Build unified Javadoc for all Java subprojects

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1

My project contains about two dozen subprojects. Most of those subprojects use the java-libraries plugin to produce a main jar (from the main source set), along with corresponding HTML-rendered Javadoc. Some subprojects also use the java-test-fixtures plugin to produce a test-fixtures jar (from the testFixtures source set), again with corresponding HTML-rendered Javadoc.

We would like to augment the per-jar documentation with HTML-rendered Javadoc that includes all Java sources from all jar archives built in all subprojects.

My current approach adds the following code to our top-level build.gradle:

tasks.register('aggregatedJavadocs', Javadoc) { aggregated ->
	destinationDir = file("$buildDir/docs/javadoc")

	subprojects.each { proj ->
		proj.tasks.withType(Javadoc) { javadocTask ->
			aggregated.source += javadocTask.source
			aggregated.classpath += javadocTask.classpath
			aggregated.excludes += javadocTask.excludes
			aggregated.includes += javadocTask.includes
		}
	}
}

Although the aggregated Javadoc looks reasonable, numerous warnings like the following suggest that this is not a good strategy:

Resolution of the configuration :[...]:compileClasspath was attempted from a context different than the project context. Have a look at the documentation to understand why this is a problem and how it can be resolved. This behaviour has been deprecated and is scheduled to be removed in Gradle 8.0. See https://docs.gradle.org/7.3.3/userguide/viewing_debugging_dependencies.html#sub:resolving-unsafe-configuration-resolution-errors for more details.

What’s the right way to do this?