Iterating `combineLatest`, `merge`, `zip` and `debounce` when Task is already cancelled

[swhitty]

Version 0.0.4 added a preconditionFailure() to combineLatest, merge, zip and debounce that prevents iteration if the task is already cancelled.

The following pattern reproduces the issue in each of the operators:

let t = Task {
  try? await Task.sleep(nanoseconds: 1_000_000_000)
  let c1 = AsyncChannel<Int>()
  let c2 = AsyncChannel<Int>()
  for await (v1, v2) in combineLatest(c1, c2) {
    print(v1, v2)
  }
}
t.cancel()

The failure occurs within each operators version of func cancelled():

  mutating func cancelled() -> CancelledAction? {
    switch self.state {
    case .initial:
      preconditionFailure("Internal inconsistency current state \(self.state) and received cancelled()")

Is this intentional? The workaround is a tedious manual check before any iteration...

if !Task.isCancelled {
  for await v1 in merge(c1, c2) {
    print(v1)
  }
}

[FranzBusch]

Thanks for reporting this. Fixed over here: #250