r8-bug-demo

This sample demonstrates that an application shrunk with R8 can crash at runtime with an AbstractMethodError if the following conditions are met:

• an interface is defined which contains a nullable parameter

interface MainPresenterContract {
    fun onCrashButtonClick(unusedParameter: String?)
}

• a parent class defines a function with the same signature as the interface method containing a nullable parameter

abstract class BasePresenter {

    fun onCrashButtonClick(unusedParameter: String?) {
        Log.d("BasePresenter", "Crash!")
    }
}

• a child class inherits from the previously defined parent class and implements the previously defined interface; since the parent class already implements a method with the correct signature, it doesn't need to override the corresponding method to implement the interface

class MainPresenter : BasePresenter(), MainPresenterContract

• at runtime, the interface method is called via a variable of the interface type:

class MainActivity : AppCompatActivity() {

    private val presenter: MainPresenterContract = MainPresenter()

    override fun onCreate(savedInstanceState: Bundle?) {
        // ...

        crashButton.setOnClickListener {
            // This method invocation will crash the app
            presenter.onCrashButtonClick("Crash!")
        }
    }
}

How to use this sample

1. Run the sample
2. Tap the Crash! button
3. Observe that the app crashes with the following error:

java.lang.AbstractMethodError: abstract method "void com.example.r8bugdemo.MainPresenterContract.a(java.lang.String)"
        at com.example.r8bugdemo.MainActivity$onCreate$1.onClick(:16)
        at android.view.View.performClick(View.java:6597)
        at android.view.View.performClickInternal(View.java:6574)
        at android.view.View.access$3100(View.java:778)
        at android.view.View$PerformClick.run(View.java:25885)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Workarounds

Workaround #1 : Explicitly override the method in the child class

abstract class BasePresenter {
    // Make this method open so it can be overriden
    open fun onCrashButtonClick(unusedParameter: String?) {
        Log.d("BasePresenter", "Crash!")
    }
}

class MainPresenter : BasePresenter(), MainPresenterContract {

    override fun onCrashButtonClick(unusedParameter: String?) {
        Log.d("BasePresenter", "This will work!")
    }
}

Workaround #2 : Use the method parameter

abstract class BasePresenter {

    fun onCrashButtonClick(unusedParameter: String?) {
        val useThisParameterAnyway = unusedParameter
        Log.d("BasePresenter", "This will work!")
    }
}