如何修复 iOS/Xcode 构建错误，未定义符号`__C.NSURLSession.DataTaskPublisher`？

Question

在添加 cocoapods 依赖项时，我们开始收到如下构建错误：

Undefined symbols for architecture x86_64:
  "type metadata accessor for (extension in Foundation):__C.NSURLSession.DataTaskPublisher", referenced from:
      (extension in TinyNetworkingObjcIO):__C.NSURLSession.load<A>(TinyNetworkingObjcIO.Endpoint<A>) -> Combine.AnyPublisher<A, Swift.Error> in libTinyNetworkingObjcIO.a(Endpoint.o)
      lazy protocol witness table accessor for type (extension in Foundation):__C.NSURLSession.DataTaskPublisher and conformance (extension in Foundation):__C.NSURLSession.DataTaskPublisher : Combine.Publisher in Foundation in libTinyNetworkingObjcIO.a(Endpoint.o)
  "protocol conformance descriptor for (extension in Foundation):__C.NSURLSession.DataTaskPublisher : Combine.Publisher in Foundation", referenced from:
      lazy protocol witness table accessor for type (extension in Foundation):__C.NSURLSession.DataTaskPublisher and conformance (extension in Foundation):__C.NSURLSession.DataTaskPublisher : Combine.Publisher in Foundation in libTinyNetworkingObjcIO.a(Endpoint.o)
  "(extension in Foundation):__C.NSURLSession.dataTaskPublisher(for: Foundation.URLRequest) -> (extension in Foundation):__C.NSURLSession.DataTaskPublisher", referenced from:
      (extension in TinyNetworkingObjcIO):__C.NSURLSession.load<A>(TinyNetworkingObjcIO.Endpoint<A>) -> Combine.AnyPublisher<A, Swift.Error> in libTinyNetworkingObjcIO.a(Endpoint.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

在我们向 Podfile 添加新的依赖项后，这些错误看起来有点“突如其来”，没有关于导致它们的原因以及它源自代码的哪一部分的信息，它们只是在构建后打印出来的在链接阶段，现在失败了。

这个错误是什么意思？可以做些什么来尝试解决它？

这恰好是一个 react-native 生成​​的 XCode 项目，不确定是否相关。

Answer 1

问题似乎是我们由react-native init 生成的项目将LIBRARY_SEARCH_PATHS 设置为以下内容：

LIBRARY_SEARCH_PATHS = "$(TOOLCHAIN_DIR)/usr/lib/swift/$(PLATFORM_NAME)" "$(TOOLCHAIN_DIR)/usr/lib/swift-5.0/$(PLATFORM_NAME)" "$(inherited)"

如果你生成一个普通的 Xcode 项目，LIBRARY_SEARCH_PATHS 没有设置。

事实证明，我们添加的依赖项需要 Swift 5.1，因为它与旧版本的 Swift 二进制不兼容。这导致了损坏，因为 swift 5.0 出于某种原因被react-native init 明确添加到项目中。也许这里的具体问题是编译代码的命名约定已经改变，Swift 5.1 需要URLSession.DataTaskPublisher 而不是NSURLSession.DataTaskPublisher？谁知道..

只需清除 LIBRARY_SEARCH_PATHS 使其为空，即可为我们解决问题。没有它，构建在其他所有方面都可以正常工作。

相关拉取请求：https://github.com/facebook/react-native/pull/29178