#sbt-cross

A better solution for building multiple Scala versions (cross compiling) in SBT.

Purpose

The results of Scala compilation are not always compatible across Scala versions, i.e. binary incompatibility. SBT has some built-in features to make working with Scala projects less painful, including crossScalaVersions.

However, cross compiling an SBT project with crossScalaVersions is less than ideal:

1. Performance - Each Scala version is handled sequentially (not in parallel).
2. Subprojects - Sharing a (classpath) subproject for two versions is tricky.
3. Aggregation - Aggregation doesn't take into account crossScalaVersions of subprojects.

Install

Requires SBT 0.13. (Tested with 0.13.7.)

In project/plugins.sbt, add

resolvers += Resolver.sonatypeRepo("releases")

addSbtPlugin("com.lucidchart" % "sbt-cross" % "1.1")

If you use Build.scala, you'll need to import com.lucidchart.sbtcross.SbtCrossImport._.

Example

Suppose there is a project foo that uses Scala 2.10, a project bar that uses Scala 2.11, and they depend on a project common that compiles with Scala 2.10 and 2.11.

You can do this with sbt-cross like so:

lazy val foo = (project in file("foo")).dependsOn(common_2_10)
  .settings(scalaVersion := "2.10.4")

lazy val bar = (project in file("bar")).dependsOn(common_2_11)
  .settings(scalaVersion := "2.11.5")

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

lazy val common_2_10 = common("2.10.4")

lazy val common_2_11 = common("2.11.5")

This defines four projects: foo, bar, common-2_10, and common-2_11.

SBT will concurrently compile the right ones in the right order.

• sbt foo/compile will compile common-2_10 then foo.

• sbt bar/compile will compile common-2_11 then bar.

• sbt compile will compile common-2_10 then foo and, in parallel, common-2_11 then bar

See examples for more.

Alternative syntax

The previous example can be written more succinctly as

lazy val foo = (project in file("foo")).dependsOn(common_2_10)
  .settings(scalaVersion := "2.10.4")

lazy val bar = (project in file("bar")).dependsOn(common_2_11)
  .settings(scalaVersion := "2.11.5")

lazy val (common_2_10, common_2_11) = Project("common", file("common")).cross
  .forVersions("2.10.4", "2.11.5")

though that only works in .scala files, or in .sbt files for SBT versions prior to 0.13.7.

Contributions

We welcome issues, questions, and contributions on our GitHub project (https://github.com/lucidsoftware/sbt-cross).

Each major version has a branch. Development for the next major version is on master. If a change is needed for an existing major version, it is cherry-picked to that branch.