How to force SBT to use Java 8?

Support in scalac for jvm-1.8 was added in 2.11.4.

Scala version (2.11.2) does not support -target:jvm-1.8 option.

$ scala -version
Scala code runner version 2.11.2 -- Copyright 2002-2013, LAMP/EPFL

$ scala -target
Usage: -target:<target>
 where <target> choices are jvm-1.5, jvm-1.6, jvm-1.7 (default: jvm-1.6)

bad option: '-target'

Usage: scala <options> [<script|class|object|jar> <arguments>]
   or  scala -help

All options to scalac (see scalac -help) are also allowed.

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")
}