Throw original exception from await about protopromise

[timcassell]

With this code:

private void Awake()
{
    Promise.Config.DebugCausalityTracer = Promise.TraceLevel.All;

    LevelOne().Forget();
}

private async Promise LevelOne()
{
    await LevelTwo();
}

private async Promise LevelTwo()
{
    await Promise.Resolved();

    throw new System.Exception();
}

Current master stacktrace:

Exception: Exception of type 'System.Exception' was thrown.
ProtoPromiseExample+<LevelTwo>d__8.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:30)
Rethrow as RejectionException: Exception of type 'Proto.Promises.Internal+RejectionException' was thrown.
ProtoPromiseExample+<LevelOne>d__7.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:25)
Rethrow as UnhandledExceptionInternal: An exception was not handled. -- This exception's Stacktrace contains the causality trace of all async callbacks that ran.
ProtoPromiseExample.LevelOne () (at <97cf00e20a414fd39017285ad6d97db9>:0)
ProtoPromiseExample.Awake () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:20)
UnityEngine.Debug:LogException(Exception)
Proto.Promises.Unity.<UpdateRoutine>d__10:MoveNext() (at Assets/Plugins/ProtoPromise/Core/Promises/Unity/PromiseBehaviour.cs:165)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Type	Method	N	Mean	Code Size	Allocated	Survived
AwaitPending	ProtoPromise_V2	100	385.01 us	13,226 B	-	416 B
AwaitResolved	ProtoPromise_V2	100	10.43 us	1,906 B	72 B	-

With ExceptionDispatchInfo prototype 1:

Exception: Exception of type 'System.Exception' was thrown.
ProtoPromiseExample+<LevelTwo>d__8.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:32)
--- End of stack trace from previous location where exception was thrown ---
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <c8d0d7b9135640958bff528a1e374758>:0)
Proto.Promises.Async.CompilerServices.PromiseAwaiterVoid.GetResult () (at Assets/Plugins/ProtoPromise/Core/Promises/Internal/AwaitInternal.cs:310)
ProtoPromiseExample+<LevelOne>d__7.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:25)
Rethrow as UnhandledExceptionInternal: An exception was not handled. -- This exception's Stacktrace contains the causality trace of all async callbacks that ran.
ProtoPromiseExample.LevelOne () (at <51200dc91719437a9d3fa38b34e8ed6e>:0)
ProtoPromiseExample.Awake () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:20)
UnityEngine.Debug:LogException(Exception)
Proto.Promises.Unity.<UpdateRoutine>d__10:MoveNext() (at Assets/Plugins/ProtoPromise/Core/Promises/Unity/PromiseBehaviour.cs:165)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Type	Method	N	Mean	Code Size	Allocated	Survived
AwaitPending	ProtoPromise_V2	100	382.70 us	14,356 B	-	416 B
AwaitResolved	ProtoPromise_V2	100	13.67 us	2,176 B	72 B	-

With ExceptionDispatchInfo prototype 2:

Exception: Exception of type 'System.Exception' was thrown.
ProtoPromiseExample+<LevelTwo>d__8.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:32)
--- End of stack trace from previous location where exception was thrown ---
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <c8d0d7b9135640958bff528a1e374758>:0)
Proto.Promises.Internal+PromiseRef.GetResult[T] (System.Int16 promiseId) (at Assets/Plugins/ProtoPromise/Core/Promises/Internal/AwaitInternal.cs:115)
Proto.Promises.Internal+PromiseAwaiterInternal`1[T].GetResult () (at Assets/Plugins/ProtoPromise/Core/Promises/Internal/AwaitInternal.cs:222)
Proto.Promises.Async.CompilerServices.PromiseAwaiterVoid.GetResult () (at Assets/Plugins/ProtoPromise/Core/Promises/Internal/AwaitInternal.cs:312)
ProtoPromiseExample+<LevelOne>d__7.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:25)
Rethrow as UnhandledExceptionInternal: An exception was not handled. -- This exception's Stacktrace contains the causality trace of all async callbacks that ran.
ProtoPromiseExample.LevelOne () (at <6168812879244f9bbef2b5b8e297fcc9>:0)
ProtoPromiseExample.Awake () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:20)
UnityEngine.Debug:LogException(Exception)
Proto.Promises.Unity.<UpdateRoutine>d__10:MoveNext() (at Assets/Plugins/ProtoPromise/Core/Promises/Unity/PromiseBehaviour.cs:165)
UnityEngine.SetupCoroutine:InvokeMoveNext(IEnumerator, IntPtr) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

Type	Method	N	Mean	Code Size	Allocated	Survived
AwaitPending	ProtoPromise_V2	100	380.88 us	13,445 B	-	416 B
AwaitResolved	ProtoPromise_V2	100	10.21 us	1,906 B	72 B	-

[timcassell]

It's rather unfortunate that this method includes the internal stacktraces that we're trying to remove. It would be nice to pair this with #43 to hide all internal methods and not affect performance, but Unity does not yet support .Net 6.

[timcassell]

Considering that UniTask's stacktrace with the same code looks like this:

Exception: Exception of type 'System.Exception' was thrown.
ProtoPromiseExample+<UniTaskLevelTwo>d__10.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:46)
--- End of stack trace from previous location where exception was thrown ---
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <c8d0d7b9135640958bff528a1e374758>:0)
Cysharp.Threading.Tasks.UniTask+ExceptionResultSource.GetResult (System.Int16 token) (at Assets/Plugins/UniTask/Runtime/UniTask.Factory.cs:205)
Cysharp.Threading.Tasks.UniTask+Awaiter.GetResult () (at Assets/Plugins/UniTask/Runtime/UniTask.cs:312)
ProtoPromiseExample+<UniTaskLevelOne>d__9.MoveNext () (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:39)
--- End of stack trace from previous location where exception was thrown ---
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <c8d0d7b9135640958bff528a1e374758>:0)
Cysharp.Threading.Tasks.UniTask+ExceptionResultSource.GetResult (System.Int16 token) (at Assets/Plugins/UniTask/Runtime/UniTask.Factory.cs:205)
Cysharp.Threading.Tasks.UniTask+Awaiter.GetResult () (at Assets/Plugins/UniTask/Runtime/UniTask.cs:312)
Cysharp.Threading.Tasks.UniTaskExtensions.Forget (Cysharp.Threading.Tasks.UniTask task) (at Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs:557)
UnityEngine.Debug:LogException(Exception)
Cysharp.Threading.Tasks.UniTaskScheduler:PublishUnobservedTaskException(Exception) (at Assets/Plugins/UniTask/Runtime/UniTaskScheduler.cs:90)
Cysharp.Threading.Tasks.UniTaskExtensions:Forget(UniTask) (at Assets/Plugins/UniTask/Runtime/UniTaskExtensions.cs:561)
ProtoPromiseExample:Awake() (at Assets/Plugins/ProtoPromise/Demo/ProtoPromiseExample.cs:22)

I think the option where we only have 1 extra GetResult() per async frame (prototype 1) is worth it to be able to try/catch on the original exception. I can refactor the PromiseAwaiters to optimize them so that it won't slow down the execution in non-exceptional cases (performance of prototype 2, but without the 2 extra GetResult() frames).

Then it will be primed for .Net 6 to clean up the stack traces for good (which Unity is currently working on).