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Eclipse project files

For important details on building, debugging and file encodings, please see the excellent tutorial on scala-ide.org.

The following points describe how to build Scala using Eclipse.

  1. Download the Scala IDE bundle. It comes preconfigured for optimal performance.

  2. Run ant build to download some necessary jars and see a successful build.

  3. You need to define a path variable and a classpath variable inside Eclipse, both pointing to the Scala checkout directory:

  • (experimental): run ./update-workspace.sh scala_checkout_dir [workspace_dir]. This should update your workspace settings (restart Eclipse if it was running). For example:
./update-workspace.sh $HOME/git/scala ~/Documents/workspace-scalac
  • If the above didn't work, you can perform these steps manually: 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 also as a classpath variable in Java/Build Path/Classpath Variables.
  1. Import the project (in src/eclipse) via File → Import Existing Projects and navigate to scala/src/eclipse. Check all projects and click ok.

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).

  1. 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.

  1. 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`
  1. The 2.12, sources of Scala need to be built with a 2.12 version of the compiler. One can configure a 2.12 Scala installation in Eclipse. In order to do this, go to Window -> Preferences -> Scala -> Installations and add a 2.12 installation. You can either download a prepackaged version of 2.12 from the Scala homepage or you add the Scala installation that is part of the build/pack/lib directory. The latter is required in case you absolutely need to depend on a nightly build of the compiler to compile the compiler itself. Once the 2.12 Scala installation is created you need to select all Scala projects, do a right click and select Scala -> Set the Scala installation where you have to choose the newly created 2.12 Scala installation.

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 versions.properties 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 versions.properties 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.

DETAILS

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).