Overeager @Shared deprecation warning in a View context

[seanmrich]

I think I’ve isolated what looks like a TCA issue involving @Shared state and BindableAction.

Reading a @Shared property is fine in all of these cases:

• Read directly from State

Example

@Reducer
struct Feature {
  @ObservableState
  struct State: Equatable {
    @Shared(.inMemory("value")) var value: Int = 0
  }
}

extension Feature.State {
  var readState: Int {
    self.value // No issues here
  }
}

• Read through store.state.value

Example

@Reducer
struct Feature {
  @ObservableState
  struct State: Equatable {
    @Shared(.inMemory("value")) var value: Int = 0
  }
}

struct FeatureView: View {
  let store: StoreOf<Feature>

  var body: some View {
    let _ = store.state.value  // No issues here
  }
}

• Read a plain @Observable model

Example

@Observable
final class FeatureModel {
  @ObservationIgnored
  @Shared(.inMemory("value")) var value: Int = 0
}

struct FeatureView: View {
  let model = FeatureModel()

  var body: some View {
    let _ = model.value  // No issues here
  }
}

• Read from a non-bindable store

Example

@Reducer
struct Feature {
  @ObservableState
  struct State: Equatable {
    @Shared(.inMemory("value")) var value: Int = 0
  }
  enum Action {}
}

struct FeatureView: View {
  let store: StoreOf<Feature>

  var body: some View {
    let _ = store.value  // No issues here
  }
}

But reading a shared property from a store whose Action conforms to BindableAction within a View emits a @Shared setter deprecation/unavailability warning.

Example

@Reducer
struct Feature {
  @ObservableState
  struct State: Equatable {
    @Shared(.inMemory("value")) var value: Int = 0
  }
  enum Action: BindableAction {
    case binding(BindingAction<State>)
  }
}

struct FeatureView: View {
  let store: StoreOf<Feature>

  var body: some View {
    let _ = store.value
    // 🛑 Setter for 'value' is deprecated: Use '$shared.withLock' to modify a shared value with exclusive access; when constructing a SwiftUI binding, use 'Binding($shared)'
  }
}

My guess is that the culprit is the bindable store dynamic-member overload in Binding+Observation.swift:

extension Store where State: ObservableState, Action: BindableAction, Action.State == State {
  public subscript<Value: Equatable & Sendable>(
    dynamicMember keyPath: WritableKeyPath<State, Value>
  ) -> Value {
    get { self.state[keyPath: keyPath] }
    set { ... }
  }
}

The bindable case resolves through a WritableKeyPath and forming that key path forces Swift to consider @Shared's setter even though this is just a read op. Reading through the state property like let _ = store.state.value resolves the warning, but I'm not sure if I'm just papering over a bigger issue. Is this just something that will have to remain until TCA 2?

[stephencelis]

@seanmrich This is feeling like a bug (either in Swift or in our library if this is expected behavior in the language). I won't have time to look at it until tomorrow, but would a @_disfavoredOverload on that subscript potentially route the get elsewhere and silence the warning?

[seanmrich]

You nailed it. Applied @_disfavoredOverload to both of the dynamic lookup subscripts on BindableAction and the issue is fixed. Added PR #3906 that resolves the issue.