Publisher+Timeout.swift

import Combine

enum PublisherTimeoutError<Failure>: Error where Failure: Error {
    case failure(Failure)
    case timeout
}

extension Publisher {
    func timeoutToNil<S>(after interval: S.SchedulerTimeType.Stride, scheduler: S) -> AnyPublisher<Output?, Failure> where S: Scheduler {
        mapError({ error -> PublisherTimeoutError<Failure> in .failure(error) })
            .map({ output -> Output? in output })
            .timeout(interval, scheduler: scheduler, options: nil, customError: { .timeout })
            .catch({ error -> AnyPublisher<Output?, Failure> in
                switch error {
                case let .failure(error):
                    return Fail(outputType: Output?.self, failure: error)
                        .eraseToAnyPublisher()
                case .timeout:
                    return Just<Output?>(nil)
                        .setFailureType(to: Failure.self)
                        .eraseToAnyPublisher()
                }
            })
            .eraseToAnyPublisher()
    }

    func firstOrNil<S>(timeout interval: S.SchedulerTimeType.Stride, scheduler: S) -> AnyPublisher<Output?, Failure> where S: Scheduler {
        timeoutToNil(after: interval, scheduler: scheduler)
            .first()
            .eraseToAnyPublisher()
    }
}