Introduce new scalaVersionsByJvm setting

[lrytz]

Make it easier for modules to use multiple Scala versions depending on the JVM version. Example config in a module:

// Map[JvmVersion, List[(ScalaVersion, UseForPublishing)]]
scalaVersionsByJvm := {
  val v211 = "2.11.8"
  val v212 = "2.12.2"

  Map(
    6 -> List(v211 -> true),
    7 -> List(v211 -> false),
    8 -> List(v212 -> true, v211 -> false),
    9 -> List(v212 -> false, v211 -> false)
  )
}

This will set crossScalaVersions according to the JVM version. If the TRAVIS_TAG environment variable is defined and we're publishing a release, the selection of Scala versions is filtered accordingly.

[lrytz]

CC @gourlaysama, suggestions welcome.

[SethTisue]

cc our other module maintainers: @benhutchison @danslapman @ashawley @biswanaths (it would be good if y'all watched this repo if you aren't already — it's low-noise)

[danslapman]

Looks nice, I like the concept!

[lrytz]

I've tested this with scala-continuations and scala-swing, seems to work fine. I'll merge and publish a new release of this plugin.

[ashawley]

Will this change be compatible with the scalajs plugin?

[lrytz]

That's also a good question!

I'll look at the scala-xml repo and see what needs to be done to make sure it works fine in scala-xml.

[lrytz]

Another problem is in the https://github.com/scala/scala-parallel-collections build which only sets scalaModuleSettings for one of its sub-projects. So setting scalaVersionsByJvm (leaving scalaVersion / crossScalaVersions undefined) leads to this:

> scalaVersion
[info] testmacros/*:scalaVersion
[info] 	2.10.6
[info] scalacheck/*:scalaVersion
[info] 	2.10.6
[info] junit/*:scalaVersion
[info] 	2.10.6
[info] core/*:scalaVersion
[info] 	2.13.0-M1
[info] scala-parallel-collections/*:scalaVersion
[info] 	2.10.6

Maybe instead of making it a setting, I better define a method that the module builds can invoke when setting crossScalaVersions.

[ashawley]

I'll look at the scala-xml repo and see what needs to be done to make sure it works fine in scala-xml.

So far I have

scalaVersionsByJvm := {
  val v213 = "2.13.0-M1"
  val v212 = "2.12.2"
  val v211 = "2.11.11"
  val vs = List(v213, v212, v211)
  // Map[JvmMajorVersion, List[(ScalaVersion, UseForPublishing)]]
  Map(
    6 -> List(v211 -> true),
    7 -> List(v211 -> false),
    8 -> List(v213 -> true, v212 -> true, v211 -> false),
    9 -> vs.map(_ -> false)
  )
}

But I get

[error] No Scala version for Java major version 8. Adjust `scalaVersionsByJvm` in build.sbt

[sjrd]

I don't see anything in here that would interfere with sbt-scalajs. I could be overlooking something, of course.