Get enclosing class from extension function not working from 2.0.0

Language Design
1

Hi!

While upgrading Kotlin I noticed a difference in behaviour on ‘javaClass.enclosingClass’. This no longer seems to work from an extension. See the test below, it fails from version 2.0.0:

class EnclosingClassTest {

    @Test
    fun test() {
        val enclosingClass = someExtension {}

        // works in 1.9.25, but not in 2.0.0 or newer
        assertEquals(EnclosingClassTest::class.java, enclosingClass)
    }
}

fun <T> someExtension(call: () -> T): Class<*>? {
    return call.javaClass.enclosingClass
}

Was this intended?

Regards,
Pepijn

2

My guess would be there were never guarantees that it behaves as you expected. I don’t think Kotlin specifies where exactly is the lambda located in the resulting bytecode.

3

This is probably because lamdas are no longer compiled to nested classes. See What's new in Kotlin 2.0.0 | Kotlin Documentation

1 Like
5

Thanks for pointing that out, you’re right! To get the old behaviour you can annotate the lambda with @JvmSerializableLambda:

class EnclosingClassTest {

    @Test
    fun test() {
        val enclosingClass = someExtension @JvmSerializableLambda {}

        assertEquals(EnclosingClassTest::class.java, enclosingClass)
    }
}

fun <T> someExtension(call: () -> T): Class<*>? {
    return call.javaClass.enclosingClass
}
1 Like