generate java code for primitive types and global functions

Author: madsodgaard

Sources/JExtractSwiftLib/ImportedDecls.swift

@@ -60,7 +60,6 @@ public final class ImportedFunc: ImportedDecl, CustomStringConvertible {
     self.swiftDecl.signatureString
   }
 
-
   var parentType: SwiftType? {
     guard let selfParameter = functionSignature.selfParameter else {
       return nil

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator.swift

@@ -0,0 +1,152 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 JavaTypes
+
+struct JNISwift2JavaGenerator: Swift2JavaGenerator {
+  let analysis: AnalysisResult
+  let swiftModuleName: String
+  let javaPackage: String
+  let logger: Logger
+  let swiftOutputDirectory: String
+  let javaOutputDirectory: String
+
+  var javaPackagePath: String {
+    javaPackage.replacingOccurrences(of: ".", with: "/")
+  }
+
+  init(
+    translator: Swift2JavaTranslator,
+    javaPackage: String,
+    swiftOutputDirectory: String,
+    javaOutputDirectory: String
+  ) {
+    self.logger = Logger(label: "jni-generator", logLevel: translator.log.logLevel)
+    self.analysis = translator.result
+    self.swiftModuleName = translator.swiftModuleName
+    self.javaPackage = javaPackage
+    self.swiftOutputDirectory = swiftOutputDirectory
+    self.javaOutputDirectory = javaOutputDirectory
+  }
+
+  func generate() throws {
+    try writeExportedJavaSources()
+  }
+}
+
+extension JNISwift2JavaGenerator {
+  func writeExportedJavaSources() throws {
+    var printer = CodePrinter()
+
+    let filename = "\(self.swiftModuleName).java"
+    logger.trace("Printing module class: \(filename)")
+    printModule(&printer)
+
+    if let outputFile = try printer.writeContents(
+      outputDirectory: javaOutputDirectory,
+      javaPackagePath: javaPackagePath,
+      filename: filename
+    ) {
+      logger.info("[swift-java] Generated: \(self.swiftModuleName).java (at \(outputFile))")
+    }
+  }
+}
+
+extension JNISwift2JavaGenerator {
+  private func printModule(_ printer: inout CodePrinter) {
+    printHeader(&printer)
+    printPackage(&printer)
+
+    printModuleClass(&printer) { printer in
+      for decl in analysis.importedGlobalFuncs {
+        self.logger.trace("Print global function: \(decl)")
+        printFunctionBinding(&printer, decl)
+      }
+    }
+  }
+
+  private func printHeader(_ printer: inout CodePrinter) {
+    printer.print(
+      """
+      // Generated by jextract-swift
+      // Swift module: \(swiftModuleName)
+
+      """
+    )
+  }
+
+  private func printPackage(_ printer: inout CodePrinter) {
+    printer.print(
+      """
+      package \(javaPackage);
+
+      """
+    )
+  }
+
+  private func printModuleClass(_ printer: inout CodePrinter, body: (inout CodePrinter) -> Void) {
+    printer.printBraceBlock("public final class \(swiftModuleName)") { printer in
+      body(&printer)
+    }
+  }
+
+  private func printFunctionBinding(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
+    let returnType = decl.functionSignature.result.type.javaType
+    let params = decl.functionSignature.parameters.map {
+      "\($0.type.javaType) \($0.parameterName!)"
+    }
+
+    printer.print("public static native \(returnType) \(decl.name)(\(params.joined(separator: ", ")));")
+  }
+}
+
+extension SwiftType {
+  var javaType: JavaType {
+    switch self {
+    case .nominal(let nominalType):
+      if let knownType = nominalType.nominalTypeDecl.knownStandardLibraryType {
+        guard let javaType = knownType.javaType else {
+          fatalError("unsupported known type: \(knownType)")
+        }
+        return javaType
+      }
+
+      fatalError("unsupported nominal type: \(nominalType)")
+
+    case .tuple([]):
+      return .void
+
+    case .metatype, .optional, .tuple, .function:
+      fatalError("unsupported")
+    }
+  }
+}
+
+extension KnownStandardLibraryType {
+  var javaType: JavaType? {
+    switch self {
+    case .bool: .boolean
+    case .int, .uint: .long // TODO: Handle 32-bit or 64-bit
+    case .int8, .uint8: .byte
+    case .uint16: .char
+    case .int16: .short
+    case .int32, .uint32: .int
+    case .int64, .uint64: .long
+    case .float: .float
+    case .double: .double
+    case .void: .void
+    case .unsafeRawPointer, .unsafeMutableRawPointer, .unsafePointer, .unsafeMutablePointer, .unsafeBufferPointer, .unsafeMutableBufferPointer, .string: nil
+    }
+  }
+}

Sources/JExtractSwiftLib/Swift2Java.swift

@@ -97,6 +97,16 @@ public struct SwiftToJava {
         javaOutputDirectory: outputJavaDirectory
       )
 
+      try generator.generate()
+
+    case .jni:
+      let generator = JNISwift2JavaGenerator(
+        translator: translator,
+        javaPackage: config.javaPackage ?? "",
+        swiftOutputDirectory: outputSwiftDirectory,
+        javaOutputDirectory: outputJavaDirectory
+      )
+
       try generator.generate()
     }
 

Sources/JavaKitConfigurationShared/GenerationMode.swift

@@ -15,4 +15,7 @@
 public enum GenerationMode: String, Codable {
   /// Foreign Value and Memory API
   case ffm
+
+  /// Java Native Interface
+  case jni
 }