A community effort to collect a curated set of analysis pipelines built using Nextflow.

nf-core

Hello everyone,
I’m trying to compile a Nextflow plugin. The compilation works without any errors on my side. However, when I try to use the plugin on a computing cluster, I get the following error:
```java.lang.UnsupportedClassVersionError: nextflow/executor/slurm_no_memory/SlurmNoMemoryPlugin has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognises class file versions up to 55.0```
To fix this, I attempted to compile the plugin using Java 11. The build completes successfully, but I still get the same error on the cluster. I checked the compiled classes with this command:
```find build/classes/groovy/main/ -name '*.class' -exec javap -verbose {} 2&gt;/dev/null \; | grep 'major'```
and the output still shows `major version: 61` instead of 55.
I also tried building the plugin inside a Singularity container, but the problem remains.
Below is my `build.gradle`. If anyone has suggestions on how to force Gradle/Groovy to compile the plugin with Java 11 bytecode, I would really appreciate your help.
Thanks in advance!

```plugins {
    id 'io.nextflow.nextflow-plugin' version '0.0.1-alpha'
}

compileJava.options.fork = true
compileJava.options.forkOptions.executable = '/usr/bin/javac'

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

tasks.withType(JavaCompile) {
    options.release = 11
}


version = '0.1.0'

nextflowPlugin {
    nextflowVersion = '24.10.0'

    provider = 'CUBIC-Curie'
    className = 'nextflow.executor.slurm_no_memory.SlurmNoMemoryPlugin'
    extensionPoints = [
        'nextflow.executor.slurm_no_memory.SlurmNoMemoryExecutor',
    ]


}


sourceSets {
    main.java.srcDirs = []
    main.groovy.srcDirs = ['src/main/groovy']
    main.resources.srcDirs = ['src/resources']
    test.groovy.srcDirs = ['src/test/groovy']
    test.java.srcDirs = []
    test.resources.srcDirs = ['src/testResources']
}

configurations {
    // Exclude slf4j-api to avoid conflicts with Nextflow's logging
    runtimeClasspath.exclude group: 'org.slf4j', module: 'slf4j-api'
}

ext {
    nextflowVersion = '24.10.0'
}

java {
    sourceCompatibility = JavaVersion.VERSION_11
    targetCompatibility = JavaVersion.VERSION_11
}


dependencies {
    compileOnly "io.nextflow:nextflow:$nextflowVersion"
    compileOnly 'org.slf4j:slf4j-api:2.0.17'
    compileOnly 'org.pf4j:pf4j:3.12.0'
    
    testImplementation "org.apache.groovy:groovy:4.0.26"
    testImplementation "org.apache.groovy:groovy-nio:4.0.26"
    testImplementation "io.nextflow:nextflow:$nextflowVersion"
    testImplementation "org.apache.groovy:groovy-test:4.0.26"
    testImplementation "cglib:cglib-nodep:3.3.0"
    testImplementation "org.objenesis:objenesis:3.1"
    testImplementation "org.spockframework:spock-core:2.3-groovy-4.0"
    testImplementation "org.spockframework:spock-junit4:2.3-groovy-4.0"
    testImplementation "com.google.jimfs:jimfs:1.1"
    
    testImplementation(testFixtures("io.nextflow:nextflow:$nextflowVersion"))
    testImplementation(testFixtures("io.nextflow:nf-commons:$nextflowVersion"))
}```

I'm not sure that you'll be able to make it work with Java 11. When we developed the Nextflow Gradle plugin, Nextflow was already requiring Java &gt;=17, so we never tried to make it work with Java 11. It might happen to work, but I wouldn't be surprised if it doesn't

I think the easiest way forward would be to target Java 17 and use Java 17 in your cluster

Thanks for the clarification. I’ll reach out to the cluster administrators and ask whether they can recompile or upgrade Nextflow to Java 17. That seems like the most straightforward solution.