Javadoc task fails on JDK 15, Gradle 6.7

Help/Discuss
1

I have a project I am trying to upgrade to Gradle 6.7. Currently, I’m on Gradle 6.3.

After I upgrade, I can’t build my project. It fails on the javadoc task with:

Caused by: java.lang.ClassCastException: class java.lang.String cannot be cast to class java.util.List (java.lang.String and java.util.List are in module java.base of loader 'bootstrap')
        at org.gradle.external.javadoc.CoreJavadocOptions.modulePath(CoreJavadocOptions.java:325)
        at org.gradle.api.tasks.javadoc.Javadoc.generate(Javadoc.java:148)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:104)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.doExecute(StandardTaskAction.java:58)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:51)
        at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:29)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$3.run(ExecuteActionsTaskExecuter.java:555)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:75)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:68)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:153)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:68)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:56)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.lambda$run$1(DefaultBuildOperationExecutor.java:71)
        at org.gradle.internal.operations.UnmanagedBuildOperationWrapper.runWithUnmanagedSupport(UnmanagedBuildOperationWrapper.java:45)
        at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:71)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:540)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:523)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.access$300(ExecuteActionsTaskExecuter.java:108)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$TaskExecution.executeWithPreviousOutputFiles(ExecuteActionsTaskExecuter.java:271)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$TaskExecution.execute(ExecuteActionsTaskExecuter.java:260)
        at org.gradle.internal.execution.steps.ExecuteStep.lambda$execute$1(ExecuteStep.java:34)
        at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:34)
        at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:26)
        at org.gradle.internal.execution.steps.CleanupOutputsStep.execute(CleanupOutputsStep.java:67)
        at org.gradle.internal.execution.steps.CleanupOutputsSte.....

Looks like a Gradle bug to me.

Any suggestions?

2

I downgraded to Java 11, but the problem remains.

3

Are you using the javadoc task directly in your build? Or are you invoking the javadoc task via a third party plugin? Can you include the javadoc configuration snippet from your build.gradle?

4

Hi @Lance,

I don’t call the javadoc task directly, usually, it’s automatically called when I run ./gradlew build. There’s no plugin I am aware of that’s doing that.

Calling javadoc directly causes the same error.

I did not explicitly configure the javadoc task.

There might be something to do with the fact I use this plugin?

id 'org.javamodularity.moduleplugin' version '1.6.0'

You can see my current build file here if you think it helps: https://github.com/renatoathaydes/LogFX/blob/next/build.gradle

This branch uses Gradle 6.3. If I just change it to 6.7 and nothing else, it fails with this error.

Here’s the output when I run ./gradlew build --console=plain:

:arrow_forward: ./gradlew build --console=plain

Task :buildSrc:compileJava UP-TO-DATE
Task :buildSrc:compileGroovy NO-SOURCE
Task :buildSrc:processResources NO-SOURCE
Task :buildSrc:classes UP-TO-DATE
Task :buildSrc:jar UP-TO-DATE
Task :buildSrc:assemble UP-TO-DATE
Task :buildSrc:compileTestJava UP-TO-DATE
Task :buildSrc:compileTestGroovy NO-SOURCE
Task :buildSrc:processTestResources NO-SOURCE
Task :buildSrc:testClasses UP-TO-DATE
Task :buildSrc:test UP-TO-DATE
Task :buildSrc:check UP-TO-DATE
Task :buildSrc:build UP-TO-DATE

Configure project :
Project : => ‘com.athaydes.logfx’ Java module

Task :generateJavaSources
Task :compileJava UP-TO-DATE
Task :compileGroovy NO-SOURCE
Task :processResources UP-TO-DATE
Task :classes UP-TO-DATE
Task :jar UP-TO-DATE
Task :startScripts UP-TO-DATE
Task :distTar UP-TO-DATE
Task :distZip UP-TO-DATE
Task :fatJar UP-TO-DATE
Task :javadoc FAILED

FAILURE: Build failed with an exception.

  • What went wrong:
    Execution failed for task ‘:javadoc’.

class java.lang.String cannot be cast to class java.util.List (java.lang.String and java.util.List are in module java.base of loader ‘bootstrap’)

5

I think you’ve answered my question, you’re not including the javadoc task yourself, it’s being included via a third party plugin.

Its quite likely that the org.javamodularity.moduleplugin is compiled against an old version of the Javadoc task (and CoreJavadocOptions) but at runtime it’s running against a newer version where CoreJavadocOptions.modulePath(...) has changed.

Is there a newer version of the javamodularity plugin that you can try?

6

Yes, I was on 1.6.0 but they’ve already released 1.7.0.

Upgrading it fixed the problem. I had assumed the javadoc task was part of the Java Plugin, so did not suspect any other plugins… I guess you’re correct then, that they are calling it on behalf of my build :slight_smile:

Well, in any case, the problem has gone away. Thanks for the help.

7

I had assumed the javadoc task was part of the Java Plugin

The javadoc task is a core task available on the classpath, but it’s not wired into the task graph by the java plugin. You need to do that yourself (or via a third party plugin)

Just a couple of pointers

  1. There’s lots of logic in your build.gradle, I suggest putting the logic in custom tasks/plugins under buildSrc and keeping build.gradle purely declarative

  2. I see a few tasks (eg deps and generateJavaSources) which don’t declare task inputs/outputs which means no up to date checks. The sign of a good build is to run a clean build then run a non-clean build (aka dirty build) after. Ideally the second build should do nothing, as every task should be up to date and have no work to do

8

@Lance yeah, I know :slight_smile: but nearly all the logic is publishing and the jlink stuff… which I had to do like that because the existing plugins and functionality in Gradle are just not working well yet… I was hoping most of that was going to be temporary, but time goes by and it’s been there for a couple of years now :smiley:… one day I will clean that all up and hopefully the plugins will have evolved to do the stuff that I needed (I did try some before but had lots of bugs)… I am hoping to get rid of that java.modularity plugin, because all I am doing there is standard stuff that Gradle should manage for me (I haven’t looked more closely yet, but l hope Gradle has better support for JPMS nowadays).

Cheers.