Publisher animation is not working

[heoblitz]

Description

In certain cases, the publisher animation is not working, but using run animation solves the problem.

Looking at the logs, it seems that transactions are not being updated correctly when using publisher animations.

If you modify your current animation structure to fire "withTransaction" when you assign a value to a store state, publisher animations will work fine.

// Store.Swift
//
public func send(
 //...
) -> Task<Void, Never>? {
  // ...
  defer {
    withTransaction(transaction) {
      self.state.value = currentState
    }
  }

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

Transaction is updated correctly and the animation works.

Actual behavior

Transaction doesn't update and the animation doesn't work.

Steps to reproduce

branch: https://github.com/heoblitz/swift-composable-architecture/tree/issue/animation

file: swift-composable-architecture.zip

1. Download the project file and build it with the "AnimationTest Scheme."

2. Proceed with testing while changing the effect return values.

var body: some Reducer<State, Action> {
  Reduce { state, action in
    switch action {
    case .showDetailButtonTapped:
      // 1. publisher animation is not working
      //
//        return .send(.changeShowingDetailView).animation(.default)
      
      // 2. run animation is working
      //
      return .run { send in
        await send(.changeShowingDetailView)
      }
      .animation(.default)
      
    case .changeShowingDetailView:
      state.isShowingDetailView.toggle()
      return .none
    }
  }
}

1. publisher animation

RPReplay_Final1698111785.MP4

2. run animation

RPReplay_Final1698111825.MP4

The Composable Architecture version information

c472ea4

Destination operating system

iOS 17.0.3, iOS 15.1

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)

[raduncicen]

I am experiencing the same issue

[mbrandonw]

Hi @heoblitz, this is happening because effect actions that emit actions immediately (such as is the case with Effect.send) are handled differently than asynchronous effect actions. The synchronous action is processed immediately in the same call stack as when the original action was sent, and so I don't believe there is a way to process that action with an animation.

Note that this doesn't have anything to do with Effect.publisher vs Effect.run. It entirely has to do with synchronous actions from effects. If you update your action like so:

return .publisher {
  Just(.changeShowingDetailView)
    .delay(for: 0, scheduler: DispatchQueue.main)
}
.animation(.default)

…it will also work.

I'm not really sure there is anything the library can do to change this behavior. Our choice to process synchronous actions in the same call stack as when the original action was sent is due to people relying and expecting that kind of behavior. Breaking that expectation will lead to a lot of problems.

I'm inclined to convert this to a discussion since I don't think the library can really do anything to remedy this, and there are simple workarounds. How does that sound?

[heoblitz]

@mbrandonw Thanks for the clarification.

It's a minor comment, but it would be nice to have the publisher animation usage in the documentation or comments.

As you say, it would be great to close the issue and turn it into a discussion!