scala - How to force SBT to use Java 8?

Question

How can I force SBT to compile to Java 8 class files. I added scalacOptions += "-target:jvm-1.8" but it gives the following error message:

[error] 'jvm-1.8' is not a valid choice for '-target'
[error] bad option: '-target:jvm-1.8'
[error] (compile:compile) Compilation failed

I am using SBT version 0.15.5.

I know I am using Java 8 to compile as I added this to build.sbt, but I still wonder why the scalacOptions fails and I don't know what output the scalac produces.

initialize := {
  val _ = initialize.value
  if (sys.props("java.specification.version") != "1.8")
    sys.error("Java 8 is required for this project.")
}

Answer 1

You need the following on your build.sbt file.

javacOptions ++= Seq("-source", "1.8", "-target", "1.8", "-Xlint")

initialize := {
  val _ = initialize.value
  val javaVersion = sys.props("java.specification.version")
  if (javaVersion != "1.8")
    sys.error("Java 1.8 is required for this project. Found " + javaVersion + " instead")
}