Support Embedded Swift in WebGPUDemo (#44)

This adopts new `DefaultExecutorFactory`, which means we can mark `main` entrypoint as `async`. Due to swiftlang/swift#83750 we have to use `JSPromise`-returning functions from WebAPIKit, but otherwise this is now fully compatible with Embedded Swift.

Final binary size with full optimization: 390.5 kB.

Author: MaxDesiatov

WebGPUDemo/.sourcekit-lsp/config.json

@@ -1,5 +1,5 @@
 {
     "swiftPM": {
-        "swiftSDK": "swift-DEVELOPMENT-SNAPSHOT-2025-06-03-a_wasm"
+        "swiftSDK": "swift-DEVELOPMENT-SNAPSHOT-2025-08-14-a_wasm-embedded"
     }
 }

WebGPUDemo/Package.resolved

@@ -1,4 +1,4 @@
-// swift-tools-version: 6.1
+// swift-tools-version: 6.2
 
 import PackageDescription
 
@@ -11,7 +11,7 @@ let package = Package(
     ),
     .package(
       url: "https://github.com/swiftwasm/JavaScriptKit.git",
-      branch: "main",
+      from: "0.33.1",
     ),
   ],
   targets: [

WebGPUDemo/Package.swift

@@ -9,6 +9,16 @@ the Swift SDK in the following command to the version that matches your installe
 swift package --swift-sdk swift-6.2-DEVELOPMENT-SNAPSHOT-2025-06-17-a_wasm js --use-cdn
 ```
 
+If you'd like to produce a smaller binary (under 400 kB), you'll have to use
+`swift-DEVELOPMENT-SNAPSHOT-2025-08-11` or later development snapshot of the `main` Swift toolchain
+branch. Earlier versions (including Swift 6.2) have no support for `async` functions in Embedded Swift,
+which is required for WebGPU setup. Use the following command to build with Embedded Swift (update for
+your installed toolchain version if needed):
+
+```
+swift package --swift-sdk swift-DEVELOPMENT-SNAPSHOT-2025-08-11-a_wasm-embedded js --use-cdn -c release
+```
+
 WebGPU is enabled by default in beta and technical preview versions of Safari. Safari 17 and 18 require enabling
 WebGPU feature flag as shown on the screenshot:
 

WebGPUDemo/README.md

@@ -30,32 +30,34 @@ func fetchImageBitmap(url: String) async throws(JSException) -> ImageBitmap {
   )
 }
 
+typealias DefaultExecutorFactory = JavaScriptEventLoop
+
 @main
 struct Entrypoint {
-  static func main() {
-    JavaScriptEventLoop.installGlobalExecutor()
+  static func main() async {
     let gpu = Window.global.navigator.gpu
-    Task {
-      do throws(JSException) {
-        let adapter = try await gpu.requestAdapter()!
-        let device = try await adapter.requestDevice()
-
-        let renderer = try await Renderer(
-          device: device,
-          gpu: gpu,
-          assets: .init(
-            shaders: fetchString(url: "Resources/shaders.wgsl"),
-            model: fetchString(url: "Resources/SwiftLogo/Swift3DLogo.obj"),
-            albedo: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_BaseColor.png"),
-            normal: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_Normal.png"),
-            metalRoughness: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_MetalRoughness.png"),
-          ),
-        )
-
-        draw(renderer: renderer)
-      } catch {
-        console.error(data: error.thrownValue)
-      }
+
+    do throws(JSException) {
+      // Using promises instead of `async` functions due to https://github.com/swiftlang/swift/issues/83750
+      let adapterPromise: JSPromise = gpu.requestAdapter()
+      let devicePromise = JSPromise(from: try await adapterPromise.value().requestDevice())!
+      let device = try await GPUDevice(unsafelyWrapping: devicePromise.value().object!)
+
+      let renderer = try await Renderer(
+        device: device,
+        gpu: gpu,
+        assets: .init(
+          shaders: fetchString(url: "Resources/shaders.wgsl"),
+          model: fetchString(url: "Resources/SwiftLogo/Swift3DLogo.obj"),
+          albedo: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_BaseColor.png"),
+          normal: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_Normal.png"),
+          metalRoughness: fetchImageBitmap(url: "Resources/SwiftLogo/T_M_swiftLogo_MetalRoughness.png"),
+        ),
+      )
+
+      draw(renderer: renderer)
+    } catch {
+      console.error(data: error.thrownValue)
     }
   }
 }