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

Questions & Answers
1

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!

2

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");