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Eclipse project files

The following points describe how to get Scala to run in Eclipse:

  1. To get Scala to work inside of Eclipse Kepler it is necessary to build the Scala IDE by your own because for the moment there is no update site provided for the newest development version of Scala. To do so enter the following commands one after the other:

    git clone
    cd scala-ide
    ./ clean install -Pscala-2.11.x -Peclipse-kepler -DskipTests

    After that you have an update site in scala-ide/org.scala-ide.sdt.update-site/target/site, which needs to be installed in Eclipse.

  2. The second thing that needs to be done is building Scala in order to get all necessary dependencies. To do that simply enter


    and wait until it is completed. To verify that everything has been built successfully, execute the REPL that can be found at scala/build/pack/bin/scala.

  3. Import all projects inside of Eclipse by choosing File/Import Existing Projects and navigate to scala/src/eclipse. Check all projects and click ok.

  4. You need to define a path variable inside Eclipse. Define SCALA_BASEDIR in Preferences/General/Workspace/Linked Resources. The value should be the absolute path to your Scala checkout. All paths in the project files are relative to this one, so nothing will work before you do so.

    The same SCALA_BASEDIR variable needs to be defined as a classpath variable in Java/Build Path/Classpath Variables.

    Additionally, we start using Maven dependencies (e.g. JUnit) so you need to define another classpath variable inside Eclipse. Define M2_REPO in Java/Build Path/Classpath Variables to point to your local Maven repository (e.g. $HOME/.m2/repository).

    Lastly, the JRE used by Eclipse needs to know the path to the JLine library, which is used by the REPL. To set the JAR file, navigate to Java/Installed JREs, select the default JRE, press Edit/Add External JARs... and enter the path to JLine whose location is SCALA_BASEDIR/build/deps/repl/jline-2.11.jar (SCALA_BASEDIR cannot be entered, it needs to be replaced with its absolute path).

  5. The Eclipse Java compiler does not allow certain calls to restricted APIs in the JDK. The Scala library uses such APIs, so you'd see this error:

    Access restriction: The method compareAndSwapObject(Object, long, Object, Object)
    from the type Unsafe is not accessible due to restriction on required library.

    You can fix it by allowing calls to restricted APIs in Java/Compiler/Errors/Warnings/Deprecated and Restricted API settings.

  6. Project files are tracked by Git, so adding them to .gitignore won't prevent them from being shown as dirty in git status. You can still ignore them by telling Git to consider them unchanged:

    git update-index --assume-unchanged `find src/eclipse -iname .classpath -or -iname .project`

    If you want to go back to normal (for instance, to commit your changes to project files), run:

      git update-index --no-assume-unchanged `find src/eclipse -iname .classpath -or -iname .project`

If it doesn’t compile

The likely reason is that the build path of the imported projects isn’t correct. This can happen for instance when the file is updated, and Eclipse .classpath of the different projects isn’t updated accordingly. The fix is simple, manually inspect the build path of each project and make sure the version of the declared dependencies is in sync with the version declared in the file. If it isn’t, update it manually and, when done, don’t forget to share your changes via a pull request. (We are aware this is cumbersome. If you feel like scripting the process, pull requests are of course welcome.)

Launching & Debugging scalac

Read here.


The compiler project depends on the library, reflect, and asm projects. The builder will take care of the correct ordering, and changes in one project will be picked up by the dependent projects.

The output directory is set to be build/quick, so the runner scripts in quick work as they are (they are generated after an ant build).

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