The
Android Resolver will strip all architectures that are not in use from the AARs in Plugins/Android. We ship AARs with native libraries (srcaar files under Firebase/m2repository) . for all architectures supported by Unity at the moment x86, armeabi-v7a and arm64 .
For example:
$ unzip -l Assets/Firebase/m2repository/com/google/firebase/firebase-app-unity/5.3.1/firebase-app-unity-5.3.1.srcaar
Archive: Assets/Firebase/m2repository/com/google/firebase/firebase-app-unity/5.3.1/firebase-app-unity-5.3.1.srcaar
Length Date Time Name
--------- ---------- ----- ----
343 10-05-2018 03:29 AndroidManifest.xml
0 10-05-2018 03:19 R.txt
22 10-05-2018 03:29 classes.jar
0 10-05-2018 18:10 jni/
0 10-05-2018 18:10 jni/arm64-v8a/
0 10-05-2018 18:10 jni/armeabi-v7a/
0 10-05-2018 18:10 jni/x86/
923 10-05-2018 03:29 proguard.txt
--------- -------
9832376 11 files
If you select x86 as one of the target architectures in Unity with
auto-resolution enabled in the Android Resolver, you'll end up with the appropriate contents of the AAR processed and placed in Assets/Plugins/Android e.g...
$ find Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1 -type f
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/proguard.txt.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/AndroidManifest.xml
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/project.properties
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/R.txt.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/libs/x86.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/libs/classes.jar
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/libs/x86/libFirebaseCppApp-5.3.1.so.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/libs/classes.jar.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/proguard.txt
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/R.txt
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/AndroidManifest.xml.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/libs.meta
Assets/Plugins/Android/com.google.firebase.firebase-app-unity-5.3.1/project.properties.meta
So it sounds like you may have auto-resolution disabled in the Android resolver when switching target architectures.
Cheers,
Stewart