Scala SBT: scala.tools.nsc isn't running

Question

I have a problem with scala.tools.sbt

scala file

Here I used parser functionality to make abstract syntax tree of code 2 + 3

import scala.tools.nsc._
object Main extends App {
    var i = new Interpreter
    println(i.parse("2 + 3"))
}

SBT configuration

name := "scalaSample"

version := "1.0-SNAPSHOT"

scalaVersion := "2.9.1"

libraryDependencies += "org.scalatest" %% "scalatest" % "1.7.1" % "test"

libraryDependencies += "org.scala-lang" % "scala-compiler" % "2.9.1"

Error

Failed to initialize compiler: object scala not found. ** Note that as of 2.8 scala does not assume use of the java classpath. ** For the old behavior pass -usejavacp to scala, or if using a Settings ** object programatically, settings.usejavacp.value = true.

[error] (run-main) java.lang.NullPointerException java.lang.NullPointerException at scala.tools.nsc.CompilationUnits$CompilationUnit. (CompilationUnits.scala:16) at scala.tools.nsc.interpreter.ExprTyper$codeParser$.applyRule(ExprTyper.scala:22) at scala.tools.nsc.interpreter.ExprTyper$codeParser$.stmts(ExprTyper.scala:36) at scala.tools.nsc.interpreter.ExprTyper$$anonfun$parse$2.apply(ExprTyper.scala:47) at scala.tools.nsc.interpreter.ExprTyper$$anonfun$parse$2.apply(ExprTyper.scala:46) at scala.tools.nsc.reporters.Reporter.withIncompleteHandler(Reporter.scala:46) at scala.tools.nsc.interpreter.ExprTyper$class.parse(ExprTyper.scala:46) at scala.tools.nsc.interpreter.IMain$exprTyper$.parse(IMain.scala:1012) at scala.tools.nsc.interpreter.IMain.parse(IMain.scala:1013) at eu.semantiq.scalaToJS.Main$delayedInit$body.apply(Main.scala:7) at scala.Function0$class.apply$mcV$sp(Function0.scala:34) at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12) at scala.App$$anonfun$main$1.apply(App.scala:60) at scala.App$$anonfun$main$1.apply(App.scala:60) at scala.collection.LinearSeqOptimized$class.foreach(LinearSeqOptimized.scala:59) at scala.collection.immutable.List.foreach(List.scala:45) at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:30) at scala.App$class.main(App.scala:60) at eu.semantiq.scalaToJS.Main$.main(Main.scala:5) at eu.semantiq.scalaToJS.Main.main(Main.scala) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) java.lang.RuntimeException: Nonzero exit code: 1 at scala.sys.package$.error(package.scala:27)

In scala REPL everything works

Welcome to Scala version 2.9.0.1 (OpenJDK 64-Bit Server VM, Java 1.6.0_23). Type in expressions to have them evaluated. Type :help for more information.

scala> import scala.tools.nsc._

import scala.tools.nsc._

scala> var i = new Interpreter

warning: there were 4 deprecation warnings; re-run with -deprecation for details warning: there were 1 deprecation warnings; re-run with -deprecation for details

i: scala.tools.nsc.Interpreter = scala.tools.nsc.Interpreter@786bfd73

scala> println(i.parse("2 + 3"))

Some(List(2.$plus(3)))

I feel really sorry for my bad English

Answer 1

According to xsbt's FAQ:

sbt runs tests in the same JVM as sbt itself and Scala classes are not in the same class loader as the application classes.

And there's more:

The key is to initialize the Settings for the interpreter using embeddedDefaults.

The example that is given there uses some arbitrary type MyType. In fact, you can use any of your types to help sbt find the appropriate class loader (see this answer).

Hence, your code should look like this:

import scala.tools.nsc._

trait Foo // Arbitrary type added to get stuff working

object Main extends App {
    val settings = new Settings
    settings.embeddedDefaults[Foo]
    val interpreter = new Interpreter(settings)
    println(interpreter.parse("2 + 3"))
}