Crash task-local: illegal task-local value binding

[corysullivan]

I am updating my app to TCA 1.0 and using the latest Xcode beta (Version 15.0 beta 6 (15A5219j)). After resolving all compilation errors, I encountered a crash from the Dependency library. I intend to investigate this further, but I wanted to know if anyone else has experienced this or has any ideas on why it might happen.

[stephencelis]

@corysullivan That error is due to executing task local code inside an invalid context, like within a withTaskGroup block but outside an addTask. Here's a vanilla test case demonstrating the issue:

func testIllegalTaskLocal() async {
  enum Test {
    @TaskLocal static var isSetting = false
  }

  await withTaskGroup(of: Void.self) { group in
    Test.$isSetting.withValue(true) {
      print(Test.isSetting)
    }
    print(Test.isSetting)
  }
}

If you follow your trace to the effect causing the crash, you're likely in a withTaskGroup context. You'll want to avoid accessing dependencies in that scope, and instead move dependency access inside group.addTask, or outside the task group entirely.

My only guess as to why you didn't encounter this issue earlier is that you were on a version of Dependencies that didn't access the task local at this time.

[corysullivan]

Thanks Stephen, This was helpful, I found the issue, and although I wasn't accessing a dependency directly in the group context, I was sending an action back into the system.

return .run { send in
  await withTaskGroup(of: Void.self) { group in
    for task in tasks {
      group.addTask {
        ...
      }
    }
    await send(.someAction)
  }
}

Moving the action sending outside the group context resolved the issue.