<fn>
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dart:isolate-patch/isolate_patch.dart 192:12 _RawReceivePortImpl._handleMessage
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That's a lot of text! If you look closely, though, you can see that `main` is
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listed in the first trace in the chain.
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Thankfully, you can call `Chain.terse` just like `Trace.terse` to get rid of all
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the frames you don't care about. The terse version of the stack chain above is
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this:
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test.dart 17:3 runAsync
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test.dart 13:28 scheduleAsync.<fn>
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===== asynchronous gap ===========================
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dart:async _Future.then
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test.dart 13:12 scheduleAsync
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test.dart 7:18 main.<fn>
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package:stack_trace Chain.capture
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test.dart 6:16 main
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That's a lot easier to understand!
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[Zone]: https://api.dart.dev/stable/dart-async/Zone-class.html
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