Preserve caches between interactive and client/server mode (#342)

We were incorrectly duplicating the JDK classpath as part of the application classpath when we spawned the Mill server from the Mill client. This makes the transmission of application classpath to the Mill server explicit via an environment variable, so we don't end up including random things from the client classloader hierarchy that we didn't expect

build.sc

@@ -316,7 +316,10 @@ object dev extends MillModule{
     val classpath = runClasspath().map(_.path.toString)
     val args = forkArgs().distinct
     val (shellArgs, cmdArgs) =
-      if (!scala.util.Properties.isWin) (args, args)
+      if (!scala.util.Properties.isWin) (
+        Seq("-DMILL_CLASSPATH=" + classpath.mkString(":")) ++ args,
+        Seq("-DMILL_CLASSPATH=" + classpath.mkString(";")) ++ args
+      )
       else (
         Seq("""-XX:VMOptionsFile="$( dirname "$0" )"/mill.vmoptions"""),
         Seq("""-XX:VMOptionsFile=%~dp0\mill.vmoptions""")
@@ -345,6 +348,7 @@ def release = T{
   val dest = T.ctx().dest
   val filename = if (scala.util.Properties.isWin) "mill.bat" else "mill"
   val args = Seq(
+    "-DMILL_CLASSPATH=$0",
     "-DMILL_VERSION=" + publishVersion()._2,
     // Workaround for Zinc/JNA bug
     // https://github.com/sbt/sbt/blame/6718803ee6023ab041b045a6988fafcfae9d15b5/main/src/main/scala/sbt/Main.scala#L130

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

@@ -11,20 +11,8 @@
 
 public class MillClientMain {
     static void initServer(String lockBase, boolean setJnaNoSys) throws IOException,URISyntaxException{
-        ArrayList<String> selfJars = new ArrayList<String>();
-        ClassLoader current = MillClientMain.class.getClassLoader();
-        while(current != null){
-            if (current instanceof java.net.URLClassLoader) {
-                URL[] urls = ((java.net.URLClassLoader) current).getURLs();
-                for (URL url: urls) {
-                    selfJars.add(new File(url.toURI()).getCanonicalPath());
-                }
-            }
-            current = current.getParent();
-        }
-        if (Util.isJava9OrAbove) {
-            selfJars.addAll(Arrays.asList(System.getProperty("java.class.path").split(File.pathSeparator)));
-        }
+        String[] selfJars = System.getProperty("MILL_CLASSPATH").split(File.pathSeparator);
+
         ArrayList<String> l = new java.util.ArrayList<String>();
         l.add("java");
         Properties props = System.getProperties();

main/src/mill/main/RunScript.scala

@@ -76,6 +76,7 @@ object RunScript{
                          log: Logger
                         ): Res[mill.define.BaseModule] = {
 
+    log.info("RunScript.evaluateRootModule")
     val (pkg, wrapper) = Util.pathToPackageWrapper(Seq(), path relativeTo wd)
 
     for {

scratch/build.sc

@@ -1,3 +1,3 @@
 def thingy = T {
-  1234567
+  12345678
 }