Preserve stack trace by default in controller (#280)

[retendo]

This should preserve the stack trace when exceptions are thrown while using controllers that have no dedicated error handler.

This solves a part of #280

[NinoFloris]

Thanks for the contribution!

A bit better, as opposed to reflection of exception internals, would be to use ExceptionDispatchInfo.Capture(ex).Throw() (System.Runtime.ExceptionServices)

This is the supported api to do what you want (and it's used in the F# compiler, F# core, and clr core libraries)

[retendo]

With ExceptionDispatchInfo.Capture(ex).Throw() there would just be a lot of added lines like --- End of stack trace from previous location where exception was thrown ---. I don't mind that, should I change it?

[NinoFloris]

Looking at the problem from a slightly different angle, it might be better to change the internal controller state to take an ErrorHandler option. In controllerWithErrorHandler guard on it being Some in the try ... with ex when state.ErrorHandler.IsSome -> state.ErrorHandler.Value ex and the compiler will then emit the EDI call :)

[retendo]

Without a fallback like this?

let controllerWithErrorHandler nxt ctx : HttpFuncResult =
    task {
      try
        return! initialController nxt ctx
      with
      | ex when state.ErrorHandler.IsSome -> return! state.ErrorHandler.Value ctx ex
    }

That would lead the exception to fall through to the router/application level, so no need for the explicit EDI call?

[NinoFloris]

Exactly! See https://github.com/dotnet/fsharp/issues/8529

[Krzysztof-Cieslak]

The same thing should be done for the Endpoint-Routing version of Controllers in https://github.com/SaturnFramework/Saturn/blob/master/src/Saturn/ControllerEndpoint.fs

[Krzysztof-Cieslak]

Published in 0.15.0-preview03