JNI: align inherited protocol requirement names across bindings

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/ProtocolRequirementNames.swift

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 NamingCallback {
+  func message() -> String
+}
+
+extension NamingCallback {
+  public func message() -> String { "default" }
+}
+
+struct DefaultNamingCallback: NamingCallback {}
+
+public func callNamingCallback(_ callback: some NamingCallback) -> String {
+  callback.message()
+}
+
+public func makeNamingCallback() -> any NamingCallback { DefaultNamingCallback() }
+
+public protocol NamingParent {
+  var id: Int64 { get }
+  func value(number: Int64) -> Int64
+}
+
+public protocol NamingChild: NamingParent {
+  var tag: Int64 { get }
+  func value(text: Int64) -> Int64
+}
+
+struct NamingValue: NamingChild {
+  var id: Int64 { 1 }
+  var tag: Int64 { 2 }
+  func value(number: Int64) -> Int64 { number + 10 }
+  func value(text: Int64) -> Int64 { text + 20 }
+}
+
+public func makeNamingChild() -> any NamingChild { NamingValue() }

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

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 ProtocolRequirementNamesTest {
+    @Test
+    void javaCallbackOverridesTheDefaultImplementation() {
+        NamingCallback callback = () -> "Java";
+        assertEquals("Java", MySwiftLibrary.callNamingCallback(callback));
+    }
+
+    @Test
+    void returnedBoxUsesTheDefaultImplementation() {
+        try (var arena = SwiftArena.ofConfined()) {
+            assertEquals("default", MySwiftLibrary.makeNamingCallback(arena).message());
+        }
+    }
+
+    @Test
+    void inheritedOverloadsDispatchToTheCorrectWitness() {
+        try (var arena = SwiftArena.ofConfined()) {
+            NamingChild child = MySwiftLibrary.makeNamingChild(arena);
+            assertEquals(1, child.getId());
+            assertEquals(2, child.getTag());
+            assertEquals(13, child.value(3));
+            assertEquals(23, child.valueText(3));
+        }
+    }
+}

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -173,7 +173,7 @@ extension JNISwift2JavaGenerator {
     let filename = "\(decl.effectiveJavaSimpleName).java"
     logger.debug("Printing contents: \(filename)")
 
-    resetForNewOutputFile(decl.initializers + decl.variables + decl.methods)
+    resetForNewOutputFile(decl.swiftNominal.kind == .protocol ? self.allProtocolRequirementMethods(of: decl) : decl.initializers + decl.variables + decl.methods)
 
     printHeader(&printer)
     printPackage(&printer)
@@ -283,6 +283,7 @@ extension JNISwift2JavaGenerator {
       printer.println()
 
       for method in self.allProtocolRequirementMethods(of: decl) {
+        self.currentJavaIdentifiers = identifiers(forProtocolRequirement: method)
         printExistentialBoxMethod(&printer, decl, method)
         printer.println()
       }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -311,7 +311,7 @@ extension JNISwift2JavaGenerator {
     printer.println()
 
     self.currentJavaIdentifiers = JavaIdentifierFactory(
-      type.initializers + type.variables + type.methods
+      type.swiftNominal.kind == .protocol ? self.allProtocolRequirementMethods(of: type) : type.initializers + type.variables + type.methods
     )
 
     switch type.swiftNominal.kind {
@@ -396,6 +396,7 @@ extension JNISwift2JavaGenerator {
     let boxParentName = SwiftQualifiedTypeName(type.swiftNominal.javaExistentialBoxName)
 
     for method in self.allProtocolRequirementMethods(of: type) {
+      self.currentJavaIdentifiers = identifiers(forProtocolRequirement: method)
       guard var translated = try? self.javaTranslator.translate(method) else {
         self.logger.debug("Failed to translate protocol requirement for existential box dispatch thunk: \(method)")
         continue

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator.swift

@@ -203,11 +203,25 @@ extension JNISwift2JavaGenerator {
   /// (getters/setters), excluding statics and anything whose signature
   /// doesn't translate (e.g. referencing `Self`/associated types).
   func supportedProtocolRequirements(of type: ExtractedNominalType) -> [ExtractedFunc] {
+    // Probe support without caching names before the declaring interface's
+    // complete requirement set has been selected for overload disambiguation.
     (type.methods + type.variables).filter { requirement in
-      requirement.isProtocolRequirement && !requirement.isStatic && !requirement.isClass && self.translatedDecl(for: requirement) != nil
+      requirement.isProtocolRequirement && !requirement.isStatic && !requirement.isClass
+        && (try? self.javaTranslator.translate(requirement)) != nil
     }
   }
 
+  /// Use the declaring interface's names when implementing an inherited requirement.
+  /// A refined protocol may introduce overloads, but cannot rename a parent's API.
+  func identifiers(forProtocolRequirement requirement: ExtractedFunc) -> JavaIdentifierFactory {
+    guard let name = requirement.parentType?.asNominalType?.nominalTypeDecl.qualifiedName,
+      let owner = analysis.extractedTypes[name]
+    else {
+      fatalError("Missing declaring protocol for requirement: \(requirement)")
+    }
+    return JavaIdentifierFactory(allProtocolRequirementMethods(of: owner))
+  }
+
   /// All wrappable requirements for `type` (a protocol), including those
   /// inherited from refined protocols — the transitive closure of
   /// `supportedProtocolRequirements(of:)`. Used to build an existential

Tests/JExtractSwiftTests/JNI/JNIProtocolRequirementNamesTests.swift

@@ -0,0 +1,80 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 JExtractSwiftLib
+import SwiftJavaConfigurationShared
+import Testing
+
+@Suite
+struct JNIProtocolRequirementNamesTests {
+  @Test("Default implementations do not rename Java requirements")
+  func defaultImplementation_java() throws {
+    var config = Configuration()
+    config.enableJavaCallbacks = true
+    try assertOutput(
+      input: """
+        public protocol Callback { func message() -> String }
+        extension Callback { public func message() -> String { "default" } }
+        public func makeCallback() -> any Callback
+        """,
+      config: config,
+      .jni,
+      .java,
+      expectedChunks: ["public java.lang.String message();", "public java.lang.String message() {"],
+      notExpectedChunks: ["message_()"]
+    )
+  }
+
+  private let inheritedSource = """
+    public protocol Parent {
+      var id: Int64 { get }
+      func value(number: Int64) -> Int64
+    }
+    public protocol Child: Parent {
+      var tag: Int64 { get }
+      func value(text: Int64) -> Int64
+    }
+    public func makeChild() -> any Child
+    """
+
+  @Test("Inherited box methods retain the declaring interface's names")
+  func inheritedRequirements_java() throws {
+    try assertOutput(
+      input: inheritedSource,
+      .jni,
+      .java,
+      expectedChunks: [
+        "public long value(long number);",
+        "public long valueText(long text);",
+        "public long value(long number) {",
+        "public long valueText(long text) {",
+      ],
+      notExpectedChunks: ["valueNumber("]
+    )
+  }
+
+  @Test("Inherited box dispatch thunks use the same names as Java")
+  func inheritedRequirements_swift() throws {
+    try assertOutput(
+      input: inheritedSource,
+      .jni,
+      .swift,
+      expectedChunks: [
+        "@_cdecl(\"Java_com_example_swift_ChildBox__00024value__JJJ\")",
+        "@_cdecl(\"Java_com_example_swift_ChildBox__00024valueText__JJJ\")",
+      ],
+      notExpectedChunks: ["ChildBox__00024valueNumber__"]
+    )
+  }
+}