Run scripted tests in parallel

Add binary-compatible methods to run scripted tests in parallel using
parallel collections. Parallel collections are not tuned and a default
of 4 cores is used for the `ForkJoinPool`. This can be a matter of
experimentation in the future but for now I prefer to stay with it.

The non-parallel methods are not affected by this change.

The changes to the scripted plugin have not been used, only the sbt
scripted plugin is using `runInParallel`. In the future, this change can
also happen so that plugin authors can benefit from parallel sbt
testing. This is not a priority for me now :)

project/Scripted.scala

@@ -89,12 +89,12 @@ object Scripted {
 
   // Interface to cross class loader
   type SbtScriptedRunner = {
-    def run(resourceBaseDirectory: File,
-            bufferLog: Boolean,
-            tests: Array[String],
-            bootProperties: File,
-            launchOpts: Array[String],
-            prescripted: java.util.List[File]): Unit
+    def runInParallel(resourceBaseDirectory: File,
+                      bufferLog: Boolean,
+                      tests: Array[String],
+                      bootProperties: File,
+                      launchOpts: Array[String],
+                      prescripted: java.util.List[File]): Unit
   }
 
   def doScripted(launcher: File,
@@ -120,7 +120,12 @@ object Scripted {
         def get(x: Int): sbt.File = ???
         def size(): Int = 0
       }
-      bridge.run(sourcePath, bufferLog, args.toArray, launcher, launchOpts.toArray, callback)
+      bridge.runInParallel(sourcePath,
+                           bufferLog,
+                           args.toArray,
+                           launcher,
+                           launchOpts.toArray,
+                           callback)
     } catch { case ite: java.lang.reflect.InvocationTargetException => throw ite.getCause }
   }
 }

scripted/sbt/src/main/scala/sbt/test/ScriptedTests.scala

@@ -8,21 +8,21 @@ package test
 import java.io.File
 
 import scala.util.control.NonFatal
-
 import sbt.internal.scripted.{
   CommentHandler,
   FileCommands,
   ScriptRunner,
-  TestScriptParser,
-  TestException
+  TestException,
+  TestScriptParser
 }
 import sbt.io.{ DirectoryFilter, HiddenFileFilter }
 import sbt.io.IO.wrapNull
 import sbt.internal.io.Resources
-
 import sbt.internal.util.{ BufferedLogger, ConsoleLogger, FullLogger }
 import sbt.util.{ AbstractLogger, Logger }
 
+import scala.collection.parallel.mutable.ParSeq
+
 final class ScriptedTests(resourceBaseDirectory: File,
                           bufferLog: Boolean,
                           launcher: File,
@@ -40,7 +40,7 @@ final class ScriptedTests(resourceBaseDirectory: File,
   def scriptedTest(group: String,
                    name: String,
                    prescripted: File => Unit,
-                   log: Logger): Seq[() => Option[String]] = {
+                   log: Logger): Seq[TestRunner] = {
     import sbt.io.syntax._
     for (groupDir <- (resourceBaseDirectory * group).get; nme <- (groupDir * name).get) yield {
       val g = groupDir.getName
@@ -119,6 +119,10 @@ final class ScriptedTests(resourceBaseDirectory: File,
 }
 
 object ScriptedTests extends ScriptedRunner {
+
+  /** Represents the function that runs the scripted tests. */
+  type TestRunner = () => Option[String]
+
   val emptyCallback: File => Unit = { _ =>
     ()
   }
@@ -136,8 +140,6 @@ object ScriptedTests extends ScriptedRunner {
 }
 
 class ScriptedRunner {
-  import ScriptedTests._
-
   // This is called by project/Scripted.scala
   // Using java.util.List[File] to encode File => Unit
   def run(resourceBaseDirectory: File,
@@ -166,17 +168,56 @@ class ScriptedRunner {
     runAll(allTests)
   }
 
-  def runAll(tests: Seq[() => Option[String]]): Unit = {
+  def runInParallel(resourceBaseDirectory: File,
+                    bufferLog: Boolean,
+                    tests: Array[String],
+                    bootProperties: File,
+                    launchOpts: Array[String],
+                    prescripted: java.util.List[File]): Unit = {
+    val logger = ConsoleLogger()
+    val addTestFile = (f: File) => { prescripted.add(f); () }
+    runInParallel(resourceBaseDirectory,
+                  bufferLog,
+                  tests,
+                  logger,
+                  bootProperties,
+                  launchOpts,
+                  addTestFile)
+  }
+
+  def runInParallel(
+      resourceBaseDirectory: File,
+      bufferLog: Boolean,
+      tests: Array[String],
+      logger: AbstractLogger,
+      bootProperties: File,
+      launchOpts: Array[String],
+      prescripted: File => Unit
+  ): Unit = {
+    val runner = new ScriptedTests(resourceBaseDirectory, bufferLog, bootProperties, launchOpts)
+    val scriptedTests = get(tests, resourceBaseDirectory, logger)
+    val scriptedTestRunners = scriptedTests
+      .flatMap(t => runner.scriptedTest(t.group, t.name, prescripted, logger))
+    runAllInParallel(scriptedTestRunners.toParArray)
+  }
+
+  def runAll(tests: Seq[ScriptedTests.TestRunner]): Unit = {
     val errors = for (test <- tests; err <- test()) yield err
     if (errors.nonEmpty)
       sys.error(errors.mkString("Failed tests:\n\t", "\n\t", "\n"))
   }
 
+  def runAllInParallel(tests: ParSeq[ScriptedTests.TestRunner]): Unit = {
+    val executedTests = tests.flatMap(test => test.apply().toList).toList
+    if (executedTests.nonEmpty)
+      sys.error(executedTests.mkString("Failed tests:\n\t", "\n\t", "\n"))
+  }
+
   def get(tests: Seq[String], baseDirectory: File, log: Logger): Seq[ScriptedTest] =
     if (tests.isEmpty) listTests(baseDirectory, log) else parseTests(tests)
 
   def listTests(baseDirectory: File, log: Logger): Seq[ScriptedTest] =
-    (new ListTests(baseDirectory, _ => true, log)).listTests
+    new ListTests(baseDirectory, _ => true, log).listTests
 
   def parseTests(in: Seq[String]): Seq[ScriptedTest] =
     for (testString <- in) yield {