Actually use our linker as the linker for sample/fastLinkJS.

Now, `sample/fastLinkJS` uses our WebAssembly linker, and
`sample/run` actually executes the `main` method of the sample
project, linked to WebAssembly.

.github/workflows/ci.yml

@@ -24,9 +24,9 @@ jobs:
         run: npm install
       - name: Tests
         run: sbt tests/test
-      - name: Run the Sample
-        run: sbt sample/run
       - name: Compile wasmJVM
         run: sbt wasmJVM/compile
+      - name: Run the Sample
+        run: sbt sample/run
       - name: Format
         run: sbt scalafmtCheckAll

README.md

@@ -2,40 +2,61 @@
 
 [![CI](https://github.com/tanishiking/scala-wasm/actions/workflows/ci.yml/badge.svg)](https://github.com/tanishiking/scala-wasm/actions/workflows/ci.yml)
 
-### Usage
+### Prerequisites
 
-- first, `npm install`
-- then `sample/run` to compile `sample/src/main/scala/Sample.scala`.
-  - prints the WebAssembly Text Format (WAT) (Stack IR form) to the console, for debugging
-  - writes the binary format (WASM) to `target/output.wasm`
+This project requires Node.js >= 22, which is available as nightly builds as of this writing.
+This is necessary to get enough support of WasmGC.
 
-Run the binary using through `run.js` using a JavaScript engine that supports WasmGC, such as Deno
+If you are using NVM, you can instal Node.js 22 as follows:
 
 ```sh
-$ deno run --allow-read run.mjs
+# Enable resolution of nightly builds
+$ NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/nightly nvm install v22
+# Switch to Node.js 22
+$ nvm use 22
 ```
 
-### Debugging tools
+Otherwise, you can [manually download nightly builds of Node.js](https://nodejs.org/download/nightly/).
 
-- The WasmGC reference interpreter can be used to validate and convert between the binary and text form:
-  - https://github.com/WebAssembly/gc/tree/main/interpreter
-  - Use docker image for it https://github.com/tanishiking/wasmgc-docker
+### Setup
 
-### Testing
+Before doing anything else, run `npm install`.
 
-Requires NodeJS >= 22 (for enough support of WasmGC).
+### Run the sample
 
-```sh
-# if you are using NVM, you can install Node 22 with
-$ NVM_NODEJS_ORG_MIRROR=https://nodejs.org/download/nightly nvm install v22
-# switch to use Node 22
-$ nvm use 22
-```
+In `sample/src/main/scala/Sample.scala` you can find a sandbox to play around.
+
+You can build and run it like any other Scala.js project from sbt:
+
+- `sample/fastLinkJS` compiles and links the project with the WebAssembly backend.
+- `sample/run` runs the sample linked to WebAssembly with `node`.
+
+You may want to look at the output in `sample/target/scala-2.12/sample-fastopt/` to convince yourself that it was compiled to WebAssembly.
+
+In that directory, you will also find a `main.wat` file, which is not used for execution.
+It contains the WebAsembly Text Format representation of `main.wasm`, for debugging purposes.
+
+:warning: If you modify the linker code, you need to `reload` and `sample/clean` for your changes to take effect on the sample.
+
+You can also use the `run.mjs` script to play with `@JSExportTopLevel` exports.
+
+- Run from the command line with `node run.mjs`.
+- Run from the browser by starting an HTTP server (e.g., `python -m http.server`) and navigate to `testrun.html`.
+
+### Test suite
+
+Run the test suite with `tests/test`.
 
 - `tests/test` will
   - Run `testSuite/run` to compile the Scala code under `test-suite` to WebAssembly
   - Run the WebAssembly binary using NodeJS
-- Each Scala program in `test-suite` should have a function that has no arguments and return a Boolean value. The test passes if the function returns `true`.
-- When you add a test, 
+- Each Scala program in `test-suite` should have a `def main(): Unit` function. The test passes if the function successfully executes without throwing.
+- When you add a test,
   - Add a file under `test-suite`
   - Add a test case to `cli/src/main/scala/TestSuites.scala` (`methodName` should be a exported function name).
+
+### Debugging tools
+
+- The WasmGC reference interpreter can be used to validate and convert between the binary and text form:
+  - https://github.com/WebAssembly/gc/tree/main/interpreter
+  - Use docker image for it https://github.com/tanishiking/wasmgc-docker

build.sbt

@@ -3,6 +3,10 @@ import org.scalajs.linker.interface.OutputPatterns
 
 val scalaV = "2.12.19"
 
+// Include wasm.jvm on the classpath used to dynamically load Scala.js linkers
+Global / scalaJSLinkerImpl / fullClasspath :=
+  (wasm.jvm / Compile / fullClasspath).value
+
 inThisBuild(Def.settings(
   scalacOptions ++= Seq(
     "-encoding",
@@ -49,22 +53,10 @@ lazy val wasm = crossProject(JVMPlatform, JSPlatform)
 
 lazy val sample = project
   .in(file("sample"))
-  .enablePlugins(ScalaJSPlugin)
+  .enablePlugins(WasmLinkerPlugin)
   .settings(
     scalaVersion := scalaV,
     scalaJSUseMainModuleInitializer := true,
-    Compile / jsEnv := {
-      import org.scalajs.jsenv.nodejs.NodeJSEnv
-      val cp = Attributed
-        .data((Compile / fullClasspath).value)
-        .mkString(";")
-      val env = Map(
-        "SCALAJS_CLASSPATH" -> cp,
-        "SCALAJS_MODE" -> "sample",
-      )
-      new NodeJSEnv(NodeJSEnv.Config().withEnv(env).withArgs(List("--enable-source-maps")))
-    },
-    Compile / jsEnvInput := (`cli` / Compile / jsEnvInput).value
   )
 
 lazy val testSuite = project

project/WasmLinkerPlugin.scala

@@ -0,0 +1,51 @@
+package build
+
+import sbt._
+import sbt.Keys._
+
+import org.scalajs.linker._
+import org.scalajs.linker.interface.{ModuleKind, _}
+
+import org.scalajs.sbtplugin._
+import org.scalajs.sbtplugin.ScalaJSPlugin.autoImport._
+
+object WasmLinkerPlugin extends AutoPlugin {
+  override lazy val requires = ScalaJSPlugin
+
+  /** A `LinkerImpl` that reflectively loads our `WebAssemblyLinkerImpl`. */
+  private class WasmLinkerImpl(base: LinkerImpl.Reflect)
+      extends LinkerImpl.Forwarding(base) {
+
+    private val loader = base.loader
+
+    private val clearableLinkerMethod = {
+      Class.forName("wasm.WebAssemblyLinkerImpl", true, loader)
+        .getMethod("clearableLinker", classOf[StandardConfig])
+    }
+
+    override def clearableLinker(config: StandardConfig): ClearableLinker =
+      clearableLinkerMethod.invoke(null, config).asInstanceOf[ClearableLinker]
+  }
+
+  override def projectSettings: Seq[Setting[_]] = Def.settings(
+    // Use a separate cache box for the LinkerImpl in this project (don't use the Global one)
+    scalaJSLinkerImplBox := new CacheBox,
+
+    // Use our custom WasmLinkerImpl as the linker implementation used by fast/fullLinkJS
+    scalaJSLinkerImpl := {
+      val cp = (scalaJSLinkerImpl / fullClasspath).value
+      scalaJSLinkerImplBox.value.ensure {
+        new WasmLinkerImpl(LinkerImpl.reflect(Attributed.data(cp)))
+      }
+    },
+
+    // Automatically install all the configs required by the Wasm backend
+    scalaJSLinkerConfig ~= { prev =>
+      prev
+        .withModuleKind(ModuleKind.ESModule)
+        .withSemantics(_.optimized)
+        .withOutputPatterns(OutputPatterns.fromJSFile("%s.mjs"))
+        .withOptimizer(false)
+    },
+  )
+}

run.mjs

@@ -1,4 +1,4 @@
-import { test, field } from "./target/sample/main.mjs";
+import { test, field } from "./sample/target/scala-2.12/sample-fastopt/main.mjs";
 
 console.log(field);
 const o = test(7);

sample/src/main/scala/Sample.scala

@@ -15,6 +15,10 @@ object Main {
     true
   }
 
+  def main(args: Array[String]): Unit = {
+    println("hello world")
+  }
+
   private def println(x: Any): Unit =
     js.Dynamic.global.console.log("" + x)
 }