ViewModel.swift

extension Publisher {
  public func tryAwaitMap<T>(_ transform: @escaping (Self.Output) async throws -> T) -> Publishers.FlatMap<Future<T, Error>, Self> {
    flatMap { value in
      Future { promise in
        Task {
          do {
            let result = try await transform(value)
            promise(.success(result))
          }
          catch {
            promise(.failure(error))
          }
        }
      }
    }
  }
  
  public func tryAwaitMap<T>(_ transform: @escaping (Self.Output) async throws -> T) -> Publishers.FlatMap<Future<T, Error>, Publishers.SetFailureType<Self, Error>> {
    // The same implementation but the returned publisher transforms failures with SetFailureType.
  }
}

// Case 1: throwing downstream publisher
$imageURL
  .tryMap({ try Self.validateURL($0) })
  .tryAwaitMap({ try await ImageProcessor.process($0) })
  .map({ Image(uiImage: $0) })
  .sink(receiveCompletion: { print("completion: \($0)") },
        receiveValue: { print($0) })
  .store(in: &cancellables)

// Case 2: non-throwing downstream publisher
$imageURL
  .compactMap({ $0 })
  .tryAwaitMap({ try await ImageProcessor.process($0) })
  .map({ Image(uiImage: $0) })
  .sink(receiveCompletion: { print("completion: \($0)") },
        receiveValue: { print($0) })
  .store(in: &cancellables)