Nice looks and git info into the sbt shell

sbt-prompt-git.scala

addCommandAlias("git", "; sh git")

commands ++= Seq(
  Command.args("sh", "<shell command>") { (state, args) => 
    // using script here maintains ansi colors, see http://stackoverflow.com/a/13587964/467390
    val ret = ("script -q /dev/null " ++ args.mkString(" ")) !;
    state
  }
)

shellPrompt := { state =>
  val oldErr = System.err
  val extracted = Project.extract(state)
  val project = extracted.currentRef.project;
  object bg{
    val blue = "\u001B[44m"
    val magenta = "\u001B[45m"
    val green = "\u001B[42m"
    val white = "\u001B[47m"
  }
  object fg{
    val black = "\u001B[30m"
    val blue = "\u001B[34m"
    val green = "\u001B[32m"
    val white = "\u001B[37m"
    val magenta = "\u001B[35m"
  }
  val reset = "\u001B[0m"
  val sep = "\uE0B0"

  import java.io.{OutputStream, PrintStream}
  class VoidOutputStream extends OutputStream {
    override def write(b: Int) = ()
    override def write(b: Array[Byte]) = ()
    override def write(b: Array[Byte], off: Int, len: Int) = ()
  }
  val nullStream = new PrintStream(new VoidOutputStream())
  System.setOut(nullStream)
  System.setErr(nullStream)
  val branchOrSeparator = try{
    val branch = "git rev-parse --abbrev-ref HEAD".split(" ").toSeq.!!.replace(System.lineSeparator, "")
    val modified = "git status -s --ignore-submodules=dirty".split(" ").toSeq.!!.nonEmpty
    val (bgColor, fgColor)= if(modified) (bg.magenta, fg.magenta) else (bg.green, fg.green)
    val modifiedSymbol = if(modified) "±" else ""
    bgColor ++ fg.blue ++ sep ++ " " ++ fg.black ++ "" ++ branch ++ " " ++ modifiedSymbol ++ bg.white ++ fgColor
  } catch {
    case e:java.lang.RuntimeException =>
      bg.white ++ fg.blue
  } finally {
      System.setErr(oldErr)
      System.setOut(oldErr)
  }
  (
    fg.black ++ bg.blue
    ++ project
    ++ branchOrSeparator
    ++ sep ++ " " ++ fg.black ++ "sbt"
    ++ reset ++ fg.white ++ sep ++ reset
    ++ " "
  )
}