If I run Eclipse with Java 8, and configure my project to compile with Java 7, I will get a classpath with mixed entries:
- core JDK (rt.jar) comes from the project-specific JRE (in this case, Java 7) -- as expected
- extdirs of the runtime JRE (used by Eclipse are also added to the classpath (in this case, Java 8)
This may lead to scalac crashes, see SI-8435
Since javaextdirs are already merged into the java bootclasspath (by Eclipse), the Scala IDE should explicitly set -javaextdirs to Nil in Scala settings (otherwise, defaults kick in the Scala compiler, and picks up the running JVM extdirs).