java.lang.ClassNotFoundException: kotlinx.serialization.ElementValueEncoder

Describe the bug I am building a plugin for minecraft spigot and wanted to store / load settings using Kotlin’s serializable and charleskorn’s Yaml. However, when calling com.charleskorn.kaml.Yaml.stringify with a serializable data class’ serializer().list from import kotlinx.serialization.builtins.list I am getting the following error: Caused by: java.lang.ClassNotFoundException: kotlinx.serialization.ElementValueEncoder https://pastebin.com/C9hZB7yB

Code that is causing the issue

Yaml.default.stringify(Gauntlet.serializer().list, gauntlets)

Where Gauntlet is a @Serializable

This is my Gradle build file

plugins {
	id 'java'
	id 'org.jetbrains.kotlin.jvm' version "$kotlin_version"
	id "org.jetbrains.kotlin.plugin.serialization" version "$kotlin_version"
	id 'com.github.johnrengelman.shadow' version '2.0.4'
}

group 'com.krulvis.gauntlet'
version '1.0'

repositories {
	mavenLocal()
	mavenCentral()
	maven {
		name = "spigot"
		url = uri("https://hub.spigotmc.org/nexus/content/repositories/snapshots/")
	}
}

dependencies {
	implementation "com.charleskorn.kaml:kaml:0.15.0"
	implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
	api "org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:0.20.0"
	compile "org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:0.20.0"
	compileOnly("org.spigotmc:spigot-api:${minecraft_version}-R0.1-SNAPSHOT")
}

compileKotlin {
	kotlinOptions.jvmTarget = "1.8"
}
compileTestKotlin {
	kotlinOptions.jvmTarget = "1.8"
}

I read somewhere on another issue that some class couldn’t be found and the dependency should be loaded as api rather than compile in dependencies in the gradle build file. I tried both, which didn’t resolve the issue.

Expected behavior Stringify list of serializable data classes Environment

• Kotlin version: 1.3.72
• Library version: 0.20.0
• Kotlin platforms: JVM
• Gradle version: 6

[Krulvis]

Thanks for clearing that up! Really appreciate the effort you guys put into this!

[qwwdfsad]

Why does it search for an old non-existed class?

Because your dependency (implementation "com.charleskorn.kaml:kaml:0.15.0" or maybe spigot-api) is compiled against older version of kotlinx.serialization where this class actually exists.

You have your application that depends on 0.20.0 version and kaml that depends on 0.15.0 version. These versions are incompatible, so either kaml should be updated, or your own dependency on serialization downgraded back to 0.15.0