Method references are not taken into account by proguard

[denis-itskovich]

I'm not sure whether it's an issue of retrolambda itself or gradle-retrolambda

Background

Proguard seems to shrink methods, referenced as method references. See an example below:

public class AsyncTaskBuilder<Progress, Result> {

    public interface BackgroundWorkWithProgress<_Progress, _Result> {
        _Result execute(ProgressObserver<_Progress> progressObserver);
    }

    private BackgroundWorkWithProgress<Progress, Result> work;

    public AsyncTask<Void, Progress, Result> build() {

        return new AsyncTask<Void, Progress, Result>() {
            @Override
            protected Result doInBackground(Void... voids) {
                // this reference will not be taken into account by Proguard
                return work.execute(this::publishProgress);
            }

        };
    }
}

After building, the following error is shown:

:app:proguardRelease
Warning: com.github.retrolambda_methodref_repro.AsyncTaskBuilder$1$$Lambda$1: can't find referenced method 'void publishProgress(java.lang.Object[])' in library class android.os.AsyncTask
Warning: there were 1 unresolved references to library class members.
         You probably need to update the library versions.
         (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedlibraryclassmember)
Exception while processing task 
java.io.IOException: Please correct the above warnings first.
    at proguard.Initializer.execute(Initializer.java:473)
    at proguard.ProGuard.initialize(ProGuard.java:233)
    at proguard.ProGuard.execute(ProGuard.java:98)
    at proguard.gradle.ProGuardTask.proguard(ProGuardTask.java:1074)
    at com.android.build.gradle.tasks.AndroidProGuardTask.doMinification(AndroidProGuardTask.java:139)
    at com.android.build.gradle.tasks.AndroidProGuardTask$1.run(AndroidProGuardTask.java:115)
    at com.android.builder.tasks.Job.runTask(Job.java:48)
    at com.android.build.gradle.tasks.SimpleWorkQueue$EmptyThreadContext.runTask(SimpleWorkQueue.java:41)
    at com.android.builder.tasks.WorkQueue.run(WorkQueue.java:227)
    at java.lang.Thread.run(Thread.java:745)

Full log is available at travis-ci

Sample android project

Simple android project (with 1 class), reproducing the issue can be found here:
https://github.com/denis-itskovich/retrolambda-method-ref-repro

Related issues

The issue seems to be related to this retrolambda issue: luontola/retrolambda#48

[luontola]

The log has some warnings about "AsyncTaskBuilder.java uses unchecked or unsafe operations." Does fixing those help?

[denis-itskovich]

Fixed the warning (replaced varargs generic parameter by generic array parameter), but the issue still exists: https://travis-ci.org/denis-itskovich/retrolambda-method-ref-repro/builds/85513111

One more observation:

The issue does not reproduce if I replace method reference by lambda: this::publishProgress with progress -> publishProgress(progress). In this case the build succeeds.

[gmarizy]

In my case, method references were causing failure even with proguard disabled, with error like:

E/AndroidRuntime: java.lang.NoClassDefFoundError: java.util.Objects

The reason was incompatibility with gradle-errorprone-plugin. Given that this plug-in play with compiler it's not that a surprise. It used to work with previous version of gradle-retrolambda though.

[konmik]

Did you try using the latest retrolambda version?

dependencies {
    retrolambdaConfig 'net.orfjackal.retrolambda:retrolambda:2.0.6'

[denis-itskovich]

Recently tried - getting the same error with 2.0.6

[tomblenz]

I'm getting this same error with 3.3.0-beta4.

[formatBCE]

Getting NoClassDefFound error on java.utils.Objects on both latest stable and 3.3.0 beta versions.
Could you please fix that?
We use lambdas in pretty big project, and it will take too much time to replace all method references to usual lambdas.

[evant]

You need to update to the latest retrolamba, see luontola/retrolambda#75

[formatBCE]

Same issue: java.lang.NoClassDefFoundError: java.util.Objects
build.gradle: classpath 'me.tatarka:gradle-retrolambda:3.2.5'

[evant]

You did

dependencies {
    retrolambdaConfig 'net.orfjackal.retrolambda:retrolambda:2.3.0'
}

correct?

[formatBCE]

I'm TRULY sorry...
Works! :)

[sunny-chung]

Reproducible in an Android project with
gradle-retrolambda 3.2.5 + retrolambda 2.3.0/2.4.0/2.5.0
gradle-retrolambda 3.5.0 + retrolambda 2.5.0,

apply plugin: 'me.tatarka.retrolambda' is put at the last.

This plugin was working at past time.

[ncruces]

Ignoring these warnings is enough to fix it:

-dontwarn **$$Lambda$*