为子项目交叉编译具有不同crossScalaVersions的聚合项目

我们有一个项目，有几个子项目可以在 Scala 2.10 和 2.11 下编译，一个子项目只能在 2.10 下编译(实际上是 Scala-Virtualized 2.10.2)，一个子项目只能在 2.11 下编译.有没有一种简单的方法来创建一个聚合项目，该项目为 2.10 和 2.11 交叉构建所有可能的子项目?或者，为 2.10 和 2.11 设置不同的默认项目?

We have a project with several subprojects which can compile under both Scala 2.10 and 2.11, one subproject which only compiles under 2.10 (actually, Scala-Virtualized 2.10.2) and one subproject which only compiles under 2.11. Is there a simple way to create an aggregate project which cross-builds all possible subprojects for both 2.10 and 2.11? Or, alternately, to have different default projects for 2.10 and 2.11?

特别是，这里是当前的 Build.scala.如果我将 lmsBackend 添加到 root，我得到

In particular, here is current Build.scala. If I add lmsBackend to root, I get

> show scalaVersion
[info] common/*:scalaVersion
[info]  2.10.4
[info] lms-backend/*:scalaVersion
[info]  2.10.2
[info] meta/*:scalaVersion
[info]  2.10.4
[info] community-edition/*:scalaVersion
[info]  2.10.4
[info] core/*:scalaVersion
[info]  2.10.4
[info] scalan/*:scalaVersion
[info]  2.10.4
> show crossScalaVersions
[info] common/*:crossScalaVersions
[info]  List(2.10.4, 2.11.5)
[info] lms-backend/*:crossScalaVersions
[info]  List(2.10.2)
[info] meta/*:crossScalaVersions
[info]  List(2.10.4, 2.11.5)
[info] community-edition/*:crossScalaVersions
[info]  List(2.10.4, 2.11.5)
[info] core/*:crossScalaVersions
[info]  List(2.10.4, 2.11.5)
[info] scalan/*:crossScalaVersions
[info]  List(2.10.4, 2.11.5)

SBT 能够在这个聚合项目上很好地运行 update、compile 等.然而，一旦我尝试任何交叉构建，事情就会崩溃:

SBT is able to run update, compile, etc. fine on this aggregate project. However, once I try any cross-building, things break:

> +update
[info] Setting version to 2.10.4
[info] Reapplying settings...
[info] Set current project to scalan (in build file:/home/aromanov/IdeaProjects/scalan-lite/)
...
[info] Updating {file:/home/aromanov/IdeaProjects/scalan-lite/}lms-backend...
[info] Resolving org.scala-lang.virtualized#scala-library;2.10.4 ...
[warn]  module not found: org.scala-lang.virtualized#scala-library;2.10.4
...
[info] Resolving org.scala-lang.virtualized#scala-compiler;2.10.4 ...
[warn]  module not found: org.scala-lang.virtualized#scala-compiler;2.10.4
...
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  ::          UNRESOLVED DEPENDENCIES         ::
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn]  :: org.scala-lang.virtualized#scala-library;2.10.4: not found
[warn]  :: org.scala-lang.virtualized#scala-compiler;2.10.4: not found
[warn]  ::::::::::::::::::::::::::::::::::::::::::::::
[warn] 
[warn]  Note: Unresolved dependencies path:
[warn]      org.scala-lang.virtualized:scala-library:2.10.4 ((sbt.Classpaths) Defaults.scala#L1169)
[warn]        +- com.huawei.scalan:lms-backend_2.10:0.2.6-SNAPSHOT
[warn]      org.scala-lang.virtualized:scala-compiler:2.10.4
[warn]        +- com.huawei.scalan:lms-backend_2.10:0.2.6-SNAPSHOT
[trace] Stack trace suppressed: run last lms-backend/*:update for the full output.
[error] (lms-backend/*:update) sbt.ResolveException: unresolved dependency: org.scala-lang.virtualized#scala-library;2.10.4: not found
[error] unresolved dependency: org.scala-lang.virtualized#scala-compiler;2.10.4: not found
[error] Total time: 2 s, completed Jan 28, 2015 1:33:49 PM

show scalaVersion 现在显示所有子项目的 2.10.4.有没有什么办法可以在聚合项目中包含lms-backend并且仍然避免这个问题?

show scalaVersion now shows 2.10.4 for all subprojects. Is there any way to include lms-backend in the aggregate project and still avoid this problem?