swiftwasm · kateinoigakukun · Jun 16, 2025 · Jun 16, 2025
diff --git a/Plugins/BridgeJS/README.md b/Plugins/BridgeJS/README.md
@@ -135,3 +135,4 @@ TBD
     declare var Foo: FooConstructor;
     ```
 - [ ] Use `externref` once it's widely available
+- [ ] Test SwiftObject roundtrip
diff --git a/Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift b/Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift
@@ -111,6 +111,7 @@ struct BridgeJSLink {
 
                 let tmpRetString;
                 let tmpRetBytes;
+                let tmpRetException;
                 return {
                     /** @param {WebAssembly.Imports} importObject */
                     addImports: (importObject) => {
@@ -134,6 +135,9 @@ struct BridgeJSLink {
                             target.set(tmpRetBytes);
                             tmpRetBytes = undefined;
                         }
+                        bjs["swift_js_throw"] = function(id) {
+                            tmpRetException = swift.memory.retainByRef(id);
+                        }
                         bjs["swift_js_retain"] = function(id) {
                             return swift.memory.retainByRef(id);
                         }
@@ -188,6 +192,11 @@ struct BridgeJSLink {
         var bodyLines: [String] = []
         var cleanupLines: [String] = []
         var parameterForwardings: [String] = []
+        let effects: Effects
+
+        init(effects: Effects) {
+            self.effects = effects
+        }
 
         func lowerParameter(param: Parameter) {
             switch param.type {
@@ -245,7 +254,24 @@ struct BridgeJSLink {
         }
 
         func callConstructor(abiName: String) -> String {
-            return "instance.exports.\(abiName)(\(parameterForwardings.joined(separator: ", ")))"
+            let call = "instance.exports.\(abiName)(\(parameterForwardings.joined(separator: ", ")))"
+            bodyLines.append("const ret = \(call);")
+            return "ret"
+        }
+
+        func checkExceptionLines() -> [String] {
+            guard effects.isThrows else {
+                return []
+            }
+            return [
+                "if (tmpRetException) {",
+                // TODO: Implement "take" operation
+                "    const error = swift.memory.getObject(tmpRetException);",
+                "    swift.memory.release(tmpRetException);",
+                "    tmpRetException = undefined;",
+                "    throw error;",
+                "}",
+            ]
         }
 
         func renderFunction(
@@ -261,6 +287,7 @@ struct BridgeJSLink {
             )
             funcLines.append(contentsOf: bodyLines.map { $0.indent(count: 4) })
             funcLines.append(contentsOf: cleanupLines.map { $0.indent(count: 4) })
+            funcLines.append(contentsOf: checkExceptionLines().map { $0.indent(count: 4) })
             if let returnExpr = returnExpr {
                 funcLines.append("return \(returnExpr);".indent(count: 4))
             }
@@ -274,7 +301,7 @@ struct BridgeJSLink {
     }
 
     func renderExportedFunction(function: ExportedFunction) -> (js: [String], dts: [String]) {
-        let thunkBuilder = ExportedThunkBuilder()
+        let thunkBuilder = ExportedThunkBuilder(effects: function.effects)
         for param in function.parameters {
             thunkBuilder.lowerParameter(param: param)
         }
@@ -304,16 +331,17 @@ struct BridgeJSLink {
         jsLines.append("class \(klass.name) extends SwiftHeapObject {")
 
         if let constructor: ExportedConstructor = klass.constructor {
-            let thunkBuilder = ExportedThunkBuilder()
+            let thunkBuilder = ExportedThunkBuilder(effects: constructor.effects)
             for param in constructor.parameters {
                 thunkBuilder.lowerParameter(param: param)
             }
-            let returnExpr = thunkBuilder.callConstructor(abiName: constructor.abiName)
             var funcLines: [String] = []
             funcLines.append("constructor(\(constructor.parameters.map { $0.name }.joined(separator: ", "))) {")
+            let returnExpr = thunkBuilder.callConstructor(abiName: constructor.abiName)
             funcLines.append(contentsOf: thunkBuilder.bodyLines.map { $0.indent(count: 4) })
-            funcLines.append("super(\(returnExpr), instance.exports.bjs_\(klass.name)_deinit);".indent(count: 4))
             funcLines.append(contentsOf: thunkBuilder.cleanupLines.map { $0.indent(count: 4) })
+            funcLines.append(contentsOf: thunkBuilder.checkExceptionLines().map { $0.indent(count: 4) })
+            funcLines.append("super(\(returnExpr), instance.exports.bjs_\(klass.name)_deinit);".indent(count: 4))
             funcLines.append("}")
             jsLines.append(contentsOf: funcLines.map { $0.indent(count: 4) })
 
@@ -324,7 +352,7 @@ struct BridgeJSLink {
         }
 
         for method in klass.methods {
-            let thunkBuilder = ExportedThunkBuilder()
+            let thunkBuilder = ExportedThunkBuilder(effects: method.effects)
             thunkBuilder.lowerSelf()
             for param in method.parameters {
                 thunkBuilder.lowerParameter(param: param)

diff --git a/Plugins/BridgeJS/Sources/BridgeJSSkeleton/BridgeJSSkeleton.swift b/Plugins/BridgeJS/Sources/BridgeJSSkeleton/BridgeJSSkeleton.swift
@@ -16,13 +16,19 @@ struct Parameter: Codable {
     let type: BridgeType
 }
 
+struct Effects: Codable {
+    var isAsync: Bool
+    var isThrows: Bool
+}
+
 // MARK: - Exported Skeleton
 
 struct ExportedFunction: Codable {
     var name: String
     var abiName: String
     var parameters: [Parameter]
     var returnType: BridgeType
+    var effects: Effects
 }
 
 struct ExportedClass: Codable {
@@ -34,6 +40,7 @@ struct ExportedClass: Codable {
 struct ExportedConstructor: Codable {
     var abiName: String
     var parameters: [Parameter]
+    var effects: Effects
 }
 
 struct ExportedSkeleton: Codable {

diff --git a/Plugins/BridgeJS/Sources/BridgeJSTool/ExportSwift.swift b/Plugins/BridgeJS/Sources/BridgeJSTool/ExportSwift.swift
@@ -155,14 +155,43 @@ class ExportSwift {
                 abiName = "bjs_\(className)_\(name)"
             }
 
+            guard let effects = collectEffects(signature: node.signature) else {
+                return nil
+            }
+
             return ExportedFunction(
                 name: name,
                 abiName: abiName,
                 parameters: parameters,
-                returnType: returnType
+                returnType: returnType,
+                effects: effects
             )
         }
 
+        private func collectEffects(signature: FunctionSignatureSyntax) -> Effects? {
+            let isAsync = signature.effectSpecifiers?.asyncSpecifier != nil
+            var isThrows = false
+            if let throwsClause: ThrowsClauseSyntax = signature.effectSpecifiers?.throwsClause {
+                // Limit the thrown type to JSException for now
+                guard let thrownType = throwsClause.type else {
+                    diagnose(
+                        node: throwsClause,
+                        message: "Thrown type is not specified, only JSException is supported for now"
+                    )
+                    return nil
+                }
+                guard thrownType.trimmedDescription == "JSException" else {
+                    diagnose(
+                        node: throwsClause,
+                        message: "Only JSException is supported for thrown type, got \(thrownType.trimmedDescription)"
+                    )
+                    return nil
+                }
+                isThrows = true
+            }
+            return Effects(isAsync: isAsync, isThrows: isThrows)
+        }
+
         override func visit(_ node: InitializerDeclSyntax) -> SyntaxVisitorContinueKind {
             guard node.attributes.hasJSAttribute() else { return .skipChildren }
             guard case .classBody(let name) = state else {
@@ -180,9 +209,14 @@ class ExportSwift {
                 parameters.append(Parameter(label: label, name: name, type: type))
             }
 
+            guard let effects = collectEffects(signature: node.signature) else {
+                return .skipChildren
+            }
+
             let constructor = ExportedConstructor(
                 abiName: "bjs_\(name)_init",
-                parameters: parameters
+                parameters: parameters,
+                effects: effects
             )
             exportedClasses[name]?.constructor = constructor
             return .skipChildren
@@ -245,6 +279,8 @@ class ExportSwift {
 
         @_extern(wasm, module: "bjs", name: "swift_js_retain")
         private func _swift_js_retain(_ ptr: Int32) -> Int32
+        @_extern(wasm, module: "bjs", name: "swift_js_throw")
+        private func _swift_js_throw(_ id: Int32)
         """
 
     func renderSwiftGlue() -> String? {
@@ -268,6 +304,11 @@ class ExportSwift {
         var abiParameterForwardings: [LabeledExprSyntax] = []
         var abiParameterSignatures: [(name: String, type: WasmCoreType)] = []
         var abiReturnType: WasmCoreType?
+        let effects: Effects
+
+        init(effects: Effects) {
+            self.effects = effects
+        }
 
         func liftParameter(param: Parameter) {
             switch param.type {
@@ -350,35 +391,40 @@ class ExportSwift {
             }
         }
 
-        func call(name: String, returnType: BridgeType) {
+        private func renderCallStatement(callee: ExprSyntax, returnType: BridgeType) -> StmtSyntax {
+            var callExpr: ExprSyntax =
+                "\(raw: callee)(\(raw: abiParameterForwardings.map { $0.description }.joined(separator: ", ")))"
+            if effects.isAsync {
+                callExpr = ExprSyntax(AwaitExprSyntax(awaitKeyword: .keyword(.await), expression: callExpr))
+            }
+            if effects.isThrows {
+                callExpr = ExprSyntax(
+                    TryExprSyntax(
+                        tryKeyword: .keyword(.try).with(\.trailingTrivia, .space),
+                        expression: callExpr
+                    )
+                )
+            }
             let retMutability = returnType == .string ? "var" : "let"
-            let callExpr: ExprSyntax =
-                "\(raw: name)(\(raw: abiParameterForwardings.map { $0.description }.joined(separator: ", ")))"
             if returnType == .void {
-                body.append("\(raw: callExpr)")
+                return StmtSyntax("\(raw: callExpr)")
             } else {
-                body.append(
-                    """
-                    \(raw: retMutability) ret = \(raw: callExpr)
-                    """
-                )
+                return StmtSyntax("\(raw: retMutability) ret = \(raw: callExpr)")
             }
         }
 
+        func call(name: String, returnType: BridgeType) {
+            let stmt = renderCallStatement(callee: "\(raw: name)", returnType: returnType)
+            body.append(CodeBlockItemSyntax(item: .stmt(stmt)))
+        }
+
         func callMethod(klassName: String, methodName: String, returnType: BridgeType) {
             let _selfParam = self.abiParameterForwardings.removeFirst()
-            let retMutability = returnType == .string ? "var" : "let"
-            let callExpr: ExprSyntax =
-                "\(raw: _selfParam).\(raw: methodName)(\(raw: abiParameterForwardings.map { $0.description }.joined(separator: ", ")))"
-            if returnType == .void {
-                body.append("\(raw: callExpr)")
-            } else {
-                body.append(
-                    """
-                    \(raw: retMutability) ret = \(raw: callExpr)
-                    """
-                )
-            }
+            let stmt = renderCallStatement(
+                callee: "\(raw: _selfParam).\(raw: methodName)",
+                returnType: returnType
+            )
+            body.append(CodeBlockItemSyntax(item: .stmt(stmt)))
         }
 
         func lowerReturnValue(returnType: BridgeType) {
@@ -440,19 +486,54 @@ class ExportSwift {
         }
 
         func render(abiName: String) -> DeclSyntax {
+            let body: CodeBlockItemListSyntax
+            if effects.isThrows {
+                body = """
+                    do {
+                        \(CodeBlockItemListSyntax(self.body))
+                    } catch let error {
+                        if let error = error.thrownValue.object {
+                            withExtendedLifetime(error) {
+                                _swift_js_throw(Int32(bitPattern: $0.id))
+                            }
+                        } else {
+                            let jsError = JSError(message: String(describing: error))
+                            withExtendedLifetime(jsError.jsObject) {
+                                _swift_js_throw(Int32(bitPattern: $0.id))
+                            }
+                        }
+                        \(raw: returnPlaceholderStmt())
+                    }
+                    """
+            } else {
+                body = CodeBlockItemListSyntax(self.body)
+            }
             return """
                 @_expose(wasm, "\(raw: abiName)")
                 @_cdecl("\(raw: abiName)")
                 public func _\(raw: abiName)(\(raw: parameterSignature())) -> \(raw: returnSignature()) {
-                \(CodeBlockItemListSyntax(body))
+                \(body)
                 }
                 """
         }
 
+        private func returnPlaceholderStmt() -> String {
+            switch abiReturnType {
+            case .i32: return "return 0"
+            case .i64: return "return 0"
+            case .f32: return "return 0.0"
+            case .f64: return "return 0.0"
+            case .pointer: return "return UnsafeMutableRawPointer(bitPattern: -1)"
+            case .none: return "return"
+            }
+        }
+
         func parameterSignature() -> String {
-            abiParameterSignatures.map { "\($0.name): \($0.type.swiftType)" }.joined(
-                separator: ", "
-            )
+            var nameAndType: [(name: String, abiType: String)] = []
+            for (name, type) in abiParameterSignatures {
+                nameAndType.append((name, type.swiftType))
+            }
+            return nameAndType.map { "\($0.name): \($0.abiType)" }.joined(separator: ", ")
         }
 
         func returnSignature() -> String {
@@ -461,7 +542,7 @@ class ExportSwift {
     }
 
     func renderSingleExportedFunction(function: ExportedFunction) -> DeclSyntax {
-        let builder = ExportedThunkBuilder()
+        let builder = ExportedThunkBuilder(effects: function.effects)
         for param in function.parameters {
             builder.liftParameter(param: param)
         }
@@ -520,7 +601,7 @@ class ExportSwift {
     func renderSingleExportedClass(klass: ExportedClass) -> [DeclSyntax] {
         var decls: [DeclSyntax] = []
         if let constructor = klass.constructor {
-            let builder = ExportedThunkBuilder()
+            let builder = ExportedThunkBuilder(effects: constructor.effects)
             for param in constructor.parameters {
                 builder.liftParameter(param: param)
             }
@@ -529,7 +610,7 @@ class ExportSwift {
             decls.append(builder.render(abiName: constructor.abiName))
         }
         for method in klass.methods {
-            let builder = ExportedThunkBuilder()
+            let builder = ExportedThunkBuilder(effects: method.effects)
             builder.liftParameter(
                 param: Parameter(label: nil, name: "_self", type: .swiftHeapObject(klass.name))
             )

diff --git a/Plugins/BridgeJS/Tests/BridgeJSToolTests/Inputs/Throws.swift b/Plugins/BridgeJS/Tests/BridgeJSToolTests/Inputs/Throws.swift
@@ -0,0 +1,3 @@
+@JS func throwsSomething() throws(JSException) {
+    throw JSException(JSError(message: "TestError").jsValue)
+}
diff --git a/...BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/ArrayParameter.Import.js b/...BridgeJS/Tests/BridgeJSToolTests/__Snapshots__/BridgeJSLinkTests/ArrayParameter.Import.js
@@ -12,6 +12,7 @@ export async function createInstantiator(options, swift) {
 
     let tmpRetString;
     let tmpRetBytes;
+    let tmpRetException;
     return {
         /** @param {WebAssembly.Imports} importObject */
         addImports: (importObject) => {
@@ -35,6 +36,9 @@ export async function createInstantiator(options, swift) {
                 target.set(tmpRetBytes);
                 tmpRetBytes = undefined;
             }
+            bjs["swift_js_throw"] = function(id) {
+                tmpRetException = swift.memory.retainByRef(id);
+            }
             bjs["swift_js_retain"] = function(id) {
                 return swift.memory.retainByRef(id);
             }