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)