Make downloadListFile public for Gradle 9 compatibility

[otheng03]

Summary

In Gradle 9 (Groovy 4), as you know, closures can no longer access private members of a class when the runtime instance is a subclass — which is always the case for decorated task types such asDownloadJavadocPackageListTask. Calling a private method from a closure in such a class fails with:

Could not find method downloadListFile() for arguments [...] on task ':...' of type DownloadJavadocPackageListTask

See: Gradle 9 upgrade guide — Private properties and methods may be inaccessible in closures

downloadListFile is currently only called from plain method bodies(addOfflineLink), so nothing is broken today — this is a defensive change so that a future call from a closure does not fail at runtime.

How to re-produce the problem:

Please see:

• https://github.com/otheng03/gradle-scripts/blob/738ea7361a332729109ee79618c612198a58a22c/tests/gradle9-private-members/case-a-task-class/build.gradle#L24-L36
• https://github.com/otheng03/gradle-scripts/blob/test-downloadListFile/tests/gradle9-private-members/README.md

[CLAassistant]

All committers have signed the CLA.

[imasahiro]

@minwoox @ikhoon Hi, would you mind to take a look at this if you have time? We've required small modification during Gradle 9 upgrade. We are now trying to backport the change to here.

[minwoox]

Thanks! 👍 👍

[jrhee17]

👍 👍

[ikhoon]

👍