How to annotate an annotation property in kotlin?

Question

I am attempting to place an annotation on an annotation property. My understanding is that I should be able to access it in code -- but I am not able to. What am I missing?

package com.example.annotations

import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
import kotlin.reflect.full.findAnnotation

class AnnotationIssueTest {
    @Test
    fun testAnnotations() {
        Assertions.assertNotNull(MyTestAnnotation::value.findAnnotation<PropertyMarker>())
    }

    @Test
    fun testRegularClass() {
        Assertions.assertNotNull(MyTestClass::value.findAnnotation<PropertyMarker>())
    }
}


@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.PROPERTY)
annotation class PropertyMarker

annotation class MyTestAnnotation(
        @PropertyMarker val value: String
)

class MyTestClass(
        @PropertyMarker val value: String
)

When I run the given test, testAnnotations fails while testRegularClass passes. Is this a bug or am I doing something wrong?

Answer 1

For some reason annotations of annotation properties don't make their way into the bytecode. However, you can annotate property getters instead:

class AnnotationIssueTest {
    @Test
    fun testAnnotations() {
        Assertions.assertNotNull(MyTestAnnotation::value.getter.findAnnotation<PropertyMarker>())
    }

    @Test
    fun testRegularClass() {
        Assertions.assertNotNull(MyTestClass::value.getter.findAnnotation<PropertyMarker>())
    }
}


@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.PROPERTY_GETTER)
annotation class PropertyMarker

annotation class MyTestAnnotation(
        @get:PropertyMarker val value: String
)

class MyTestClass(
        @get:PropertyMarker val value: String
)