"Your first feature" tutorial doesn't compile

[cameronmcefee]

Description

In the Your First Feature tutorial (and probably others), the given code doesn't compile due to a lack of satisfying the conformance to Reducer. I don't know if it's written this way intentionally so I didn't make a pull request to update it. However, I was able to get it compile by copying similar (but different) code from the Getting Started guide.

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

The code should compile

Actual behavior

Received the error: Type 'CounterFeature' does not conform to protocol 'Reducer' without further explanation of what doesn't conform, and no "fix it" to add stubs.

Reproducing project

import ComposableArchitecture


@Reducer
struct CounterFeature {
  @ObservableState
  struct State {
    var count = 0
  }
  
  enum Action {
    case decrementButtonTapped
    case incrementButtonTapped
  }
  
-  // Does not compile
-  var body: some ReducerOf<Self> {
+  // Compiles
+  var body: some Reducer<State, Action>
    Reduce { state, action in
      switch action {
      case .decrementButtonTapped:
        state.count -= 1
        return .none
        
      case .incrementButtonTapped:
        state.count += 1
        return .none
      }
    }
  }
}

The Composable Architecture version information

1.20.2

Destination operating system

MacOS 15.5

Xcode version information

Version 26.0 beta 4

Swift Compiler version information

6.2 (whatever the defaults of the project are)

[stephencelis]

@cameronmcefee That code compiles just fine for me in Xcode 16.4:

Can you please provide more information on how to reproduce, ideally with a project that shows the issue, as well as more of a description of what goes wrong.

[cameronmcefee]

Sorry about that @stephencelis. This was in a brand new project so my brain just omitted the "I should add repro" step 🤦 . I updated the OP but it's 26 Beta 4. The compiler message provides no further info, unfortunately. I tried looking at the definitions but it wasn't obvious to me what was wrong.

tca-experiment.zip

[stephencelis]

@cameronmcefee Xcode 26 uses main actor isolation by default, which means you need to explicitly make everything nonisolated or switch back to nonisolated as the default.

There are pending changes to the language that will give us the ability to signal this to the compiler, but they haven't shipped as of beta 4.

Since this isn't a bug with the library I'm going to convert to a discussion.

[cameronmcefee]

Ah, that makes sense, thanks for clarifying. It's a shame the warnings didn't make that more clear as they've done in other cases where I've seen that conflict.

[stephencelis]

@cameronmcefee In this case it very well could be a Swift bug/regression with how type checking is handled in main actor isolation mode. Are you up to filing an issue with the Swift repo?

[cameronmcefee]

Sure thing. I'm a bit out of my depth here, but I gave it a shot: swiftlang/swift#83312