AppMetrica stopped working after Firebase was updated to version 31+

This is what happens when you update Firebase:

1. When building your app, the Firebase Performance Monitoring plugin replaces the network code with its own classes. These changes are applied for all processes.

2. When you launch the app using ContentProvider, it initializes FirebaseApp, which is necessary for FirebasePerfomance to work.

3. When sending an AppMetrica network request, the FirebasePerfUrlConnection class that got replaced at step 1 throws an exception.

   java.lang.NoClassDefFoundError: com.google.firebase.perf.config.RemoteConfigManager
   ....
   Caused by: java.lang.ExceptionInInitializerError 
   at com.google.firebase.perf.config.RemoteConfigManager.getInstance(RemoteConfigManager.java:119)
   ....
   Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.example.firebaseperfomancewithappmetrica:Metrica. Make sure to call FirebaseApp.initializeApp(Context) first.

   This happens because at step 1 FirebaseApp was activated only for the main process, while the network stack was substituted across the board.

How to fix it

1. Activate FirebaseApp for all processes, including the AppMetrica SDK process. For Application#onCreate(), call FirebaseApp.initializeApp(this) before activating the AppMetrica SDK.

   Example:

   class MainApplication : Application() {
       
       override fun onCreate() {
           super.onCreate()
           
           // Init FirebaseApp for all processes
           FirebaseApp.initializeApp(this)
           
           // Then activate AppMetrica SDK
           YandexMetrica.activate(
               this,
               YandexMetricaConfig.newConfigBuilder(API_KEY)
                   .build()
           )
       }
   }

2. Temporarily opt out of using Firebase Performance. To do this, stop applying the firebase-performance-plugin by removing it from build.gradle com.google.firebase.firebase-perf.

3. Use an older version of Firebase.

This doesn't seem to be the expected behavior of the Firebase SDK and may be fixed in future versions.