Kotlin method parameter names are not included in bytecode

[ruifigueira]

I just had a similar issue to #11010. I declared an @Endpoint kotlin class with a method with a @Selector parameter, but the parameter name is "lost in compilation".

I noticed that, for Java classes, this is normally not an issue, because Spring Boot configures maven-compiler-plugin to include parameter name information in bytecode (#9323), and we can definitely do the same for kotlin-maven-plugin by providing a -java-parameters argument in its configuration.

How to reproduce

• Add the following kotlin code into a standard Spring Boot project with maven (ensure you have spring-boot-starter-tests):

import org.assertj.core.api.Assertions.*
import org.junit.Test
import kotlin.reflect.jvm.javaMethod

class KotlincJavaParametersTest {

    private fun say(hello: String, world: String) = "$hello $world"

    @Test
    fun testMethodParameterName() {
        val javaMethod = ::say.javaMethod!!
        val parameters = javaMethod.parameters
        assertThat(parameters).isNotEmpty
        assertThat(parameters.map { it.name }).containsExactly("hello", "world")
    }
}

• Run it with mvn clean test

How to fix

Kotlin compiler (kotlinc) supports a -java-parameters argument that was introduced in version 1.1 (https://kotlinlang.org/docs/reference/whatsnew11.html#parameter-names-in-the-bytecode):

<plugin>
  <groupId>org.jetbrains.kotlin</groupId>
  <artifactId>kotlin-maven-plugin</artifactId>
  <configuration>
    <args>
      <arg>-java-parameters</arg>
    </args>
  </configuration>
</plugin>

[philwebb]

Thanks for the detailed report. I'll close this one in favor of the PR that you raised (#12641).