From fdc5814617ef18d97673fd41ae945076d8af0847 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sat, 2 Nov 2024 22:22:15 +0100
Subject: [PATCH 01/13] Emit wasm

---
 .../src/mill/scalajslib/ScalaJSModule.scala   | 15 +++-
 .../scalajslib/worker/ScalaJSWorker.scala     |  6 +-
 .../test/resources/wasm/src/app/App.scala     | 10 +++
 .../mill/scalajslib/EsModuleRemapTests.scala  |  2 +-
 .../test/src/mill/scalajslib/WasmTests.scala  | 87 +++++++++++++++++++
 .../worker/api/ScalaJSWorkerApi.scala         |  3 +-
 .../scalajslib/worker/ScalaJSWorkerImpl.scala | 19 +++-
 7 files changed, 130 insertions(+), 12 deletions(-)
 create mode 100644 scalajslib/test/resources/wasm/src/app/App.scala
 create mode 100644 scalajslib/test/src/mill/scalajslib/WasmTests.scala

diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 10b412d1741..0fc66f84cdb 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -140,7 +140,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleSplitStyle = moduleSplitStyle(),
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
-      importMap = scalaJSImportMap()
+      importMap = scalaJSImportMap(),
+      emitWasm = emitWasm()
     )
   }
 
@@ -191,7 +192,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleSplitStyle: ModuleSplitStyle,
       outputPatterns: OutputPatterns,
       minify: Boolean,
-      importMap: Seq[ESModuleImportMapping]
+      importMap: Seq[ESModuleImportMapping],
+      emitWasm: Boolean
   )(implicit ctx: mill.api.Ctx): Result[Report] = {
     val outputPath = ctx.dest
 
@@ -212,7 +214,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       moduleSplitStyle = moduleSplitStyle,
       outputPatterns = outputPatterns,
       minify = minify,
-      importMap = importMap
+      importMap = importMap,
+      emitWasm
     )
   }
 
@@ -293,6 +296,9 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   /** Whether to emit a source map. */
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
+  /** Whether to emit WASM map. As of Nov 2024 scala JS wasm support is experimental */
+  def emitWasm: T[Boolean] = Task { false }
+
   /** Name patterns for output. */
   def scalaJSOutputPatterns: T[OutputPatterns] = Task { OutputPatterns.Defaults }
 
@@ -370,7 +376,8 @@ trait TestScalaJSModule extends ScalaJSModule with TestModule {
       moduleSplitStyle = moduleSplitStyle(),
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
-      importMap = scalaJSImportMap()
+      importMap = scalaJSImportMap(),
+      emitWasm = emitWasm()
     )
   }
 
diff --git a/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala b/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
index 321e0b55cf8..437ca0a6132 100644
--- a/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
+++ b/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
@@ -169,7 +169,8 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       moduleSplitStyle: api.ModuleSplitStyle,
       outputPatterns: api.OutputPatterns,
       minify: Boolean,
-      importMap: Seq[api.ESModuleImportMapping]
+      importMap: Seq[api.ESModuleImportMapping],
+      emitWasm: Boolean
   )(implicit ctx: Ctx.Home): Result[api.Report] = {
     bridge(toolsClasspath).link(
       runClasspath = runClasspath.iterator.map(_.path.toNIO).toSeq,
@@ -185,7 +186,8 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       moduleSplitStyle = toWorkerApi(moduleSplitStyle),
       outputPatterns = toWorkerApi(outputPatterns),
       minify = minify,
-      importMap = importMap.map(toWorkerApi)
+      importMap = importMap.map(toWorkerApi),
+      emitWasm = emitWasm
     ) match {
       case Right(report) => Result.Success(fromWorkerApi(report))
       case Left(message) => Result.Failure(message)
diff --git a/scalajslib/test/resources/wasm/src/app/App.scala b/scalajslib/test/resources/wasm/src/app/App.scala
new file mode 100644
index 00000000000..5bd4668058b
--- /dev/null
+++ b/scalajslib/test/resources/wasm/src/app/App.scala
@@ -0,0 +1,10 @@
+package app
+
+import scala.scalajs.js
+import scala.scalajs.js.annotation._
+
+object App {
+  def main(args: Array[String]): Unit = {
+    println("hello, wasm!")
+  }
+}
diff --git a/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala b/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
index 488c051082e..be5119fa63d 100644
--- a/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
@@ -65,7 +65,7 @@ object EsModuleRemapTests extends TestSuite {
     }
 
     test("should throw for older scalaJS versions") {
-      val evaluator = UnitTester(EsModuleRemap, millSourcePath)
+      val evaluator = UnitTester(OldJsModule, millSourcePath)
       val Left(Result.Exception(ex, _)) = evaluator(OldJsModule.fastLinkJS)
       val error = ex.getMessage
       assert(error == "scalaJSImportMap is not supported with Scala.js < 1.16.")
diff --git a/scalajslib/test/src/mill/scalajslib/WasmTests.scala b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
new file mode 100644
index 00000000000..35189e36a18
--- /dev/null
+++ b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
@@ -0,0 +1,87 @@
+package mill.scalajslib
+
+import mill.api.Result
+import mill.define.Discover
+import mill.testkit.UnitTester
+import mill.testkit.TestBaseModule
+import utest._
+import mill.scalajslib.api._
+import mill.T
+
+object WasmTests extends TestSuite {
+  val remapTo = "https://cdn.jsdelivr.net/gh/stdlib-js/array-base-linspace@esm/index.mjs"
+
+  object Wasm extends TestBaseModule with ScalaJSModule {
+    override def scalaVersion = sys.props.getOrElse("TEST_SCALA_2_13_VERSION", ???)
+
+    override def scalaJSVersion = "1.17.0"
+
+    override def moduleKind = ModuleKind.ESModule
+
+    override def moduleSplitStyle = ModuleSplitStyle.FewestModules
+
+    override def emitWasm: T[Boolean] = true
+
+    override lazy val millDiscover = {
+      import mill.main.TokenReaders.given
+      Discover[this.type]
+    }
+  }
+
+  object OldWasmModule extends TestBaseModule with ScalaJSModule {
+    override def scalaVersion = sys.props.getOrElse("TEST_SCALA_2_13_VERSION", ???)
+    override def scalaJSVersion = "1.16.0"
+
+    override def moduleKind = ModuleKind.ESModule
+    override def moduleSplitStyle = ModuleSplitStyle.FewestModules
+
+    override def emitWasm: T[Boolean] = true
+
+    override lazy val millDiscover = {
+      import mill.main.TokenReaders.given
+      Discover[this.type]
+    }
+  }
+
+  val millSourcePath = os.Path(sys.env("MILL_TEST_RESOURCE_DIR")) / "wasm"
+
+  val tests: Tests = Tests {
+    test("should emit wasm") {
+      val evaluator = UnitTester(Wasm, millSourcePath)
+      val Right(result) =
+        evaluator(Wasm.fastLinkJS)
+      val publicModules = result.value.publicModules.toSeq
+      val path = result.value.dest.path
+      val main = publicModules.head
+      assert(main.jsFileName == "main.js")
+      val mainPath = path / "main.js"
+      assert(os.exists(mainPath))
+      val wasmPath = path / "main.wasm"
+      assert(os.exists(wasmPath))
+      val wasmMapPath = path / "main.wasm.map"
+      assert(os.exists(wasmMapPath))
+    }
+
+    test("wasm is runnable") {
+      val evaluator = UnitTester(Wasm, millSourcePath)
+      val Right(result) = evaluator(Wasm.fastLinkJS)
+      val path = result.value.dest.path
+      os.proc("node", "--experimental-wasm-exnref", "main.js").call(
+        cwd = path,
+        check = true,
+        stdin = os.Inherit,
+        stdout = os.Inherit,
+        stderr = os.Inherit
+      )
+
+    }
+
+    test("should throw for older scalaJS versions") {
+      val evaluator = UnitTester(OldWasmModule, millSourcePath)
+      val Left(Result.Exception(ex, _)) = evaluator(OldWasmModule.fastLinkJS)
+      val error = ex.getMessage
+      assert(error == "Emitting wasm is not supported with Scala.js < 1.17")
+    }
+
+  }
+}
diff --git a/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala b/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
index b28a9358d8a..d4a60ae91ce 100644
--- a/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
+++ b/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
@@ -18,7 +18,8 @@ private[scalajslib] trait ScalaJSWorkerApi {
       moduleSplitStyle: ModuleSplitStyle,
       outputPatterns: OutputPatterns,
       minify: Boolean,
-      importMap: Seq[ESModuleImportMapping]
+      importMap: Seq[ESModuleImportMapping],
+      emitWasm: Boolean
   ): Either[String, Report]
 
   def run(config: JsEnvConfig, report: Report): Unit
diff --git a/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala b/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
index d6f2164ff72..d7bf687edc5 100644
--- a/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
+++ b/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
@@ -37,7 +37,8 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       moduleSplitStyle: ModuleSplitStyle,
       outputPatterns: OutputPatterns,
       minify: Boolean,
-      dest: File
+      dest: File,
+      emitWasm: Boolean
   )
   private def minorIsGreaterThanOrEqual(number: Int) = ScalaJSVersions.current match {
     case s"1.$n.$_" if n.toIntOption.exists(_ < number) => false
@@ -153,7 +154,15 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
         if (minorIsGreaterThanOrEqual(16)) withOutputPatterns.withMinify(input.minify)
         else withOutputPatterns
 
-      val linker = StandardImpl.clearableLinker(withMinify)
+      val withWasm =
+        (minorIsGreaterThanOrEqual(17), input.emitWasm) match {
+          case (_, false) => withMinify
+          case (true, true) => withMinify.withExperimentalUseWebAssembly(true)
+          case (false, true) =>
+            throw new Exception("Emitting wasm is not supported with Scala.js < 1.17")
+        }
+
+      val linker = StandardImpl.clearableLinker(withWasm)
       val irFileCacheCache = irFileCache.newCache
       (linker, irFileCacheCache)
     }
@@ -180,7 +189,8 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       moduleSplitStyle: ModuleSplitStyle,
       outputPatterns: OutputPatterns,
       minify: Boolean,
-      importMap: Seq[ESModuleImportMapping]
+      importMap: Seq[ESModuleImportMapping],
+      emitWasm: 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
@@ -195,7 +205,8 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       moduleSplitStyle = moduleSplitStyle,
       outputPatterns = outputPatterns,
       minify = minify,
-      dest = dest
+      dest = dest,
+      emitWasm = emitWasm
     ))
     val irContainersAndPathsFuture = PathIRContainer.fromClasspath(runClasspath)
     val testInitializer =

From 1b302a31f5cfd7f827bd117abfcae30bc34deebd Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sat, 2 Nov 2024 22:42:58 +0100
Subject: [PATCH 02/13] .

---
 scalajslib/src/mill/scalajslib/ScalaJSModule.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 0fc66f84cdb..824f41471f5 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -296,7 +296,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   /** Whether to emit a source map. */
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
-  /** Whether to emit WASM map. As of Nov 2024 scala JS wasm support is experimental */
+  /** Whether to emit WASM. As of Nov 2024 scala JS wasm support is experimental */
   def emitWasm: T[Boolean] = Task { false }
 
   /** Name patterns for output. */

From 1e3a47ded988c59c0c6dddcf0c434e63db658aa0 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sat, 2 Nov 2024 22:43:51 +0100
Subject: [PATCH 03/13] .

---
 scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala b/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
index be5119fa63d..488c051082e 100644
--- a/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/EsModuleRemapTests.scala
@@ -65,7 +65,7 @@ object EsModuleRemapTests extends TestSuite {
     }
 
     test("should throw for older scalaJS versions") {
-      val evaluator = UnitTester(OldJsModule, millSourcePath)
+      val evaluator = UnitTester(EsModuleRemap, millSourcePath)
       val Left(Result.Exception(ex, _)) = evaluator(OldJsModule.fastLinkJS)
       val error = ex.getMessage
       assert(error == "scalaJSImportMap is not supported with Scala.js < 1.16.")

From 142836dbfa0f6e404b68677471b7046b18317ef9 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 10:08:23 +0100
Subject: [PATCH 04/13] Node 22

---
 .github/workflows/run-mill-action.yml               | 5 +++++
 scalajslib/src/mill/scalajslib/ScalaJSModule.scala  | 6 +++---
 scalajslib/test/src/mill/scalajslib/WasmTests.scala | 4 ++--
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/run-mill-action.yml b/.github/workflows/run-mill-action.yml
index 84f4cc75b72..1629231c138 100644
--- a/.github/workflows/run-mill-action.yml
+++ b/.github/workflows/run-mill-action.yml
@@ -58,6 +58,11 @@ jobs:
           java-version: ${{ inputs.java-version }}
           distribution: temurin
 
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+
+
       - name: Prepare git config
         run: |
           git config --global user.name "Mill GithHub Actions"
diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 824f41471f5..766a5d54e51 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -141,7 +141,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      emitWasm = emitWasm()
+      emitWasm = scalaJSEmitWasm()
     )
   }
 
@@ -297,7 +297,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
   /** Whether to emit WASM. As of Nov 2024 scala JS wasm support is experimental */
-  def emitWasm: T[Boolean] = Task { false }
+  def scalaJSEmitWasm: T[Boolean] = Task { false }
 
   /** Name patterns for output. */
   def scalaJSOutputPatterns: T[OutputPatterns] = Task { OutputPatterns.Defaults }
@@ -377,7 +377,7 @@ trait TestScalaJSModule extends ScalaJSModule with TestModule {
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      emitWasm = emitWasm()
+      emitWasm = scalaJSEmitWasm()
     )
   }
 
diff --git a/scalajslib/test/src/mill/scalajslib/WasmTests.scala b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
index 35189e36a18..effe7553a59 100644
--- a/scalajslib/test/src/mill/scalajslib/WasmTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
@@ -20,7 +20,7 @@ object WasmTests extends TestSuite {
 
     override def moduleSplitStyle = ModuleSplitStyle.FewestModules
 
-    override def emitWasm: T[Boolean] = true
+    override def scalaJSEmitWasm: T[Boolean] = true
 
     override lazy val millDiscover = {
       import mill.main.TokenReaders.given
@@ -35,7 +35,7 @@ object WasmTests extends TestSuite {
     override def moduleKind = ModuleKind.ESModule
     override def moduleSplitStyle = ModuleSplitStyle.FewestModules
 
-    override def emitWasm: T[Boolean] = true
+    override def scalaJSEmitWasm: T[Boolean] = true
 
     override lazy val millDiscover = {
       import mill.main.TokenReaders.given

From 249146aeb2507f414222b63e9e79a7fc87da34f5 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 10:57:20 +0100
Subject: [PATCH 05/13] doc

---
 .../ROOT/pages/scalalib/web-examples.adoc     |  6 ++-
 example/scalalib/web/8-wasm/build.mill        | 49 +++++++++++++++++++
 .../scalalib/web/8-wasm/wasm/src/hello.scala  |  7 +++
 3 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 example/scalalib/web/8-wasm/build.mill
 create mode 100644 example/scalalib/web/8-wasm/wasm/src/hello.scala

diff --git a/docs/modules/ROOT/pages/scalalib/web-examples.adoc b/docs/modules/ROOT/pages/scalalib/web-examples.adoc
index 5ef5ece8807..f448f3b4bf8 100644
--- a/docs/modules/ROOT/pages/scalalib/web-examples.adoc
+++ b/docs/modules/ROOT/pages/scalalib/web-examples.adoc
@@ -35,4 +35,8 @@ include::partial$example/scalalib/web/6-cross-version-platform-publishing.adoc[]
 
 == Publishing Cross-Platform Scala Modules Alternative
 
-include::partial$example/scalalib/web/7-cross-platform-version-publishing.adoc[]
\ No newline at end of file
+include::partial$example/scalalib/web/7-cross-platform-version-publishing.adoc[]
+
+== Scala.js WebAssembly Example
+
+include::partial$example/scalalib/web/8-wasm.adoc[]
\ No newline at end of file
diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
new file mode 100644
index 00000000000..4d9bb204a68
--- /dev/null
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -0,0 +1,49 @@
+package build
+import mill._, scalalib._, scalajslib._
+import mill.scalajslib.api._
+
+
+object wasm extends ScalaJSModule {
+  override def scalaVersion = "3.3.4"
+
+  override def scalaJSVersion = "1.17.0"
+
+  override def moduleKind = ModuleKind.ESModule
+
+  override def moduleSplitStyle = ModuleSplitStyle.FewestModules
+
+  override def scalaJSEmitWasm = true
+}
+
+// This build defines a single `ScalaJSModule` that uses the `WASM` backend of the scala JS linker.
+// The release notes that introduced scalaJS wasm are here;
+// https://www.scala-js.org/news/2024/09/28/announcing-scalajs-1.17.0/
+// and are worth reading. They include information such as the scala JS requirements to successful emit wasm,
+// the flags needed to run in browser and the minimum node version (22) required to actually run the wasm output.
+//
+// You can check if you've emitted WASM by checking
+
+/** Usage
+
+> mill show wasm.fastLinkJS
+[1/1] show
+{
+  ...
+  "dest": "... out/wasm/fastLinkJS.dest"
+}
+
+> ls out/wasm/fastLinkJS.dest
+__loader.js     main.js         main.wasm       main.wasm.map
+
+> node out/foo/fullLinkJS.dest/main.js
+Debugger listening on ws://127.0.0.1:57753/d17db228-5159-4e60-be1f-4cc47a396ddf
+For help, see: https://nodejs.org/en/docs/inspector
+Debugger attached.
+hello  wasm!
+
+*/
+
+// Here we see that scala JS emits a single WASM module, as well as a loader and main.js file.
+// `main.js` is the entry point of the program, and calls into the wasm module.
+
+
diff --git a/example/scalalib/web/8-wasm/wasm/src/hello.scala b/example/scalalib/web/8-wasm/wasm/src/hello.scala
new file mode 100644
index 00000000000..d8cbbc60ce5
--- /dev/null
+++ b/example/scalalib/web/8-wasm/wasm/src/hello.scala
@@ -0,0 +1,7 @@
+package hi
+
+object Foo {
+  def main(args: Array[String]): Unit = {
+    println("hello  wasm!")
+  }
+}

From 1056a044927948bd2378b3920225a7a16dd49f01 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 10:58:42 +0100
Subject: [PATCH 06/13] .

---
 example/scalalib/web/8-wasm/build.mill | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 4d9bb204a68..59702f946bc 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -18,10 +18,8 @@ object wasm extends ScalaJSModule {
 // This build defines a single `ScalaJSModule` that uses the `WASM` backend of the scala JS linker.
 // The release notes that introduced scalaJS wasm are here;
 // https://www.scala-js.org/news/2024/09/28/announcing-scalajs-1.17.0/
-// and are worth reading. They include information such as the scala JS requirements to successful emit wasm,
+// and are worth reading. They include information such as the scala JS requirements to successfully emit wasm,
 // the flags needed to run in browser and the minimum node version (22) required to actually run the wasm output.
-//
-// You can check if you've emitted WASM by checking
 
 /** Usage
 

From e88fca732007b8ac9a3aa300ad987bd213884c89 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 12:24:14 +0100
Subject: [PATCH 07/13] rename vars

---
 example/scalalib/web/8-wasm/build.mill                 |  2 +-
 scalajslib/src/mill/scalajslib/ScalaJSModule.scala     | 10 +++++-----
 .../src/mill/scalajslib/worker/ScalaJSWorker.scala     |  4 ++--
 scalajslib/test/src/mill/scalajslib/WasmTests.scala    |  4 ++--
 .../mill/scalajslib/worker/api/ScalaJSWorkerApi.scala  |  2 +-
 .../src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala |  8 ++++----
 6 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 59702f946bc..e0560a65ac0 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -12,7 +12,7 @@ object wasm extends ScalaJSModule {
 
   override def moduleSplitStyle = ModuleSplitStyle.FewestModules
 
-  override def scalaJSEmitWasm = true
+  override def scalaJSExperimentalUseWebAssembly = true
 }
 
 // This build defines a single `ScalaJSModule` that uses the `WASM` backend of the scala JS linker.
diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 766a5d54e51..016d1b7737e 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -141,7 +141,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      emitWasm = scalaJSEmitWasm()
+      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly()
     )
   }
 
@@ -193,7 +193,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      emitWasm: Boolean
+      experimentalUseWebAssembly: Boolean
   )(implicit ctx: mill.api.Ctx): Result[Report] = {
     val outputPath = ctx.dest
 
@@ -215,7 +215,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
       outputPatterns = outputPatterns,
       minify = minify,
       importMap = importMap,
-      emitWasm
+      experimentalUseWebAssembly = experimentalUseWebAssembly
     )
   }
 
@@ -297,7 +297,7 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
   /** Whether to emit WASM. As of Nov 2024 scala JS wasm support is experimental */
-  def scalaJSEmitWasm: T[Boolean] = Task { false }
+  def scalaJSExperimentalUseWebAssembly: T[Boolean] = Task { false }
 
   /** Name patterns for output. */
   def scalaJSOutputPatterns: T[OutputPatterns] = Task { OutputPatterns.Defaults }
@@ -377,7 +377,7 @@ trait TestScalaJSModule extends ScalaJSModule with TestModule {
       outputPatterns = scalaJSOutputPatterns(),
       minify = scalaJSMinify(),
       importMap = scalaJSImportMap(),
-      emitWasm = scalaJSEmitWasm()
+      experimentalUseWebAssembly = scalaJSExperimentalUseWebAssembly()
     )
   }
 
diff --git a/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala b/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
index 437ca0a6132..3ce55097cc0 100644
--- a/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
+++ b/scalajslib/src/mill/scalajslib/worker/ScalaJSWorker.scala
@@ -170,7 +170,7 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       outputPatterns: api.OutputPatterns,
       minify: Boolean,
       importMap: Seq[api.ESModuleImportMapping],
-      emitWasm: Boolean
+      experimentalUseWebAssembly: Boolean
   )(implicit ctx: Ctx.Home): Result[api.Report] = {
     bridge(toolsClasspath).link(
       runClasspath = runClasspath.iterator.map(_.path.toNIO).toSeq,
@@ -187,7 +187,7 @@ private[scalajslib] class ScalaJSWorker extends AutoCloseable {
       outputPatterns = toWorkerApi(outputPatterns),
       minify = minify,
       importMap = importMap.map(toWorkerApi),
-      emitWasm = emitWasm
+      experimentalUseWebAssembly = experimentalUseWebAssembly
     ) match {
       case Right(report) => Result.Success(fromWorkerApi(report))
       case Left(message) => Result.Failure(message)
diff --git a/scalajslib/test/src/mill/scalajslib/WasmTests.scala b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
index effe7553a59..a43f372be9b 100644
--- a/scalajslib/test/src/mill/scalajslib/WasmTests.scala
+++ b/scalajslib/test/src/mill/scalajslib/WasmTests.scala
@@ -20,7 +20,7 @@ object WasmTests extends TestSuite {
 
     override def moduleSplitStyle = ModuleSplitStyle.FewestModules
 
-    override def scalaJSEmitWasm: T[Boolean] = true
+    override def scalaJSExperimentalUseWebAssembly: T[Boolean] = true
 
     override lazy val millDiscover = {
       import mill.main.TokenReaders.given
@@ -35,7 +35,7 @@ object WasmTests extends TestSuite {
     override def moduleKind = ModuleKind.ESModule
     override def moduleSplitStyle = ModuleSplitStyle.FewestModules
 
-    override def scalaJSEmitWasm: T[Boolean] = true
+    override def scalaJSExperimentalUseWebAssembly: T[Boolean] = true
 
     override lazy val millDiscover = {
       import mill.main.TokenReaders.given
diff --git a/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala b/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
index d4a60ae91ce..d9a7601c035 100644
--- a/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
+++ b/scalajslib/worker-api/src/mill/scalajslib/worker/api/ScalaJSWorkerApi.scala
@@ -19,7 +19,7 @@ private[scalajslib] trait ScalaJSWorkerApi {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      emitWasm: Boolean
+      experimentalUseWebAssembly: Boolean
   ): Either[String, Report]
 
   def run(config: JsEnvConfig, report: Report): Unit
diff --git a/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala b/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
index d7bf687edc5..f1022fae005 100644
--- a/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
+++ b/scalajslib/worker/1/src/mill/scalajslib/worker/ScalaJSWorkerImpl.scala
@@ -38,7 +38,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       dest: File,
-      emitWasm: Boolean
+      experimentalUseWebAssembly: Boolean
   )
   private def minorIsGreaterThanOrEqual(number: Int) = ScalaJSVersions.current match {
     case s"1.$n.$_" if n.toIntOption.exists(_ < number) => false
@@ -155,7 +155,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
         else withOutputPatterns
 
       val withWasm =
-        (minorIsGreaterThanOrEqual(17), input.emitWasm) match {
+        (minorIsGreaterThanOrEqual(17), input.experimentalUseWebAssembly) match {
           case (_, false) => withMinify
           case (true, true) => withMinify.withExperimentalUseWebAssembly(true)
           case (false, true) =>
@@ -190,7 +190,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       outputPatterns: OutputPatterns,
       minify: Boolean,
       importMap: Seq[ESModuleImportMapping],
-      emitWasm: Boolean
+      experimentalUseWebAssembly: 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
@@ -206,7 +206,7 @@ class ScalaJSWorkerImpl extends ScalaJSWorkerApi {
       outputPatterns = outputPatterns,
       minify = minify,
       dest = dest,
-      emitWasm = emitWasm
+      experimentalUseWebAssembly = experimentalUseWebAssembly
     ))
     val irContainersAndPathsFuture = PathIRContainer.fromClasspath(runClasspath)
     val testInitializer =

From 8943f1452633259bb51cb97bb4ccb61fd8275c6c Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 12:56:33 +0100
Subject: [PATCH 08/13] tighten docs

---
 example/scalalib/web/8-wasm/build.mill | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index e0560a65ac0..01205c7bf19 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -23,20 +23,14 @@ object wasm extends ScalaJSModule {
 
 /** Usage
 
-> mill show wasm.fastLinkJS
-[1/1] show
+> ./mill show wasm.fastLinkJS # mac/linux
 {
-  ...
-  "dest": "... out/wasm/fastLinkJS.dest"
+...
+..."jsFileName": "main.js",
+  "dest": ".../out/wasm/fastLinkJS.dest"
 }
 
-> ls out/wasm/fastLinkJS.dest
-__loader.js     main.js         main.wasm       main.wasm.map
-
-> node out/foo/fullLinkJS.dest/main.js
-Debugger listening on ws://127.0.0.1:57753/d17db228-5159-4e60-be1f-4cc47a396ddf
-For help, see: https://nodejs.org/en/docs/inspector
-Debugger attached.
+> node --experimental-wasm-exnref out/foo/fullLinkJS.dest/main.js # mac/linux
 hello  wasm!
 
 */

From 14e0ebb7caa232dfa9a9439bd04df2b09236cd5d Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 14:10:18 +0100
Subject: [PATCH 09/13] .

---
 example/scalalib/web/8-wasm/build.mill           | 2 +-
 example/scalalib/web/8-wasm/wasm/src/hello.scala | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 01205c7bf19..0c1f4ad47cb 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -4,7 +4,7 @@ import mill.scalajslib.api._
 
 
 object wasm extends ScalaJSModule {
-  override def scalaVersion = "3.3.4"
+  override def scalaVersion = "2.13.14"
 
   override def scalaJSVersion = "1.17.0"
 
diff --git a/example/scalalib/web/8-wasm/wasm/src/hello.scala b/example/scalalib/web/8-wasm/wasm/src/hello.scala
index d8cbbc60ce5..18b869667f7 100644
--- a/example/scalalib/web/8-wasm/wasm/src/hello.scala
+++ b/example/scalalib/web/8-wasm/wasm/src/hello.scala
@@ -1,6 +1,6 @@
-package hi
+package wasm
 
-object Foo {
+object wasm {
   def main(args: Array[String]): Unit = {
     println("hello  wasm!")
   }

From 5afe8d5e8ed02bee3c67ddc8ff55fd0e60f98ec2 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 14:38:02 +0100
Subject: [PATCH 10/13] *sigh

---
 example/scalalib/web/8-wasm/build.mill             |  1 +
 scalajslib/src/mill/scalajslib/ScalaJSModule.scala | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 0c1f4ad47cb..722f9f2be69 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -27,6 +27,7 @@ object wasm extends ScalaJSModule {
 {
 ...
 ..."jsFileName": "main.js",
+...
   "dest": ".../out/wasm/fastLinkJS.dest"
 }
 
diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 016d1b7737e..0c4f1ffba32 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -296,7 +296,18 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   /** Whether to emit a source map. */
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
-  /** Whether to emit WASM. As of Nov 2024 scala JS wasm support is experimental */
+  /** Specifies whether to use the experimental WebAssembly backend.. Requires scalaJS > 1.17.0
+   *  When using this setting, the following properties must also hold:
+   *
+   *  - `moduleKind = ModuleKind.ESModule`
+   *  - `moduleSplitStyle = ModuleSplitStyle.FewestModules`
+   *
+   *  @note
+   *    Currently, the WebAssembly backend silently ignores `@JSExport` and
+   *    `@JSExportAll` annotations. This behavior may change in the future,
+   *    either by making them warnings or errors, or by adding support for them.
+   *    All other language features are supported.
+   */
   def scalaJSExperimentalUseWebAssembly: T[Boolean] = Task { false }
 
   /** Name patterns for output. */

From 9803345b86510f9459410a398056252b7d085a79 Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 15:00:11 +0100
Subject: [PATCH 11/13] urgh

---
 example/scalalib/web/8-wasm/build.mill | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 722f9f2be69..101779c581e 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -31,7 +31,7 @@ object wasm extends ScalaJSModule {
   "dest": ".../out/wasm/fastLinkJS.dest"
 }
 
-> node --experimental-wasm-exnref out/foo/fullLinkJS.dest/main.js # mac/linux
+> node --experimental-wasm-exnref out/wasm/fullLinkJS.dest/main.js # mac/linux
 hello  wasm!
 
 */

From 2281c1daa1c37443b30d21025fd92c56c7fb11aa Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 15:19:50 +0100
Subject: [PATCH 12/13] Bah, format

---
 scalajslib/src/mill/scalajslib/ScalaJSModule.scala | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
index 0c4f1ffba32..db3248000a9 100644
--- a/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
+++ b/scalajslib/src/mill/scalajslib/ScalaJSModule.scala
@@ -296,7 +296,8 @@ trait ScalaJSModule extends scalalib.ScalaModule { outer =>
   /** Whether to emit a source map. */
   def scalaJSSourceMap: T[Boolean] = Task { true }
 
-  /** Specifies whether to use the experimental WebAssembly backend.. Requires scalaJS > 1.17.0
+  /**
+   * Specifies whether to use the experimental WebAssembly backend.. Requires scalaJS > 1.17.0
    *  When using this setting, the following properties must also hold:
    *
    *  - `moduleKind = ModuleKind.ESModule`

From 5829f92e589a6901d55564f890303eedaf474e9d Mon Sep 17 00:00:00 2001
From: Simon Parten <quafadas@gmail.com>
Date: Sun, 3 Nov 2024 15:20:43 +0100
Subject: [PATCH 13/13] .

---
 example/scalalib/web/8-wasm/build.mill | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/example/scalalib/web/8-wasm/build.mill b/example/scalalib/web/8-wasm/build.mill
index 101779c581e..1eaa52edfa8 100644
--- a/example/scalalib/web/8-wasm/build.mill
+++ b/example/scalalib/web/8-wasm/build.mill
@@ -31,7 +31,7 @@ object wasm extends ScalaJSModule {
   "dest": ".../out/wasm/fastLinkJS.dest"
 }
 
-> node --experimental-wasm-exnref out/wasm/fullLinkJS.dest/main.js # mac/linux
+> node --experimental-wasm-exnref out/wasm/fastLinkJS.dest/main.js # mac/linux
 hello  wasm!
 
 */