How to have SBT subproject with multiple Scala versions?

Question

I have a project using Scala 2.10 and one using Scala 2.11. They depend on a common project, which can compile with both.

lazy val foo = (project in file(\"foo\"         


        

Answer 1

I created an SBT plugin for this.

project/plugins.sbt

resolvers += Resolver.sonatypeRepo("releases")

addSbtPlugin("com.lucidchart" % "sbt-cross" % "1.0")

build.sbt

lazy val foo = (project in file("foo")).dependsOn(baz_2_10).settings(
  scalaVersion := "2.10.4"
)

lazy val bar = (project in file("bar")).dependsOn(baz_2_11).settings(
  scalaVersion := "2.11.5"
)

lazy val baz = (project in file("baz")).cross

lazy val baz_2_10 = baz("2.10.4")

lazy val baz_2_11 = baz("2.11.5")

It takes a couple more lines, but now everything compiles as expected: sbt foo/compile works, and sbt bar/compile works.

You don't have to remember unique commands, you don't have bugs from crossPath := false, and unlike ++, this is parallelizable: sbt compile will compile foo, bar, and baz with the correct Scala versions concurrently.