Explicitly, optimistically close export streams early: workaround for #937

This is a temporary workaround: it assumes nothing else uses these streams later.
This condition is ok for 'export' and test streams, since these are unlikely to
reuse these streams.  However, the proper fix is for the TaskStreams methods
to be smarter- they could open in append mode if the stream was closed.  The
streams associated with a task could be optimistically closed after it finishes executing.
(Any task can write to another task's streams, which is why it is an optimization only.)

main/src/main/scala/sbt/CommandStrings.scala

@@ -35,6 +35,7 @@ $ShowCommand <task>
 	val LastCommand = "last"
 	val LastGrepCommand = "last-grep"
 	val ExportCommand = "export"
+	val ExportStream = "export"
 
 	val lastGrepBrief = (LastGrepCommand, "Shows lines from the last output for 'key' that match 'pattern'.")
 	val lastGrepDetailed =

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

@@ -26,6 +26,7 @@ package sbt
 	import java.util.concurrent.Callable
 	import sbinary.DefaultProtocol.StringFormat
 	import Cache.seqFormat
+	import CommandStrings.ExportStream
 
 	import Types._
 	import Path._
@@ -401,7 +402,7 @@ object Defaults extends BuildCommon
 		val opts = forkOptions.value
 		Seq(new Tests.Group("<default>", tests, if(fk) Tests.SubProcess(opts) else Tests.InProcess))
 	}
-	private[this] def forkOptions: Initialize[Task[ForkOptions]] = 
+	private[this] def forkOptions: Initialize[Task[ForkOptions]] =
 		(baseDirectory, javaOptions, outputStrategy, envVars, javaHome, connectInput) map {
 			(base, options, strategy, env, javaHomeDir, connectIn) =>
 				// bootJars is empty by default because only jars on the user's classpath should be on the boot classpath
@@ -460,7 +461,7 @@ object Defaults extends BuildCommon
 			val newConfig = config.copy(options = modifiedOpts)
 			val output = allTestGroupsTask(s, loadedTestFrameworks.value, testLoader.value, testGrouping.value, newConfig, fullClasspath.value, javaHome.value)
 			val processed =
-				for(out <- output) yield 
+				for(out <- output) yield
 					Tests.showResults(s.log, out, noTestsMessage(resolvedScoped.value))
 			Def.value(processed)
 		}
@@ -491,8 +492,8 @@ object Defaults extends BuildCommon
 				}
 		}
 		val output = Tests.foldTasks(groupTasks, config.parallel)
-		output map { out => 
-			val summaries = 
+		output map { out =>
+			val summaries =
 				runners map { case (tf, r) =>
 					Tests.Summary(frameworks(tf).name, r.done())
 				}
@@ -708,8 +709,11 @@ object Defaults extends BuildCommon
 
 	private[this] def exported(w: PrintWriter, command: String): Seq[String] => Unit = args =>
 		w.println( (command +: args).mkString(" ") )
-	private[this] def exported(s: TaskStreams, command: String): Seq[String] => Unit = args =>
-		exported(s.text("export"), command)
+	private[this] def exported(s: TaskStreams, command: String): Seq[String] => Unit = args => {
+		val w = s.text(ExportStream)
+		try exported(w, command)
+		finally w.close() // workaround for #937
+	}
 
 	@deprecated("Use inTask(compile)(compileInputsSettings)", "0.13.0")
 	def compileTaskSettings: Seq[Setting[_]] = inTask(compile)(compileInputsSettings)
@@ -717,10 +721,11 @@ object Defaults extends BuildCommon
 	def compileTask: Initialize[Task[inc.Analysis]] = Def.task { compileTaskImpl(streams.value, (compileInputs in compile).value) }
 	private[this] def compileTaskImpl(s: TaskStreams, ci: Compiler.Inputs): inc.Analysis =
 	{
-		lazy val x = s.text("export")
+		lazy val x = s.text(ExportStream)
 		def onArgs(cs: Compiler.Compilers) = cs.copy(scalac = cs.scalac.onArgs(exported(x, "scalac")), javac = cs.javac.onArgs(exported(x, "javac")))
 		val i = ci.copy(compilers = onArgs(ci.compilers))
-		Compiler(i,s.log)
+		try Compiler(i,s.log)
+		finally x.close() // workaround for #937
 	}
 	def compileIncSetupTask =
 		(dependencyClasspath, skip in compile, definesClass, compilerCache, streams, incOptions) map { (cp, skip, definesC, cache, s, incOptions) =>
@@ -882,7 +887,9 @@ object Classpaths
 		s.mapInitialize(init => Def.task { exportClasspath(streams.value, init.value) })
 	private[this] def exportClasspath(s: TaskStreams, cp: Classpath): Classpath =
 	{
-		s.text("export").println(Path.makeString(data(cp)))
+		val w = s.text(ExportStream)
+		try w.println(Path.makeString(data(cp)))
+		finally w.close() // workaround for #937
 		cp
 	}
 
@@ -1403,7 +1410,7 @@ object Classpaths
 		plugins.map("-Xplugin:" + _.getAbsolutePath).toSeq
 	}
 
-	private[this] lazy val internalCompilerPluginClasspath: Initialize[Task[Classpath]] = 
+	private[this] lazy val internalCompilerPluginClasspath: Initialize[Task[Classpath]] =
 		(thisProjectRef, settingsData, buildDependencies) flatMap { (ref, data, deps) =>
 			internalDependencies0(ref, CompilerPlugin, CompilerPlugin, data, deps)
 		}
@@ -1564,7 +1571,7 @@ trait BuildExtra extends BuildCommon
 		}
 	}
 	private[this] def inBase(name: String): Initialize[File] = Def.setting { baseDirectory.value / name }
-	
+
 	def externalIvyFile(file: Initialize[File] = inBase("ivy.xml"), iScala: Initialize[Option[IvyScala]] = ivyScala): Setting[Task[ModuleSettings]] =
 		moduleSettings := new IvyFileConfiguration(file.value, iScala.value, ivyValidate.value, managedScalaInstance.value)
 	def externalPom(file: Initialize[File] = inBase("pom.xml"), iScala: Initialize[Option[IvyScala]] = ivyScala): Setting[Task[ModuleSettings]] =

main/src/main/scala/sbt/Main.scala

@@ -307,7 +307,7 @@ object BuiltinCommands
 			kvs = Act.keyValues(structure)(lastOnly_keys._2)
 			f <- if(lastOnly_keys._1) success(() => s) else Aggregation.evaluatingParser(s, structure, show)(kvs)
 		} yield () => {
-			def export0(s: State): State = lastImpl(s, kvs, Some("export"))
+			def export0(s: State): State = lastImpl(s, kvs, Some(ExportStream))
 			val newS = try f() catch { case e: Exception =>
 				try export0(s)
 				finally { throw e }