IssueTracker

I have been having an issue dealing with R8/obfuscation with an Android library written in Kotlin.

Below is the sample code

typealias MyLambdaCallback = (String, Map<String, Any>) -> Unit

@Keep
object MyApi {

    private var callback: MyLambdaCallback? = null

    @JvmStatic
    fun setCallback(callback: MyLambdaCallback) {
        this.callback = callback
    }
}

Similar to above, I've a public API method which is annotated with @JvmStatic and that method takes a Lambda as parameter.

When I release the library without minification, everything is fine and calling code (from app side) written in Java and Kotlin can call this method and works as expected.

Now if I enable minification and call same method from a demo app then I get a crashing error with message similar to below

java.lang.IncompatibleClassChangeError: The method 'void setCallback(kotlin.jvm.functions.Function2)' was expected to be of type virtual but instead was found to be of type static (declaration of 'com.demo.basic.Application' appears in /data/app/com.demo.basic-_0uJXPbtfs3UZ2Rp2h-RdQ==/base.apk!classes2.dex)

What have I tried ?

• Removing @Jvmstatic resolves the issue but it created ugly Java calling code as I would have to call like MyApi.INSTANCE.setCallback()
• Kept @Jvmstatic but removed Lambda by converting Lambda into an Interface with one method and everything is working fine. Unfortunately SAM for Kotlin classes is not there yet, so calling Kotlin code looks ugly then
• I also tried disabling R8 via setting these lines in gradle.properties which forcefully enabled Proguard and then everything work with both @Jvmstatic and Lambda

android.enableR8=false
android.enableR8.libraries=false

So my last try confirms that this problem has something to do with R8.

Would you please help me out with this ?

Whether it's something wrong on my side as incorrect use of R8 or it's genuine R8 bug ? I don't know.

I posted a Stackoverflow question with same details here: https://stackoverflow.com/questions/62249685/dealing-with-r8-jvmstatic-annotation-lambda-in-public-api-for-android-librar