What exactly "Do not mix sources in a single sourceset" means for project configuration?

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1

Hi.

Webinar “What’s new in Gradle 5.0” has part “Do not mix sources in a single sourceset”. I’m confused, because by default, Kotlin sourceSet contains src/main/kotlin and src/main/java directories. As verification, I’ve just generated empty Kotlin project with gradle init command and printed sourcesets like that:

println("java sourcesets: ${sourceSets.main.java.srcDirs}")
println("kotlin sourcesets: ${sourceSets.main.kotlin.srcDirs}")

Could you please give more details about “Do not mix sources in a single sourceset” idea? What additional configuration is needed? Does it mean, that I have to change default configuration and remove src/main/java directory from Kotlin sourceset?

Thank you.
Svyatoslav.