Fix onDismiss not called when view controller is explicitly dismissed

[acosmicflamingo]

Looks like present(item:content:) function in UIKit does not successfully call onDismiss as one would expect. I'm not seeing a print statement when I do this:

// Using item parameter
present(item: $model.destination.alert, id: \.self, onDismiss: {
  print("Yay!!!")
}) { message in
  let alert = UIAlertController(
    title: "This is an alert",
    message: message,
    preferredStyle: .alert
  )
  alert.addAction(UIAlertAction(title: "OK", style: .default))
  return alert
}

// Using isPresented parameter
present(isPresented: UIBinding($model.destination.alert), onDismiss: {
  print("Yay!!!")
}) { //message in
  let alert = UIAlertController(
    title: "This is an alert",
    message: "LOL",
    preferredStyle: .alert
  )
  alert.addAction(UIAlertAction(title: "OK", style: .default))
  return alert
}

Going through breakpoints, it appears that controller is always nil: https://github.com/pointfreeco/swift-navigation/blob/main/Sources/UIKitNavigation/Navigation/Presentation.swift#L377. I find it strange because I the debugger does at some point set the dict with a value: https://github.com/pointfreeco/swift-navigation/blob/main/Sources/UIKitNavigation/Navigation/Presentation.swift#L365. Dismissal was working properly, and I have a better understanding of how caching works after spending a few minutes reading the code, so it didn't look like the problem resided there.

The next thing that stood out to me was the weakified controller property in Presented, and that the dictionary's controller properties were being immediately deallocated. Removing weak will certainly fix this, and I explicitly deallocate it in the deinit to mimic the weak behavior.

[mbrandonw]

Hi @acosmicflamingo, thanks for looking into this! However, it seems to have broken the test testPushViewController_ManualPop. I don't have time to look into why right now, but that is something that would need to be taken care of.

It would also be good to get some test coverage on this change to prove that it behaves the way you say it does.

[acosmicflamingo]

Oh okay! Sure, I can investigate and the test suggestion is a great one :)

[acosmicflamingo]

@mbrandonw I added a test that checks whether vc.isPresented is false during explicit dismissal. It works as expected when dismissal occurs using UITraitCollection functionality (in testPresents_TraitDismissal function), but it looks like calling vc.presentedViewController?.dismiss(animated: false) does not actually set vc.isPresented to false as one would expect.