Use the latest IntelliJ IDEA release and install the Scala plugin from within the IDE.

The following steps are required to use IntelliJ IDEA on Scala trunk
 - compile "locker" using "ant locker.done"
 - Copy the *.iml.SAMPLE / *.ipr.SAMPLE files to *.iml / *.ipr
 - In IDEA, create a global library named "ant" which contains "ant.jar"
 - Also create an SDK entry named "1.6" containing the java 1.6 SDK
 - In the Scala Facet of the "library" and "reflect" modules, update the path in the
   command-line argument for "-sourcepath"
 - In the Project Settings, update the "Version Control" to match your checkout

Known problems
 - Due to SI-4365, the "library" module has to be built using "-Yno-generic-signatures"