Class 'kotlin.Unit' was compiled with an incompatible version of Kotlin

[raxod502]

I have a working Android project (that is, ./gradlew build builds an apk file that can be installed and run) which is written in Kotlin. When I open the project in Emacs with LSP using kotlin-language-server, I receive the following diagnostic on every line of code:

Class 'kotlin.Unit' was compiled with an incompatible version of Kotlin. The binary version of its metadata is 1.8.0, expected version is 1.6.0.
The class is loaded from /home/raxod502/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.8.20/e72fc5e03ec6c064c678a6bd0d955c88d55b0c4a/kotlin-stdlib-1.8.20.jar!/kotlin/Unit.class

I checked Editor integration and Troubleshooting but did not see any relevant tips. I also searched the issue tracker but found only https://github.com/fwcd/kotlin-language-server/issues/198#issuecomment-1367081783 as a reference, which doesn't seem relevant in this case.

Here's my build.gradle.kts:

plugins {
    id("com.android.application") version "7.4.2"
    id("org.jetbrains.kotlin.android") version "1.8.20"
}

repositories {
    google()
    mavenCentral()
}

android {
    compileSdkVersion(32)
    namespace = "redacted"
    defaultConfig {
        applicationId = "redacted"
        minSdkVersion(16)
        targetSdkVersion(32)
        versionCode = 1
        versionName = "0.1.0"
    }
    buildTypes {
        getByName("release") {
            isMinifyEnabled = false
        }
    }

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }
}

dependencies {
    implementation("androidx.appcompat:appcompat:1.2.0")
    implementation("com.google.android.material:material:1.2.0")
    implementation("androidx.constraintlayout:constraintlayout:2.0.4")
}

I don't, to my knowledge, have Kotlin installed globally on my system. The only place it's installed is via Gradle in this project, where the version is specified in build.gradle.kts as 1.8.20. I am not sure where this other 1.6.0 version number is coming from that is being referenced by kotlin-language-server.

If it would help in diagnosing the issue, I am happy to provide a sample project that reproduces the issue, or relevant logs.

[raxod502]

Maybe the version of Kotlin used by kotlin-language-server is hardcoded to 1.6.0 and I need to upgrade to a build from source as https://github.com/fwcd/kotlin-language-server/pull/414 has not made it into a release yet? (If so, would be great to document the supported Kotlin versions somewhere; I had assumed all versions were supported.)

[raxod502]

Followed the instructions in Building and with that version the error no longer occurs. Would be great to have this documented. I'm happy to help if that would be handy.

[themkat]

This is sadly a known issue. ~Only one person is able to do releases, and they are super busy with other things.~ I guess those of us who are fairly active here was hoping that we would get a new release, to avoid this issue being posted many times both here and in the VSCode plugin repo 🙁 Hopefully we can get the automatic releases PR merged soon 🙂

433 is a PR that will fix automatic releases on merges to main. That PR is only waiting for one specific comment to be resolved before merging. Hopefully also for @fwcd to address the requested changes.

EDIT: Seems I have rights to push tags now (failed last time I tried), but the release pipeline is broken...

[themkat]

A new version was released last night! 😄 (thank you @fwcd !!!). This will probably be resolved by using that newest version.