When using Kotlin companion objects from JRuby, we get an "already initialized constant Companion" warning simply by loading the class. The companion object works correctly and is accessible as a constant from the parent class.

We're seeing this on JRuby 9.2.11.1. I tested prior versions and this warning first appears in JRuby 9.2.9.0.

Detailed Description

Given a Kotlin class like:

package kotlintest

class Test {
	companion object {
		const val FOO = "foo"
	}
}

And a ruby class like:

require 'java'
require './build/libs/test-all.jar'

p Java::Kotlintest::Test::FOO

We get the following output:

$ ruby test.rb
test.rb:4: warning: already initialized constant Companion
"foo"

The warning is triggered just by loading the class. So if you just reference Java::Kotlintest::Test, without the companion object, you still get the warning.

Gradlefile used to build the jar:

plugins {
    id("org.jetbrains.kotlin.jvm") version "1.3.70"
    id("com.github.johnrengelman.shadow") version "5.2.0"
}

repositories {
    jcenter()
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
}