WIP pipeline main works in sequential mode

```
/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/bin/java -Xmx1G -Xss1M "-javaagent:/Users/jz/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/183.2407.10/IntelliJ IDEA 2018.3 EAP.app/Contents/lib/idea_rt.jar=60195:/Users/jz/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/183.2407.10/IntelliJ IDEA 2018.3 EAP.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/tools.jar:/Users/jz/code/scala/build/quick/classes/compiler:/Users/jz/code/scala/build/quick/classes/library:/Users/jz/code/scala/build/quick/classes/reflect:/Users/jz/.ivy2/cache/org.apache.ant/ant/jars/ant-1.9.4.jar:/Users/jz/.ivy2/cache/org.apache.ant/ant-launcher/jars/ant-launcher-1.9.4.jar:/Users/jz/.ivy2/cache/org.scala-lang.modules/scala-asm/bundles/scala-asm-6.2.0-scala-2.jar:/Users/jz/.ivy2/cache/org.scala-lang.modules/scala-xml_2.12/bundles/scala-xml_2.12-1.0.6.jar:/Users/jz/.ivy2/cache/jline/jline/jars/jline-2.14.6.jar scala.tools.nsc.PipelineMain /code/scala-2.12.x/target/compiler/compile.args /code/scala-2.12.x/target/interactive/compile.args /code/scala-2.12.x/target/library/compile.args /code/scala-2.12.x/target/partest-extras/compile.args /code/scala-2.12.x/target/reflect/compile.args /code/scala-2.12.x/target/repl-jline/compile.args /code/scala-2.12.x/target/repl/compile.args /code/scala-2.12.x/target/scaladoc/compile.args /code/scala-2.12.x/target/scalap/compile.args
Round #1: /code/scala-2.12.x/target/library/compile.args
warning: there were 37 deprecation warnings (since 2.10.0)
warning: there were 24 deprecation warnings (since 2.11.0)
warning: there were 46 deprecation warnings (since 2.12.0)
warning: there were 107 deprecation warnings in total; re-run with -deprecation for details
four warnings found
Round #2: /code/scala-2.12.x/target/reflect/compile.args
warning: there was one deprecation warning
warning: there were three deprecation warnings (since 2.10.0)
warning: there were four deprecation warnings (since 2.10.1)
warning: there were 17 deprecation warnings (since 2.11.0)
warning: there were 15 deprecation warnings (since 2.12.0)
warning: there were 40 deprecation warnings in total; re-run with -deprecation for details
warning: there were four unchecked warnings; re-run with -unchecked for details
7 warnings found
Round #3: /code/scala-2.12.x/target/compiler/compile.args
warning: there were two deprecation warnings
warning: there were 12 deprecation warnings (since 2.10.0)
warning: there were 55 deprecation warnings (since 2.11.0)
warning: there were three deprecation warnings (since 2.11.2)
warning: there were 26 deprecation warnings (since 2.12.0)
warning: there was one deprecation warning (since 2.12.4)
warning: there was one deprecation warning (since 2.12.5)
warning: there were three deprecation warnings (since 2.12.7)
warning: there were 103 deprecation warnings in total; re-run with -deprecation for details
warning: there were 31 unchecked warnings; re-run with -unchecked for details
warning: there were 6 feature warnings; re-run with -feature for details
Round #4: /code/scala-2.12.x/target/interactive/compile.args
11 warnings found
warning: there were four deprecation warnings (since 2.11.0)
Round #4: /code/scala-2.12.x/target/scaladoc/compile.args
warning: there was one deprecation warning (since 2.12.0)
warning: there were 5 deprecation warnings in total; re-run with -deprecation for details
warning: there were two unchecked warnings; re-run with -unchecked for details
four warnings found
Round #4: /code/scala-2.12.x/target/scalap/compile.args
warning: there were two deprecation warnings (since 2.12.0); re-run with -deprecation for details
warning: there were two unchecked warnings; re-run with -unchecked for details
two warnings found
warning: there was one deprecation warning (since 2.12.0); re-run with -deprecation for details
Round #5: /code/scala-2.12.x/target/repl/compile.args
one warning found
warning: there were 10 deprecation warnings (since 2.11.0)
Round #6: /code/scala-2.12.x/target/repl-jline/compile.args
warning: there were three deprecation warnings (since 2.12.0)
warning: there was one deprecation warning (since 2.9.0)
warning: there were 14 deprecation warnings in total; re-run with -deprecation for details
four warnings found
Round #7: /code/scala-2.12.x/target/partest-extras/compile.args

```

Author: retronym

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

@@ -22,33 +22,40 @@ class PipelineMainClass {
   def process(args: Array[String]): Boolean = {
     reporter = new ConsoleReporter(new Settings(scalacError))
 
-    def commandFor(argFileArg: String): CompilerCommand = {
+    def commandFor(argFileArg: String): Task = {
       val ss   = new Settings(scalacError)
-      new CompilerCommand(args.toList, ss)
+      Task(argFileArg, new CompilerCommand(("@" + argFileArg) :: Nil, ss))
     }
-    val projects: List[CompilerCommand] = args.toList.map(commandFor)
-    val produces = mutable.HashMap[Path, CompilerCommand]()
+    val projects: List[Task] = args.toList.map(commandFor)
+    val produces = mutable.HashMap[Path, Task]()
     for (p <- projects) {
-      val outputDir = p.settings.outputDirs.getSingleOutput.get.file.toPath.toAbsolutePath.normalize()
+      val outputDir = p.command.settings.outputDirs.getSingleOutput.get.file.toPath.toAbsolutePath.normalize()
       produces(outputDir) = p
     }
-    val dependsOn = mutable.HashMap[CompilerCommand, List[CompilerCommand]]()
+    val dependsOn = mutable.HashMap[Task, List[Task]]()
     for (p <- projects) {
-      val value: Seq[String] = ClassPath.expandPath(p.settings.classpath.value, expandStar = true)
+      val value: Seq[String] = ClassPath.expandPath(p.command.settings.classpath.value, expandStar = true)
       dependsOn(p) = value.flatMap(s => produces.get(Paths.get(s).toAbsolutePath.normalize())).toList
     }
     var toProcess = projects.toList
-    val done = mutable.HashSet[CompilerCommand]()
+    val done = mutable.HashSet[Task]()
+    var round = 0
     while (toProcess.nonEmpty) {
+      round += 1
       val (nextRound, blocked) = toProcess.partition(x => dependsOn.getOrElse(x, Nil).forall(done))
+      if (nextRound.isEmpty) throw new RuntimeException("cyclic dependency")
       toProcess = blocked
       for (p <- nextRound) {
-        if (!compile(p)) return false
+        println(s"Round #$round: ${p.argsFile}")
+        if (!compile(p.command)) return false
         done += p
       }
     }
     true
   }
+  private case class Task(argsFile: String, command: CompilerCommand) {
+    override def toString: String = argsFile
+  }
 
   def compile(command: CompilerCommand): Boolean = {
     val compiler = newCompiler(command.settings)