组合-使用flatMap时错误类型不匹配

我对Combine很陌生。在这种情况下,我面临着编译程序抱怨错误类型不匹配的问题:

struct Service {
   func save(text: String) -> AnyPublisher<Void, Error> {
      Just(())
        .setFailureType(to: Error.self)
        .eraseToAnyPublisher()
   }
}

let service = Service()
let saveTrigger = PassthroughSubject<Void, Never>()

let cancellable = saveTrigger.map { "text to save"}
   .flatMap { service.save(text: $0) }
   .sink {
       print("Saved")
   }

saveTrigger.send(())

生成失败,出现错误: No exact matches in call to instance method 'flatMap'

如果我使用 setFailureType 这样地:

let cancellable = saveTrigger.map { "text to save"}
   .setFailureType(to: Error.self)
   .flatMap { service.save(text: $0) }
   .sink {
       print("Saved")
   }

我最终出现了不同的错误: Referencing instance method 'sink(receiveValue:)' on 'Publisher' requires the types 'any Error' and 'Never' be equivalent

知道如何解决这个问题吗?