Scala cross-version support for shared source directory

[fthomas]

Since version 0.13.8, sbt adds Scala version specific source directories to unmanagedSources, see sbt/sbt#1799 or https://github.com/sbt/sbt/blob/0.13.8/notes/0.13.8.markdown#cross-version-support-for-scala-sources. That means that besides src/main/scala src/main/scala-2.x is added to the list of source directories. This is extremely useful for projects that target multiple Scala versions but want to use different sources per version.

Unfortunately a Scala.js CrossProject with CrossType.Full does not yet add Scala version specific directories for the shared source directory. This is unmanagedSourceDirectories for one of my projects:

> coreJVM/unmanagedSourceDirectories
[info] List(
  $PROJECT_ROOT/core/jvm/src/main/scala-2.11,
  $PROJECT_ROOT/core/jvm/src/main/scala,
  $PROJECT_ROOT/core/jvm/src/main/java,
  $PROJECT_ROOT/core/shared/src/main/scala)
> coreJS/unmanagedSourceDirectories
[info] List(
  $PROJECT_ROOT/core/js/src/main/scala-2.11,
  $PROJECT_ROOT/core/js/src/main/scala,
  $PROJECT_ROOT/core/js/src/main/java,
  $PROJECT_ROOT/core/shared/src/main/scala)

Ideally both lists should also contain $PROJECT_ROOT/core/shared/src/main/scala-2.11.

[sjrd]

That would make sense, indeed.

[ghost]

Not perfect, but for current workaround:
https://github.com/InTheNow/sbt-catalysts/blob/master/src/main/scala/sbtcatalysts/CatalystsPlugin.scala#L156-L172

[fthomas]

Awesome, thanks for implementing this!