JNI: reuse protocol parameter adapters across overloads

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/ProtocolParameterOverloads.swift

@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+public protocol OverloadedCallback {
+  func value() -> Int64
+}
+
+public final class ProtocolParameterOverloads {
+  public let result: Int64
+
+  public init(callback: some OverloadedCallback) {
+    result = callback.value()
+  }
+
+  public init(callback: some OverloadedCallback, extra: Int64) {
+    result = callback.value() + extra
+  }
+
+  public func calculate(_ callback: some OverloadedCallback) -> Int64 {
+    result + callback.value()
+  }
+
+  public func calculate(_ callback: some OverloadedCallback, extra: Int64) -> Int64 {
+    result + callback.value() + extra
+  }
+}

Samples/SwiftJavaExtractJNISampleApp/src/test/java/com/example/swift/ProtocolParameterOverloadsTest.java

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+import org.junit.jupiter.api.Test;
+import org.swift.swiftkit.core.SwiftArena;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ProtocolParameterOverloadsTest {
+    @Test
+    void overloadedInitializersAndMethodsAcceptJavaCallbacks() {
+        OverloadedCallback callback = () -> 10;
+        try (var arena = SwiftArena.ofConfined()) {
+            var first = ProtocolParameterOverloads.init(callback, arena);
+            var second = ProtocolParameterOverloads.init(callback, 5, arena);
+            assertEquals(10, first.getResult());
+            assertEquals(15, second.getResult());
+            assertEquals(20, first.calculate(callback));
+            assertEquals(27, second.calculate(callback, 2));
+        }
+    }
+}

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -572,6 +572,12 @@ extension JNISwift2JavaGenerator {
         parentName: decl.parentType?.asNominalType?.nominalTypeDecl.qualifiedTypeName ?? SwiftQualifiedTypeName(swiftModuleName),
       )
       let implementingProtocols = protocolWrappers.map(\.wrapperName).joined(separator: .comma)
+      // Overloads with the same protocol parameter share an identical adapter.
+      if let existing = emittedProtocolParameterWrappers[swiftClassName] {
+        precondition(existing == implementingProtocols, "Conflicting protocol adapters for \(swiftClassName)")
+        continue
+      }
+      emittedProtocolParameterWrappers[swiftClassName] = implementingProtocols
 
       printer.printBraceBlock("final class \(swiftClassName): \(implementingProtocols)") { printer in
         let variables: [(String, String)] = protocolWrappers.map { wrapper in

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator.swift

@@ -60,6 +60,7 @@ package class JNISwift2JavaGenerator: Swift2JavaGenerator {
       .map(\.swiftNominal.identity)
   )
   var interfaceProtocolWrappers: [ExtractedNominalType: JavaInterfaceSwiftWrapper] = [:]
+  var emittedProtocolParameterWrappers: [String: String] = [:]
 
   /// Protocols that should be boxed to support returning them as `any P / some P`
   private(set) var existentialProtocolBoxes: [ExtractedNominalType] = []

Tests/JExtractSwiftTests/JNI/JNIProtocolParameterOverloadTests.swift

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import CodePrinting
+import Foundation
+import JExtractSwiftLib
+import SwiftJavaConfigurationShared
+import Testing
+
+@Suite
+struct JNIProtocolParameterOverloadTests {
+  @Test("Overloads share one adapter per protocol parameter")
+  func identicalAdaptersAreEmittedOnce() throws {
+    var config = Configuration()
+    config.swiftModule = "SwiftModule"
+    config.enableJavaCallbacks = true
+    let analyzer = makeSwiftJavaAnalyzer(config: config)
+    try analyzer.analyze(
+      path: "/fake/Overloads.swiftinterface",
+      text: """
+        public protocol Callback { func value() -> Int64 }
+        public struct Client {
+          public init(store: some Callback)
+          public init(store: some Callback, extra: Int64)
+        }
+        public func use(_ callback: some Callback)
+        public func use(_ callback: some Callback, extra: Int64)
+        public func other(_ callback: some Callback)
+        """
+    )
+    let generator = JNISwift2JavaGenerator(
+      config: config,
+      translator: analyzer,
+      javaPackage: "com.example.swift",
+      swiftOutputDirectory: "/fake",
+      javaOutputDirectory: "/fake",
+      javaClassLookupTable: [:],
+      moduleJavaPackages: [:]
+    )
+    var printer = SwiftPrinter(mode: .accumulateAll)
+    try generator.writeSwiftThunkSources(&printer)
+    let output = printer.finalize()
+    for name in ["_Client_init_store_Wrapper", "_SwiftModule_use_callback_Wrapper", "_SwiftModule_other_callback_Wrapper"] {
+      #expect(output.components(separatedBy: "final class \(name):").count - 1 == 1)
+    }
+  }
+}