Why do I get a linking error after updating to Xcode 12 ?

Question

Hello,

I have a Unity project that uses a native Swift + ObjC library that I made using Firebase MLKit. When trying to build for iOS, the Unity project always builds with Xcode 11.3.1, but when updating to any Xcode 12.X version, I get the following errors :

ld: warning: Could not find or use auto-linked library 'swiftCoreMIDI' ld: warning: Could not find or use auto-linked library 'swiftUniformTypeIdentifiers' Undefined symbols for architecture armv7:
"__swift_FORCE_LOAD_$swiftUniformTypeIdentifiers", referenced from: swift_FORCE_LOAD$swiftUniformTypeIdentifiers$NativeLibrary_iOS in NativeLibrary_iOS.a(NativeLibrary.o) swift_FORCE_LOAD$swiftUniformTypeIdentifiers$NativeLibrary_iOS in NativeLibrary_iOS.a(UIImage.o) (maybe you meant: swift_FORCE_LOAD$swiftUniformTypeIdentifiers$NativeLibrary_iOS) "swift_FORCE_LOAD$swiftCoreMIDI", referenced from: swift_FORCE_LOAD$swiftCoreMIDI$NativeLibrary_iOS in NativeLibrary_iOS.a(NativeLibrary.o) swift_FORCE_LOAD$swiftCoreMIDI$NativeLibrary_iOS in NativeLibrary_iOS.a(UIImage.o) (maybe you meant: swift_FORCE_LOAD$swiftCoreMIDI$_NativeLibrary_iOS) ld: symbol(s) not found for architecture armv7 clang: error: linker command failed with exit code 1 (use -v to see invocation)

I am not using either swiftCoreMIDI nor swiftUniformTypeIdentifiers in my code. For the record, I did recompile my native library with Xcode 12 before importing it again in Unity.

Things I have tried:

Building a Unity project with a Swift library that doesn’t use Firebase MLKit : works fine
Building an Xcode only project that uses Firebase MLKit : works fine
Building the project with a more recent Unity version : fails
Integrating the Firebase SDK frameworks directly instead of using CocoaPods : fails
Adding an empty Swift file + bridging header to my project : fails
Adding the user defined setting LD_VERIFY_BITCODE = NO in XCode : fails

I’m using:

Xcode 12.2
Firebase 6.34
Swift 5.0
Unity 2019.3.6f1

Any help would be appreciated, I’ve been stuck on this for a while!

Answer 1

SOLUTION

I finally found the solution, it was linked to the UnityFramework target in Xcode. I had to remove some architectures that are not concerned by my build: i386 and x86_64. In addition, I updated the Library Search Paths to include $(SDKROOT)/usr/lib/swift.

To execute those actions automatically, you can add those lines in a PostProcessBuild file in your Unity project :

 var projPath = pathToBuiltProject + "/Unity-iPhone.xcodeproj/project.pbxproj";
 var proj = new PBXProject();
 proj.ReadFromFile(projPath);
 
 // Update the Library Search Paths of the whole Xcode project
 proj.AddBuildProperty(proj.ProjectGuid(), "LIBRARY_SEARCH_PATHS", "$(SDKROOT)/usr/lib/swift");
 
 // Get the UnityFramework target and exclude the unwanted architectures
 var unityFrameworkGuid = proj.TargetGuidByName("UnityFramework");
 proj.SetBuildProperty(unityFrameworkGuid, "EXCLUDED_ARCHS", "i386");
 proj.AddBuildProperty(unityFrameworkGuid, "EXCLUDED_ARCHS", "x86_64");

Why do I get a linking error after updating to Xcode 12 ?

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