Tree-based navigation deeplinking shows mostly blank screens

[TheEskil]

Description

When deep linking using tree-based navigation, with PresentationState/PresentationAction and View.navigationDestination it sends you to the right place, but after the first destination everything falls apart, i.e. blank screens.

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 expected each new destination to work as if the user navigated there themselves (which does work splendidly).

Actual behavior

Destinations past the first one only shows blank screens. Only the back button is visible, and sometimes the navigation title, but not always.

Steps to reproduce

I've made a minimal reproduction available here: https://github.com/TheEskil/TCA-TreeBasedNavBug

The Composable Architecture version information

1.2.0

Destination operating system

iOS 17

Xcode version information

Version 15.0 (15A240d)

Swift Compiler version information

swift-driver version: 1.87.1 Apple Swift version 5.9 (swiftlang-5.9.0.128.108 clang-1500.0.40.1)
Target: arm64-apple-macosx13.0

[x-0o0]

Additional comment for the issue

According to the logs that are provided by _printChanges(),
at the first, the states are well-assigned but immediately .destination(.dismiss) is called from the parent reducer via navigationDestination method:

received action:
  AppReducer.Action.secondTapped
- AppReducer.State(_destination: nil)
+ AppReducer.State(
+   _destination: .first(
+     FirstReducer.State(
+       _destination: .second(
+         SecondReducer.State(_destination: nil)
+       )
+     )
+   )
+ )

received action:  // ❌ unexpected action is called
  AppReducer.Action.destination(
    .presented(
      .first(
        .destination(.dismiss)
      )
    )
  )
  AppReducer.State(
    _destination: .first(
-     FirstReducer.State(
-       _destination: .second(
-         SecondReducer.State(_destination: nil)
-       )
-     )
+     FirstReducer.State(_destination: nil)
    )
  )

[stephencelis]

I believe this is a vanilla SwiftUI bug with navigationDestination, though if you can show it working there we can look into if it's a TCA bug.

We provide a workaround in our SwiftUINavigation package, but have decided against doing so in TCA, since it introduces a flakey code path that could break at any time when Apple fixes things. There's recent discussion here about how the modifier has regressed in iOS 17, and a possible workaround you can bring to your TCA project: https://github.com/pointfreeco/swiftui-navigation/discussions/121

I'm going to convert this to a discussion, since it appears to be an Apple bug and not a bug with the library.

[TheEskil]

Looks like you're right. I ran the repro through an iPhone 14 Pro running iOS 16.4 and everything works as expected. Thank you for looking into it and for providing a workaround!