Avoid quadratic performance wrt classpath length

Author: retronym

src/compiler/scala/tools/nsc/PipelineMain.scala

@@ -234,7 +234,7 @@ class PipelineMainClass(label: String, parallelism: Int, strategy: BuildStrategy
           println(f" Wall Clock: ${timer.durationMs}%.0f ms")
       case Pipeline =>
         projects.foreach { p =>
-          val depsReady = Future.sequence(dependsOn.getOrElse(p, Nil).map(task => p.dependencyReadyFuture(task.t)))
+          val depsReady = Future.sequence(dependsOn.getOrElse(p, Nil).iterator.map(task => p.dependencyReadyFuture(task.t)))
           val f = for {
             _ <- depsReady
             _ <- {
@@ -348,10 +348,10 @@ class PipelineMainClass(label: String, parallelism: Int, strategy: BuildStrategy
     private def expand(s: command.settings.PathSetting): List[Path] = {
       ClassPath.expandPath(s.value, expandStar = true).map(s => Paths.get(s).toAbsolutePath.normalize())
     }
-    def classPath: Seq[Path] = expand(command.settings.classpath)
-    def macroClassPath: Seq[Path] = expand(command.settings.YmacroClasspath)
-    def macroClassPathSet: Set[Path] = macroClassPath.toSet
-    def pluginClassPath: Set[Path] = {
+    lazy val classPath: Seq[Path] = expand(command.settings.classpath)
+    lazy val macroClassPath: Seq[Path] = expand(command.settings.YmacroClasspath)
+    lazy val macroClassPathSet: Set[Path] = macroClassPath.toSet
+    lazy val pluginClassPath: Set[Path] = {
       def asPath(p: String) = ClassPath split p
 
       val paths = command.settings.plugin.value filter (_ != "") flatMap (s => asPath(s) map (s => Paths.get(s)))