Why is crossScalaVersion not scalaVersion? - scala

Question

build.sbt
scalaVersion := "2.11.4"
project/build.properties
sbt.version=0.13.7
Then
> show scalaVersion
[info] 2.11.4
> show crossScalaVersions
[info] List(2.10.4)
> inspect crossScalaVersions
[info] Setting: scala.collection.Seq[java.lang.String] = List(2.10.4)
[info] Description:
[info] The versions of Scala used when cross-building.
[info] Provided by:
[info] */*:crossScalaVersions
[info] Defined at:
[info] (sbt.Defaults) Defaults.scala:237
[info] Delegates:
[info] *:crossScalaVersions
[info] {.}/*:crossScalaVersions
[info] */*:crossScalaVersions
[info] Related:
[info] */*:crossScalaVersions
It seems like crossScalaVersions should be List(2.11.4).
Look at SBT's source code, that's also what I would think.
crossScalaVersions := Seq(scalaVersion.value)
Why doesn't crossScalaVersions correspond to scalaVersion?

Answer 1

scalaVersion.value is context-dependent. So in Defaults.scala it's */*:scalaVersion from appConfiguration.value.provider.scalaProvider. It's the version used to compile your project's definition, including your build.sbt file (sbt 0.13.7 uses 2.10.4 scala-compiler to compile your project definitions). And that the only way as your project's definitions (including scalaVersion) isn't compiled yet when Defaults executed and crossScalaVersions defined. So, */*:crossScalaVersions depends on */*:scalaVersion not proj/*:scalaVersion.
Just compare Provided by with explicit scalaVersion := 2.11.4 inside build.sbt:
> inspect scalaVersion
[info] Setting: java.lang.String = 2.11.4
[info] Description:
[info] The version of Scala used for building.
[info] Provided by:
[info] {file:/Users/user/dev/proj/}proj/*:scalaVersion
[info] Defined at:
[info] /Users/user/dev/proj/build.sbt:1
[info] Reverse dependencies (D=derives):
[info] *:allDependencies
[info] D *:scalaBinaryVersion
[info] *:libraryDependencies
[info] *:scalaInstance
[info] *:crossScalaVersions
[info] *:update
[info] Delegates:
[info] *:scalaVersion
[info] {.}/*:scalaVersion
[info] */*:scalaVersion
[info] Related:
[info] */*:scalaVersion
And without one (just empty project):
> inspect scalaVersion
[info] Setting: java.lang.String = 2.10.4
[info] Description:
[info] The version of Scala used for building.
[info] Provided by:
[info] */*:scalaVersion
[info] Defined at:
[info] (sbt.Defaults) Defaults.scala:232
[info] Reverse dependencies:
[info] *:allDependencies
[info] *:libraryDependencies
[info] *:update
[info] *:scalaInstance
[info] Delegates:
[info] *:scalaVersion
[info] {.}/*:scalaVersion
[info] */*:scalaVersion
[info] Related:
[info] */*:scalaVersion
So, you just need to redefine */*:scalaVersion in your build.sbt:
scalaVersion in GlobalScope := "2.11.2"