Scala Development Environment with Intellij IDEA and SBT
posted at November 28, 2012 with tags intellij, java, sbt, scala

Resisting against the Functional Programming Principles in Scala buzz was meaningless. After all, this or that way I know I would be repeating those steps on my own regardless of the presence of such a lecture. To warm up, I looked around for an appropriate development environment for Scala. The last time (~2 years ago) I repeated this same step ended up with a desperate search. Fortunately, reading dozens of blog posts, forum/mailing-list threads, GitHub README’s, repeating try-and-fail procedures leaded me to a working setup. To mitigate the friction at least to an extent for new comers, I put up this blog post to make a list of steps in order to setup a working Scala development environment on top of IntelliJ IDEA with SBT integration.

Is there a Scala plugin available for IDEA?

Good news, yes. It is under active development, works way better than its alternatives, has a responsive maintainer and an active community. Plugin lets you create Scala projects, compile/run/debug Scala source files, scripts, and worksheets. Navigation, refactoring, tab-completion, code snippets are included as well. (Note that it is strongly advised to use an EAP version for a smooth experience.)

Is there a quick start guide for IDEA Scala plugin?

Yes, see Getting Started with IntelliJ IDEA Scala Plugin.

How do I manage project dependencies?

While one can setup a Maven/Ivy/Ant configuration for a Scala project, SBT is known to be the de-facto tool for build management throughout the Scala community. (Otherwise, you will need to set explicit scala-compiler and scala-library dependencies in XML mazes.) Fortunately, there is an SBT plugin for IDEA. It offers a console where SBT commands can be entered interactively, and a Before Launch task to delegate project compilation to SBT, as an alternative to the built in IntelliJ Make.

Is there a quick start guide for SBT?

Yes, see Hello, World in SBT documentation.

How can I integrate libraries installed by SBT to IDEA?

At its core, SBT uses Apache Ivy, which has its own nasty ways of dealing with downloaded JARs under ~/.ivy2. Instead of manually defining IDEA module dependencies for each JAR a project uses, lucky for us, there exists an SBT plugin for this purpose: sbt-idea. Basically, sbt-idea enhances SBT with a new task, called gen-idea, which creates IDEA project files with necessary module dependencies induced by SBT. That is,

  1. Add your dependencies to your SBT configuration,
  2. Call sbt update to download/update project dependencies,
  3. Call sbt gen-idea to create IDEA project files,
  4. Open created project from IDEA.

What are the IDEA modules created by sbt-idea?

In addition to below directories, SBT dependencies are added to the IDEA module configuration.

  • Source Folders: src/main/{scala,java,resources}
  • Test Source Folders: src/test/{scala,java,resources}

What about testing?

SBT supports a couple of testing frameworks, e.g., specs2, ScalaCheck, and ScalaTest. See Testing section of the SBT documentation for a detailed discussion.

What about my .gitignore?

Here you go.


I read enough, gimme the code!

Create a project directory.

$ export PROJECT_DIR=~/scala/ScalaHelloWorld
$ mkdir $PROJECT_DIR

Create $PROJECT_DIR/build.sbt as follows. (In this example, I used ScalaTest framework.)

name := "ScalaHelloWorld"
version := "0.0.1"
scalaVersion := "2.9.2"
libraryDependencies += "org.scalatest" %% "scalatest" % "1.8" % "test"

Create $PROJECT_DIR/project directory and add below lines to $PROJECT_DIR/project/plugins.sbt to add sbt-idea plugin.

resolvers += "Sonatype snapshots" at ""
addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.2.0-SNAPSHOT")

Run sbt in $PROJECT_DIR and execute gen-idea task.

$ sbt
[info] Loading project definition from /home/vy/scala/ScalaHelloWorld/project
[info] Updating {file:/home/vy/scala/ScalaHelloWorld/project/}default-70d248...
[info] Resolving org.scala-sbt#precompiled-2_10_0-m7;0.12.1 ...
[info] Done updating.
[info] Set current project to ScalaHelloWorld (in build file:/home/vy/scala/ScalaHelloWorld/)
> gen-idea
[info] Trying to create an Idea module ScalaHelloWorld
[info] Updating {file:/home/vy/scala/ScalaHelloWorld/}default-3005c4...
[info] Resolving org.scalatest#scalatest_2.9.2;1.8 ...
[info] Done updating.
[info] Resolving org.scalatest#scalatest_2.9.2;1.8 ...
[info] Excluding folder target
[info] Created /home/vy/scala/ScalaHelloWorld/.idea/IdeaProject.iml
[info] Created /home/vy/scala/ScalaHelloWorld/.idea
[info] Excluding folder /home/vy/scala/ScalaHelloWorld/target
[info] Created /home/vy/scala/ScalaHelloWorld/.idea_modules/ScalaHelloWorld.iml
[info] Created /home/vy/scala/ScalaHelloWorld/.idea_modules/ScalaHelloWorld-build.iml

In src/main/scala/Main.scala, create a main() stub with a testable function in it.

object Main {
  def main(args: Array[String]) {
    println("Hello, World!")
    println("# of arguments: %d" format count(args))

  def count[T](it: Iterable[T]): Int = it.size

In src/test/scala/MainSuite.scala, create a sample test suite.

import org.scalatest.FunSuite

class MainSuite extends FunSuite {
  test("counting an empty collection") {
    assert(Main.count(Array[Int]()) == 0)
    assert(Main.count(Map()) == 0)
    assert(Main.count(Set()) == 0)

  test("counting a non-empty collection") {
    assert(Main.count(Array(1)) == 1)
    assert(Main.count(Map(1 -> 1)) == 1)
    assert(Main.count(Set(1)) == 1)

Enjoy the rest by either creating your own IDEA run configurations, or manually running tasks within the SBT console. (As a final note, while creating IDEA run configurations, you can use SBT Before Launch task provided by IDEA SBT plugin.)