BridgeJS: Improve diagnostics with multi-module AOT

Author: wfltaylor

Examples/MultiModule/Sources/MultiModule/bridge-js.config.json

@@ -0,0 +1 @@
+{}

Plugins/BridgeJS/Sources/BridgeJSCommandPlugin/BridgeJSCommandPlugin.swift

@@ -164,6 +164,15 @@ extension BridgeJSCommandPlugin.Context {
             guard let dependencyTarget = bridgeJSTargets[dependency.name] else { continue }
             let dependencySkeletonPath = dependencyTarget.directoryURL
                 .appending(path: "Generated/JavaScript/BridgeJS.json")
+            guard FileManager.default.fileExists(atPath: dependencySkeletonPath.path) else {
+                throw BridgeJSCommandPluginError(
+                    """
+                    Dependency '\(dependencyTarget.name)' is configured for BridgeJS, but its AOT skeleton has not been generated yet. \
+                    Run `swift package bridge-js --target \(dependencyTarget.name)` to generate it first, \
+                    or run without `--target` to process in dependency order.
+                    """
+                )
+            }
             generateArguments.append(contentsOf: [
                 "--dependency-skeleton",
                 "\(dependencyTarget.name)=\(dependencySkeletonPath.path)",
@@ -206,6 +215,14 @@ private func printStderr(_ message: String) {
     fputs(message + "\n", stderr)
 }
 
+struct BridgeJSCommandPluginError: Error, CustomStringConvertible {
+    let description: String
+
+    init(_ message: String) {
+        self.description = message
+    }
+}
+
 extension SwiftSourceModuleTarget {
     func hasDependency(named name: String) -> Bool {
         return dependencies.contains(where: {

Tests/JavaScriptEventLoopTests/JSClosure+AsyncTests.swift

@@ -72,7 +72,7 @@ class JSClosureAsyncTests: XCTestCase {
         )!.value()
         XCTAssertEqual(result, 42.0)
     }
-
+    
     func testAsyncOneshotClosureWithPriority() async throws {
         let priority = UnsafeSendableBox<TaskPriority?>(nil)
         let closure = JSOneshotClosure.async(priority: .high) { _ in
@@ -83,7 +83,7 @@ class JSClosureAsyncTests: XCTestCase {
         XCTAssertEqual(result, 42.0)
         XCTAssertEqual(priority.value, .high)
     }
-
+    
     @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
     func testAsyncOneshotClosureWithTaskExecutor() async throws {
         let executor = AnyTaskExecutor()
@@ -93,7 +93,7 @@ class JSClosureAsyncTests: XCTestCase {
         let result = try await JSPromise(from: closure.function!())!.value()
         XCTAssertEqual(result, 42.0)
     }
-
+    
     @available(macOS 15.0, iOS 18.0, watchOS 11.0, tvOS 18.0, visionOS 2.0, *)
     func testAsyncOneshotClosureWithTaskExecutorPreference() async throws {
         let executor = AnyTaskExecutor()