Use snapshotScalaBinaryVersion when building against -SNAPSHOT

Author: adriaanm

build.sbt

@@ -1,3 +1,5 @@
+import VersionKeys.{snapshotScalaBinaryVersion,deriveBinaryVersion}
+
 organization := "org.scala-lang.modules"
 
 name := "scala-parser-combinators"
@@ -6,9 +8,16 @@ version := "1.0.0-SNAPSHOT"
 
 scalaVersion := "2.11.0-M7"
 
+snapshotScalaBinaryVersion := "2.11.0-M7"
+
+// DOUBLETHINK YOUR WAY OUT OF EDITING BELOW (THERE IS NO BELOW)
+
+scalaBinaryVersion := deriveBinaryVersion(scalaVersion.value, snapshotScalaBinaryVersion.value)
+
 // to allow compiling against snapshot versions of Scala
 resolvers += Resolver.sonatypeRepo("snapshots")
 
+
 libraryDependencies ++= Seq(
   "junit" % "junit" % "4.11" % "test",
   "com.novocode" % "junit-interface" % "0.10" % "test")

project/keys.scala

@@ -1,8 +1,11 @@
-object TestKeys {
+object VersionKeys {
   import sbt.settingKey
 
-  // for testing with partest
-  val includeTestDependencies = settingKey[Boolean]("Doesn't declare test dependencies.")
+  val snapshotScalaBinaryVersion = settingKey[String]("The Scala binary version to use when building against Scala SNAPSHOT.")
 
-  val partestVersion = settingKey[String]("Partest version.")
-}
+  def deriveBinaryVersion(sv: String, snapshotScalaBinaryVersion: String) = sv match {
+    case snap_211 if snap_211.startsWith("2.11") &&
+                     snap_211.contains("-SNAPSHOT") => snapshotScalaBinaryVersion
+    case sv => sbt.CrossVersion.binaryScalaVersion(sv)
+  }
+}