TypingOperationQueue.swift fails to compile on Xcode 26.4 / Swift 6.2 due to actor-isolation error

[sethdeckard]

Building ably-chat-swift with Xcode 26.4 / Swift 6.2 fails in Sources/AblyChat/TypingOperationQueue.swift because of stricter actor-isolation/sendability
checking.

Compiler error

TypingOperationQueue.swift:96:38: error: sending 'pendingRequest' risks causing data races
await pendingRequest.performOperation()
      ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

note: sending main actor-isolated 'pendingRequest' to nonisolated instance method 'performOperation()' risks causing data races between nonisolated and main
actor-isolated uses

Code

TypingOperationQueue is @mainactor, and the failure happens in didFinishExecutingOperation() when a pending request is executed inside a Task:

@MainActor
internal class TypingOperationQueue<Failure: Error> {
  private struct Request {
    func performOperation() async {
      let result = await operation()
        complete(with: result)
    }

    func complete(with result: Result<Void, Failure>) {
      continuation.resume(returning: result)
    }
  }

  private func didFinishExecutingOperation() {
    if let pendingRequest {
      state = .executing(pendingRequest: nil)
        Task {
          await pendingRequest.performOperation()
            didFinishExecutingOperation()
        }
    } else {
      state = .idle
    }
  }
}

What fixed it locally

We were able to get the package compiling by explicitly marking the nested Request methods as @mainactor and making the task main-actor isolated as well:

@MainActor
func performOperation() async { ... }

@MainActor
func complete(with result: Result<Void, Failure>) { ... }

Task { @MainActor in
    await pendingRequest.performOperation()
    didFinishExecutingOperation()
}

Environment

• Xcode 26.4
• Swift 6.2
• iOS simulator build
• Reproduced with ably-chat-swift 1.2.0

┆Issue is synchronized with this Jira Task by Unito

[lawrence-forooghian]

Thanks for reporting this, @sethdeckard. I've got a fix for it in ably/ably-chat-swift#482; once it's released I'll let you know.

[lawrence-forooghian]

This is fixed in version 1.2.1.