How do you share a custom task in a SBT multi-project - scala

Question

I have a project set up as a SBT multi-build. That looks like this:
- project
Dependencies.scala
- core
build.sbt
- server
build.sbt
build.sbt
I want to use Dependencies.scala as a container for version numbers of libraries that are shared between the sub-projects.
sealed trait Dependencies {
val commonsIo = "2.4"
}
object DependencyVersions extends Dependencies
In the root build.sbt I added a Setting that is given to each sub-project.
lazy val dependencies = settingKey[Dependencies]("versions")
val defaultSettings = Defaults.coreDefaultSettings ++ Seq(
dependencies := DependencyVersions)
def projectFolder(name: String, theSettings: Seq[Def.Setting[_]] = Nil) = Project(name, file(name), settings = theSettings)
lazy val core = projectFolder("core", defaultSettings)
I can't access the dependencies setting in core/build.sbt.
"commons-io" % "commons-io" % dependencies.value.commonsIo, <-- doesn't work
How can I get this to work?

Answer 1

You can define common settings (dependencies) in an object Common extends AutoPlugin (in project/Common.scala), and then use .enablePlugin(Common) on sub-project descriptor (see it in Anorm).

Answer 2

Thanks #cchantep got it working now using the AutoPlugin below
import sbt._
sealed trait Dependencies {
val commonsIo = "2.4"
}
object DependencyVersions extends Dependencies
object DependencyVersionsPlugin extends AutoPlugin {
override def trigger = allRequirements
object autoImport {
lazy val dependencies = settingKey[Dependencies]("Bundles dependency versions")
}
import autoImport._
override def projectSettings = Seq(
dependencies := DependencyVersions
)
}