Support Scala.js minify via scalaJSMinify: Target[String] (#3094)

`minify` is a new feature released in Scala.js 1.16.0
https://www.scala-js.org/news/2024/03/19/announcing-scalajs-1.16.0

Pull Request: #3094

build.sc

@@ -70,7 +70,7 @@ object Deps {
   val testScala33Version = "3.3.1"
 
   object Scalajs_1 {
-    val scalaJsVersion = "1.15.0"
+    val scalaJsVersion = "1.16.0"
     val scalajsEnvJsdomNodejs = ivy"org.scala-js::scalajs-env-jsdom-nodejs:1.1.0"
     val scalajsEnvExoegoJsdomNodejs = ivy"net.exoego::scalajs-env-jsdom-nodejs:2.1.0"
     val scalajsEnvNodejs = ivy"org.scala-js::scalajs-env-nodejs:1.4.0"

scalajslib/src/mill/scalajslib/ScalaJSModule.scala

@@ -129,7 +129,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleKind = moduleKind(),
       esFeatures = esFeatures(),
       moduleSplitStyle = moduleSplitStyle(),
-      outputPatterns = scalaJSOutputPatterns()
+      outputPatterns = scalaJSOutputPatterns(),
+      minify = scalaJSMinify()
     )
   }
 
@@ -170,7 +171,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleKind: ModuleKind,
       esFeatures: ESFeatures,
       moduleSplitStyle: ModuleSplitStyle,
-      outputPatterns: OutputPatterns
+      outputPatterns: OutputPatterns,
+      minify: Boolean
   )(implicit ctx: mill.api.Ctx): Result[Report] = {
     val outputPath = ctx.dest
 
@@ -189,7 +191,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleKind = moduleKind,
       esFeatures = esFeatures,
       moduleSplitStyle = moduleSplitStyle,
-      outputPatterns = outputPatterns
+      outputPatterns = outputPatterns,
+      minify = minify
     )
   }
 
@@ -269,6 +272,21 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   /** Name patterns for output. */
   def scalaJSOutputPatterns: Target[OutputPatterns] = T { OutputPatterns.Defaults }
 
+  /**
+   * Apply Scala.js-specific minification of the produced .js files.
+   *
+   *  When enabled, the linker more aggressively reduces the size of the
+   *  generated code, at the cost of readability and debuggability. It does
+   *  not perform size optimizations that would negatively impact run-time
+   *  performance.
+   *
+   *  The focus is on optimizations that general-purpose JavaScript minifiers
+   *  cannot do on their own. For the best results, we expect the Scala.js
+   *  minifier to be used in conjunction with a general-purpose JavaScript
+   *  minifier.
+   */
+  def scalaJSMinify: Target[Boolean] = T { true }
+
   override def prepareOffline(all: Flag): Command[Unit] = {
     val tasks =
       if (all.value) Seq(scalaJSToolsClasspath)
@@ -327,7 +345,8 @@ trait TestScalaJSModule extends ScalaJSModule with TestModule {
       moduleKind = moduleKind(),
       esFeatures = esFeatures(),
       moduleSplitStyle = moduleSplitStyle(),
-      outputPatterns = scalaJSOutputPatterns()
+      outputPatterns = scalaJSOutputPatterns(),
+      minify = scalaJSMinify()
     )
   }
 

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

@@ -160,7 +160,8 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       moduleKind: api.ModuleKind,
       esFeatures: api.ESFeatures,
       moduleSplitStyle: api.ModuleSplitStyle,
-      outputPatterns: api.OutputPatterns
+      outputPatterns: api.OutputPatterns,
+      minify: Boolean
   )(implicit ctx: Ctx.Home): Result[api.Report] = {
     bridge(toolsClasspath).link(
       runClasspath = runClasspath.iterator.map(_.path.toNIO).toSeq,
@@ -174,7 +175,8 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       moduleKind = toWorkerApi(moduleKind),
       esFeatures = toWorkerApi(esFeatures),
       moduleSplitStyle = toWorkerApi(moduleSplitStyle),
-      outputPatterns = toWorkerApi(outputPatterns)
+      outputPatterns = toWorkerApi(outputPatterns),
+      minify = minify
     ) match {
       case Right(report) => Result.Success(fromWorkerApi(report))
       case Left(message) => Result.Failure(message)

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

@@ -16,7 +16,8 @@ private[scalajslib] trait ScalaJSWorkerApi {
       moduleKind: ModuleKind,
       esFeatures: ESFeatures,
       moduleSplitStyle: ModuleSplitStyle,
-      outputPatterns: OutputPatterns
+      outputPatterns: OutputPatterns,
+      minify: Boolean
   ): Either[String, Report]
 
   def run(config: JsEnvConfig, report: Report): Unit

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

@@ -34,6 +34,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       esFeatures: ESFeatures,
       moduleSplitStyle: ModuleSplitStyle,
       outputPatterns: OutputPatterns,
+      minify: Boolean,
       dest: File
   )
   private def minorIsGreaterThanOrEqual(number: Int) = ScalaJSVersions.current match {
@@ -146,7 +147,11 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
             )
         else withModuleSplitStyle
 
-      val linker = StandardImpl.clearableLinker(withOutputPatterns)
+      val withMinify =
+        if (minorIsGreaterThanOrEqual(16)) withOutputPatterns.withMinify(input.minify)
+        else withOutputPatterns
+
+      val linker = StandardImpl.clearableLinker(withMinify)
       val irFileCacheCache = irFileCache.newCache
       (linker, irFileCacheCache)
     }
@@ -163,7 +168,8 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       moduleKind: ModuleKind,
       esFeatures: ESFeatures,
       moduleSplitStyle: ModuleSplitStyle,
-      outputPatterns: OutputPatterns
+      outputPatterns: OutputPatterns,
+      minify: Boolean
   ): Either[String, Report] = {
     // 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
@@ -177,6 +183,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       esFeatures = esFeatures,
       moduleSplitStyle = moduleSplitStyle,
       outputPatterns = outputPatterns,
+      minify = minify,
       dest = dest
     ))
     val irContainersAndPathsFuture = PathIRContainer.fromClasspath(runClasspath)