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.

/.idea
/.idea_modules
target/

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 "http://oss.sonatype.org/content/repositories/snapshots/"
 
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.)