Stepping over await in the Visual Studio debugger crashes the Unity editor

[randomPoison]

I'm running into an issue where using Visual Studio in combination with UniTask is causing the Unity editor to crash.

Reproduction Steps

1. Write an async function that returns a UniTaskVoid, UniTask, or UniTask<T> and awaits at least once.
2. Using Visual Studio, set a breakpoint on the await statement and attach the debugger to the editor.
3. Run your game in the editor until Visual Studio hits the breakpoint.
4. Try to step over the await statement.

Notes

• I've tested this with Visual Studio 2019 on Windows with Unity 2019.2.4f1.
• Stepping over await statements appears to work correctly when using async void, async Task, and async Task<T>, so the issue appears to have something to do with UniTask.
• It's not clear if the issue is with Visual Studio, Unity, or UniTask. To test this, it would be good to try the following things:
  • Create a non-Unity C# project with Visual Studio 2019 and create a custom task-like type, matching what UniTask provides. See if you can use the debugger here.
  • Create a basic task-like type, similar to what UniTask provides but as minimal as possible, and see if that still causes the editor to crash.

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I'll try to dig into this issue more, but I wanted to open this ticket in case I don't have time.

[NoxMortem]

Just wanted to create the same ticket. Also happens with Rider 2019.3 and Unity 2019.3.3f1 so I think we can likely narrow it down to:

• Unity (very likely)
• UniTask (less likely)

[neuecc]

It certainly happens, but it seems to be difficult to solve here.

[neuecc]

discussed at #66 and fixed in 1.3.1.