scala-sbt change javacOptions in task - scala

Question

I'm trying to create a simple ant task, which depends on compile. The problem I'm having is that I can't seem to set the javacOptions from within my task (only in the global scope).
val metamodelSettings = TaskKey[Unit]("metamodelSettings")
val metamodel = TaskKey[Unit]("metamodel")
metamodelSettings := {
print("Metamodel generation started")
javacOptions := Seq(
"-verbose",
"-g",
"-processor", "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor",
"-s", "app",
"-proc:only"
)
}
metamodel := {
print("Metamodel generation complete")
}
metamodel <<= metamodel.dependsOn(metamodelSettings, compile in Compile)
How can I change the javacOptions just for my metamodel task?
Edit:
[info] This is sbt 0.13.0
$ inspect metamodelSettings:javacOptions
[info] Task: scala.collection.Seq[java.lang.String]
[info] Description:
[info] Options for the Java compiler.
[info] Provided by:
[info] */*:javacOptions
[info] Defined at:
[info] (sbt.Defaults) Defaults.scala:209
[info] Delegates:
[info] metamodelSettings:javacOptions
[info] *:javacOptions
[info] {.}/metamodelSettings:javacOptions
[info] {.}/*:javacOptions
[info] */metamodelSettings:javacOptions
[info] */*:javacOptions
[info] Related:
[info] *:metamodelSettings::javacOptions
[info] compile:javacOptions
[info] *:metamodel::javacOptions
[info] */*:javacOptions
[info] compile:doc::javacOptions
show metamodelSettings::javacOptions is showing the expected values, but still not using them.
[test] $ show metamodelSettings::javacOptions
[info] List(-verbose, -g, -processor, org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor, -s, app, -proc:only)
[success] Total time: 0 s, completed 04-Feb-2014 11:29:56

Answer 1

If you want to set javacOptions only for metamodelSettings then use in to provide a scope for settings:
javacOptions in metamodelSettings := Seq(...)
You can also use different style whith inTask;
inTask(metamodelSettings) {
// your settings
}

Answer 2

As I was unable to override the settings, I resorted to invoking the compiler directly. This seems like a nasty solution to me, but maybe somebody will find it useful.
val metamodel = TaskKey[Unit]("metamodel")
javacOptions := Seq("-proc:none")
cleanFiles <++= baseDirectory (_ ** "*_.java" get)
metamodel := {
managedClasspath in Compile <<= (classpathTypes, update) map {
(ct, report) =>
Classpaths.managedJars(Compile, Set("jar", "zip"), report)
}
val javac = (Keys.compileInputs in Keys.compile in Compile).value.compilers.javac
val src = (file("app") / "models") ** "*.java"
val cp = (managedClasspath in Compile).value.map(x => x.data)
val out = file("app/models")
val args = Seq(
"-processor", "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor",
"-s", "app",
"-proc:only"
)
javac(sources=src.get, classpath=cp, outputDirectory=out, options=args)(ConsoleLogger())
}