Update for review

Author: rintaro

Sources/JExtractSwiftLib/Swift2JavaTranslator+JavaBindingsPrinting.swift

@@ -130,7 +130,7 @@ extension Swift2JavaTranslator {
 
   /// Print required helper classes/interfaces for describing the CFunction.
   ///
-  /// * function pointer parameter as a function interface.
+  /// * function pointer parameter as a functional interface.
   /// * Unnamed-struct parameter as a record. (unimplemented)
   func printParameterDescriptorClasses(
     _ printer: inout CodePrinter,
@@ -151,6 +151,7 @@ extension Swift2JavaTranslator {
   ///
   ///   ```java
   ///   class $<parameter-name> {
+  ///     @FunctionalInterface
   ///     interface Function {
   ///       <return-type> apply(<parameters>);
   ///     }
@@ -167,7 +168,7 @@ extension Swift2JavaTranslator {
     _ cType: CType
   ) {
     guard case .pointer(.function(let cResultType, let cParameterTypes, variadic: false)) = cType else {
-      preconditionFailure("must be a C function pointer type")
+      preconditionFailure("must be a C function pointer type; name=\(name), cType=\(cType)")
     }
 
     let cParams = cParameterTypes.enumerated().map { i, ty in
@@ -187,6 +188,7 @@ extension Swift2JavaTranslator {
     ) { printer in
       printer.print(
         """
+        @FunctionalInterface
         public interface Function {
           \(cResultType.javaType) apply(\(paramDecls.joined(separator: ", ")));
         }
@@ -206,7 +208,7 @@ extension Swift2JavaTranslator {
 
   /// Print the helper type container for a user-facing Java API.
   ///
-  /// * User-facing function interfaces.
+  /// * User-facing functional interfaces.
   func printJavaBindingWrapperHelperClass(
     _ printer: inout CodePrinter,
     _ decl: ImportedFunc
@@ -228,22 +230,22 @@ extension Swift2JavaTranslator {
     }
   }
 
-  /// Print "wrapper" function interface representing a Swift closure type.
+  /// Print "wrapper" functional interface representing a Swift closure type.
   func printJavaBindingWrapperFunctionTypeHelper(
     _ printer: inout CodePrinter,
     _ functionType: TranslatedFunctionType,
     _ bindingDescriptorName: String
   ) {
-    let cdeclDescritor = "\(bindingDescriptorName).$\(functionType.name)"
-    if functionType.isTrivial {
-      // If the usser-facing function interface is C-compatible, just extend the
-      // lowered function pointer parameter interface.
+    let cdeclDescriptor = "\(bindingDescriptorName).$\(functionType.name)"
+    if functionType.isCompatibleWithC {
+      // If the user-facing functional interface is C ABI compatible, just extend
+      // the lowered function pointer parameter interface.
       printer.print(
         """
-        public interface \(functionType.name) extends \(cdeclDescritor).Function {
-          default MemorySegment toUpcallStub(Arena arena) {
-            return \(bindingDescriptorName).$\(functionType.name).toUpcallStub(this, arena);
-          }
+        @FunctionalInterface
+        public interface \(functionType.name) extends \(cdeclDescriptor).Function {}
+        private static MemorySegment $toUpcallStub(\(functionType.name) fi, Arena arena) {
+          return \(bindingDescriptorName).$\(functionType.name).toUpcallStub(fi, arena);
         }
         """
       )
@@ -256,13 +258,14 @@ extension Swift2JavaTranslator {
 
       printer.print(
         """
+        @FunctionalInterface
         public interface \(functionType.name) {
           \(functionType.result.javaResultType) apply(\(apiParams.joined(separator: ", ")));
-          private default MemorySegment toUpcallStub(Arena arena) {
-            return \(cdeclDescritor).toUpcallStub((<cdecl-params>) -> {
-              <maybe-return> fi(<converted-args>)
-            }, arena);
-          }
+        }
+        private static MemorySegment $toUpcallStub(\(functionType.name) fi, Arena arena) {
+          return \(cdeclDescriptor).toUpcallStub((<cdecl-params>) -> {
+            <maybe-return> fi(<converted-args>)
+          }, arena);
         }
         """
       )

Sources/JExtractSwiftLib/Swift2JavaTranslator+JavaTranslation.swift

@@ -89,7 +89,7 @@ struct TranslatedFunctionDecl {
   /// Java function name.
   let name: String
 
-  /// Function interfaces (i.e. lambda types) required for the Java method.
+  /// Functional interfaces required for the Java method.
   let functionTypes: [TranslatedFunctionType]
 
   /// Function signature.
@@ -114,7 +114,8 @@ struct TranslatedFunctionType {
   var parameters: [TranslatedParameter]
   var result: TranslatedResult
 
-  var isTrivial: Bool {
+  /// Whether or not this functional interface with C ABI compatible.
+  var isCompatibleWithC: Bool {
     result.conversion.isPass && parameters.allSatisfy(\.conversion.isPass)
   }
 }
@@ -185,7 +186,7 @@ struct JavaTranslation {
     )
   }
 
-  /// Translate Swift closure type to Java function interface.
+  /// Translate Swift closure type to Java functional interface.
   func translateFunctionType(
     name: String,
     swiftType: SwiftFunctionType
@@ -365,7 +366,7 @@ struct JavaTranslation {
             type: JavaType.class(package: nil, name: "\(methodName).\(parameterName)"),
             name: parameterName)
         ],
-        conversion: .method(methodName: "toUpcallStub", withArena: true)
+        conversion: .call(function: "\(methodName).$toUpcallStub", withArena: true)
       )
 
     case .optional: