Custom Gradle Task having Kotlin Delegate

Question

Gradle tasks using Kotlin are implemented as either abstract class ... or interface .... In either case it is not clear how to use delegation. The following works correctly but requires delegation to be performed manually (i.e. it does not use Kotlin delegation).

@CacheableTask
abstract class FooTask : DefaultTask(), CopySourceSpec {

    @get:InputFiles
    @get:Optional
    @get:SkipWhenEmpty
    @get:IgnoreEmptyDirectories
    @get:PathSensitive(PathSensitivity.RELATIVE)
    abstract val sourceFiles: ConfigurableFileCollection

    @TaskAction
    fun canonize() {
        val sourceFileTree = sourceFiles.asFileTree
        // do something with the sourceFileTree
    }
    
    override fun from(vararg sourcePaths: Any?): ProtobufHeaderTask {
        this.sourceFiles.from(sourcePaths)
        return this
    }
    override fun from(sourcePath: Any, closure: Closure<*>): ProtobufHeaderTask {
        this.sourceFiles.from(sourcePath, closure)
        return this
    }
    override fun from(sourcePath: Any, configureAction: Action<in CopySpec>): ProtobufHeaderTask {
        this.sourceFiles.from(sourcePath, configureAction)
        return this
    }
}

It seems like this could be done more simply using Kotlin delegation.

@CacheableTask
abstract class FooTask : DefaultTask(), ConfigurableFileCollection by sourceFiles {

    @get:InputFiles
    @get:Optional
    @get:SkipWhenEmpty
    @get:IgnoreEmptyDirectories
    @get:PathSensitive(PathSensitivity.RELATIVE)
    abstract val sourceFiles: ConfigurableFileCollection

    @TaskAction
    fun canonize() {
        val sourceFileTree = sourceFiles.asFileTree
        // do something with the sourceFileTree
    }
}

This latter case produces an error that sourceFiles is not defined. Is it possible to use Kotlin delegation in this way?