Weird runtime crash

[RuiAAPeres]

I have the following state, as part of a child:

  public struct State: Equatable {
    public enum Status: Equatable {
      case initial
      case loading
      case error(VitalError)
    }
    
    public var status: Status = .initial
    public var alert: AlertState<Action>?
    public var code: String = ""
    
    init(
      status: Status = .initial,
      alert: AlertState<Action>? = nil,
      code: String = ""
    ) {
      self.status = status
      self.alert = alert
      self.code = code
    }
  }

And the child being used in the parent:

  public var body: some ReducerProtocol<State, Action> {
    
    Reduce { state, action in
      switch action {
        case let .handleResult(credentials):
          if let credentials = credentials {
            state = .authenticated(.init(credentials: credentials))
            return Effect(value: .authenticated(.setup))
          } else {
            state = .noCode(.init())
            return .none
          }
          
        case .checkStatus:
          let value = appDependencies.credentials()
          return Effect(value: .handleResult(value))
          
        case .noCode, .authenticated:
          return .none
      }
    }
    .ifCaseLet(/State.noCode, action: /Action.noCode) {
      NoCodeReducer()
    }
    .ifCaseLet(/State.authenticated, action: /Action.authenticated) {
      AuthenticatedReducer()
    }
  }

If I run the above code, it crashes:

However, if I put the code as the second property of the state, like this:

    public var status: Status = .initial
    public var code: String = ""
    public var alert: AlertState<Action>?

I get this crash instead:

If I remove the code property completely, there's no crash.

I am using Version 14.0.1 (14A400) with TCA pointing to main.

What's happening here? :)

[stephencelis]

@RuiAAPeres Hard to pinpoint the issue without more context, but a few things stand out:

1. What does the state look like that each case path refers to (e.g. what does the enum look like that contains State.noCode and State.authenticated)?
2. When you got the crash to "move," were you incrementally compiling? Was the crash consistent across cleaning your build folder and running fresh?
3. If you define your case paths from scratch using CasePath.init(embed:extract:), does everything work just fine?

There are some known bugs in case path reflection. While they are generally edge cases involving existentials and enums with one case, you might be hitting one here. We'd love to track them down (or better, we'd love for Apple to support native case paths), so any more info about the types involved here would be helpful!

[RuiAAPeres]

This is so odd, but doing a clean build fixed it and I have feeling that what I mentioned here, was the same thing.

[stephencelis]

Now that reducers live inside types/conformances, they're more compatible with Swift's incremental build system (meaning they work with things like Injection for Xcode out of the box), but this means they are also prone to some of the issues with conditional compilation, unfortunately. Glad you got sorted!

[mluisbrown]

I get this a lot too. Don't know if it's just with TCA projects, but about once a week or so I start getting unexplained crashes like the above, and a clean build or clean build + restart Xcode solves it. Must be an Xcode / Swift compiler bug related to incremental builds.

[mbrandonw]

A few months back we found the following incremental compilation crash: swiftlang/swift#60706. It's reproducible in plain Swift code without TCA. The sample project shows the exact steps to produce the bug too.