Separate location of analysis cache if we're cross compiling scala.

* Add task to determine file-name of analysis cache
* If crossPaths := true, then add scala binary version to the analysis cache name.

This makes it possible to leverage incremental compilation with the `+` command.

Fixes #1267

main/src/main/scala/sbt/Defaults.scala

@@ -246,6 +246,14 @@ object Defaults extends BuildCommon
 	lazy val configTasks = docTaskSettings(doc) ++ inTask(compile)(compileInputsSettings) ++ configGlobal ++ Seq(
 		compile <<= compileTask tag(Tags.Compile, Tags.CPU),
 		printWarnings <<= printWarningsTask,
+		compileAnalysisFilename := {
+			// Here, if the user wants cross-scala-versioning, we also append it
+			// to the analysis cache, so we keep the scala versions separated.
+			val extra = 
+			  if(crossPaths.value) s"_${scalaBinaryVersion.value}"
+			  else ""
+			s"inc_compile${extra}"
+		},
 		compileIncSetup <<= compileIncSetupTask,
 		console <<= consoleTask,
 		consoleQuick <<= consoleQuickTask,
@@ -763,9 +771,15 @@ object Defaults extends BuildCommon
 		}
 		finally x.close() // workaround for #937
 	}
-	def compileIncSetupTask =
-		(dependencyClasspath, skip in compile, definesClass, compilerCache, streams, incOptions) map { (cp, skip, definesC, cache, s, incOptions) =>
-			Compiler.IncSetup(analysisMap(cp), definesC, skip, s.cacheDirectory / "inc_compile", cache, incOptions)
+	def compileIncSetupTask = Def.task {
+		Compiler.IncSetup(
+			analysisMap(dependencyClasspath.value), 
+			definesClass.value, 
+			(skip in compile).value, 
+			// TODO - this is kind of a bad way to grab the cache directory for streams...
+			streams.value.cacheDirectory / compileAnalysisFilename.value,
+			compilerCache.value, 
+			incOptions.value)
 	}
 	def compileInputsSettings: Seq[Setting[_]] =
 		Seq(compileInputs := {

main/src/main/scala/sbt/Keys.scala

@@ -142,6 +142,7 @@ object Keys
 	val consoleProject = TaskKey[Unit]("console-project", "Starts the Scala interpreter with the sbt and the build definition on the classpath and useful imports.", AMinusTask)
 	val compile = TaskKey[Analysis]("compile", "Compiles sources.", APlusTask)
 	val compilers = TaskKey[Compiler.Compilers]("compilers", "Defines the Scala and Java compilers to use for compilation.", DTask)
+	val compileAnalysisFilename = TaskKey[String]("compileAnalysisFilename", "Defines the filename used to store the incremental compiler analysis file (inside the streams cacheDirectory).", DTask)
 	val compileIncSetup = TaskKey[Compiler.IncSetup]("inc-compile-setup", "Configures aspects of incremental compilation.", DTask)
 	val compilerCache = TaskKey[GlobalsCache]("compiler-cache", "Cache of scala.tools.nsc.Global instances.  This should typically be cached so that it isn't recreated every task run.", DTask)
 	val stateCompilerCache = AttributeKey[GlobalsCache]("compiler-cache", "Internal use: Global cache.")

sbt/src/sbt-test/compiler-project/separate-analysis-per-scala/build.sbt

@@ -0,0 +1,12 @@
+name := "foo"
+
+scalaVersion := "2.10.4"
+
+crossScalaVersions := List("2.10.4", "2.11.0")
+
+incOptions := incOptions.value.withNewClassfileManager(
+  sbt.inc.ClassfileManager.transactional(
+    crossTarget.value / "classes.bak",
+    (streams in (Compile, compile)).value.log
+  )
+)

sbt/src/sbt-test/compiler-project/separate-analysis-per-scala/foo.scala

@@ -0,0 +1,6 @@
+package foo
+
+object Foo extends App {
+  println("yay")
+}
+

sbt/src/sbt-test/compiler-project/separate-analysis-per-scala/test

@@ -0,0 +1,3 @@
+> + compile
+$ exists target/scala-2.10
+$ exists target/scala-2.11