Issue #6206: Add withParallel Scala.js linker option

libs/scalajslib/api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala

@@ -19,7 +19,8 @@ private[scalajslib] trait ScalaJSWorkerApi extends AutoCloseable {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      experimentalUseWebAssembly: Boolean
+      experimentalUseWebAssembly: Boolean,
+      parallel: Boolean
   ): Either[String, Report]
 
   def run(config: JsEnvConfig, report: Report): Unit

libs/scalajslib/src/mill/scalajslib/ScalaJSModule.scala

@@ -28,6 +28,7 @@ trait ScalaJSModule extends scalalib.ScalaModule with ScalaJSModuleApi { outer =
     override def esFeatures = outer.esFeatures()
     override def jsEnvConfig: T[JsEnvConfig] = outer.jsEnvConfig()
     override def scalaJSOptimizer: T[Boolean] = outer.scalaJSOptimizer()
+    override def scalaJSParallel: T[Boolean] = outer.scalaJSParallel()
   }
 
   def scalaJSBinaryVersion = Task { JvmWorkerUtil.scalaJSBinaryVersion(scalaJSVersion()) }
@@ -133,7 +134,8 @@ trait ScalaJSModule extends scalalib.ScalaModule with ScalaJSModuleApi { outer =
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly()
+      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly(),
+      parallel = scalaJSParallel()
     )
   }
 
@@ -185,7 +187,8 @@ trait ScalaJSModule extends scalalib.ScalaModule with ScalaJSModuleApi { outer =
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      experimentalUseWebAssembly: Boolean
+      experimentalUseWebAssembly: Boolean,
+      parallel: Boolean
   )(using ctx: mill.api.TaskCtx): Result[Report] = {
     val outputPath = ctx.dest
 
@@ -207,7 +210,8 @@ trait ScalaJSModule extends scalalib.ScalaModule with ScalaJSModuleApi { outer =
       outputPatterns = outputPatterns,
       minify = minify,
       importMap = importMap,
-      experimentalUseWebAssembly = experimentalUseWebAssembly
+      experimentalUseWebAssembly = experimentalUseWebAssembly,
+      parallel = parallel
     )
   }
 
@@ -281,6 +285,12 @@ trait ScalaJSModule extends scalalib.ScalaModule with ScalaJSModuleApi { outer =
 
   def scalaJSOptimizer: T[Boolean] = Task { true }
 
+  /**
+   * Whether Scala.js operations that can be parallelized should be parallelized.
+   *  On the JavaScript platform, this does not have any effect.
+   */
+  def scalaJSParallel: T[Boolean] = Task { true }
+
   def scalaJSImportMap: T[Seq[ESModuleImportMapping]] = Task {
     Seq.empty[ESModuleImportMapping]
   }
@@ -382,7 +392,8 @@ trait TestScalaJSModule extends ScalaJSModule with TestModule {
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly()
+      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly(),
+      parallel = scalaJSParallel()
     )
   }
 

libs/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala

@@ -206,7 +206,8 @@ private[scalajslib] class ScalaJSWorker(jobs: Int)
       outputPatterns: api.OutputPatterns,
       minify: Boolean,
       importMap: Seq[api.ESModuleImportMapping],
-      experimentalUseWebAssembly: Boolean
+      experimentalUseWebAssembly: Boolean,
+      parallel: Boolean
   ): Result[api.Report] = {
     withValue(toolsClasspath) { case (_, bridge) =>
       bridge.link(
@@ -224,7 +225,8 @@ private[scalajslib] class ScalaJSWorker(jobs: Int)
         outputPatterns = toWorkerApi(outputPatterns),
         minify = minify,
         importMap = importMap.map(toWorkerApi),
-        experimentalUseWebAssembly = experimentalUseWebAssembly
+        experimentalUseWebAssembly = experimentalUseWebAssembly,
+        parallel = parallel
       ) match {
         case Right(report) => Result.Success(fromWorkerApi(report))
         case Left(message) => Result.Failure(message)

libs/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala

@@ -37,7 +37,8 @@ class ScalaJSWorkerImpl(jobs: Int) extends ScalaJSWorkerApi {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       dest: File,
-      experimentalUseWebAssembly: Boolean
+      experimentalUseWebAssembly: Boolean,
+      parallel: Boolean
   )
   private def minorIsGreaterThanOrEqual(number: Int) = ScalaJSVersions.current match {
     case s"1.$n.$_" if n.toIntOption.exists(_ < number) => false
@@ -104,6 +105,7 @@ class ScalaJSWorkerImpl(jobs: Int) extends ScalaJSWorkerApi {
         .withModuleKind(scalaJSModuleKind)
         .withESFeatures(scalaJSESFeatures)
         .withSourceMap(input.sourceMap)
+        .withParallel(input.parallel)
 
       def withModuleSplitStyle_1_3_plus(config: StandardConfig): StandardConfig = {
         config.withModuleSplitStyle(
@@ -192,7 +194,8 @@ class ScalaJSWorkerImpl(jobs: Int) extends ScalaJSWorkerApi {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      experimentalUseWebAssembly: Boolean
+      experimentalUseWebAssembly: Boolean,
+      parallel: Boolean
   ): Either[String, Report] = ScalaJSLinker.withValue(LinkerInput(
     isFullLinkJS = isFullLinkJS,
     optimizer = optimizer,
@@ -203,7 +206,8 @@ class ScalaJSWorkerImpl(jobs: Int) extends ScalaJSWorkerApi {
     outputPatterns = outputPatterns,
     minify = minify,
     dest = dest,
-    experimentalUseWebAssembly = experimentalUseWebAssembly
+    experimentalUseWebAssembly = experimentalUseWebAssembly,
+    parallel = parallel
   )) { (linker, irFileCacheCache) =>
     // On Scala.js 1.2- we want to use the legacy mode either way since
     // the new mode is not supported and in tests we always use legacy = false