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jextract: Translate Swift () -> () to java Runnable #820

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d55d7f3
jextract: Translate Swift () -> () to java Runnable
AmrDeveloper Jul 7, 2026
9b4f4c4
Create extractKnownJavaFunctionalInterfaceType to handle known interf…
AmrDeveloper Jul 9, 2026
b5e39bb
Support JNI and Native translation
AmrDeveloper Jul 9, 2026
97a2fed
Use full class name for java.lang.Runnable
AmrDeveloper Jul 9, 2026
39d6dbe
Use Runnable in the sample app
AmrDeveloper Jul 10, 2026
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4 changes: 2 additions & 2 deletions Samples/SwiftJavaExtractFFMSampleApp/src/test/java/com/example/swift/MySwiftLibraryTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -81,9 +81,9 @@ void call_globalStringIdentity_empty() {
void call_globalCallMeRunnable() {
CountDownLatch countDownLatch = new CountDownLatch(3);

MySwiftLibrary.globalCallMeRunnable(new MySwiftLibrary.globalCallMeRunnable.run() {
MySwiftLibrary.globalCallMeRunnable(new java.lang.Runnable() {

@ktoso ktoso Jul 11, 2026

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Good Yeap!

@Override
public void apply() {
public void run() {
countDownLatch.countDown();
}
});
Expand Down
21 changes: 21 additions & 0 deletions Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaBindingsPrinting.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -255,6 +255,17 @@ extension FFMSwift2JavaGenerator {
}

printFunctionDescriptorDefinition(&printer, cResultType, cParams)
if cParameterTypes.isEmpty && cResultType.isVoid {
printer.print(
"""
private static final MethodHandle HANDLE = SwiftRuntime.upcallHandle(java.lang.Runnable.class, "run", DESC);
private static MemorySegment toUpcallStub(java.lang.Runnable fi, Arena arena) {
return Linker.nativeLinker().upcallStub(HANDLE.bindTo(fi), DESC, arena);
}
"""
)
return
}
printer.print(
"""
private static final MethodHandle HANDLE = SwiftRuntime.upcallHandle(Function.class, "apply", DESC);
Expand Down Expand Up @@ -296,6 +307,16 @@ extension FFMSwift2JavaGenerator {
) {
let cdeclDescriptor = "\(bindingDescriptorName).$\(functionType.name)"
if functionType.isCompatibleWithC {
if !functionType.swiftType.isEscaping && functionType.parameters.isEmpty && functionType.swiftType.resultType.isVoid {
printer.print(
"""
private static MemorySegment $toUpcallStub(java.lang.Runnable fi, Arena arena) {
return \(bindingDescriptorName).$\(functionType.name).toUpcallStub(fi, arena);
}
"""
)
return
}
// If the user-facing functional interface is C ABI compatible, just extend
// the lowered function pointer parameter interface.
printer.print(
Expand Down
41 changes: 34 additions & 7 deletions Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaTranslation.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -489,13 +489,11 @@ extension FFMSwift2JavaGenerator {
genericRequirements: genericRequirements
)

case .function:
return TranslatedParameter(
parameter: JavaParameter(
name: parameterName,
type: JavaType.class(package: nil, name: "\(methodName).\(parameterName)")
),
conversion: .call(.placeholder, function: "\(methodName).$toUpcallStub", withArena: true)
case .function(let functionType):
return translateFunctionParameter(
functionType: functionType,
parameterName: parameterName,
methodName: methodName
)

case .existential, .opaque, .genericParameter:
Expand Down Expand Up @@ -568,6 +566,35 @@ extension FFMSwift2JavaGenerator {
)
}

// Extract Java known functional interface type or null if not exists
func extractKnownJavaFunctionalInterfaceType(
functionType: SwiftFunctionType,
) -> JavaType? {
if functionType.parameters.isEmpty && functionType.resultType.isVoid {
JavaType.javaLangRunnable
} else {
nil
}
}

/// Translate a Swift Function parameter to the Java interface.
func translateFunctionParameter(
functionType: SwiftFunctionType,
parameterName: String,
methodName: String,
) -> TranslatedParameter {
let parameterType =
extractKnownJavaFunctionalInterfaceType(functionType: functionType) ?? JavaType.class(package: nil, name: "\(methodName).\(parameterName)")

return TranslatedParameter(
parameter: JavaParameter(
name: parameterName,
type: parameterType
),
conversion: .call(.placeholder, function: "\(methodName).$toUpcallStub", withArena: true)
)
}

/// Translate an Optional Swift API parameter to the user-facing Java API parameter.
func translateOptionalParameter(
wrappedType swiftType: SwiftType,
Expand Down
65 changes: 54 additions & 11 deletions Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -516,17 +516,14 @@ extension JNISwift2JavaGenerator {
conversion: .placeholder,
)

case .function:
return TranslatedParameter(
parameter: JavaParameter(
name: parameterName,
type: .class(
package: javaPackage,
name: String.javaQualifiedName(parentName.fullName, methodName, parameterName)
),
annotations: parameterAnnotations,
),
conversion: .placeholder,
case .function(let functionType):
return translateFunctionParameter(
swiftType: swiftType,
functionType: functionType,
parameterName: parameterName,
methodName: methodName,
parentName: parentName,
parameterAnnotations: parameterAnnotations
)

case .opaque(let proto), .existential(let proto):
Expand Down Expand Up @@ -699,6 +696,52 @@ extension JNISwift2JavaGenerator {
nativeFunctionSignature.result.outParameters.append(.init(name: "result_future", type: nativeFutureType))
}

func extractKnownJavaFunctionalInterfaceType(
swiftType: SwiftType,
functionType: SwiftFunctionType,
parameterName: String,
parameterAnnotations: [JavaAnnotation]
) -> TranslatedParameter? {
if !functionType.isEscaping && functionType.parameters.isEmpty && functionType.resultType.isVoid {
return TranslatedParameter(
parameter: JavaParameter(
name: parameterName,
type: JavaType.javaLangRunnable,
annotations: parameterAnnotations,
),
conversion: .placeholder,
)
}
return nil
}

func translateFunctionParameter(
swiftType: SwiftType,
functionType: SwiftFunctionType,
parameterName: String,
methodName: String,
parentName: SwiftQualifiedTypeName,
parameterAnnotations: [JavaAnnotation]
) -> TranslatedParameter {
extractKnownJavaFunctionalInterfaceType(
swiftType: swiftType,
functionType: functionType,
parameterName: parameterName,
parameterAnnotations: parameterAnnotations
)
?? TranslatedParameter(
parameter: JavaParameter(
name: parameterName,
type: .class(
package: javaPackage,
name: String.javaQualifiedName(parentName.fullName, methodName, parameterName)
),
annotations: parameterAnnotations,
),
conversion: .placeholder,
)
}

func translateProtocolParameter(
protocolType: SwiftType,
parameterName: String,
Expand Down
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