Expose Java-friendly instance methods and constructors for Swift types

When projecting a Swift type into a Java class, map Swift methods into
instance methods (rather than static methods) and Swift initializers
into Java constructors (rather than static 'init' methods).

Author: DougGregor

JavaSwiftKitDemo/src/main/java/org/example/HelloJava2Swift.java

@@ -60,9 +60,12 @@ static void tests() {
 
         JavaKitExample.globalTakeInt(1337);
 
-        MySwiftClass obj = MySwiftClass.init(2222, 7777);
+        MySwiftClass obj = new MySwiftClass(2222, 7777);
 
         SwiftKit.retain(obj.$memorySegment());
         System.out.println("[java] obj ref count = " + SwiftKit.retainCount(obj.$memorySegment()));
+
+        obj.voidMethod();
+        obj.takeIntMethod(42);
     }
 }

Sources/JExtractSwift/ImportedDecls.swift

@@ -48,6 +48,14 @@ public struct ImportedNominalType: ImportedDecl {
       javaType: javaType
     )
   }
+
+  /// The Java class name without the package.
+  public var javaClassName: String {
+    switch javaType {
+    case .class(package: _, name: let name): name
+    default: javaType.description
+    }
+  }
 }
 
 public enum NominalTypeKind {
@@ -116,7 +124,7 @@ public struct ImportedFunc: ImportedDecl, CustomStringConvertible {
   /// this will contain that declaration's imported name.
   ///
   /// This is necessary when rendering accessor Java code we need the type that "self" is expecting to have.
-  var parentName: TranslatedType?
+  public var parentName: TranslatedType?
   public var hasParent: Bool { parentName != nil }
 
   /// This is a full name such as init(cap:name:).
@@ -152,7 +160,7 @@ public struct ImportedFunc: ImportedDecl, CustomStringConvertible {
       //
       // allocating initializer takes a Self.Type instead, but it's also a pointer
       switch selfVariant {
-      case nil:
+      case nil, .wrapper:
         break
 
       case .pointer:
@@ -174,10 +182,6 @@ public struct ImportedFunc: ImportedDecl, CustomStringConvertible {
             type: parentForSelf
           )
         )
-
-      case .wrapper:
-        let selfParam: FunctionParameterSyntax = "self$: \(raw: parentName.swiftTypeName)"
-        params.append(ImportedParam(param: selfParam, type: parentName))
       }
 
       // TODO: add any metadata for generics and other things we may need to add here

Sources/JExtractSwift/Swift2JavaTranslator+Printing.swift

@@ -28,7 +28,7 @@ extension Swift2JavaTranslator {
     var printer = CodePrinter()
 
     for (_, ty) in importedTypes.sorted(by: { (lhs, rhs) in lhs.key < rhs.key }) {
-      let filename = "\(ty.javaType).java"
+      let filename = "\(ty.javaClassName).java"
       log.info("Printing contents: \(filename)")
       printImportedClass(&printer, ty)
 
@@ -165,7 +165,7 @@ extension Swift2JavaTranslator {
   }
 
   public func printClass(_ printer: inout CodePrinter, _ decl: ImportedNominalType, body: (inout CodePrinter) -> Void) {
-    printer.printTypeDecl("public final class \(decl.javaType)") { printer in
+    printer.printTypeDecl("public final class \(decl.javaClassName)") { printer in
       // ==== Storage of the class
       // FIXME: implement the self storage for the memory address and accessors
       printClassSelfProperty(&printer, decl)
@@ -274,7 +274,7 @@ extension Swift2JavaTranslator {
     printer.print(
       """
       /** Instances are created using static {@code init} methods rather than through the constructor directly. */
-      private \(decl.javaType)(MemorySegment selfMemorySegment) {
+      private \(decl.javaClassName)(MemorySegment selfMemorySegment) {
         this.selfMemorySegment = selfMemorySegment;
       }
       """
@@ -412,24 +412,32 @@ extension Swift2JavaTranslator {
       printMethodDowncallHandleForAddrDesc(&printer)
     }
 
+    printClassInitializerConstructor(&printer, decl, parentName: parentName)
+  }
+
+  public func printClassInitializerConstructor(
+    _ printer: inout CodePrinter,
+    _ decl: ImportedFunc,
+    parentName: TranslatedType
+  ) {
+    let descClassIdentifier = renderDescClassName(decl)
     printer.print(
       """
       /**
-       * Create an instance of the {@code \(parentName.javaType)} Swift class.
+       * Create an instance of {@code \(parentName.unqualifiedJavaTypeName)}.
        *
-       * {@snippet lang=Swift:
+       * {@snippet lang=swift :
        * \(decl.swiftDeclRaw ?? "")
        * }
        */
-      public static \(parentName.javaType) init(\(renderJavaParamDecls(decl, selfVariant: .none))) {
+      public \(parentName.unqualifiedJavaTypeName)(\(renderJavaParamDecls(decl, selfVariant: .wrapper))) {
         var mh$ = \(descClassIdentifier).HANDLE;
         try {
             if (TRACE_DOWNCALLS) {
               traceDowncall(\(renderForwardParams(decl, selfVariant: nil)));
             }
 
-            var self = (MemorySegment) mh$.invokeExact(\(renderForwardParams(decl, selfVariant: nil)), TYPE_METADATA);
-            return new \(parentName.javaType)(self);
+            this.selfMemorySegment = (MemorySegment) mh$.invokeExact(\(renderForwardParams(decl, selfVariant: nil)), TYPE_METADATA);
         } catch (Throwable ex$) {
             throw new AssertionError("should not reach here", ex$);
         }
@@ -542,8 +550,8 @@ extension Swift2JavaTranslator {
          * \(/*TODO: make a printSnippet func*/decl.swiftDeclRaw ?? "")
          * }
          */
-        public static \(returnTy) \(decl.baseIdentifier)(\(renderJavaParamDecls(decl, selfVariant: .wrapper))) {
-          \(maybeReturnCast) \(decl.baseIdentifier)(\(renderForwardParams(decl, selfVariant: .memorySegment)));
+        public \(returnTy) \(decl.baseIdentifier)(\(renderJavaParamDecls(decl, selfVariant: .wrapper))) {
+          \(maybeReturnCast) \(decl.baseIdentifier)(\(renderForwardParams(decl, selfVariant: .wrapper)));
         }
         """
       )
@@ -630,6 +638,11 @@ extension Swift2JavaTranslator {
       ps.append(param)
     }
 
+    // Add the forwarding "self"
+    if selfVariant == .wrapper && !decl.isInit {
+      ps.append("$memorySegment()")
+    }
+
     return ps.joined(separator: ", ")
   }
 

Sources/JExtractSwift/Swift2JavaVisitor.swift

@@ -163,7 +163,7 @@ final class Swift2JavaVisitor: SyntaxVisitor {
     }
 
     let initIdentifier =
-      "init(\(params.compactMap { $0.effectiveName ?? "_" }.joined(separator: ":")))"
+      "init(\(String(params.flatMap { "\($0.effectiveName ?? "_"):" })))"
 
     var funcDecl = ImportedFunc(
       parentName: currentType.translatedType,

Sources/JExtractSwift/TranslatedType.swift

@@ -223,6 +223,14 @@ public struct TranslatedType {
   var swiftTypeName: String {
     originalSwiftType.trimmedDescription
   }
+
+  /// Produce the "unqualified" Java type name.
+  var unqualifiedJavaTypeName: String {
+    switch javaType {
+    case .class(package: _, name: let name): name
+    default: javaType.description
+    }
+  }
 }
 
 /// Describes the C-compatible layout as it should be referenced from Java.

Tests/JExtractSwiftTests/FuncImportTests.swift

@@ -331,8 +331,8 @@ final class MethodImportTests {
          * public func helloMemberFunction()
          * }
          */
-        public static void helloMemberFunction(com.example.swift.MySwiftClass self$) {
-            helloMemberFunction(self$);
+        public void helloMemberFunction() {
+            helloMemberFunction($memorySegment());
         }
         """
     )
@@ -364,11 +364,54 @@ final class MethodImportTests {
          * public func makeInt() -> Int
          * }
          */
-        public static long makeInt(com.example.swift.MySwiftClass self$) {
-          return (long) makeInt(self$);
+        public long makeInt() {
+          return (long) makeInt($memorySegment());
         }
         """
     )
   }
 
+  @Test func class_constructor() async throws {
+    let st = Swift2JavaTranslator(
+      javaPackage: "com.example.swift",
+      swiftModuleName: "__FakeModule"
+    )
+    st.log.logLevel = .trace
+
+    try await st.analyze(swiftInterfacePath: "/fake/__FakeModule/SwiftFile.swiftinterface", text: class_interfaceFile)
+
+    let initDecl: ImportedFunc = st.importedTypes["MySwiftClass"]!.initializers.first {
+      $0.identifier == "init(len:cap:)"
+    }!
+
+    let output = CodePrinter.toString { printer in
+      st.printClassInitializerConstructor(&printer, initDecl, parentName: initDecl.parentName!)
+    }
+
+    assertOutput(
+      output,
+      expected:
+        """
+        /**
+         * Create an instance of {@code MySwiftClass}.
+         *
+         * {@snippet lang=swift :
+         * public init(len: Swift.Int, cap: Swift.Int)
+         * }
+         */
+        public MySwiftClass(long len, long cap) {
+          var mh$ = init_len_cap.HANDLE;
+          try {
+            if (TRACE_DOWNCALLS) {
+              traceDowncall(len, cap);
+            }
+
+            this.selfMemorySegment = (MemorySegment) mh$.invokeExact(len, cap, TYPE_METADATA);
+          } catch (Throwable ex$) {
+            throw new AssertionError(\"should not reach here\", ex$);
+          }
+        }
+        """
+    )
+  }
 }