Allow users to pass a custom output dir on the command-line

main/client/src/mill/main/client/OutFiles.java

@@ -8,7 +8,12 @@ public class OutFiles {
     /**
      * Path of the Mill `out/` folder
      */
-    final public static String out = "out";
+    final public static String defaultOut = "out";
+
+    /**
+     * Path of the Mill `out/` folder for Mill server-related internal files
+     */
+    final public static String serverOut = ".mill";
 
     /**
      * Path of the Mill "meta-build", used to compile the `build.sc` file so we can

runner/client/src/mill/runner/client/MillClientMain.java

@@ -41,9 +41,9 @@ public void initServer(String serverDir, boolean setJnaNoSys, Locks locks) throw
                     MillProcessLauncher.launchMillServer(serverDir, setJnaNoSys);
                 }
             };
-            int exitCode = launcher.acquireLocksAndRun(OutFiles.out).exitCode;
+            int exitCode = launcher.acquireLocksAndRun(OutFiles.serverOut).exitCode;
             if (exitCode == Util.ExitServerCodeWhenVersionMismatch()) {
-                exitCode = launcher.acquireLocksAndRun(OutFiles.out).exitCode;
+                exitCode = launcher.acquireLocksAndRun(OutFiles.serverOut).exitCode;
             }
             System.exit(exitCode);
         } catch (ServerCouldNotBeStarted e) {

runner/client/src/mill/runner/client/MillProcessLauncher.java

@@ -30,7 +30,7 @@ static int launchMillNoServer(String[] args) throws Exception {
         final String sig = String.format("%08x", UUID.randomUUID().hashCode());
 
         boolean interrupted = false;
-        final String sandbox = out + "/" + millNoServer + "-" + sig;
+        final String sandbox = serverOut + "/" + millNoServer + "-" + sig;
         try {
             return configureRunMillProcess(builder, sandbox).waitFor();
 

runner/src/mill/runner/CodeGen.scala

@@ -15,7 +15,8 @@ object CodeGen {
       allScriptCode: Map[os.Path, String],
       targetDest: os.Path,
       enclosingClasspath: Seq[os.Path],
-      millTopLevelProjectRoot: os.Path
+      millTopLevelProjectRoot: os.Path,
+      output: os.Path
   ): Unit = {
     for (scriptSource <- scriptSources) {
       val scriptPath = scriptSource.path
@@ -94,6 +95,7 @@ object CodeGen {
             projectRoot,
             enclosingClasspath,
             millTopLevelProjectRoot,
+            output,
             scriptPath,
             scriptFolderPath,
             childAliases,
@@ -112,6 +114,7 @@ object CodeGen {
       projectRoot: os.Path,
       enclosingClasspath: Seq[os.Path],
       millTopLevelProjectRoot: os.Path,
+      output: os.Path,
       scriptPath: os.Path,
       scriptFolderPath: os.Path,
       childAliases: String,
@@ -126,7 +129,8 @@ object CodeGen {
       segments,
       scriptFolderPath,
       enclosingClasspath,
-      millTopLevelProjectRoot
+      millTopLevelProjectRoot,
+      output
     )
 
     val instrument = new ObjectDataInstrument(scriptCode)
@@ -182,13 +186,15 @@ object CodeGen {
       segments: Seq[String],
       scriptFolderPath: os.Path,
       enclosingClasspath: Seq[os.Path],
-      millTopLevelProjectRoot: os.Path
+      millTopLevelProjectRoot: os.Path,
+      output: os.Path
   ): String = {
     s"""import _root_.mill.runner.MillBuildRootModule
        |@_root_.scala.annotation.nowarn
        |object MillMiscInfo extends MillBuildRootModule.MillMiscInfo(
        |  ${enclosingClasspath.map(p => literalize(p.toString))},
        |  ${literalize(scriptFolderPath.toString)},
+       |  ${literalize(output.toString)},
        |  ${literalize(millTopLevelProjectRoot.toString)},
        |  _root_.scala.Seq(${segments.map(pprint.Util.literalize(_)).mkString(", ")})
        |)

runner/src/mill/runner/FileImportGraph.scala

@@ -43,7 +43,11 @@ object FileImportGraph {
    * starting from `build.mill`, collecting the information necessary to
    * instantiate the [[MillRootModule]]
    */
-  def parseBuildFiles(topLevelProjectRoot: os.Path, projectRoot: os.Path): FileImportGraph = {
+  def parseBuildFiles(
+      topLevelProjectRoot: os.Path,
+      projectRoot: os.Path,
+      output: os.Path
+  ): FileImportGraph = {
     val seenScripts = mutable.Map.empty[os.Path, String]
     val seenIvy = mutable.Set.empty[String]
     val seenRepo = mutable.ListBuffer.empty[(String, os.Path)]
@@ -185,7 +189,7 @@ object FileImportGraph {
         projectRoot,
         followLinks = true,
         skip = p =>
-          p == projectRoot / out ||
+          p == output ||
             p == projectRoot / millBuild ||
             (os.isDir(p) && !os.exists(p / nestedBuildFileName))
       )

runner/src/mill/runner/MillBuildBootstrap.scala

@@ -8,7 +8,7 @@ import mill.eval.Evaluator
 import mill.main.RunScript
 import mill.resolve.SelectMode
 import mill.define.{BaseModule, Discover, Segments}
-import mill.main.client.OutFiles._
+import mill.main.client.OutFiles.{millBuild, millRunnerState}
 
 import java.net.URLClassLoader
 
@@ -30,6 +30,7 @@ import java.net.URLClassLoader
 @internal
 class MillBuildBootstrap(
     projectRoot: os.Path,
+    output: os.Path,
     home: os.Path,
     keepGoing: Boolean,
     imports: Seq[String],
@@ -46,15 +47,15 @@ class MillBuildBootstrap(
 ) {
   import MillBuildBootstrap._
 
-  val millBootClasspath: Seq[os.Path] = prepareMillBootClasspath(projectRoot / out)
+  val millBootClasspath: Seq[os.Path] = prepareMillBootClasspath(output)
   val millBootClasspathPathRefs: Seq[PathRef] = millBootClasspath.map(PathRef(_, quick = true))
 
   def evaluate(): Watching.Result[RunnerState] = CliImports.withValue(imports) {
     val runnerState = evaluateRec(0)
 
     for ((frame, depth) <- runnerState.frames.zipWithIndex) {
       os.write.over(
-        recOut(projectRoot, depth) / millRunnerState,
+        recOut(output, depth) / millRunnerState,
         upickle.default.write(frame.loggedData, indent = 4),
         createFolders = true
       )
@@ -102,7 +103,8 @@ class MillBuildBootstrap(
       } else {
         val parsedScriptFiles = FileImportGraph.parseBuildFiles(
           projectRoot,
-          recRoot(projectRoot, depth) / os.up
+          recRoot(projectRoot, depth) / os.up,
+          output
         )
 
         if (parsedScriptFiles.millImport) evaluateRec(depth + 1)
@@ -111,6 +113,7 @@ class MillBuildBootstrap(
             new MillBuildRootModule.BootstrapModule(
               projectRoot,
               recRoot(projectRoot, depth),
+              output,
               millBootClasspath
             )(
               mill.main.RootModule.Info(
@@ -340,8 +343,8 @@ class MillBuildBootstrap(
     mill.eval.EvaluatorImpl(
       home,
       projectRoot,
-      recOut(projectRoot, depth),
-      recOut(projectRoot, depth),
+      recOut(output, depth),
+      recOut(output, depth),
       rootModule,
       PrefixLogger(logger, "", tickerContext = bootLogPrefix),
       classLoaderSigHash = millClassloaderSigHash,
@@ -422,8 +425,8 @@ object MillBuildBootstrap {
     projectRoot / Seq.fill(depth)(millBuild)
   }
 
-  def recOut(projectRoot: os.Path, depth: Int): os.Path = {
-    projectRoot / out / Seq.fill(depth)(millBuild)
+  def recOut(output: os.Path, depth: Int): os.Path = {
+    output / Seq.fill(depth)(millBuild)
   }
 
 }

runner/src/mill/runner/MillBuildRootModule.scala

@@ -120,7 +120,8 @@ abstract class MillBuildRootModule()(implicit
         parsed.seenScripts,
         T.dest,
         millBuildRootModuleInfo.enclosingClasspath,
-        millBuildRootModuleInfo.topLevelProjectRoot
+        millBuildRootModuleInfo.topLevelProjectRoot,
+        millBuildRootModuleInfo.output
       )
       Result.Success(Seq(PathRef(T.dest)))
     }
@@ -264,12 +265,14 @@ object MillBuildRootModule {
   class BootstrapModule(
       topLevelProjectRoot0: os.Path,
       projectRoot: os.Path,
+      output: os.Path,
       enclosingClasspath: Seq[os.Path]
   )(implicit baseModuleInfo: RootModule.Info) extends MillBuildRootModule()(
         implicitly,
         MillBuildRootModule.Info(
           enclosingClasspath,
           projectRoot,
+          output,
           topLevelProjectRoot0
         )
       ) {
@@ -280,25 +283,29 @@ object MillBuildRootModule {
   case class Info(
       enclosingClasspath: Seq[os.Path],
       projectRoot: os.Path,
+      output: os.Path,
       topLevelProjectRoot: os.Path
   )
 
   def parseBuildFiles(millBuildRootModuleInfo: MillBuildRootModule.Info): FileImportGraph = {
     FileImportGraph.parseBuildFiles(
       millBuildRootModuleInfo.topLevelProjectRoot,
-      millBuildRootModuleInfo.projectRoot / os.up
+      millBuildRootModuleInfo.projectRoot / os.up,
+      millBuildRootModuleInfo.output
     )
   }
 
   class MillMiscInfo(
       enclosingClasspath: Seq[String],
       projectRoot: String,
+      output: String,
       topLevelProjectRoot: String,
       segments: Seq[String]
   ) {
     implicit lazy val millBuildRootModuleInfo: MillBuildRootModule.Info = MillBuildRootModule.Info(
       enclosingClasspath.map(os.Path(_)),
       os.Path(projectRoot),
+      os.Path(output),
       os.Path(topLevelProjectRoot)
     )
     implicit lazy val millBaseModuleInfo: RootModule.Info = RootModule.Info(

runner/src/mill/runner/MillCliConfig.scala

@@ -1,6 +1,8 @@
 package mill.runner
 
 import mainargs.{Flag, Leftover, arg}
+import mill.api.WorkspaceRoot
+import mill.main.client.OutFiles
 
 class MillCliConfig private (
     @arg(
@@ -10,6 +12,12 @@ class MillCliConfig private (
            where it looks for config and caches."""
     )
     val home: os.Path,
+    @arg(
+      short = 'o',
+      doc =
+        """(internal) The directory to write Mill tasks output to."""
+    )
+    val output: os.Path,
     // We need to keep it, otherwise, a given --repl would be silently parsed as target and result in misleading error messages.
     // Instead we fail programmatically when this flag is set.
     @deprecated("No longer supported.", "Mill 0.11.0-M8")
@@ -164,6 +172,7 @@ object MillCliConfig {
    */
   def apply(
       home: os.Path = mill.api.Ctx.defaultHome,
+      output: os.Path = defaultOutput,
       @deprecated("No longer supported.", "Mill 0.11.0-M8")
       repl: Flag = Flag(),
       noServer: Flag = Flag(),
@@ -188,6 +197,57 @@ object MillCliConfig {
       allowPositionalCommandArgs: Flag = Flag()
   ): MillCliConfig = new MillCliConfig(
     home = home,
+    output = output,
+    repl = repl,
+    noServer = noServer,
+    bsp = bsp,
+    showVersion = showVersion,
+    ringBell = ringBell,
+    disableTicker = disableTicker,
+    enableTicker = enableTicker,
+    debugLog = debugLog,
+    keepGoing = keepGoing,
+    extraSystemProperties = extraSystemProperties,
+    threadCountRaw = threadCountRaw,
+    imports = imports,
+    interactive = interactive,
+    help = help,
+    watch = watch,
+    silent = silent,
+    leftoverArgs = leftoverArgs,
+    color = color,
+    disableCallgraphInvalidation,
+    metaLevel = metaLevel,
+    allowPositionalCommandArgs = allowPositionalCommandArgs
+  )
+  @deprecated("Bin-compat shim", "Mill after 0.12.0-RC1")
+  def apply(
+      home: os.Path,
+      @deprecated("No longer supported.", "Mill 0.11.0-M8")
+      repl: Flag,
+      noServer: Flag,
+      bsp: Flag,
+      showVersion: Flag,
+      ringBell: Flag,
+      disableTicker: Flag,
+      enableTicker: Option[Boolean],
+      debugLog: Flag,
+      keepGoing: Flag,
+      extraSystemProperties: Map[String, String],
+      threadCountRaw: Option[Int],
+      imports: Seq[String],
+      interactive: Flag,
+      help: Flag,
+      watch: Flag,
+      silent: Flag,
+      leftoverArgs: Leftover[String],
+      color: Option[Boolean],
+      disableCallgraphInvalidation: Flag,
+      metaLevel: Option[Int],
+      allowPositionalCommandArgs: Flag
+  ): MillCliConfig = new MillCliConfig(
+    home = home,
+    output = defaultOutput,
     repl = repl,
     noServer = noServer,
     bsp = bsp,
@@ -236,6 +296,7 @@ object MillCliConfig {
       metaLevel: Option[Int]
   ): MillCliConfig = new MillCliConfig(
     home = home,
+    output = defaultOutput,
     repl = repl,
     noServer = noServer,
     bsp = bsp,
@@ -285,6 +346,7 @@ object MillCliConfig {
       predefFile: Option[os.Path]
   ): MillCliConfig = apply(
     home,
+    output = defaultOutput,
     repl,
     noServer,
     bsp,
@@ -304,6 +366,9 @@ object MillCliConfig {
     leftoverArgs,
     color
   )
+
+  private def defaultOutput: os.Path =
+    os.Path(OutFiles.defaultOut, WorkspaceRoot.workspaceRoot)
 }
 
 import mainargs.ParserForClass

runner/src/mill/runner/MillMain.scala

@@ -8,6 +8,7 @@ import mill.java9rtexport.Export
 import mill.api.{MillException, SystemStreams, WorkspaceRoot, internal}
 import mill.bsp.{BspContext, BspServerResult}
 import mill.main.BuildInfo
+import mill.main.client.OutFiles
 import mill.util.PrintLogger
 
 import java.lang.reflect.InvocationTargetException
@@ -224,6 +225,7 @@ object MillMain {
 
                       new MillBuildBootstrap(
                         projectRoot = WorkspaceRoot.workspaceRoot,
+                        output = config.output,
                         home = config.home,
                         keepGoing = config.keepGoing.value,
                         imports = config.imports,