object scala in compiler mirror not found - running Scala compiler programmatically

Running w/ a simple SBT project w/ Java 7 (details below) and invoking sbt run at the command line (no IntelliJ or anything)

source

import scala.tools.nsc.{ Global, Settings }

object Playground extends App {
  val compiler = new Global(new Settings())
  val testFiles = List("Test.scala")
  val runner = new compiler.Run()
  val result = runner.compile(testFiles)
  println(result)
}

error

error: error while loading Object, Missing dependency 'object scala in compiler mirror', required by /Library/Java/JavaVirtualMachines/jdk1.7.0_60.jdk/Contents/Home/jre/lib/rt.jar(java/lang/Object.class)
[error] (run-main-0) scala.reflect.internal.MissingRequirementError: object scala in compiler mirror not found.
scala.reflect.internal.MissingRequirementError: object scala in compiler mirror not found.
    at scala.reflect.internal.MissingRequirementError$.signal(MissingRequirementError.scala:17)
    at scala.reflect.internal.MissingRequirementError$.notFound(MissingRequirementError.scala:18)
    at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:53)
    at scala.reflect.internal.Mirrors$RootsBase.getModuleOrClass(Mirrors.scala:66)
    at scala.reflect.internal.Mirrors$RootsBase.getPackage(Mirrors.scala:173)
    at scala.reflect.internal.Definitions$DefinitionsClass.ScalaPackage$lzycompute(Definitions.scala:161)
    at scala.reflect.internal.Definitions$DefinitionsClass.ScalaPackage(Definitions.scala:161)
    at scala.reflect.internal.Definitions$DefinitionsClass.ScalaPackageClass$lzycompute(Definitions.scala:162)
    at scala.reflect.internal.Definitions$DefinitionsClass.ScalaPackageClass(Definitions.scala:162)
    at scala.reflect.internal.Definitions$DefinitionsClass.init(Definitions.scala:1388)
    at scala.tools.nsc.Global$Run.<init>(Global.scala:1053)
    <etc...>

build.sbt

scalaVersion := "2.11.4"

val scalaV = "2.11.4"

libraryDependencies ++= Seq(
  "org.scala-lang"    %   "scala-compiler"      % scalaV,
  "org.scala-lang"    %   "scala-library"       % scalaV,
  "org.scala-lang"    %   "scala-reflect"       % scalaV
)

java

$ java -version
java version "1.7.0_60-ea"
Java(TM) SE Runtime Environment (build 1.7.0_60-ea-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.60-b09, mixed mode)

Solution

This is the one where you have to say:

trait Probe

object Playground extends App {
  //val compiler = new Global(new Settings())
  val s = new Settings()
  s.embeddedDefaults[Probe]
  val compiler = new Global(s)
  val testFiles = List("Test.scala")
  val runner = new compiler.Run()
  val result = runner.compile(testFiles)
  println(result)
}

That took me a couple of minutes. That method name, "embeddedDefaults", is as cryptic as any to come out of sbt.

The comment on MutableSettings (which suggests a side effect):

  /** Initializes these settings for embedded use by type `T`.
  * The class loader defining `T` should provide resources `app.class.path`
  * and `boot.class.path`.  These resources should contain the application
  * and boot classpaths in the same form as would be passed on the command line.*/

The indentation is as in the source code.