where can I find documentation and sources for:

org.jetbrains.kotlin.serialization.ProtoBuf

and

org.jetbrains.kotlin.serialization.jvm.JvmProtoBuf

?

That’s not the classes you want –

kotlin.serialization

is internal classes in compiler, and library uses

kotlinX.serialization

package

Indeed it is. I am using a hacky library for annotation processing to get info about kotlin types (for example whether they are data classes) and that library relies on ProtoBuf

I’m afraid there is no documentation on it. Some usage of it can be seen here: https://github.com/Kotlin/kotlinx.reflect.lite and you can find sources somewhere in compiler