Add the ability to emit wasm to scala js cli

.github/workflows/ci.yml

@@ -20,6 +20,9 @@ jobs:
       - uses: VirtusLab/scala-cli-setup@9bc68588ab2d49dae03e5395a5f411e20914f97e
         with:
           jvm: "temurin:17"
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
       - name: Test CLI
         run: ./mill -i 'tests.test'
 
@@ -60,6 +63,9 @@ jobs:
       - uses: coursier/[email protected]
         with:
           jvm: temurin:17
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
       - run: |
           ./mill -i "native.writeNativeImageScript" generate.sh "" && \
           ./generate.sh && \
@@ -98,6 +104,9 @@ jobs:
       - uses: coursier/[email protected]
         with:
           jvm: temurin:17
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
       - run: |
           ./mill -i "native-static.writeNativeImageScript" generate.sh "" && \
           ./generate.sh && \
@@ -128,6 +137,9 @@ jobs:
       - uses: coursier/[email protected]
         with:
           jvm: temurin:17
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
       - run: |
           ./mill -i "native-mostly-static.writeNativeImageScript" generate.sh "" && \
           ./generate.sh && \

cli/src/org/scalajs/cli/Scalajsld.scala

@@ -54,7 +54,8 @@ object Scalajsld {
       jsHeader: String = "",
       logLevel: Level = Level.Info,
       importMap: Option[File] = None,
-      longRunning: Boolean = false
+      longRunning: Boolean = false,
+      emitWasm: Boolean = false
   )
 
   private def moduleInitializer(
@@ -238,6 +239,9 @@ object Scalajsld {
       opt[Unit]("longRunning")
         .action { (_, c) => c.copy(longRunning = true) }
         .text("Run linking incrementally every time a line is printed to stdin")
+      opt[Unit]("emitWasm")
+        .action { (_, c) => c.copy(emitWasm = true) }
+        .text("If present, use the _experimental_ web assembly backend in the linker")
       opt[Unit]('d', "debug")
         .action { (_, c) => c.copy(logLevel = Level.Debug) }
         .text("Debug mode: Show full log")
@@ -277,13 +281,32 @@ object Scalajsld {
             }
           }
         }
-        val allValidations = Seq(outputCheck, importMapCheck)
+
+        val wasEsModule = c.emitWasm match {
+          case true =>
+            if (c.moduleKind != ModuleKind.ESModule) {
+              failure("Wasm can only be emitted with module kind EsModule")
+            } else success
+          case false => success
+        }
+
+        val wasmFewestModules = c.emitWasm match {
+          case true => {
+            if (c.moduleSplitStyle != ModuleSplitStyle.FewestModules.toString) {
+              failure("Wasm can only be emitted with module split style FewestModules")
+            } else success
+          }
+          case false => success
+        }
+
+        val allValidations = Seq(outputCheck, importMapCheck, wasEsModule, wasmFewestModules)
         allValidations.forall(_.isRight) match {
           case true  => success
           case false => failure(allValidations.filter(_.isLeft).map(_.left.get).mkString("\n\n"))
         }
       }
 
+
       override def showUsageOnError = Some(true)
     }
 
@@ -319,6 +342,7 @@ object Scalajsld {
         .withBatchMode(true)
         .withJSHeader(options.jsHeader)
         .withMinify(options.fullOpt)
+        .withExperimentalUseWebAssembly(options.emitWasm)
 
       val linker = StandardImpl.linker(config)
       val logger = new ScalaConsoleLogger(options.logLevel)
@@ -347,6 +371,7 @@ object Scalajsld {
                   logger
                 )
               case (None, Some(outputDir)) =>
+
                 linker.link(
                   irImportMappedFiles,
                   moduleInitializers,

tests/test/src/org/scalajs/cli/tests/Tests.scala

@@ -498,4 +498,64 @@ class Tests extends munit.FunSuite {
     val rawJs = os.read.lines(dir / "out" / "main.js")
     assert(rawJs(1).contains(substTo))
   }
+
+
+  test("wasm flag emits wasm") {
+    val dir = os.temp.dir()
+    os.write(
+      dir / "foo.scala",
+      """object Foo {
+        |  def main(args: Array[String]): Unit = {
+        |    println("Hello")
+        |  }
+        |
+        |}
+        |""".stripMargin
+    )
+
+    val scalaJsLibraryCp = getScalaJsLibraryCp(dir)
+
+    os.makeDir.all(dir / "bin")
+    os.proc(
+      "cs",
+      "launch",
+      "scalac:2.13.15",
+      "--",
+      "-classpath",
+      scalaJsLibraryCp,
+      s"-Xplugin:${getScalaJsCompilerPlugin(dir)}",
+      "-d",
+      "bin",
+      "foo.scala"
+    ).call(cwd = dir, stdin = os.Inherit, stdout = os.Inherit)
+
+    os.makeDir.all(dir / "out")
+    val res = os
+      .proc(
+        launcher,
+        "--stdlib",
+        scalaJsLibraryCp,
+        "-s",
+        "--emitWasm",
+        "--moduleKind",
+        "ESModule",
+        "--moduleSplitStyle",
+        "FewestModules",
+        "--outputDir",
+        "out",
+        "-mm",
+        "Foo.main",
+        "bin"
+      )
+      .call(cwd = dir, mergeErrIntoOut = true)
+
+    os.walk(dir).foreach(println)
+    val testSize = os.size(dir / "out" / "main.wasm")
+    val testMapSize = os.size(dir / "out" / "main.wasm.map")
+    assert(testSize > 0)
+    assert(testMapSize > 0)
+
+    os.proc("node", "--experimental-wasm-exnref", "main.js").call(cwd = dir / "out", check = true, stdin = os.Inherit, stdout = os.Inherit, stderr = os.Inherit)
+
+  }
 }