Limit TaskProgress threads

I noticed some flickering in super shell progress lines and realized
that it was because there were multiple progress threads running
concurrently. This is problematic because each thread has a completely
different state so if each thread has an active task, the display will
flicker between the two tasks. I think this is caused primarily by
dynamic tasks. At least the example where I was seeing it was caused by
a dynamic task.

main/src/main/scala/sbt/EvaluateTask.scala

@@ -224,29 +224,33 @@ object EvaluateTask {
       structure: BuildStructure,
       state: State
   ): ExecuteProgress[Task] = {
-    val maker: Seq[Keys.TaskProgress] = getSetting(
-      Keys.progressReports,
-      Seq(),
-      extracted,
-      structure
-    )
-    val progressReporter = extracted.get(progressState in ThisBuild).map { ps =>
-      ps.reset()
-      ConsoleAppender.setShowProgress(true)
-      val appender = MainAppender.defaultScreen(StandardMain.console)
-      appender match {
-        case c: ConsoleAppender => c.setProgressState(ps)
-        case _                  =>
+    state.get(currentTaskProgress).map(_.progress).getOrElse {
+      val maker: Seq[Keys.TaskProgress] = getSetting(
+        Keys.progressReports,
+        Seq(),
+        extracted,
+        structure
+      )
+      val progressReporter = extracted.getOpt(progressState in ThisBuild).flatMap {
+        case Some(ps) =>
+          ps.reset()
+          ConsoleAppender.setShowProgress(true)
+          val appender = MainAppender.defaultScreen(StandardMain.console)
+          appender match {
+            case c: ConsoleAppender => c.setProgressState(ps)
+            case _                  =>
+          }
+          val log = LogManager.progressLogger(appender)
+          Some(new TaskProgress(log))
+        case _ => None
+      }
+      val reporters = maker.map(_.progress) ++ progressReporter ++
+        (if (SysProp.taskTimings) new TaskTimings(reportOnShutdown = false) :: Nil else Nil)
+      reporters match {
+        case xs if xs.isEmpty   => ExecuteProgress.empty[Task]
+        case xs if xs.size == 1 => xs.head
+        case xs                 => ExecuteProgress.aggregate[Task](xs)
       }
-      val log = LogManager.progressLogger(appender)
-      new TaskProgress(log)
-    }
-    val reporters = maker.map(_.progress) ++ progressReporter ++
-      (if (SysProp.taskTimings) new TaskTimings(reportOnShutdown = false) :: Nil else Nil)
-    reporters match {
-      case xs if xs.isEmpty   => ExecuteProgress.empty[Task]
-      case xs if xs.size == 1 => xs.head
-      case xs                 => ExecuteProgress.aggregate[Task](xs)
     }
   }
   // TODO - Should this pull from Global or from the project itself?

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

@@ -482,6 +482,7 @@ object Keys {
   object TaskProgress {
     def apply(progress: ExecuteProgress[Task]): TaskProgress = new TaskProgress(progress)
   }
+  private[sbt] val currentTaskProgress = AttributeKey[TaskProgress]("current-task-progress")
   val useSuperShell = settingKey[Boolean]("Enables (true) or disables the super shell.")
   val turbo = settingKey[Boolean]("Enables (true) or disables optional performance features.")
   // This key can be used to add custom ExecuteProgress instances

main/src/main/scala/sbt/MainLoop.scala

@@ -179,10 +179,18 @@ object MainLoop {
     val channelName = exec.source map (_.channelName)
     StandardMain.exchange publishEventMessage
       ExecStatusEvent("Processing", channelName, exec.execId, Vector())
-
     try {
       def process(): State = {
-        val newState = Command.process(exec.commandLine, state)
+        val progressState = state.get(sbt.Keys.currentTaskProgress) match {
+          case Some(_) => state
+          case _ =>
+            if (state.get(Keys.stateBuildStructure).isDefined) {
+              val extracted = Project.extract(state)
+              val progress = EvaluateTask.executeProgress(extracted, extracted.structure, state)
+              state.put(sbt.Keys.currentTaskProgress, new Keys.TaskProgress(progress))
+            } else state
+        }
+        val newState = Command.process(exec.commandLine, progressState)
         if (exec.commandLine.contains("session"))
           newState.get(hasCheckedMetaBuild).foreach(_.set(false))
         val doneEvent = ExecStatusEvent(
@@ -198,7 +206,8 @@ object MainLoop {
         } else { // send back a notification
           StandardMain.exchange publishEventMessage doneEvent
         }
-        newState
+        newState.get(sbt.Keys.currentTaskProgress).foreach(_.progress.stop())
+        newState.remove(sbt.Keys.currentTaskProgress)
       }
       // The split on space is to handle 'reboot full' and 'reboot'.
       state.currentCommand.flatMap(_.commandLine.trim.split(" ").headOption) match {