Conditional scalacOptions with SBT

Question

I am using a project with cross-build for Scala 2.8, 2.9 and (hopefully) 2.10, using SBT. I would like to add the -feature option when compiling with 2.10 only.

In other words, when I compile with a version smaller than 2.10.0, I would like to set the compiler options as:

scalacOptions ++= Seq( "-deprecation", "-unchecked" )

and when compiling with a version greater or equal than 2.10.0:

scalacOptions ++= Seq( "-deprecation", "-unchecked", "-feature" )

Is there a way to achieve this ?

Answer 1

I found this was quick and concise way of doing it:

scalaVersion := "2.10.0"

crossScalaVersions := "2.9.2" :: "2.10.0" :: Nil

scalacOptions <<= scalaVersion map { v: String =>
  val default = "-deprecation" :: "-unchecked" :: Nil
  if (v.startsWith("2.9.")) default else default :+ "-feature"            
}

Answer 2

When cross-building, scalaVersion reflects the version your project is currently built against. So depending on scalaVersion should do the trick:

val scalaVersionRegex = "(\\d+)\\.(\\d+).*".r
...
scalacOptions <++= scalaVersion { sv =>
  sv match {
    case scalaVersionRegex(major, minor) if major.toInt > 2 || (major == "2" && minor.toInt >= 10) =>
      Seq( "-deprecation", "-unchecked", "-feature" )
    case _ => Seq( "-deprecation", "-unchecked" )
}