gradle jacoco plugin with java 15

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In my latest experiments I upgraded a project to Java 15 and received exceptions during the build from jacoco that state that the used Java version isn’t supported. Here the exceptions stacktrace I received:

java.lang.instrument.IllegalClassFormatException: Error while instrumenting sun/util/resources/cldr/provider/CLDRLocaleDataMetaInfo.
        at org.jacoco.agent.rt.internal_43f5073.CoverageTransformer.transform(CoverageTransformer.java:94)
        at java.instrument/java.lang.instrument.ClassFileTransformer.transform(ClassFileTransformer.java:246)
        at java.instrument/sun.instrument.TransformerManager.transform(TransformerManager.java:188)
        at java.instrument/sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:563)
        at java.base/java.lang.ClassLoader.defineClass2(Native Method)
        at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1108)
        at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:183)
        at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:784)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClassInModuleOrNull(BuiltinClassLoader.java:705)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClass(BuiltinClassLoader.java:586)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:634)
        at java.base/java.lang.Class.forName(Class.java:546)
        at java.base/java.util.ServiceLoader.loadProvider(ServiceLoader.java:854)
        at java.base/java.util.ServiceLoader$ModuleServicesLookupIterator.hasNext(ServiceLoader.java:1078)
        at java.base/java.util.ServiceLoader$2.hasNext(ServiceLoader.java:1301)
        at java.base/java.util.ServiceLoader$3.hasNext(ServiceLoader.java:1386)
        at java.base/sun.util.cldr.CLDRLocaleProviderAdapter$1.run(CLDRLocaleProviderAdapter.java:89)
        at java.base/sun.util.cldr.CLDRLocaleProviderAdapter$1.run(CLDRLocaleProviderAdapter.java:86)
        at java.base/java.security.AccessController.doPrivileged(AccessController.java:554)
        at java.base/sun.util.cldr.CLDRLocaleProviderAdapter.<init>(CLDRLocaleProviderAdapter.java:86)
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:64)
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481)
        at java.base/sun.util.locale.provider.LocaleProviderAdapter.forType(LocaleProviderAdapter.java:188)
        at java.base/sun.util.locale.provider.LocaleProviderAdapter.findAdapter(LocaleProviderAdapter.java:287)
        at java.base/sun.util.locale.provider.LocaleProviderAdapter.getAdapter(LocaleProviderAdapter.java:258)
        at java.base/java.util.Calendar.createCalendar(Calendar.java:1693)
        at java.base/java.util.Calendar.getInstance(Calendar.java:1661)
        at java.base/java.text.SimpleDateFormat.initializeCalendar(SimpleDateFormat.java:677)
        at java.base/java.text.SimpleDateFormat.<init>(SimpleDateFormat.java:621)
        at java.base/java.text.SimpleDateFormat.<init>(SimpleDateFormat.java:600)
        at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.getLastResortErrorLogFile(SystemApplicationClassLoaderWorker.java:168)
        at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:111)
        at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:69)
        at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:68)
        at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:73)
Caused by: java.io.IOException: Error while instrumenting sun/util/resources/cldr/provider/CLDRLocaleDataMetaInfo.
        at org.jacoco.agent.rt.internal_43f5073.core.instr.Instrumenter.instrumentError(Instrumenter.java:159)
        at org.jacoco.agent.rt.internal_43f5073.core.instr.Instrumenter.instrument(Instrumenter.java:109)
        at org.jacoco.agent.rt.internal_43f5073.CoverageTransformer.transform(CoverageTransformer.java:92)
        ... 37 more
Caused by: java.lang.IllegalArgumentException: Unsupported class file major version 59
        at org.jacoco.agent.rt.internal_43f5073.asm.ClassReader.<init>(ClassReader.java:195)
        at org.jacoco.agent.rt.internal_43f5073.asm.ClassReader.<init>(ClassReader.java:176)
        at org.jacoco.agent.rt.internal_43f5073.asm.ClassReader.<init>(ClassReader.java:162)
        at org.jacoco.agent.rt.internal_43f5073.core.internal.instr.InstrSupport.classReaderFor(InstrSupport.java:280)
        at org.jacoco.agent.rt.internal_43f5073.core.instr.Instrumenter.instrument(Instrumenter.java:75)
        at org.jacoco.agent.rt.internal_43f5073.core.instr.Instrumenter.instrument(Instrumenter.java:107)
        ... 38 more

Especially “Unsupported class file major version 59” is a good indicator that Java 15 isn’t supported yet. To get around that you need to upgrade the jacoco tool version in your gradle project by adding:

jacoco {
    toolVersion = "0.8.6"
}

You need at least 0.8.6 because there experimental Java 15 was added. You can find the release history under https://www.jacoco.org/jacoco/trunk/doc/changes.html. Right now 0.8.6 is the latest release that solves the issue without the need to go to a snapshot build of 0.8.7.