Enforcing Java version for Scala project in sbt?

Question

My scala application will only run with Java 7 as it depends on libraries that only appeared in that version of the JDK.

How do I enforce that in sbt, so that the correct error message is shown immediately to the user if she is using the wrong version of Java when starting sbt to run/compile the application?

NOTE: There is NO Java™ source code to compile here. I only have Scala source code. The Scala code requires an import java.nio.file.Path that's available from Java 7.

Answer 1

Using javacOptions ++= Seq("-source", "1.7", "-target", "1.7") does not work if you have no Java sources.

But you can set the target JVM for the Scala compiler in build.sbt or Build.scala:

scalacOptions += "-target:jvm-1.7" 

As a result it prints on a JDK 6:

$ sbt clean run [info] Set current project to default-cd5534 (in build file:/tmp/so/) [success] Total time: 0 s, completed 27.10.2013 14:31:43 [info] Updating {file:/tmp/so/}default-cd5534... [info] Resolving org.fusesource.jansi#jansi;1.4 ... [info] Done updating. [info] Compiling 1 Scala source to /tmp/so/target/scala-2.10/classes... [info] Running Main  [error] (run-main) java.lang.UnsupportedClassVersionError: Main : Unsupported major.minor version 51.0 java.lang.UnsupportedClassVersionError: Main : Unsupported major.minor version 51.0         at java.lang.ClassLoader.defineClass1(Native Method)         at java.lang.ClassLoader.defineClass(ClassLoader.java:634)         at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)         at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)         at java.net.URLClassLoader.access$000(URLClassLoader.java:73)         at java.net.URLClassLoader$1.run(URLClassLoader.java:212)         at java.security.AccessController.doPrivileged(Native Method)         at java.net.URLClassLoader.findClass(URLClassLoader.java:205)         at java.lang.ClassLoader.loadClass(ClassLoader.java:321)         at java.lang.ClassLoader.loadClass(ClassLoader.java:314) [trace] Stack trace suppressed: run last compile:run for the full output. java.lang.RuntimeException: Nonzero exit code: 1         at scala.sys.package$.error(package.scala:27) [trace] Stack trace suppressed: run last compile:run for the full output. [error] (compile:run) Nonzero exit code: 1 [error] Total time: 4 s, completed 27.10.2013 14:31:47 

Note: Maybe it works only for the latest SBT/Scalac version.