Java classes may contain equivalent Kotlin types.

[traceyyoshima]

import java.lang.StringBuilder
class Test {
    fun method() {
        val sb = StringBuilder()
        sb.trimToSize()
    }
}

sb.trimToSize() should return a java.lang.void, but produces a kotlin.Unit. The void return type is represented by a kotlin.Unit in the FIR.

[knutwannheden]

I think this is still an "unsolved" problem. Also where the Java parser would produce primitive types or wrapper types in the type attribution, we for Kotlin have the corresponding Kotlin types. I am still unsure what we should do about that.

[traceyyoshima]

I think this is still an "unsolved" problem. Also where the Java parser would produce primitive types or wrapper types in the type attribution, we for Kotlin have the corresponding Kotlin types. I am still unsure what we should do about that.

I agree; I'm unsure why this happens since Java types like java.lang.void will appear on some Java classes and will be replaced in others. I checked the IR for this case; the return type was kotlin.Unit, too. I don't know of any meaningful impacts where Kotlin types like Int, Unit, etc. exist in place of Java types will have unless someone is searching for a use of an API from their Java code in their Kotlin code.