SBT Create a DockerFile Using a Function - scala

Question

I was trying this piece of code:
// Get the Docker Configurations
def dockerConfForModule(moduleName: String): Dockerfile = {
val jarFile: File = (Compile / packageBin / sbt.Keys.`package`).value
val classpath = (Compile / managedClasspath).value
val mainclass = (Compile / packageBin / mainClass).value.getOrElse(sys.error("Expected exactly one main class"))
val jarTarget = s"/app/${jarFile.getName}"
// Make a colon separated classpath with the JAR file
val classpathString = classpath.files.map("/app/" + _.getName)
.mkString(":") + ":" + jarTarget
new Dockerfile {
// Base image
from("openjdk:8-jre")
// Add all files on the classpath
add(classpath.files, "/app/")
// Add the JAR file
add(jarFile, jarTarget)
// On launch run Java with the classpath and the main class
entryPoint("java", "-cp", classpathString, mainclass)
}
}
Which I'm calling as a function in one of my module like below:
// Define Sub Modules and its settings
lazy val cleanse = (project in file(MODULE_NAME_CLEANSE)).dependsOn(core)
.settings(
commonSettings,
enablingCoverageSettings,
name := MODULE_NAME_CLEANSE,
description := "Clean the incoming data for training purposes",
docker / dockerfile := dockerConfForModule(MODULE_NAME_CLEANSE)
)
.enablePlugins(DockerPlugin)
But this runs into an error:
/home/joesan/Projects/Private/ml-projects/housing-price-prediction-data-preparation/build.sbt:22: error: `value` can only be called on a task within a task definition macro, such as :=, +=, ++=, or Def.task.
val jarFile: File = (Compile / packageBin / sbt.Keys.`package`).value
^
/home/joesan/Projects/Private/ml-projects/housing-price-prediction-data-preparation/build.sbt:23: error: `value` can only be called on a task within a task definition macro, such as :=, +=, ++=, or Def.task.
val classpath = (Compile / managedClasspath).value
^
/home/joesan/Projects/Private/ml-projects/housing-price-prediction-data-preparation/build.sbt:24: error: `value` can only be called on a task within a task definition macro, such as :=, +=, ++=, or Def.task.
val mainclass = (Compile / packageBin / mainClass).value.getOrElse(sys.error("Expected exactly one main class"))
^
sbt.compiler.EvalException: Type error in expression
[error] sbt.compiler.EvalException: Type error in expression
[error] Use 'last' for the full log.
[warn] Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore? (default: r)
What is wrong in what I'm trying?