ClassNotFound error when applying the plugin without kotlin

[sureshg]

I have a small multi module project, where the root build.gradle.kts has the following plugin configuration

plugins {
  idea
  wrapper
  alias(libs.plugins.semver)
  alias(libs.plugins.benmanes)
  alias(libs.plugins.spotless)
  alias(libs.plugins.vanniktech.publish) apply false
}

The root project doesn't have any publishable artifact, but adding the vanniktech plugin just to avoid some weird class loading issue. One of the modules is a project with kotlin-dsl plugin applied

plugins/build.gradle.kts

plugins {
  idea
  `kotlin-dsl`
  embeddedKotlin("plugin.serialization")
  alias(libs.plugins.jte)
  alias(libs.plugins.benmanes)
  alias(libs.plugins.spotless)
  alias(libs.plugins.semver)
  alias(libs.plugins.vanniktech.publish)
}

When I run the build with this configuration, the plugin throws following error.

* What went wrong:
org/jetbrains/kotlin/gradle/plugin/KotlinBasePlugin
> org.jetbrains.kotlin.gradle.plugin.KotlinBasePlugin

* Try:
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at https://help.gradle.org.

* Exception is:
java.lang.NoClassDefFoundError: org/jetbrains/kotlin/gradle/plugin/KotlinBasePlugin
        at com.vanniktech.maven.publish.ProjectExtensionsKt.isAtLeastKotlinVersion(ProjectExtensions.kt:60)
        at com.vanniktech.maven.publish.MavenPublishBasePlugin.checkMinimumVersions$lambda$4$lambda$2(MavenPublishBasePlugin.kt:28)
        at com.vanniktech.maven.publish.MavenPublishBasePlugin.checkMinimumVersions$lambda$4$lambda$3(MavenPublishBasePlugin.kt:27)
        at org.gradle.internal.code.DefaultUserCodeApplicationContext$CurrentApplication$1.execute(DefaultUserCodeApplicationContext.java:124)
        at org.gradle.api.internal.DefaultCollectionCallbackActionDecorator$BuildOperationEmittingAction$1.run(DefaultCollectionCallbackActionDecorator.java:110)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:66)
        at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:59)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:166)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:59)
        at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:47)
        at org.gradle.api.internal.DefaultCollectionCallbackActionDecorator$BuildOperationEmittingAction.execute(DefaultCollectionCallbackActionDecorator.java:107)
        at org.gradle.api.internal.collections.CollectionFilter$1.execute(CollectionFilter.java:62)
        at org.gradle.api.internal.DefaultDomainObjectCollection.all(DefaultDomainObjectCollection.java:161)
        at org.gradle.api.internal.plugins.DefaultPluginContainer$2.execute(DefaultPluginContainer.java:163)
        at org.gradle.api.internal.plugins.DefaultPluginContainer$2.execute(DefaultPluginContainer.java:154)

IIUC, correctly, kotlin plugin is not a requirement for this plugin and should gracefully fall back to no-op.

[gabrielittner]

Could you try adding kotlin-dsl with apply false to the root project? isAtLeastKotlinVersion will only be called if either the org.jetbrains.kotlin.jvm or org.jetbrains.kotlin.multiplatform is applied to the project. The kotlin-dsl plugon will apply kotlin jvm so that the check is executed is intentional. My theory is that because the publish plugin is on the root project classloader but kotlin-dsl only on the plugin project that it can't see the Kotlin plugin properly.

[sureshg]

Could you try adding kotlin-dsl with apply false to the root project?

Still have the same error.

My theory is that because the publish plugin is on the root project classloader but kotlin-dsl only on the plugin project that it can't see the Kotlin plugin properly.

Yeah, somehow worked around this by doing something like below. Not sure whether it's a good solution or not.

 # build-logic plugin
  implementation("${libs.build.kotlin.dsl.get().module}:${expectedKotlinDslPluginsVersion}")

// Plugin Project
plugins {
  // Just apply with `kotlin-dsl` id.
  id("org.gradle.kotlin.kotlin-dsl")
  embeddedKotlin("plugin.serialization")
  com.github.`ben-manes`.versions
  com.diffplug.spotless
  gg.jte.gradle
  plugin.publishing
}

[gabrielittner]

That workaround is perfectly fine. The altnernative would be to add a dependency on the publish plugin in build logic. Both achieve that the Kotlin plugin and the publish plugin are part of the same classloader and can see each other.

[sureshg]

@gabrielittner thanks..Does it make sense to use java reflection to avoid these class loader issues for getting the plugin version?..something like

plugins.withId("org.jetbrains.kotlin.multiplatform") {
   val pluginVersion = javaClass.getMethod("getPluginVersion").invoke(this).toString()
}