Why scalaInstance is different from scalaVersion in sbt? - sbt

Question

build.sbt
val Backend = config("backend")
inConfig(Backend)(Defaults.configSettings)
scalaVersion in Backend := "2.11.2-SNAPSHOT"
sbt repl:
> show backend:scalaInstance
[info] Scala instance{version label 2.10.4, actual version 2.10.4, library jar: /home/masgui/.sbt/boot/scala-2.10.4/lib/scala-library.jar, compiler jar: /home/masgui/.sbt/boot/scala-2.10.4/lib/scala-compiler.jar}
> backend:scalaVersion
[info] 2.11.2-SNAPSHOT
current work arround:
lazy val v = Project(
id = "a",
base = file("woot"),
settings = Project.defaultSettings ++ Seq(
offline := true,
scalaVersion := "2.11.2-SNAPSHOT"
)
)
// ...
scalaInstance in (Backend, Revolver.reStart) := (scalaInstance in v).value
edit
When i add Classpaths.ivyBaseSettings to Backend it ignores ivyConfigurations += Backend
> show ivyConfigurations
[info] List(..., backend)
but
> backend:update
Cannot add dependency 'com.scalakata#backend_2.11;0.1-20140706T182100' to configuration 'backend' of module com.scalakata#plugin;0.1-20140709T150113 because this configuration doesn't exist!
edit
I solved this with one of your previous awnser: Copy a single dependency jar into a folder via build.sbt

Answer 1

TL;DR;
You have to also add Classpaths.ivyBaseSettings, Classpaths.jvmBaseSettings and Defaults.compileBase to your Backend configuration.
build.sbt
val Backend = config("backend")
inConfig(Backend)(Classpaths.ivyBaseSettings ++ Classpaths.jvmBaseSettings ++ Defaults.compileBase ++ Defaults.configSettings)
scalaVersion in Backend := "2.11.1"
Longer Version
The task scalaInstance is undefined in your Backend config, so sbt delegates to default scalaInstance.
[info] Delegates:
[info] backend:scalaInstance
[info] *:scalaInstance
[info] {.}/backend:scalaInstance
[info] {.}/*:scalaInstance
[info] */backend:scalaInstance
[info] */*:scalaInstance
If you check where it's defined, you can see it's in *:scalaInstance
> inspect definitions scalaInstance
[info]
[info] *:scalaInstance
If you want it to be defined you have to add Defaults.compileBase to your Backend configuration.
You can confirm it's not defined in the Backend scope.
> inspect definitions scalaInstance
[info]
[info] *:scalaInstance
[info] backend:scalaInstance
But that's not enough, if you check the output of the show backend:scalaInstance, you'll see that it's still 2.10.x.
> show backend:scalaInstance
[info] Scala instance{version label 2.11.1, actual version 2.10.4, library jar: /home/lpiepiora/.sbt/boot/scala-2.10.4/lib/scala-library.jar, compiler jar: /home/lpiepiora/.sbt/boot/scala-2.10.4/lib/scala-compiler.jar}
We need to configure the right classpath, by adding Classpaths.ivyBaseSettings ++ Classpaths.jvmBaseSettings.
The show backend:scalaInstance shows the right version.
> show backend:scalaInstance
[info] Scala instance{version label 2.11.1, actual version 2.11.1, library jar: /home/lpiepiora/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.11.1.jar, compiler jar: /home/lpiepiora/.ivy2/cache/org.scala-lang/scala-compiler/jars/scala-compiler-2.11.1.jar}
[success] Total time: 0 s, completed 08-Jul-2014 20:32:18