Dealing with R8 + JvmStatic Annotation + Lambda in public API for Android Library written in Kotlin

Question

First of all, please note that I'm not expecting why do you want to obfuscate library comments. This is a genuine problem I'm asking about.

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

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

For example, take a look at code below,

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

@Keep
object MyApi {

    private var callback: MyLambdaCallback? = null

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

I have added @Jvmstatic so that Java calling code can call the method statically rather than doing MyApi.INSTANCE.setCallback()

When I release the library without minification, everything is fine and calling code from both Java and Kotlin is written as expected.

But now I want to release the library while turning on minification.

That creates an issue.

Here is the error

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)

Am I making a mistake somewhere or this is expected as some kind of limitation ?

What did I Try ?

Removing @Jvmstatic resolves the issue but it created ugly Java calling code
Kept @Jvmstatic but removed Lambda 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.

@RyanM I found that the problem is around `@Jvmstatic`. I update content of the Q. Take a look if you can help with something. — shaktiman_droid, Jun 07 '20 at 23:30
This is a great question with lots of details. This really looks like a bug in the tools somewhere (i.e., not a mistake on your part) to me - I don't have time to dig into it at the moment, but I'll take a look at some point if I can find some time. — Ryan M, Jun 07 '20 at 23:31
This is reported at https://issuetracker.google.com/issues/158393309. — MortenKJ, Jun 08 '20 at 06:52
@shaktiman_droid you'd better edit question and delete that "update" part as it is misleading: the answer is below. — Den Drobiazko, Jul 21 '20 at 15:51

score 3 · Answer 1 · answered Jun 12 '20 at 11:50

This is tracked on the R8 issue tracker http://issuetracker.google.com/158393309 which has more details.

The short story is that this has been fixed in R8 version 2.1.35, which can be used by making the following changes to the top level build.gradle file:

repositories {
    maven {
        url 'https://storage.googleapis.com/r8-releases/raw'
    }
}

dependencies {
    classpath 'com.android.tools:r8:2.1.35'          // Must be before the Gradle Plugin for Android.
    classpath 'com.android.tools.build:gradle:X.Y.Z' // Your current AGP version.
 }

score 2 · Accepted Answer · answered Jun 18 '20 at 17:05

R8 team has fixed this issue along with related issue b/158400283 in R8 version 2.1.42

Fix should already be available in Android Studio 4.1 beta or higher, but if you're using stable Android Studio 4.0 then add following to your top-level build.gradle file:

buildscript {

    repositories {
        maven {
            url 'https://storage.googleapis.com/r8-releases/raw'
        }
    }

    dependencies {
        classpath 'com.android.tools:r8:2.1.42'          // Must be before the Gradle Plugin for Android.
        classpath 'com.android.tools.build:gradle:X.Y.Z' // Your current AGP version.
     }
}

Dealing with R8 + JvmStatic Annotation + Lambda in public API for Android Library written in Kotlin

2 Answers2

Linked