I see this warning in plain JVM projects, with no KMP configuration that I'm aware of. Is there a way to better diagnose where it's coming from, or worth a FR to make this message more actionable?

w: `KotlinCompilation.source(KotlinSourceSet)` method is deprecated 
and will be removed in upcoming Kotlin releases.

See <https://kotl.in/compilation-source-deprecation> for details.

Do you use ksp? I get this message when I apply then ksp plugin.

yep there's KSP

That’s indeed caused by KSP: https://github.com/google/ksp/issues/1529