ViewController is presented for Optional Destination Reducer case payload

[BastianKusserow]

Description

Hey!

I just encountered a unexpected behaviour in TCA in conjunction with swift-navigation. Whenever you have a Destination reducer that presents non TCA features, if the associated value of that case is optional, the presentation tools immediately present those features / invoke the presentation closure of swift-navigation. Additionaly, whenever I try to present the feature again, after dismissing the first screen, nothing happens.

A reproduction example of the issue is attached.

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

I'd expect that the feature is only displayed when the destination state actual matches the case.

Actual behavior

the feature is displayed immediately and cannot be presented again.

Reproducing project

UIKitNavigation.zip

The Composable Architecture version information

1.15.0

Destination operating system

iOS 17

Xcode version information

15.4

Swift Compiler version information

No response

[mbrandonw]

Hi @BastianKusserow, this is the expected behavior. The optionality of Destination.State? is what controls the presentation/dismissal of the view, regardless of what the payload is. It is completely valid to present a sheet with a piece of optional state. We do not do extra work to squash the double optional as that would be a little too magical and probably unexpected in some cases.

And as for the second issue you mentioned, your project doesn't actually compile for me, but that behavior seems to work just fine when I run the various case studies from the Swift Navigation repo. If you can create a repro project that compiles I can take a look.

Since this isn't an issue with the library I am going to convert it to a discussion. Please feel free to continue the conversation over there!

[BastianKusserow]

Hey @mbrandonw, thanks for taking a look into the issue. Sorry that the project did not work, could you try again with UIKitNavigationOptional.zip?

I get that the presentation is driven of the optionality of Destination.State?, but what I don't get is why the modal is immediately presented when starting the app although the destination is still nil in that point in time. Also, if I set the destination to the case rating(nil) or case rating(1), the sheet is not presented anymore. My expectation would be that, when I scope to $store.scope(state: \.destination?.rating, action: \.destination.rating) the case of state.destination would at least have to be .rating. Sorry if I don't get the point here, but for me the behaviour was quite unexpected.

[stephencelis]

@BastianKusserow This sadly seems to be a Swift bug around optional-chained key paths and nested optionals. We opened an issue here:

swiftlang/swift#76510

To avoid it, we would recommend not storing optionals directly in the enum payload to avoid the nested optional access, and instead wrap the optional in a struct.

[BastianKusserow]

Ah, thanks for clarifying. Does that mean the project that I sent you should work as expected?

In the meantime I boxed the optional in a struct like you've mentioned and it works as expected, thanks!