Exceptions are never reported when UniTask is executed without await and Forget()

An exception that happens inside a UniTask is never reported, not even after GC.Collect, under specific conditions:

• the UniTask method is run without await and Forget()
• the exception is thrown in the same frame the UniTask is launched

An example:

public class TestBehaviour : MonoBehaviour
{
    private void Awake()
    {
        TestAsync();
    }

    private async UniTask TestAsync()
    {
        throw new Exception();
    }
}

The exception will not be logged to the console even if I press GC.Collect in the UniTask Tracker window. However, if the exception is thrown in subsequent frames, everything is fine:

private async UniTask TestAsync()
{
    await UniTask.NextFrame();
    throw new Exception(); // logged after GC.Collect
}

The bug is unlikely to happen because usually there is a CS4014 warning that warns us the call is not awaited. However, when using async methods through interfaces, the warning is not reported, so you can forget to use either await or Forget():

public interface ITestInterface
{
    UniTask Test();
}

public class TestClass : ITestInterface
{
    public async UniTask Test()
    {
        throw new Exception();
    }
}

public class TestBehaviour : MonoBehaviour
{
    private void Awake()
    {
        ITestInterface interfaceInstance = new TestClass();
        interfaceInstance.Test(); // There is no CS4014 warning because there is no async keyword in the interface declaration.
    }
}

So when you forget to put await or Forget() in such a case, it is a very big pain to debug it later because there is no sign of what went wrong.

[neuecc]

Thanks. You are correct, I’m sorry to didn’t investigate. It would be better to change the Exception ex; field to ExceptionHolder.

[SolidAlloy]

Destroying TestBehaviour doesn’t help, unfortunately, not even destroying the game object it is in