Fatal error: No ObservableObject of type StoreObservableObject...

[artemkrachulov]

Description

After upgrading TCA to 0.55.0 I found a very useful SwichStore update which helps me to remove useless reducers from the SwitchStore. Here is the current code which works with a warning:

'scope(state:)' is deprecated: 'Store.scope' requires an explicit 'action' transform and is intended to be used to transform a store of a parent domain into a store of a child domain.

When transforming store state into view state, use the 'observe' parameter when constructing a view store.

SwitchStore(self.store.scope(state: \.content)) {

  /// useless
  CaseLet(
    state: /SwitchContentState<LoadedState, String>.loading,
    action: Action.noop,
    then: { store in
      WithViewStore(store) { viewStore in
        LoadingView(state: viewStore.state, orientation: .vertical)
      }
    })
  
  CaseLet(
    state: /SwitchContentState<LoadedState, String>.loaded,
    action: Action.main,
    then: LoadedView.init)
  
  /// useless
  CaseLet(
    state: /SwitchContentState<LoadedState, String>.error,
    action: Action.noop,
    then: { store in
      WithViewStore(store) { viewStore in
        ErrorView(text: viewStore.state)
      }
    })
}

And updated code:

SwitchStore(self.store.scope(state: \.content, action: Action.noop)) { state in
  
  switch state {
  case let .loading(state):
    LoadingView(state: state, orientation: .vertical)
    
  case .loaded:
    CaseLet(
      state: /SwitchContentState<LoadedState, String>.loaded,
      action: Action.loaded,
      then: LoadedView.init)
    
  case let .error(text):
    ErrorView(text: text)
    
  case .ready:
    EmptyView()
  }
}

Only this code triggers an error after run:

SwiftUI/EnvironmentObject.swift:82: Fatal error: No ObservableObject of type StoreObservableObject<SwitchContentState<LoadedState, String>, Action> found. A View.environmentObject(_:) for StoreObservableObject<SwitchContentState<LoadedState, String>, Action> may be missing as an ancestor of this view.

What can it be? Any way to solve it?

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

No response

Actual behavior

No response

Steps to reproduce

No response

The Composable Architecture version information

0.55.0

Destination operating system

iOS 16.5.1

Xcode version information

Version 14.3.1 (14E300c)

Swift Compiler version information

swift-driver version: 1.75.2 Apple Swift version 5.8.1 (swiftlang-5.8.0.124.5 clang-1403.0.22.11.100)
Target: x86_64-apple-macosx13.0

[mbrandonw]

The SwitchStore should be providing the environment object to the body. Are you able to reproduce this in a simple example that we can run to see what is going on?

I would also like to draw your attention to the "Important" note in the docs of SwitchStore:

Important
The SwitchStore view builder is only evaluated when the case of state passed to it changes. As such, you should not rely on this value for anything other than checking the current case, e.g. by switching on it and routing to an appropriate CaseLet.

This means for this code:

case let .loading(state):
  LoadingView(state: state, orientation: .vertical)
…    
case let .error(text):
  ErrorView(text: text)

…the views will only be rendered a single type when the case switches to loading or error. In particular, if the state inside the associated value changes it will not cause the views to re-render. That may be completely fine for your use case, but just want to call it out.

[artemkrachulov]

@mbrandonw Thank you for your response. Here is a demo project with two cases
SwitchStoreTest.zip

Also when reproducing, found something. When you remove the action from:

SwitchStore(self.store.scope(state: \.content, action: Updated.Action.noop)) { state in

crash solves but a warning appears:

'scope(state:)' is deprecated: 'Store.scope' requires an explicit 'action' transform and is intended to be used to transform a store of a parent domain into a store of a child domain.
When transforming store state into view state, use the 'observe' parameter when constructing a view store.

[sehdich]

Interesting - it also works without any crash when using an action of { $0 }:

SwitchStore(self.store.scope(state: \.content, action: { $0 })) { ...}

[mbrandonw]

Hi @artemkrachulov, thanks for the repro and now I see what is going on. The problem is that your types do not match up. You are "switching" on a store that has Never for its actions, yet you are trying to extract a "case let" store from it that has actions of Content.Action. That can't possibly work.

And the reason it works with the "old" version of your demo is because you are not scoping the main store's actions down to Never. So, the way to get your demo working is to leave the actions intact with an action: { $0 } argument.

It would of course be best if we could catch these things at compile time instead of runtime, but often that is not possible in SwiftUI. Even vanilla SwiftUI has similar problems, such as no guarantees that the value you use in .tag(…) matches the kind of binding you provide to TabView.

Since this is not an issue in the library I am going to convert it to a discussion.

[artemkrachulov]

@mbrandonw Oh yes, when I started using the switch content action, everything fell into place.

public enum SwitchContentAction<T: Equatable>: Equatable {
  case ready
  case loading(Never)
  case loaded(T)
  case error(Never)
}

Now It has followed look:

SwitchStore(self.store.scope(state: \.content, action: Action.content)) { state in
  switch state {
  case let .loading(text):
    Text(text: text)
    
  case .loaded:
    CaseLet(
      state: /SwitchContentState<LoadedState>.loaded,
      action: SwitchContentAction<LoadedAction>.loaded,
      then: LoadedView.init)
    
  case let .error(text):
    Text(text: text)
    
  case .ready:
    EmptyView()
  }
}

Thx