Ensure IsExecuting is false when command completes

[haacked]

Because ReactiveCommand decrements the in flight count in a Finally block, when we await a command's ExecuteAsync method, it still reports an in-flight count when the await returns. We want to not return until the in-flight count is decremented. This fixes that by putting the decrement in a Do statement for both the onNext block and the onError block.

[anaisbetts]

✨ Thanks @haacked!

[flagbug]

Wait, I thought

.Finally(() => decrement.Disposable = Disposable.Empty)

and

.Do(
 _ => { },
e => decrement.Disposable = Disposable.Empty,
() => decrement.Disposable = Disposable.Empty) 

are semantically the same? Is my whole Rx knowledge a lie?

[damiensawyer]

Damn I know that feeling!

[jlaanstra]

Finally runs after the subscription has been disposed, so it runs after OnCompleted and after OnError.

In the following code the Finally action runs after the actions in the Do.

.Finally(() => decrement.Disposable = Disposable.Empty)
.Do(
 _ => { },
e => decrement.Disposable = Disposable.Empty,
() => decrement.Disposable = Disposable.Empty) 

[flagbug]

Aha! Makes sense, thanks @jlaanstra!

[anaisbetts]

I need to write a blog post about this - basically Finally interacts badly with await, because the Finally block runs shortly after the awaiter returns. In practice, this almost never matters, but in a unit test, it results in very confused people.

Here's the troll scenario that this PR fixes:

bool latestIsExecuting;

someCommand.Subscribe(x => latestIsExecuting = x);
await someCommand.ExecuteAsync();
Assert.False(latestIsExecuting);    // It's true, whyyyyyyyy

[haacked]

In practice, this almost never matters, but in a unit test, it results in very confused people.

Not necessarily the case. It's hard to predict whether it'll matter or not. But you could imagine a method that has some common logic and it checks to make sure a command isn't currently executing.

You call this method from multiple locations including from the Subscribe callback on the command. In that case, the subscribe callback would always fail because it still thinks the command is executing when in fact it's done.