Why can't the Lombok library be used in Kotlin?

Overview #

When developing with Java, there's hardly anyone who hasn't used Lombok. When I switched to Kotlin, I thought Lombok wasn't used because of data classes, but it turns out it can't be used at all... I'll summarize it today.

When using Java and Kotlin together #

Kotlin compiler -> .class generation -> Java compiler -> .class generation -> Annotation processing -> .class file generation

The reason Lombok cannot be used in Kotlin is that annotation processing occurs during Java compilation, after Kotlin compilation.

data class #

Still, in Kotlin, because there's data class, there seems to be no real need to use Lombok.

Functions provided by data classes

equals()/hashCode() pair
toString() of the form "User(name=John, age=42)"
componentN() functions corresponding to the properties in their order of declaration.
copy() function (see below).

data class JeongWoo(
    val name: String,
    val age: Int
)