fix: generate mutable self binding for @JS mutating struct methods

Plugins/BridgeJS/Sources/BridgeJSCore/ExportSwift.swift

@@ -228,14 +228,24 @@ public class ExportSwift {
             }
         }
 
-        func callMethod(methodName: String, returnType: BridgeType) {
-            let (_, selfExpr) = removeFirstLiftedParameter()
-            generateParameterLifting()
-            let item = renderCallStatement(
-                callee: "\(raw: selfExpr).\(raw: methodName)",
-                returnType: returnType
-            )
-            append(item)
+        func callMethod(methodName: String, returnType: BridgeType, isMutating: Bool = false) {
+            let (selfParam, selfExpr) = removeFirstLiftedParameter()
+            if isMutating, case .swiftStruct = selfParam.type {
+                append("var _self = \(selfExpr)")
+                generateParameterLifting()
+                let item = renderCallStatement(
+                    callee: "_self.\(raw: methodName)",
+                    returnType: returnType
+                )
+                append(item)
+            } else {
+                generateParameterLifting()
+                let item = renderCallStatement(
+                    callee: "\(raw: selfExpr).\(raw: methodName)",
+                    returnType: returnType
+                )
+                append(item)
+            }
         }
 
         /// Generates intermediate variables for stack-using parameters if needed for LIFO compatibility
@@ -561,7 +571,7 @@ public class ExportSwift {
         if method.effects.isStatic {
             builder.call(name: "\(ownerTypeName).\(method.name)", returnType: method.returnType)
         } else {
-            builder.callMethod(methodName: method.name, returnType: method.returnType)
+            builder.callMethod(methodName: method.name, returnType: method.returnType, isMutating: method.effects.isMutating)
         }
         try builder.lowerReturnValue(returnType: method.returnType)
         return builder.render(abiName: method.abiName)

Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift

@@ -1198,7 +1198,8 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
             className: classNameForABI
         )
 
-        guard let effects = collectEffects(signature: node.signature, isStatic: isStatic) else {
+        let isMutating = node.modifiers.contains { $0.name.tokenKind == .keyword(.mutating) }
+        guard let effects = collectEffects(signature: node.signature, isStatic: isStatic, isMutating: isMutating) else {
             return nil
         }
 
@@ -1213,7 +1214,7 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
         )
     }
 
-    private func collectEffects(signature: FunctionSignatureSyntax, isStatic: Bool = false) -> Effects? {
+    private func collectEffects(signature: FunctionSignatureSyntax, isStatic: Bool = false, isMutating: Bool = false) -> Effects? {
         let isAsync = signature.effectSpecifiers?.asyncSpecifier != nil
         var isThrows = false
         if let throwsClause: ThrowsClauseSyntax = signature.effectSpecifiers?.throwsClause {
@@ -1234,7 +1235,7 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
             }
             isThrows = true
         }
-        return Effects(isAsync: isAsync, isThrows: isThrows, isStatic: isStatic)
+        return Effects(isAsync: isAsync, isThrows: isThrows, isStatic: isStatic, isMutating: isMutating)
     }
 
     private func extractNamespace(
@@ -1522,7 +1523,7 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
         }
     }
 
-    /// Walks extension members under the matching type’s state, returning whether the type was found.
+    /// Walks extension members under the matching type's state, returning whether the type was found.
     ///
     /// Note: The lookup scans dictionaries keyed by `makeKey(name:namespace:)`, matching only by
     /// plain name. If two types share a name but differ by namespace, `.first(where:)` picks

Plugins/BridgeJS/Sources/BridgeJSSkeleton/BridgeJSSkeleton.swift

@@ -635,11 +635,35 @@ public struct Effects: Codable, Equatable, Sendable {
     public var isAsync: Bool
     public var isThrows: Bool
     public var isStatic: Bool
+    public var isMutating: Bool
 
-    public init(isAsync: Bool, isThrows: Bool, isStatic: Bool = false) {
+    public init(isAsync: Bool, isThrows: Bool, isStatic: Bool = false, isMutating: Bool = false) {
         self.isAsync = isAsync
         self.isThrows = isThrows
         self.isStatic = isStatic
+        self.isMutating = isMutating
+    }
+
+    private enum CodingKeys: String, CodingKey {
+        case isAsync, isThrows, isStatic, isMutating
+    }
+
+    public init(from decoder: any Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        self.isAsync = try container.decode(Bool.self, forKey: .isAsync)
+        self.isThrows = try container.decode(Bool.self, forKey: .isThrows)
+        self.isStatic = try container.decode(Bool.self, forKey: .isStatic)
+        self.isMutating = try container.decodeIfPresent(Bool.self, forKey: .isMutating) ?? false
+    }
+
+    public func encode(to encoder: any Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        try container.encode(isAsync, forKey: .isAsync)
+        try container.encode(isThrows, forKey: .isThrows)
+        try container.encode(isStatic, forKey: .isStatic)
+        if isMutating {
+            try container.encode(isMutating, forKey: .isMutating)
+        }
     }
 }
 

Plugins/BridgeJS/Tests/BridgeJSToolTests/Inputs/MacroSwift/MutatingStructMethod.swift

@@ -0,0 +1,12 @@
+@JS struct Counter {
+    var number: Int
+}
+
+extension Counter {
+    @JS public mutating func increment() {
+        number += 1
+    }
+    @JS public mutating func add(_ value: Int) {
+        number += value
+    }
+}