Debugging in VS Code throws uncaught exceptions

[a7md0]

I'm not sure if this is the right place to file this issue, but this is related to #37953. The reproduction repository is provided, which uses 3rd party HTTP client package (flutterchina/dio). To recap, awaiting a Future that may fail from the library (e.g., 404 HTTP GET request) will throw an uncaught exception, even though the call is surrounded with try/catch block (the catch block get executed directly after skipping the uncaught exception).

• Preproduction repository: https://github.com/a7md0/ex_unhandled_app
• Visual Studio Code version: 1.62.1 f4af3cbf5a99787542e2a30fe1fd37cd644cc31f x64
• Dart SDK Version: Dart SDK version: 2.14.4 (stable) (Wed Oct 13 11:11:32 2021 +0200) on "windows_x64"
• Flutter SDK Version:-

Flutter 2.5.3 • channel stable • https://github.com/flutter/flutter.git  
Framework • revision 18116933e7 (4 weeks ago) • 2021-10-15 10:46:35 -0700
Engine • revision d3ea636dc5
Tools • Dart 2.14.4

• Platform: Windows 10 x64 with Android Simulator (API 29)
• Breakpoints from "Run and Debug" tab
  

[mkustermann]

@cskau-g Could you take a look at this? (Related to the break in debugger on unhandled exceptions feature you were implementing)

[a7md0]

There has been an new release for the package with the following PR cfug/dio#1317 (version 4.0.2), which resolved the unhandled exception for me while debugging. Not sure if this was expected from the package itself or its should be investigated more

[ghost]

@a7md0 I think I may have initially misunderstood what you're reporting, but correct me if I'm wrong here:

The code in the linked repo. does in fact correctly catch the expected error in the catch block here:
https://github.com/a7md0/ex_unhandled_app/blob/main/lib/main.dart#L51-L55

Rather, the actual issue you're reporting is that your Dio.get(..) triggers a separate uncaught exception from:
https://github.com/a7md0/ex_unhandled_app/blob/main/lib/main.dart#L43-L45

Which is thrown from here:
https://github.com/flutterchina/dio/blob/71b38981bb78e4506dca577fa42d92af4296f496/dio/lib/src/dio_mixin.dart#L678
Which in turn is called from here:
https://github.com/flutterchina/dio/blob/71b38981bb78e4506dca577fa42d92af4296f496/dio/lib/src/dio_mixin.dart#L585-L590

This is however working as intended.

The offending code in dio/lib/src/dio_mixin.dart is:

      _dispatchRequest(reqOpt).then(...);

The call to Future<...> _dispatchRequest<T>(...) async { .. }, as we can see, returns a Future which the caller is expected to either 1) await, or 2) pass on (e.g. return) for someone else to await.
If this does not happen, you have an unawaited future, which may indeed throw uncaught exceptions.

The reason cfug/dio#1317 changes this behaviour is that while it's still an unawaited future, they now attach an error handler to it, meaning the exception is no longer uncaught.

[mkustermann]

@cskau-g Thanks for investigating!

[markfili]

Correct! Should there be a way, in any IDE, to disable the debugger stopping on exceptions thrown from libraries used in our projects which can be handled like the one in Dio library?

…

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[ghost]

@markfili, if you're asking for a way to disable stops on uncaught exceptions, then that already exists as you can use e.g. DevTools to toggle the debugger behaviour for exceptions (stop on none, uncaught, or all) through the service protocol.

Whether this is exposed in your IDE of choice is of course up to the IDE/extension authors.

If you want more granular control, to set the behaviour per library, then I think that's a feature request for service protocol. (Please file a separate issue for that.)
Though I personally think being able to disable per library won't be that much more useful - libraries shouldn't be throwing large amounts of uncaught exceptions in the first place.

[aliyazdi75]

Hi @cskau-g,

Regarding this issue for cached_network_image plugin, this problem still persists.

This is a reproducible Gist. As you can see, with defining an errorWidget, the exceptions should be handled but the debugger throws on cached_network_image exceptions only, not all flutter exceptions.

Could you please take a look at this if possible?