Universal Main

build.sc

@@ -309,6 +309,7 @@ object main extends MillModule {
         s"""
            |package mill
            |
+           |/** Generated by mill. */
            |object BuildInfo {
            |  /** Scala version used to compile mill core. */
            |  val scalaVersion = "$scalaVersion"
@@ -341,6 +342,21 @@ object main extends MillModule {
     override def ivyDeps = Agg(
       Deps.ipcsocketExcludingJna
     )
+    def generatedBuildInfo = T{
+      val dest = T.dest
+      val code =
+        s"""package mill.main.client;
+           |
+           |/** Generated by mill. */
+           |public class BuildInfo {
+           |  /** Mill version. */
+           |  public static String millVersion() { return "${millVersion()}"; }
+           |}
+           |""".stripMargin
+      os.write(dest / "mill" / "main" / "client" / "BuildInfo.java", code, createFolders = true)
+      Seq(PathRef(dest))
+    }
+    override def generatedSources: T[Seq[PathRef]] = super.generatedSources() ++ generatedBuildInfo()
     object test extends Tests with TestModule.Junit4 {
       override def ivyDeps = Agg(Deps.junitInterface, Deps.lambdaTest)
     }
@@ -841,7 +857,7 @@ def launcherScript(
     shellClassPath: Agg[String],
     cmdClassPath: Agg[String]
 ) = {
-  val millMainClass = "mill.MillMain"
+  val millMainClass = "mill.main.client.MillClientMain"
   val millClientMainClass = "mill.main.client.MillClientMain"
 
   mill.modules.Jvm.universalScript(
@@ -875,6 +891,7 @@ def launcherScript(
          |        "-X"*) mill_jvm_opts="$${mill_jvm_opts} $$line"
          |      esac
          |    done <"$$mill_jvm_opts_file"
+         |    mill_jvm_opts="$${mill_jvm_opts} -Dmill.jvm_opts_applied=true"
          |  fi
          |}
          |
@@ -1023,7 +1040,7 @@ object dev extends MillModule {
 
   def run(args: String*) = T.command {
     args match {
-      case Nil => mill.eval.Result.Failure("Need to pass in cwd as first argument to dev.run")
+      case Nil => mill.api.Result.Failure("Need to pass in cwd as first argument to dev.run")
       case wd0 +: rest =>
         val wd = os.Path(wd0, os.pwd)
         os.makeDir.all(wd)
@@ -1032,7 +1049,7 @@ object dev extends MillModule {
           forkEnv(),
           workingDir = wd
         )
-        mill.eval.Result.Success(())
+        mill.api.Result.Success(())
     }
 
   }

main/client/src/mill/main/client/IsolatedMillMainLoader.java

@@ -0,0 +1,80 @@
+package mill.main.client;
+
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+
+class IsolatedMillMainLoader {
+
+    public static class LoadResult {
+
+        public final Optional<Method> millMainMethod;
+        public final boolean canLoad;
+        public final long loadTime;
+
+        public LoadResult(Optional<Method> millMainMethod, final long loadTime) {
+            this.millMainMethod = millMainMethod;
+            this.canLoad = millMainMethod.isPresent();
+            this.loadTime = loadTime;
+        }
+    }
+
+    private static Optional<LoadResult> canLoad = Optional.empty();
+
+    public static LoadResult load() {
+        if (canLoad.isPresent()) {
+            return canLoad.get();
+        } else {
+            long startTime = System.currentTimeMillis();
+            Optional<Method> millMainMethod = Optional.empty();
+            try {
+                Class<?> millMainClass = IsolatedMillMainLoader.class.getClassLoader().loadClass("mill.MillMain");
+                Method mainMethod = millMainClass.getMethod("main", String[].class);
+                millMainMethod = Optional.of(mainMethod);
+            } catch (ClassNotFoundException | NoSuchMethodException e) {
+                millMainMethod = Optional.empty();
+            }
+
+            long loadTime = System.currentTimeMillis() - startTime;
+            LoadResult result = new LoadResult(millMainMethod, loadTime);
+            canLoad = Optional.of(result);
+            return result;
+        }
+    }
+
+    public static void runMain(String[] args) throws Exception {
+        LoadResult loadResult = load();
+        if (loadResult.millMainMethod.isPresent()) {
+            if (!MillEnv.millJvmOptsAlreadyApplied() && MillEnv.millJvmOptsFile().exists()) {
+//                System.err.println("Warning: Settings from file `" + propOptsFile + "` are currently ignored.");
+                System.err.println("Launching Mill as sub-process ...");
+                int exitVal = launchMillAsSubProcess(args);
+                System.exit(exitVal);
+            } else {
+                // launch mill in-process
+                // it will call System.exit for us
+                Method mainMethod = loadResult.millMainMethod.get();
+                mainMethod.invoke(null, new Object[]{args});
+            }
+        } else {
+            throw new RuntimeException("Cannot load mill.MillMain class");
+        }
+    }
+
+    private static int launchMillAsSubProcess(String[] args) throws Exception {
+        boolean setJnaNoSys = System.getProperty("jna.nosys") == null;
+
+        List<String> l = new ArrayList<>();
+        l.addAll(MillEnv.millLaunchJvmCommand(setJnaNoSys));
+        l.add("mill.MillMain");
+        l.addAll(Arrays.asList(args));
+
+        Process running = new ProcessBuilder()
+            .command(l)
+            .inheritIO()
+            .start();
+        return running.waitFor();
+    }
+}