add 'about' command with sbt versions and Scala versions

main/CommandSupport.scala

@@ -33,6 +33,7 @@ object CommandSupport
 	/** The prefix used to identify a request to execute the remaining input on source changes.*/
 	val ContinuousExecutePrefix = "~"
 	val HelpCommand = "help"
+	val AboutCommand = "about"
 	val TasksCommand = "tasks"
 	val ProjectCommand = "project"
 	val ProjectsCommand = "projects"
@@ -121,6 +122,9 @@ Tasks produce values.  Use the 'show' command to run the task and print the resu
 	def helpBrief = (HelpCommand + " command*", "Displays this help message or prints detailed help on requested commands.")
 	def helpDetailed = "If an argument is provided, this prints detailed help for that command.\nOtherwise, this prints a help summary."
 
+	def aboutBrief = "Displays basic information about sbt and the build."
+	def aboutDetailed = aboutBrief
+
 	def projectBrief = (ProjectCommand + " [project]", "Displays the current project or changes to the provided `project`.")
 	def projectDetailed =
 ProjectCommand +

main/Main.scala

@@ -79,7 +79,7 @@ object BuiltinCommands
 
 	def ConsoleCommands: Seq[Command] = Seq(ignore, exit, IvyConsole.command, act, nop)
 	def ScriptCommands: Seq[Command] = Seq(ignore, exit, Script.command, act, nop)
-	def DefaultCommands: Seq[Command] = Seq(ignore, help, reboot, read, history, continuous, exit, loadProject, loadProjectImpl, loadFailed, Cross.crossBuild, Cross.switchVersion,
+	def DefaultCommands: Seq[Command] = Seq(ignore, help, about, reboot, read, history, continuous, exit, loadProject, loadProjectImpl, loadFailed, Cross.crossBuild, Cross.switchVersion,
 		projects, project, setOnFailure, clearOnFailure, ifLast, multi, shell, set, tasks, inspect, eval, alias, append, last, lastGrep, nop, sessionCommand, act)
 	def DefaultBootCommands: Seq[String] = LoadProject :: (IfLast + " " + Shell) :: Nil
 
@@ -90,6 +90,7 @@ object BuiltinCommands
 		h.detail match { case (commands, value) => if( selected exists commands ) Some(value) else None }
 
 	def help = Command.make(HelpCommand, helpBrief, helpDetailed)(helpParser)
+	def about = Command.command(AboutCommand, aboutBrief, aboutDetailed) { s => logger(s).info(aboutString(s)); s }
 
 	def helpParser(s: State) =
 	{
@@ -109,6 +110,26 @@ object BuiltinCommands
 		System.out.println(message)
 		s
 	}
+	def sbtVersion(s: State): String = s.configuration.provider.id.version
+	def scalaVersion(s: State): String = s.configuration.provider.scalaProvider.version
+	def aboutString(s: State): String =
+	{
+		"This is sbt " + sbtVersion(s) + "\n" +
+		aboutProject(s) +
+		"sbt, sbt plugins, and build definitions are using Scala " + scalaVersion(s)
+	}
+	def aboutProject(s: State): String =
+		if(Project.isProjectLoaded(s))
+		{
+			val e = Project.extract(s)
+			val current = "The current project is " + Project.display(e.currentRef) + "\n"
+			val built = e.getOpt(Keys.scalaVersion) match {
+				case Some(sv) => "The current project is built against Scala " + sv + "\n"
+				case None => ""
+			}
+			current + built
+		}
+		else "No project is currently loaded.\n"
 
 	def tasks = Command.command(TasksCommand, tasksBrief, tasksDetailed) { s =>
 		System.out.println(tasksPreamble)

main/Project.scala

@@ -68,11 +68,9 @@ final case class Extracted(structure: BuildStructure, session: SessionSettings,
 	lazy val currentProject = currentUnit defined currentRef.project
 	lazy val currentLoader: ClassLoader = currentUnit.loader
 	def get[T](key: ScopedTask[T]): Task[T] = get(key.task)
-	def get[T](key: ScopedSetting[T]): T =
+	def get[T](key: ScopedSetting[T]): T = getOrError(inCurrent(key), key.key)
-	{
+	def getOpt[T](key: ScopedSetting[T]): Option[T] = structure.data.get(inCurrent(key), key.key)
-		val scope = if(key.scope.project == This) key.scope.copy(project = Select(currentRef)) else key.scope
+	private[this] def inCurrent[T](key: ScopedSetting[T]): Scope  =  if(key.scope.project == This) key.scope.copy(project = Select(currentRef)) else key.scope
-		getOrError(scope, key.key)
-	}
 	def evalTask[T](key: ScopedTask[T], state: State): T =
 	{
 			import EvaluateTask._