I have a library written for iOS in Objective-C that we publish via Cocoapods, and recently I've been getting a pair of link errors when I try to validate the pod with the pod lib lint command. Both errors look like this (with names changed to protect the innocent):
Ld /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/Objects-normal/x86_64/Binary/App normal x86_64 (in target 'App' from project 'App')
cd /var/folders/4v/jcw9j9x126j5wsmpqmhhswx40000gn/T/CocoaPods-Lint-20191211-37020-sasgf-FooBarSDK
/Applications/Xcode-11.2.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -target x86_64-apple-ios8.0-simulator -isysroot /Applications/Xcode-11.2.1.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.2.sdk -L/Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Products/Release-iphonesimulator -L/Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Products/Release-iphonesimulator/FooBarSDK -L/Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Products/Release-iphonesimulator/TFooBarSDK -L/var/folders/4v/jcw9j9x126j5wsmpqmhhswx40000gn/T/CocoaPods-Lint-20191211-37020-sasgf-FooBarSDK/Pods/TFooBarSDK/FooBar -F/Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Products/Release-iphonesimulator -filelist /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/Objects-normal/x86_64/App.LinkFileList -Xlinker -rpath -Xlinker @executable_path/Frameworks -dead_strip -Xlinker -object_path_lto -Xlinker /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/Objects-normal/x86_64/App_lto.o -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -fobjc-link-runtime -ObjC -lFooBar_1.2.4 -lFooBarSDK -lTFooBarSDK -lz -Xlinker -sectcreate -Xlinker __TEXT -Xlinker __entitlements -Xlinker /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/App.app-Simulated.xcent -framework Foundation -lPods-App -Xlinker -dependency_info -Xlinker /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/Objects-normal/x86_64/App_dependency_info.dat -o /Users/myusername/Library/Developer/Xcode/DerivedData/App-akupndrkecikjfdfvjfyniytivhf/Build/Intermediates.noindex/App.build/Release-iphonesimulator/App.build/Objects-normal/x86_64/Binary/App
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_FooBar", referenced from:
l_OBJC_$_CATEGORY_FooBar_$_ForceLoad in libFooBarSDK.a(FooBarEmpty.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The problem may have started when I moved the project up to Xcode 10.3 or 11.2 (happens the same with both versions) from Xcode 9.x, or that might be a red herring.
My understanding is that, among other sanity checks, pod lib lint creates an application project that includes the library in question (libFooBarSDK in this case) and tries to build it, and it looks like that project's linking phase is what generates this error. However, our test application links against the library with no problems.
pod --version says I'm using version 1.7.5 of Cocoapods, by the way.
My questions:
Add the option --verbose to get a more detailed log about the failure. Add the option --no-clean to save the Xcode workspace from which you can debug the linker symbol problem.