Unable to step over when using DAP

[sidlatau]

I already registered the issue in flutter/flutter#105856, but maybe here is a more appropriate place.

The problem is with granularity property which is provided by DAP client to DAP server. According to DAP specification, it should be a string:
https://microsoft.github.io/debug-adapter-protocol/specification#:~:text=number%3B%0A%7D-,SteppingGranularity,-The%20granularity%20of

But flutter debug adapter expects map:
https://github.com/dart-lang/sdk/blob/main/pkg/dds/lib/src/dap/protocol_generated.dart#L3514

For debugging I am using:
https://github.com/akinsho/flutter-tools.nvim
https://github.com/mfussenegger/nvim-dap

Flutter crash report.

command

flutter debug-adapter

exception

_CastError: type 'String' is not a subtype of type 'Map<String, Object?>' in type cast

#0      new NextArguments.fromMap (package:dds/src/dap/protocol_generated.dart:3514:36)
#1      NextArguments.fromJson (package:dds/src/dap/protocol_generated.dart:3503:21)
#2      BaseDebugAdapter.handle (package:dds/src/dap/base_debug_adapter.dart:112:19)
#3      BaseDebugAdapter._handleIncomingRequest (package:dds/src/dap/base_debug_adapter.dart:324:7)
#4      BaseDebugAdapter._handleIncomingMessage (package:dds/src/dap/base_debug_adapter.dart:273:7)
#5      ByteStreamServerChannel._readMessage (package:dds/src/dap/protocol_stream.dart:82:18)
#6      ByteStreamServerChannel.listen.<anonymous closure> (package:dds/src/dap/protocol_stream.dart:53:24)
#7      _rootRunUnary (dart:async/zone.dart:1434:47)
#8      _CustomZone.runUnary (dart:async/zone.dart:1335:19)
#9      _CustomZone.runUnaryGuarded (dart:async/zone.dart:1244:7)
#10     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:341:11)
#11     _DelayedData.perform (dart:async/stream_impl.dart:591:14)
#12     _StreamImplEvents.handleNext (dart:async/stream_impl.dart:706:11)
#13     _PendingEvents.schedule.<anonymous closure> (dart:async/stream_impl.dart:663:7)
#14     _rootRun (dart:async/zone.dart:1418:47)
#15     _CustomZone.run (dart:async/zone.dart:1328:19)
#16     _CustomZone.runGuarded (dart:async/zone.dart:1236:7)
#17     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:1276:23)
#18     _rootRun (dart:async/zone.dart:1426:13)
#19     _CustomZone.run (dart:async/zone.dart:1328:19)
#20     _CustomZone.runGuarded (dart:async/zone.dart:1236:7)
#21     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:1276:23)
#22     _microtaskLoop (dart:async/schedule_microtask.dart:40:21)
#23     _startMicrotaskLoop (dart:async/schedule_microtask.dart:49:5)
#24     _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:122:13)
#25     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:193:5)

flutter doctor

[✓] Flutter (Channel stable, 3.0.1, on macOS 12.4 21F79 darwin-x64, locale en-GB)
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    • Framework revision fb57da5f94 (3 weeks ago), 2022-05-19 15:50:29 -0700
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    • Dart version 2.17.1
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[✓] Android toolchain - develop for Android devices (Android SDK version 32.0.0)
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    • Platform android-32, build-tools 32.0.0
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    • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7590822)
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    • macOS (desktop)    • macos                                • darwin-x64     • macOS 12.4 21F79 darwin-x64
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• No issues found!

[devoncarew]

cc @DanTup @bkonyi

(Ben - we don't have an SDK label for DAP issues; not sure if its useful to have one or not)

[bkonyi]

I've gone ahead and created dds-core and dds-dap labels for now.

[DanTup]

@sidlatau thanks! It looks like the code generation wasn't handling references to simple types correctly. I have a fix for this here:

https://dart-review.googlesource.com/c/sdk/+/248605/

After the fix lands in DDS, it'll need publishing and rolling into Flutter. I'll follow up on the Flutter issue when that happens.

It's worth noting that we don't support this field so any value will be ignored. This is indicated by supportsSteppingGranularity not being set to true (see https://microsoft.github.io/debug-adapter-protocol/specification#:~:text=number%3B%0A%7D-,SteppingGranularity,-The%20granularity%20of):

  /**
   * The debug adapter supports stepping granularities (argument 'granularity')
   * for the stepping requests.
   */
  supportsSteppingGranularity?: boolean;

I don't think it's very clear from the spec whether this flag not being sent means "the server will ignore it" or "the server doesn't support you sending it" but it may be worth tweaking your DAP client to check this flag before sending it (this is what VS Code seems to do) which may resolve your issue without needing to wait for a Flutter release that includes the fix.

[sidlatau]

@DanTup, thanks for the quick fix and for the explanation!