Fix #4143: Ignore lines printed before the start of the test

Author: nicolasstucki

compiler/test/dotty/tools/vulpix/ChildJVMMain.java

@@ -9,6 +9,7 @@
 import java.lang.reflect.Method;
 
 public class ChildJVMMain {
+    static final String MessageStart = "##THIS IS THE START FOR ME, HELLO##";
     static final String MessageEnd = "##THIS IS THE END FOR ME, GOODBYE##";
 
     private static void runMain(String dir) throws Exception {
@@ -23,6 +24,9 @@ private static void runMain(String dir) throws Exception {
         Class<?> cls = ucl.loadClass("Test");
         Method meth = cls.getMethod("main", String[].class);
         Object[] args = new Object[]{ new String[]{ "jvm" } };
+
+        System.out.println(MessageStart);
+
         meth.invoke(null, args);
     }
 

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -600,7 +600,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
       else runMain(testSource.runClassPath) match {
         case Success(_) if !checkFile.isDefined || !checkFile.get.exists => // success!
         case Success(output) => {
-          val outputLines = output.lines.filterNot(_.startsWith("Picked up _JAVA_OPTIONS")).toArray :+ DiffUtil.EOF
+          val outputLines = output.lines.toArray :+ DiffUtil.EOF
           val checkLines: Array[String] = Source.fromFile(checkFile.get).getLines().toArray :+ DiffUtil.EOF
           val sourceTitle = testSource.title
 

compiler/test/dotty/tools/vulpix/RunnerOrchestration.scala

@@ -118,7 +118,13 @@ trait RunnerOrchestration {
           if (childStdout eq null)
             childStdout = new BufferedReader(new InputStreamReader(process.getInputStream))
 
-          var childOutput = childStdout.readLine()
+          var childOutput: String = childStdout.readLine()
+
+          // Discard all messages until the test starts
+          while (childOutput != ChildJVMMain.MessageStart && childOutput != null)
+            childOutput = childStdout.readLine()
+          childOutput = childStdout.readLine()
+
           while (childOutput != ChildJVMMain.MessageEnd && childOutput != null) {
             sb.append(childOutput)
             sb += '\n'