Extensions of gradle-lombok tasks fail with Gradle 6.4

[chadlwilson]

A canonical extension task like the below fails on Gradle 6.4 with

The value for task ':myDelombok' property 'mainClass' is final and cannot be changed any further

Example

task myDelombok(type: io.franzbecker.gradle.lombok.task.DelombokTask, dependsOn: compileJava) {
    ext.outputDir = file("$buildDir/delombok")
    outputs.dir(outputDir)
    sourceSets.main.java.srcDirs.each {
        inputs.dir(it)
        args(it, "-d", outputDir)
    }
}

According to gradle/gradle#12841 this is because main is now backed by a property, and you can only set it during configuration; so setting it during exec doesn't work any longer.

Workaround - directly use a JavaExec task

task myDelombok(type: JavaExec, dependsOn: compileJava) {
    main = project.extensions.findByType(io.franzbecker.gradle.lombok.LombokPluginExtension).main
    args 'delombok'
    classpath = project.configurations.getByName('compileClasspath')

    ext.outputDir = file("$buildDir/delombok")
    outputs.dir(outputDir)
    sourceSets.main.java.srcDirs.each {
        inputs.dir(it)
        args(it, "-d", outputDir)
    }