Make "gradle javadoc" task work with Java 9

Question

I have a multi-module Gradle Java project using source/target = 1.9/1.9. There are two modules, my.base and my.dependsOnBase. The my.base module has no other dependencies:

module my.base {
    exports my.base.foo;
    exports my.base.bar;
}

The my.dependsOnBase module has only a single dependency, which is my.base:

module my.dependsOnBase {
    requires my.base;
    exports my.dependsOnBase.baz;
}

When I run $ gradle javadoc it works fine on my.base. But when it gets to my.dependsOnBase I get the following error output:

/path/to/my $ gradle javadoc

> Task :dependsOnBase:javadoc FAILED
/path/to/my/dependsOnBase/src/main/java/module-info.java:26: error: module not found: my.base
    requires my.base;
                     ^
1 error


FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':dependsOnBase:javadoc'.
> Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): '/path/to/my/dependsOnBase/build/tmp/javadoc/javadoc.options'

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

* Get more help at https://help.gradle.org

BUILD FAILED in 2s
7 actionable tasks: 3 executed, 4 up-to-date

Earlier in the project I was able to get Java compilation, which suffered a similar problem, working using:

compileJava {
    inputs.property("moduleName", moduleName)
    doFirst {
        options.compilerArgs = [
                '--module-path', classpath.asPath,
        ]
        classpath = files()
    }
}

But those properties aren't directly applicable to the Gradle javadoc task.

How can I get my Javadoc working?

Rahmann

Could you update the javadoc task details used in the question? Also, did you try ensuring the my.base module exists in the module path while executing that task as well? – Jarl

@nullpointer, I didn't try it yet because I don't know Gradle well and I can't understand how to set the javadoc task modulepath within Gradle (blind copy/paste of the compileJava block definitely didn't work). I don't have an explicit javadoc task within my build.gradle - I'm just using whatever the java plugin already provides. – Rahmann

This is a bug in Gradle's JavaDoc task... even using the new 'org.gradle.java.experimental-jigsaw' plugin, this problem is still happening as of Gradle 4.5.1. But the answer by @Thor Andreas Rognan did work for me! – Milord

Answer 1

This worked for me

javadoc {
  inputs.property("moduleName", moduleName)
  doFirst {
    options.addStringOption('-module-path', classpath.asPath)
  }
}

Concision

I'm still having this issue as of Gradle 4.6, but Thor Andreas Rognan's answer solves the problem for me in the meantime. Thank you Thor! – Rahmann

Answer 2

I tried this on Gradle 7.1 and couldn't get it working, but after a little tinkering found adding this snippet made things work:

tasks.withType(Javadoc) {
    doFirst {
        options.modulePath = [] + classpath.files
        options.classpath = []
    }
}

The [] + ... seems to be a necessary workaround to make a list from the org.gradle.api.internal.file.UnionFileCollection returned by Gradle. Alternatively you could use new ArrayList(classpath.files) to achieve the same.

Adherent