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.
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.