Plugin.scala

package demo

import scala.tools.nsc.io.AbstractFile
import scala.tools.nsc.{Global, Phase}
import scala.tools.nsc.plugins.{Plugin, PluginComponent}

class DemoPlugin(val global: Global) extends Plugin {
  import global._
  override def init(options: List[String],  error: String => Unit): Boolean = true

  val name = "demo"
  val description = "a plugin"
  val components = List[PluginComponent](DemoComponent)

  private object DemoComponent extends PluginComponent {

    val global = DemoPlugin.this.global
    import global._

    override val runsAfter = List("parser")
    override val runsBefore = List("namer")

    val phaseName = "Demo"

    override def newPhase(prev: Phase) = new GlobalPhase(prev) {
      override def run() = {

        val count = global.currentRun.units.length
        val x: Iterator[Seq[String]] = global.currentRun.units.map(_.source.file.path.split("/"))

        var start = x.next()
        for(next <- x){
          for(i <- next.indices){
            if (i < start.length && start.lift(i) != next.lift(i)){
              start = start.take(i)
            }
          }
        }
        val cwd = new java.io.File("").getAbsolutePath.split("/")

        if (start.startsWith(cwd)) start = start.drop(cwd.length)
        val msg = s"Compiling $count files in ${start.mkString("/")}"
        val spaces = " " * ((90 - msg.length) / 2)
        global.reporter.echo(
          scala.Console.BLUE_B +
          spaces + msg + spaces +
          scala.Console.RESET
        )
      }
      def name: String = phaseName
      def apply(unit: global.CompilationUnit): Unit = {}
    }
  }
}

@lihaoyi How can this be added to sbt? I tried to put it in ~/.sbt/0.13/plugins/Plugin.scala but then sbt fails to start with:

[error] ...\.sbt\0.13\plugins\CompilationBar.scala:9: method init overrides nothing
[error]   override def init(options: List[String],  error: String => Unit): Boolean = true

Removing override doesn't seem to help ;)

I tried it on a project built with sbt 0.13.13