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

Question

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，这些错误就显得有点“出乎意料”，没有关于导致这些错误的原因以及它源自代码的哪一部分的信息，它们只是在构建之后和构建期间打印出来。链接阶段，现在失败了。

这个错误是什么意思？可以采取什么措施来尝试解决这个问题？

这恰好是一个反应本机生成的 XCode 项目，不确定这是否相关。

Answer 1

问题似乎是我们的项目（由 生成react-native init）已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)"

如果生成普通 Xcode 项目，则不会设置 LIBRARY_SEARCH_PATHS。

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 不具有二进制兼容性。这导致了破坏，因为 swift 5.0 由于某种原因被明确添加到项目中react-native init。也许这里的具体问题是编译代码的命名约定已经改变，而 Swift 5.1 期望URLSession.DataTaskPublisher而不是NSURLSession.DataTaskPublisher？谁知道..

只需将其清理LIBRARY_SEARCH_PATHS干净，将其清空即可为我们解决问题。如果没有它，构建在其他方面也能正常工作。

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