Fix JavaScriptEventLoop not building with Embedded Swift

The change fixes some issues in the JavaScriptKit library when build with Embedded Swift support. Specifically, `@MainActor` type is not available in Embedded Swift, thus `Atomic` type is used instead. Similarly, existential types are not available either, so they're replaced with concrete `some` types and generics.

Author: MaxDesiatov

Sources/JavaScriptEventLoop/JavaScriptEventLoop.swift

@@ -3,6 +3,10 @@ import _Concurrency
 import _CJavaScriptEventLoop
 import _CJavaScriptKit
 
+#if hasFeature(Embedded)
+import Synchronization
+#endif
+
 // NOTE: `@available` annotations are semantically wrong, but they make it easier to develop applications targeting WebAssembly in Xcode.
 
 #if compiler(>=5.5)
@@ -105,21 +109,39 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
         return eventLoop
     }
 
-    @MainActor private static var didInstallGlobalExecutor = false
+    #if !hasFeature(Embedded)
+    @MainActor
+    private static var didInstallGlobalExecutor = false
+    #else
+    private static let didInstallGlobalExecutor = Atomic<Bool>(false)
+    #endif
 
     /// Set JavaScript event loop based executor to be the global executor
     /// Note that this should be called before any of the jobs are created.
     /// This installation step will be unnecessary after custom executor are
     /// introduced officially. See also [a draft proposal for custom
     /// executors](https://github.com/rjmccall/swift-evolution/blob/custom-executors/proposals/0000-custom-executors.md#the-default-global-concurrent-executor)
     public static func installGlobalExecutor() {
+        #if !hasFeature(Embedded)
         MainActor.assumeIsolated {
             Self.installGlobalExecutorIsolated()
         }
+        #else
+        Self.installGlobalExecutorIsolated()
+        #endif
     }
 
-    @MainActor private static func installGlobalExecutorIsolated() {
+    #if !hasFeature(Embedded)
+    @MainActor
+    #endif
+    private static func installGlobalExecutorIsolated() {
+        #if !hasFeature(Embedded)
         guard !didInstallGlobalExecutor else { return }
+        #else
+        guard !didInstallGlobalExecutor.load(ordering: .sequentiallyConsistent) else {
+            return
+        }
+        #endif
 
         #if compiler(>=5.9)
         typealias swift_task_asyncMainDrainQueue_hook_Fn = @convention(thin) (
@@ -189,7 +211,11 @@ public final class JavaScriptEventLoop: SerialExecutor, @unchecked Sendable {
             to: UnsafeMutableRawPointer?.self
         )
 
+        #if !hasFeature(Embedded)
         didInstallGlobalExecutor = true
+        #else
+        didInstallGlobalExecutor.store(true, ordering: .sequentiallyConsistent)
+        #endif
     }
 
     private func enqueue(_ job: UnownedJob, withDelay nanoseconds: UInt64) {

Sources/JavaScriptKit/BasicObjects/JSPromise.swift

@@ -84,10 +84,9 @@ public final class JSPromise: JSBridgedClass {
     }
     #endif
 
-    #if !hasFeature(Embedded)
     /// Schedules the `success` closure to be invoked on successful completion of `self`.
     @discardableResult
-    public func then(success: @escaping (JSValue) -> ConvertibleToJSValue) -> JSPromise {
+    public func then(success: @escaping (JSValue) -> some ConvertibleToJSValue) -> JSPromise {
         let closure = JSOneshotClosure {
             success($0[0]).jsValue
         }
@@ -98,7 +97,7 @@ public final class JSPromise: JSBridgedClass {
     /// Schedules the `success` closure to be invoked on successful completion of `self`.
     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
     @discardableResult
-    public func then(success: sending @escaping (sending JSValue) async throws -> ConvertibleToJSValue) -> JSPromise {
+    public func then(success: sending @escaping (sending JSValue) async throws -> some ConvertibleToJSValue) -> JSPromise {
         let closure = JSOneshotClosure.async {
             try await success($0[0]).jsValue
         }
@@ -109,8 +108,8 @@ public final class JSPromise: JSBridgedClass {
     /// Schedules the `success` closure to be invoked on successful completion of `self`.
     @discardableResult
     public func then(
-        success: @escaping (sending JSValue) -> ConvertibleToJSValue,
-        failure: @escaping (sending JSValue) -> ConvertibleToJSValue
+        success: @escaping (sending JSValue) -> some ConvertibleToJSValue,
+        failure: @escaping (sending JSValue) -> some ConvertibleToJSValue
     ) -> JSPromise {
         let successClosure = JSOneshotClosure {
             success($0[0]).jsValue
@@ -126,8 +125,8 @@ public final class JSPromise: JSBridgedClass {
     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
     @discardableResult
     public func then(
-        success: sending @escaping (sending JSValue) async throws -> ConvertibleToJSValue,
-        failure: sending @escaping (sending JSValue) async throws -> ConvertibleToJSValue
+        success: sending @escaping (sending JSValue) async throws -> some ConvertibleToJSValue,
+        failure: sending @escaping (sending JSValue) async throws -> some ConvertibleToJSValue
     ) -> JSPromise {
         let successClosure = JSOneshotClosure.async {
             try await success($0[0]).jsValue
@@ -141,7 +140,9 @@ public final class JSPromise: JSBridgedClass {
 
     /// Schedules the `failure` closure to be invoked on rejected completion of `self`.
     @discardableResult
-    public func `catch`(failure: @escaping (sending JSValue) -> ConvertibleToJSValue) -> JSPromise {
+    public func `catch`(failure: @escaping (sending JSValue) -> some ConvertibleToJSValue)
+        -> JSPromise
+    {
         let closure = JSOneshotClosure {
             failure($0[0]).jsValue
         }
@@ -152,7 +153,7 @@ public final class JSPromise: JSBridgedClass {
     /// Schedules the `failure` closure to be invoked on rejected completion of `self`.
     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
     @discardableResult
-    public func `catch`(failure: sending @escaping (sending JSValue) async throws -> ConvertibleToJSValue) -> JSPromise
+    public func `catch`(failure: sending @escaping (sending JSValue) async throws -> some ConvertibleToJSValue) -> JSPromise
     {
         let closure = JSOneshotClosure.async {
             try await failure($0[0]).jsValue
@@ -171,5 +172,4 @@ public final class JSPromise: JSBridgedClass {
         }
         return .init(unsafelyWrapping: jsObject.finally!(closure).object!)
     }
-    #endif
 }

Sources/JavaScriptKit/FundamentalObjects/JSClosure.swift

@@ -1,4 +1,5 @@
 import _CJavaScriptKit
+import _Concurrency
 
 /// `JSClosureProtocol` wraps Swift closure objects for use in JavaScript. Conforming types
 /// are responsible for managing the lifetime of the closure they wrap, but can delegate that
@@ -40,7 +41,7 @@ public class JSOneshotClosure: JSObject, JSClosureProtocol {
         fatalError("JSOneshotClosure does not support dictionary literal initialization")
     }
 
-    #if compiler(>=5.5) && !hasFeature(Embedded)
+    #if compiler(>=5.5)
     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
     public static func async(_ body: sending @escaping (sending [JSValue]) async throws -> JSValue) -> JSOneshotClosure
     {