Scala In Memory Compiler

ScalaInMemoryCompiler.scala

import scala.tools.nsc.{Global, Settings}
import scala.reflect.internal.util.BatchSourceFile
import tools.nsc.io.{VirtualDirectory, AbstractFile}
import scala.reflect.internal.util.AbstractFileClassLoader
import java.security.MessageDigest
import java.math.BigInteger
import collection.mutable
import java.io.File

object CompileTest {
  val compiler = new Compiler(None)

  def main(args: Array[String]) {
    val script = "println(List(1, 2, 3, 4).mkString(\" + \"))"
    compiler.eval[Unit](script)
  }
}

class Compiler(targetDir: Option[File]) {

  val target: AbstractFile = targetDir match {
    case Some(dir) => AbstractFile.getDirectory(dir)
    case None => new VirtualDirectory("(memory)", None)
  }

  val classCache: mutable.Map[String, Class[_]] = mutable.Map[String, Class[_]]()

  private val settings = new Settings()
  settings.deprecation.value = true // enable detailed deprecation warnings
  settings.unchecked.value = true // enable detailed unchecked warnings
  settings.outputDirs.setSingleOutput(target)
  settings.usejavacp.value = true

  private val global = new Global(settings)
  private lazy val run = new global.Run

  val classLoader = new AbstractFileClassLoader(target, this.getClass.getClassLoader)

  /** Compiles the code as a class into the class loader of this compiler.
    *
    * @param code
    * @return
    */
  def compile(code: String): Class[_] = {
    val className = classNameForCode(code)
    findClass(className).getOrElse {
      val sourceFiles = List(new BatchSourceFile("(inline)", wrapCodeInClass(className, code)))
      run.compileSources(sourceFiles)
      findClass(className).get
    }
  }

  /** Compiles the source string into the class loader and
    * evaluates it.
    *
    * @param code
    * @tparam T
    * @return
    */
  def eval[T](code: String): T = {
    val cls = compile(code)
    cls.getConstructor().newInstance().asInstanceOf[() => Any].apply().asInstanceOf[T]
  }

  def findClass(className: String): Option[Class[_]] = {
    synchronized {
      classCache.get(className).orElse {
        try {
          val cls = classLoader.loadClass(className)
          classCache(className) = cls
          Some(cls)
        } catch {
          case e: ClassNotFoundException => None
        }
      }
    }
  }

  protected def classNameForCode(code: String): String = {
    val digest = MessageDigest.getInstance("SHA-1").digest(code.getBytes)
    "sha" + new BigInteger(1, digest).toString(16)
  }

  /*
  * Wrap source code in a new class with an apply method.
  */
  private def wrapCodeInClass(className: String, code: String) = {
    "class " + className + " extends (() => Any) {\n" +
      "  def apply() = {\n" +
      code + "\n" +
      "  }\n" +
      "}\n"
  }
}