This change https://github.com/JetBrains/kotlin/commit/5ce514bd42a8e8cb2afac99ea20bc359a4222951 introduces a regression that prevent us to generate the Dokka documentation for Kotlin code without using Java code since we were using

sourceDirs = files(subprojects.collect { project -> project.sourceSets.main.kotlin.srcDirs })

. What can I use to get only the Kotlin source dirs ?

Sorry for that. What affects your build, though, is only that now the Java directories are added to the Kotlin directory set eagerly during configuration, not

afterEvaluate { ... }

as it was before. I would suggest the following workaround:

sourceDirs = files(subprojects.collect { project -> project.sourceSets.main.kotlin.srcDirs - project.sourceSets.main.java.srcDirs })