extract CustomStringConvertible as toString() and fix extensions

Samples/SwiftJavaExtractJNISampleApp/Sources/MySwiftLibrary/MySwiftClass.swift

@@ -99,3 +99,15 @@ public class MySwiftClass {
     return self.x + other.longValue()
   }
 }
+
+extension MySwiftClass: CustomStringConvertible {
+  public var description: String {
+    "MySwiftClass(x: \(x), y: \(y))"
+  }
+}
+
+extension MySwiftClass: CustomDebugStringConvertible {
+  public var debugDescription: String {
+    "debug: MySwiftClass(x: \(x), y: \(y))"
+  }
+}

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

@@ -171,4 +171,20 @@ void getAsyncVariable() throws Exception {
             assertEquals(42, c1.getGetAsync().get());
         }
     }
+
+    @Test
+    void toStringTest() {
+        try (var arena = SwiftArena.ofConfined()) {
+            MySwiftClass c1 = MySwiftClass.init(20, 10, arena);
+            assertEquals("MySwiftClass(x: 20, y: 10)", c1.toString());
+        }
+    }
+
+    @Test
+    void toDebugStringTest() {
+        try (var arena = SwiftArena.ofConfined()) {
+            MySwiftClass c1 = MySwiftClass.init(20, 10, arena);
+            assertEquals("debug: MySwiftClass(x: 20, y: 10)", c1.toDebugString());
+        }
+    }
 }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -260,12 +260,38 @@ extension JNISwift2JavaGenerator {
         printer.println()
       }
 
+      printToStringMethods(&printer, decl)
+      printer.println()
+
       printTypeMetadataAddressFunction(&printer, decl)
       printer.println()
       printDestroyFunction(&printer, decl)
     }
   }
 
+
+  private func printToStringMethods(_ printer: inout CodePrinter, _ decl: ImportedNominalType) {
+    printer.printBraceBlock("public String toString()") { printer in
+      printer.print(
+        """
+        return $toString(this.$memoryAddress());
+        """
+      )
+    }
+    printer.print("private static native java.lang.String $toString(long selfPointer);")
+
+    printer.println()
+
+    printer.printBraceBlock("public String toDebugString()") { printer in
+      printer.print(
+        """
+        return $toDebugString(this.$memoryAddress());
+        """
+      )
+    }
+    printer.print("private static native java.lang.String $toDebugString(long selfPointer);")
+  }
+
   private func printHeader(_ printer: inout CodePrinter) {
     printer.print(
       """

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -253,7 +253,7 @@ extension JNISwift2JavaGenerator {
       printer.println()
     }
 
-
+    printToStringMethods(&printer, type)
     printTypeMetadataAddressThunk(&printer, type)
     printer.println()
     printDestroyFunctionThunk(&printer, type)
@@ -267,6 +267,48 @@ extension JNISwift2JavaGenerator {
     try printSwiftInterfaceWrapper(&printer, protocolWrapper)
   }
 
+  private func printToStringMethods(_ printer: inout CodePrinter, _ type: ImportedNominalType) {
+    let selfPointerParam = JavaParameter(name: "selfPointer", type: .long)
+    let parentName = type.qualifiedName
+
+    printCDecl(
+      &printer,
+      javaMethodName: "$toString",
+      parentName: type.swiftNominal.qualifiedName,
+      parameters: [
+        selfPointerParam
+      ],
+      resultType: .javaLangString
+    ) { printer in
+      let selfVar = self.printSelfJLongToUnsafeMutablePointer(&printer, swiftParentName: parentName, selfPointerParam)
+
+      printer.print(
+        """
+        return String(describing: \(selfVar).pointee).getJNIValue(in: environment)
+        """
+      )
+    }
+
+    printer.println()
+
+    printCDecl(
+      &printer,
+      javaMethodName: "$toDebugString",
+      parentName: type.swiftNominal.qualifiedName,
+      parameters: [
+        selfPointerParam
+      ],
+      resultType: .javaLangString
+    ) { printer in
+      let selfVar = self.printSelfJLongToUnsafeMutablePointer(&printer, swiftParentName: parentName, selfPointerParam)
+
+      printer.print(
+        """
+        return String(reflecting: \(selfVar).pointee).getJNIValue(in: environment)
+        """
+      )
+    }
+  }
 
   private func printEnumDiscriminator(_ printer: inout CodePrinter, _ type: ImportedNominalType) {
     let selfPointerParam = JavaParameter(name: "selfPointer", type: .long)

Sources/JExtractSwiftLib/Swift2JavaVisitor.swift

@@ -109,6 +109,12 @@ final class Swift2JavaVisitor {
     guard let importedNominalType = translator.importedNominalType(node.extendedType) else {
       return
     }
+
+    // Add any conforming protocols in the extension
+    importedNominalType.inheritedTypes += node.inheritanceClause?.inheritedTypes.compactMap {
+      try? SwiftType($0.type, lookupContext: translator.lookupContext)
+    } ?? []
+
     for memberItem in node.memberBlock.members {
       self.visit(decl: memberItem.decl, in: importedNominalType, sourceFilePath: sourceFilePath)
     }
@@ -374,9 +380,6 @@ final class Swift2JavaVisitor {
         self.visit(decl: decl, in: imported, sourceFilePath: imported.sourceFilePath)
       }
 
-      // FIXME: why is this un-used
-      imported.variables.first?.signatureString
-
       if !imported.initializers.contains(where: {
         $0.functionSignature.parameters.count == 1
           && $0.functionSignature.parameters.first?.parameterName == "rawValue"

Sources/JExtractSwiftLib/SwiftTypes/SwiftTypeLookupContext.swift

@@ -105,6 +105,17 @@ class SwiftTypeLookupContext {
       typeDecl = try nominalTypeDeclaration(for: node, sourceFilePath: sourceFilePath)
     case .protocolDecl(let node):
       typeDecl = try nominalTypeDeclaration(for: node, sourceFilePath: sourceFilePath)
+    case .extensionDecl(let node):
+      // For extensions, we have to perform a unqualified lookup,
+      // as the extentedType is just the identifier of the type.
+
+      guard case .identifierType(let id) = Syntax(node.extendedType).as(SyntaxEnum.self),
+            let lookupResult = try unqualifiedLookup(name: Identifier(id.name)!, from: node)
+      else {
+        throw TypeLookupError.notType(Syntax(node))
+      }
+
+      typeDecl = lookupResult
     case .typeAliasDecl:
       fatalError("typealias not implemented")
     case .associatedTypeDecl:

Sources/SwiftJavaDocumentation/Documentation.docc/SupportedFeatures.md

@@ -92,7 +92,7 @@ SwiftJava's `swift-java jextract` tool automates generating Java bindings from S
 | Non-escaping closures with primitive arguments/results: `func callMe(maybe: (Int) -> (Double))`   | ✅        | ✅   |
 | Non-escaping closures with object arguments/results: `func callMe(maybe: (JavaObj) -> (JavaObj))` | ❌        | ❌   |
 | `@escaping` closures: `func callMe(_: @escaping () -> ())`                                        | ❌        | ❌   |
-| Swift type extensions: `extension String { func uppercased() }`                      | 🟡       | 🟡  |
+| Swift type extensions: `extension String { func uppercased() }`                      | ✅       | ✅  |
 | Swift macros (maybe)                                                                 | ❌        | ❌   |
 | Result builders                                                                      | ❌        | ❌   |
 | Automatic Reference Counting of class types / lifetime safety                        | ✅        | ✅   |

Tests/JExtractSwiftTests/JNI/JNIExtensionTests.swift

@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 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 Testing
+
+@Suite
+struct JNIExtensionTests {
+  let interfaceFile =
+    """
+    extension MyStruct {
+      public var variableInExtension: String { get }
+      public func methodInExtension() {}
+    }
+
+    public protocol MyProtocol {}
+    public struct MyStruct {}
+    extension MyStruct: MyProtocol {}
+    """
+
+  @Test("Import extensions: Java methods")
+  func import_javaMethods() throws {
+    try assertOutput(
+      input: interfaceFile,
+      .jni, .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        public final class MyStruct implements JNISwiftInstance, MyProtocol {
+          ...
+          public void methodInExtension() {
+          ...
+        }
+        """
+      ])
+  }
+
+  @Test("Import extensions: Computed variables")
+  func import_computedVariables() throws {
+    try assertOutput(
+      input: interfaceFile,
+      .jni, .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        public final class MyStruct implements JNISwiftInstance, MyProtocol {
+          ...
+          public java.lang.String getVariableInExtension() {
+          ...
+        }
+        """
+      ])
+  }
+}

Tests/JExtractSwiftTests/JNI/JNIToStringTests.swift

@@ -0,0 +1,96 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 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 Testing
+import SwiftJavaConfigurationShared
+
+@Suite
+struct JNIToStringTests {
+  let source =
+    """
+    public struct MyType {}
+    """
+
+  @Test("JNI toString (Java)")
+  func toString_java() throws {
+    try assertOutput(
+      input: source,
+      .jni, .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        public String toString() {
+          return $toString(this.$memoryAddress());
+        }
+        """,
+        """
+        private static native java.lang.String $toString(long selfPointer);
+        """
+      ]
+    )
+  }
+
+  @Test("JNI toString (Swift)")
+  func toString_swift() throws {
+    try assertOutput(
+      input: source,
+      .jni, .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        @_cdecl("Java_com_example_swift_MyType__00024toString__J")
+        func Java_com_example_swift_MyType__00024toString__J(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, selfPointer: jlong) -> jstring? {
+          ...
+          return String(describing: self$.pointee).getJNIValue(in: environment)
+        }
+        """,
+      ]
+    )
+  }
+
+  @Test("JNI toDebugString (Java)")
+  func toDebugString_java() throws {
+    try assertOutput(
+      input: source,
+      .jni, .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        public String toDebugString() {
+          return $toDebugString(this.$memoryAddress());
+        }
+        """,
+      ]
+    )
+  }
+
+  @Test("JNI toDebugString (Swift)")
+  func toDebugString_swift() throws {
+    try assertOutput(
+      input: source,
+      .jni, .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        """
+        @_cdecl("Java_com_example_swift_MyType__00024toDebugString__J")
+        func Java_com_example_swift_MyType__00024toDebugString__J(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, selfPointer: jlong) -> jstring? {
+          ...
+          return String(reflecting: self$.pointee).getJNIValue(in: environment)
+        }
+        """,
+      ]
+    )
+  }
+}