Are

project(":foo")

style dependencies supported when the callee is a

kotlin("jvm")

project and the project

foo

is a multiplatform project?

Yes! I'm doing this myself.

What if that

foo

is just a common module? It’s literally just annotations in my case.

I’ve seen some things fail to resolve in IDEA when you do that but it builds from gradle. https://youtrack.jetbrains.com/issue/KT-29082

I had to explicitly add a “org.jetbrains.kotlin.platform.type” attribute to my jvm “callee” subproject in order to avoid a Gradle “unable to pick variant” issue (whereas the js dependent subproject was fine)

That's probably a different issue. When you have multiple targets of the same platform type, you need to disambiguate. That's true regardless of whether it's a project dependency. https://kotlinlang.org/docs/reference/building-mpp-with-gradle.html#disambiguating-targets