Fix MILL_CLASSPATH for Windows (#354)

* Use comma as separator in MILL_CLASSPATH

There is no need to use environment-specific separator, especially since

 - other variables are using commas anyway, and
 - it is not sent to any system-level command

* Fix whitespace

* Use MILL_CLASSPATH for Windows

* Use vm options file for client on windows

* Remove overzealous distinct

* Clean up unnecessary ceremony

build.sc

@@ -294,12 +294,18 @@ def launcherScript(shellJvmArgs: Seq[String],
 object dev extends MillModule{
   def moduleDeps = Seq(scalalib, scalajslib)
   def forkArgs =
-    (scalalib.testArgs() ++
-     scalajslib.testArgs() ++
-     scalalib.worker.testArgs() ++
-     // Workaround for Zinc/JNA bug
-     // https://github.com/sbt/sbt/blame/6718803ee6023ab041b045a6988fafcfae9d15b5/main/src/main/scala/sbt/Main.scala#L130
-     Seq("-Djna.nosys=true", "-DMILL_VERSION=" + build.publishVersion()._2)).distinct
+    (
+      scalalib.testArgs() ++
+      scalajslib.testArgs() ++
+      scalalib.worker.testArgs() ++
+      // Workaround for Zinc/JNA bug
+      // https://github.com/sbt/sbt/blame/6718803ee6023ab041b045a6988fafcfae9d15b5/main/src/main/scala/sbt/Main.scala#L130
+      Seq(
+        "-Djna.nosys=true",
+        "-DMILL_VERSION=" + build.publishVersion()._2,
+        "-DMILL_CLASSPATH=" + runClasspath().map(_.path.toString).mkString(",")
+      )
+    ).distinct
 
   // Pass dev.assembly VM options via file in Window due to small max args limit
   def windowsVmOptions(taskName: String, batch: Path, args: Seq[String])(implicit ctx: mill.util.Ctx) = {
@@ -339,11 +345,11 @@ object dev extends MillModule{
 
   def prependShellScript = T{
     val classpath = runClasspath().map(_.path.toString)
-    val args = forkArgs().distinct
+    val args = forkArgs()
     val (shellArgs, cmdArgs) =
       if (!scala.util.Properties.isWin) (
-        Seq("-DMILL_CLASSPATH=" + classpath.mkString(":")) ++ args,
-        Seq("-DMILL_CLASSPATH=" + classpath.mkString(";")) ++ args
+        args,
+        args
       )
       else (
         Seq("""-XX:VMOptionsFile="$( dirname "$0" )"/mill.vmoptions"""),

main/client/src/mill/main/client/MillClientMain.java

@@ -11,25 +11,36 @@
 
 public class MillClientMain {
     static void initServer(String lockBase, boolean setJnaNoSys) throws IOException,URISyntaxException{
-        String[] selfJars = System.getProperty("MILL_CLASSPATH").split(File.pathSeparator);
+        String[] selfJars = System.getProperty("MILL_CLASSPATH").split(",");
 
-        ArrayList<String> l = new java.util.ArrayList<String>();
+        List<String> l = new ArrayList<>();
+        List<String> vmOptions = new ArrayList<>();
         l.add("java");
-        Properties props = System.getProperties();
-        Iterator<String> keys = props.stringPropertyNames().iterator();
-        while(keys.hasNext()){
-            String k = keys.next();
-            if (k.startsWith("MILL_")) l.add("-D" + k + "=" + props.getProperty(k));
+        final Properties props = System.getProperties();
+        for(final String k: props.stringPropertyNames()){
+            if (k.startsWith("MILL_") && !"MILL_CLASSPATH".equals(k)) {
+                vmOptions.add("-D" + k + "=" + props.getProperty(k));
+            }
         }
         if (setJnaNoSys) {
-            l.add("-Djna.nosys=true");
+            vmOptions.add("-Djna.nosys=true");
+        }
+        if(!Util.isWindows){
+            l.addAll(vmOptions);
+        } else {
+            final File vmOptionsFile = new File(lockBase, "vmoptions");
+            try (PrintWriter out = new PrintWriter(vmOptionsFile)) {
+                for(String opt: vmOptions)
+                out.println(opt);
+            }
+            l.add("-XX:VMOptionsFile=" + vmOptionsFile.getCanonicalPath());
         }
         l.add("-cp");
         l.add(String.join(File.pathSeparator, selfJars));
         l.add("mill.main.MillServerMain");
         l.add(lockBase);
 
-        new java.lang.ProcessBuilder()
+        new ProcessBuilder()
                 .command(l)
                 .redirectOutput(new java.io.File(lockBase + "/logs"))
                 .redirectError(new java.io.File(lockBase + "/logs"))