[teamhimeh]

Problem

With Java callbacks enabled, JNI bindings for a public protocol-typed property can generate a Swift setter that references a wrapper class under a different name from its declaration. The generated Swift code then fails to compile.

For example, the JNI sample contains this API:

public protocol OverloadedCallback {
  func value() -> Int64
}

public final class ProtocolPropertyService {
  public var callback: any OverloadedCallback

  public init(callback: some OverloadedCallback) {
    self.callback = callback
  }

  public func read() -> Int64 {
    callback.value()
  }
}

Before this change, the wrapper declaration used the Swift property name, while the setter's argument conversion used the Java setter name:

// Generated wrapper declaration
final class _ProtocolPropertyService_callback_newValue_Wrapper: SwiftJavaOverloadedCallbackWrapper {
  // ...
}

// Generated setter argument conversion
newValueswiftObject$ = _ProtocolPropertyService_setCallback_newValue_Wrapper(
  _javaOverloadedCallbackInterface: JavaOverloadedCallback(javaThis: newValue!, environment: environment)
)

After this change, both the declaration and the setter conversion use _ProtocolPropertyService_setCallback_newValue_Wrapper. A Java implementation can therefore be assigned through the generated setter and called from Swift:

try (var arena = SwiftArena.ofConfined()) {
    var service = ProtocolPropertyService.init(() -> 10, arena);
    service.setCallback(() -> 42);
    assertEquals(42, service.read());
}

The same mismatch can occur when Java method names differ from Swift names for label-disambiguated overloads or Java keywords.

Changes

• Use a shared protocol adapter naming rule for the Swift wrapper declaration and native argument conversion. Methods and setters use the translated Java method name; initializers retain the Swift init name so overloads can share an identical adapter even when their Java names are disambiguated.
• Keep the Java method name used for closure translation unchanged.
• Add generator regression coverage for existential property setters, label-disambiguated overloads, Java keywords, and initializer overloads. The tests check both wrapper declarations and references, including that shared initializer adapters are emitted only once.
• Add the JNI sample above and a Java test that assigns a callback through the setter and calls it from Swift after assignment.

Validation

Tested on macOS 27.0.1 with Apple Swift 6.4.2 and JetBrains Runtime 25.0.2.

• swift test --disable-experimental-prebuilts --disable-sandbox (full Swift suite).
• ./gradlew :Samples:SwiftJavaExtractJNISampleApp:test --no-daemon (generated Swift and Java bindings compiled; all 297 Java tests passed, including the setter callback and existing initializer overload tests).
• swift-format lint --strict on changed Swift files and git diff --check.

The callback was exercised with Java on macOS; an Android or Kotlin runtime was not tested.