VersionInfo.scala

import sbt._
import Keys._

object VersionInfoPlugin extends Plugin {
  val versionInfoPackage = SettingKey[String]("version-info-package")
  val versionInfoClassTask = TaskKey[Seq[java.io.File]]("version-info-class", "writes a java class VersionInfo with information about the versionInfo to sourceManaged")
  val versionInfo = TaskKey[String]("version-info", "the current versionInfo")
  
  private val Classname = "VersionInfo"

  val versionInfoSettings = Seq(
    versionInfo <<= version map { version =>
      Option(System.getProperty("version")).getOrElse{ //use property version if found
        version
      }
    },
    versionInfoClassTask <<= (sourceManaged in Compile, versionInfoPackage, versionInfo) map { (srcDir, versionInfoPackage, versionInfo) =>
    // depends on:            ^ source directory,       ^ the package       ^ the version 
      val classString = """
      |package %s;
      |
      |public class %s {
      |    public static String CURRENT_VERSION = "%s";
      |}""" format (versionInfoPackage, Classname, versionInfo) stripMargin

      val path = srcDir.getAbsolutePath+versionInfoPackage.replace(".", java.io.File.separator)+java.io.File.separator+Classname+".java"
      IO.write(file(path), classString)
      Seq(file(path))
    },
    sourceGenerators in Compile <+= versionInfoClassTask
    //^ add our versionInfoClass to generators so it is picked up by sbt
  )
}