I'm trying to use Firebase Objective C code in Kotlin. I added this to the "common" build.gradle: `...

# kotlin-native

[Thomas]

I'm trying to use Firebase Objective C code in Kotlin. I added this to the "common" build.gradle:

compilations.getByName("main") {
    val firebase by cinterops.creating {
        defFile("$projectDir/src/iOSMain/cinterop/firebase.def")
        val pods = "$projectDir/../ios/Pods"
        includeDirs(
            "$pods/FirebaseCore/Firebase/Core/Public"
        )

        compilerOpts("-F$pods/Firebase -F$pods/FirebaseCore")
        linkerOpts("-F$pods/Firebase -F$pods/FirebaseCore")
    }
}

And this is the firebase.def file:

language = Objective-C
headers = FirebaseCore.h

When trying to edit the Kotlin code I have no issues importing the Firebase framework. But when compiling for iOS (packForXCode) I get this error:

ld: warning: could not create compact unwind for _ffi_call_unix64: does not use RBP or RSP based frame
Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_FIRApp", referenced from:
      objc-class-ref in combined.o
ld: symbol(s) not found for architecture x86_64
error: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld invocation reported errors

Does anyone know why this is happening? Is there something wrong in my configuration?

[kpgalligan]

It’s an xcode issue. Undefined symbols for architecture x86_64:
“_OBJC_CLASS_$_FIRApp”

[kpgalligan]

Sorry, let me rephrase. That’s a native issue. The process can’t find firebase when it tries to link. I would confirm xcode/Pods are otherwise set up correctly and then check the gradle config

[Thomas]

Thanks for your answer. I have no issues when calling the Firebase code from Swift, the app builds successfully. Once I try to reference some Firebase code in a Kotlin file, this error shows up. So I think this is related to the gradle config and not to xcode.

[Thomas]

@kpgalligan any idea what could be wrong in the gradle config?

[kpgalligan]

Well, the Interop finds the header file, apparently. My guess is that somethings wrong with your linking settings. Exactly what, will be exceptionally difficult to debug without being able to play with it. I’m not really an expert on linker settings for frameworks, but the same flags in compiler and linker argsseems suspect

[ivan.savytskyi]

I had the same issue when linker was configured wrong and it couldn’t find 3rd party library

[ivan.savytskyi]

check your linker options

[ivan.savytskyi]

I believe that def file requires linkerOpts

[Thomas]

@ivan.savytskyi I think this isn't needed because they are already added in the build.gradle. I tried adding them to the def file as well (with absolute paths, no variables), but unfortunately I still got the same exception. Could it be that I am trying to add the wrong directory to the linkerOpts?

[kpgalligan]

Any reason you're not using the multiplatform firebase lib? In any case, i'd look at this for def file example https://github.com/RubyLichtenstein/Kotlin-Multiplatform-Firebase/blob/master/common-all/src/iOSMain/c_interop/firestore/FirebaseFirestore.def

[kpgalligan]

The header files define a "thing" you can call. The linker has to actually go out and find the thing. Assuming the header is correct, the only likely problem you have is a path config problem in the linker

[Joao Zao]

Any reason you’re not using the multiplatform firebase lib?

@kpgalligan Are you referring to this 👇 ?

https://github.com/RubyLichtenstein/Kotlin-Multiplatform-Firebase

[kpgalligan]

Yes. Disclaimer, I’ve never used it. Am curious why one wouldn’t

[Joao Zao]

That project seems to be binding only the Firestore stuff and not the whole firebase.

[kpgalligan]

Ah. OK.

[Joao Zao]

I was just checking the project and I’m getting this error 👇
ld: framework not found FirebaseFirestore

probably missing some includeDirs, don’t know.

[kpgalligan]

No idea. Haven’t tried it. There’s a lot there, so a lot of room of issues I’d imagin

[kpgalligan]

imagine

[Joao Zao]

true 🙂

[Joao Zao]

I believe a “multiplatform firebase lib” is more than welcome in the Kotlin Native community

[Joao Zao]

It seems that passing the path to frameworks folder in the linkerOpts through -F option is solving the issue ld: framework not found FirebaseFirestore

Something like:

linkerOpts = /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.0/lib/darwin/libclang_rt.osx.a -F ${fullpath-to-frameworks-dir} -framework FirebaseFirestore -framework ...