Crash when navigating back from navigationlink in sheet/fullscreenCover (iPhone 12 pro max)

[Nicolaidam]

Description

I'm experiencing a weird crash when navigating back programmatically from a navigationlink flow inside a sheet/fullscreenCover.

I have only been able to reproduce the crash using iPhone 12 pro max with iOS 16.0.2. On other devices such as iPhone 13 pro, iPhone 11 and iPhone 8 plus i have not been able to reproduce, even when using 16.0.2. I don't know it is just an iOS 16 thing or if other versions of iOS are also affected. (or if it a bug in the actual device or whatever)

This line is printed before the crashes and points that an action is called from a nil state. But as i understand it is this hard to prevent since the Binding set method is called after the view is set to nil. This message is just a warning and should not crash the app, right?

2022-09-27 14:38:38.691705+0100 NavigationCrash[1339:155431] [ComposableArchitecture] An "optional" reducer at "NavigationCrash/NavigationCrashApp.swift:37" received an action when state was "nil". …

Action:
FullscreenCoverAction.navigationChanged

This is generally considered an application logic error, and can happen for a few reasons:

• The optional reducer was combined with or run from another reducer that set "FullscreenCoverState" to "nil" before the optional reducer ran. Combine or run optional reducers before reducers that can set their state to "nil". This ensures that optional reducers can handle their actions while their state is still non-"nil".

• An in-flight effect emitted this action while state was "nil". While it may be perfectly reasonable to ignore this action, you may want to cancel the associated effect before state is set to "nil", especially if it is a long-living effect.

• This action was sent to the store while state was "nil". Make sure that actions for this reducer can only be sent to a view store when state is non-"nil". In SwiftUI applications, use "IfLetStore".
(lldb)

I can't guarantee that my implementation is correct, so please let me know if there is something I'm missing.

Checklist

• 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.

Expected behavior

I expect that I'm not crashing when navigating back from navigationLink flow in sheet/fullscreenCover using iPhone 12 pro max.

Actual behavior

Crash: Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1d13a4208)

Steps to reproduce

video.MP4

NavigationCrash.zip

1. Build attached project
2. Run the app on an iPhone 12 pro max with iOS 16.0.2
3. Tap on "Show Fullscreen"
4. Tap on "Navigate To NavigationLink"
5. Tap on "Close fullscreen cover"

The Composable Architecture version information

0.40.2

Destination operating system

iOS 16.0.2

Xcode version information

Version 14.0.1 (14A400), also tried 14.1 beta

Swift Compiler version information

No response

[mbrandonw]

I wasn't able to reproduce the crash with just simulators, and I don't have a device on exactly 16.0.2, but I feel pretty certain this is a SwiftUI bug and not a problem with the library (especially since it seems to be SDK/device specific). I would recommend recreating the app in vanilla SwiftUI and see if it behaves the same, and file a feedback if it does. The warning you are seeing is just a warning, and does not cause crashes.

There are still all types of crashes lurking in SwiftUI's navigation APIs. For example, if you have a navigation stack with A->B->C on the stack, and B has state for a sheet, then popping back C->B causes a crash. So, I wouldn't be surprised if dismissing a sheet with a drilled down navigation causes problems.

I'm going to convert this to a discussion until we can pinpoint that this is definitely an issue with the library.

[Nicolaidam]

cool thank you man. It is still crashing when I use that IfLetStore2 implementation.

[tgrapperon]

Thanks. The only thing I'm seeing to be slightly off is the closure being doubly escaped. We can probably simplify the implementation to do it only once in WithViewStore, or even forgo WithViewStore at the price of one additional generic. Here are two IfLetStore3 and IfLetStore4 replacements. If it still crashes for both, I can't really see what's triggering the issue.

public struct IfLetStore3<State, Action, Content: View>: View {
  private let content: Content
  public init<IfContent, ElseContent>(
    _ store: Store<State?, Action>,
    @ViewBuilder then ifContent: @escaping (Store<State, Action>) -> IfContent,
    @ViewBuilder else elseContent: () -> ElseContent
  ) where Content == WithViewStore<State?, Action, _ConditionalContent<IfContent, ElseContent>> {
    let elseContent = elseContent()
    self.content = WithViewStore<State?, Action, _ConditionalContent<IfContent, ElseContent>>(
      store,
      observe: { $0 },
      removeDuplicates: { ($0 != nil) == ($1 != nil) },
      content: {
        if var state = $0.state {
          ifContent(
            store.scope {
              state = $0 ?? state
              return state
            }
          )
        } else {
          elseContent
        }
      }
    )
  }

  public init<IfContent>(
    _ store: Store<State?, Action>,
    @ViewBuilder then ifContent: @escaping (Store<State, Action>) -> IfContent
  ) where Content == WithViewStore<State?, Action, IfContent?> {
    self.content = WithViewStore<State?, Action, IfContent?>(
      store,
      observe: { $0 },
      removeDuplicates: { ($0 != nil) == ($1 != nil) },
      content: {
        if var state = $0.state {
          ifContent(
            store.scope {
              state = $0 ?? state
              return state
            }
          )
        }
      }
    )
  }
  public var body: some View {
    content
  }
}

public struct IfLetStore4<State, Action, IfContent: View, ElseContent: View>: View {
  private let store: Store<State?, Action>
  @ObservedObject private var viewStore: ViewStore<State?, Action>
  private let ifContent: (Store<State, Action>) -> IfContent
  private let elseContent: ElseContent

  public init(
    _ store: Store<State?, Action>,
    @ViewBuilder then ifContent: @escaping (Store<State, Action>) -> IfContent,
    @ViewBuilder else elseContent: () -> ElseContent
  ) where ElseContent == EmptyView?  {
    self.store = store
    self.viewStore = ViewStore(store, removeDuplicates: { ($0 != nil) == ($1 != nil) })
    self.ifContent = ifContent
    self.elseContent = elseContent()
  }
  
  public init(
    _ store: Store<State?, Action>,
    @ViewBuilder then ifContent: @escaping (Store<State, Action>) -> IfContent
  ) where ElseContent == EmptyView?  {
    self.store = store
    self.viewStore = ViewStore(store, removeDuplicates: { ($0 != nil) == ($1 != nil) })
    self.ifContent = ifContent
    self.elseContent = nil
  }

  public var body: some View {
    if var state = viewStore.state {
      ifContent(
        store.scope {
          state = $0 ?? state
          return state
        }
      )
    } else {
      elseContent
    }
  }
}

[Nicolaidam]

Good point. I have now tried all the different IfLetStore implementations on a iPhone 12 pro max and still crashing on all of the versions.

[tgrapperon]

It's definitely an Apple bug, but I can't see how to avoid triggering it when using IfLetStore. Maybe you can use the scope with fallback to a default state value instead of IfLetStore as a workaround in your app. It shouldn't cause any issue as this screen is also controlled by the .fullscreenCover binding.

[Nicolaidam]

Sorry for the delay, I totally forgot to respond, since i was very busy with a new release.
As you suggested the problem was fixed by doing a scope fallback to a default state, instead of the IfLetStore. This seems to be working and we he haven't had the crash since that implementation change.

So I just wanna thank you so much for help @tgrapperon 🙏 This community is awesome!

[artemkrachulov]

@Nicolaidam Have the same issue, when trying to dismiss sheet with navigation stack (2 screens) by setting sheet state to nil. Reproducible only on device (sim fine) and probably on iOS 16.0+.

How to reproduce:

1. Present sheet with NavigationView
2. Push the next screen by NavigationLink
3. Dismiss sheet by setting state.sheetState = nil

The crash is not consistent.