gistfile1.scala

*** not compiled or checked, just for the idea ***

import sbt._
import Keys._

object MyBuild extends Build
{
   ... wiring into project not shown, see FullConfiguration for where to put `defaults` ...

   val protocExePath = SettingKey[File]("protoc-exe-path")
   val protoFiles = SettingKey[Seq[File]]("proto-files")
   val protoJavaDir = SettingKey[File]("proto-java-dir")
   val protoDir = SettingKey[File]("proto-dir")
   val protoDirs = SettingKey[Seq[File]]("proto-dirs")

   val protoJava = TaskKey[Seq[File]]("proto-java")

   def defaults = Seq(
      protoJavaDir <<= sourceDirectory(_ / "gen" / "java"),
      protoDir <<= sourceDirectory(_ / "main" / "proto"),
      protoDirs <<= protoDir(_ :: Nil),
      protoJava <<= protoTask("java"),
      sources in Compile <<= (sources in Compile, protoJava) map { _ ++ _ }
   )

   def protoTask(tpe: String) = (protoJavaDir, protoFiles, protocExePath, streams) map {
      (dir, files, exe, s) => proto(tpe, dir, files, exe, s.log)
   }

   def proto(tpe: String, directory: File, files: Seq[File], exe: File, log: Logger) =
   {
      IO.delete(directory)
      
      val dir = directory.getAbsolutePath

      val mkdirProc: Process = "mkdir" :: "-p" :: dir :: Nil
      val protoProc = exe :: protoPaths :: "--%s_out=%s".format(tpe,dir) :: files
      
      val result = (mkdirProc #&& protocProc) ! log

      def generated = directory.***.get
      if(result == 0) generated else error("Non-zero exit code: " + result)
   }
}