Fix Embedded, bump 6.3 Swift toolchain in test.yml

.github/workflows/test.yml

@@ -26,7 +26,7 @@ jobs:
             target: "wasm32-unknown-wasip1"
           - os: ubuntu-24.04
             toolchain:
-              download-url: https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DEVELOPMENT-SNAPSHOT-2025-12-05-a/swift-6.3-DEVELOPMENT-SNAPSHOT-2025-12-05-a-ubuntu24.04.tar.gz
+              download-url: https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DEVELOPMENT-SNAPSHOT-2026-03-05-a/swift-6.3-DEVELOPMENT-SNAPSHOT-2026-03-05-a-ubuntu24.04.tar.gz
             wasi-backend: Node
             target: "wasm32-unknown-wasip1"
           - os: ubuntu-22.04

Sources/JavaScriptEventLoop/JavaScriptEventLoop+ExecutorFactory.swift

@@ -5,7 +5,7 @@
 // See: https://forums.swift.org/t/pitch-2-custom-main-and-global-executors/78437
 
 #if compiler(>=6.3)
-@_spi(ExperimentalCustomExecutors) import _Concurrency
+@_spi(ExperimentalCustomExecutors) @_spi(ExperimentalScheduling) import _Concurrency
 #else
 import _Concurrency
 #endif
@@ -42,20 +42,29 @@ extension JavaScriptEventLoop: SchedulingExecutor {
     ) {
         let duration: Duration
         // Handle clocks we know
+        #if !hasFeature(Embedded)
         if let _ = clock as? ContinuousClock {
             duration = delay as! ContinuousClock.Duration
         } else if let _ = clock as? SuspendingClock {
             duration = delay as! SuspendingClock.Duration
         } else {
-            // Hand-off the scheduling work to Clock implementation for unknown clocks
+            #if compiler(>=6.4)
+            // Hand-off the scheduling work to Clock implementation for unknown clocks.
+            // Clock.enqueue is only available in the development branch (6.4+).
             clock.enqueue(
                 job,
                 on: self,
                 at: clock.now.advanced(by: delay),
                 tolerance: tolerance
             )
             return
+            #else
+            fatalError("Unsupported clock type; only ContinuousClock and SuspendingClock are supported")
+            #endif
         }
+        #else
+        fatalError("SchedulingExecutor.enqueue is not supported in embedded mode")
+        #endif
         let milliseconds = Self.delayInMilliseconds(from: duration)
         self.enqueue(
             UnownedJob(job),
@@ -81,6 +90,7 @@ extension JavaScriptEventLoop: ExecutorFactory {
             JavaScriptEventLoop.shared.enqueue(job)
         }
 
+        #if !hasFeature(Embedded)
         func enqueue<C: Clock>(
             _ job: consuming ExecutorJob,
             after delay: C.Duration,
@@ -94,6 +104,7 @@ extension JavaScriptEventLoop: ExecutorFactory {
                 clock: clock
             )
         }
+        #endif
         func run() throws {
             try JavaScriptEventLoop.shared.run()
         }

Sources/JavaScriptEventLoop/JavaScriptEventLoop.swift

@@ -123,13 +123,16 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
     private static func installGlobalExecutorIsolated() {
         guard !didInstallGlobalExecutor else { return }
         didInstallGlobalExecutor = true
-        #if compiler(>=6.3)
+        #if compiler(>=6.3) && !hasFeature(Embedded)
         if #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, visionOS 9999, *) {
             // For Swift 6.3 and above, we can use the new `ExecutorFactory` API
             _Concurrency._createExecutors(factory: JavaScriptEventLoop.self)
         }
         #else
-        // For Swift 6.1 and below, we need to install the global executor by hook API
+        // For Swift 6.1 and below, or Embedded Swift, we need to install
+        // the global executor by hook API. The ExecutorFactory mechanism
+        // does not work in Embedded Swift because ExecutorImpl.swift is
+        // excluded from the embedded Concurrency library.
         installByLegacyHook()
         #endif
     }