CodePrinting: make CodePrinter generic over a Language type

Package.swift

@@ -301,7 +301,8 @@ let package = Package(
     ),
 
     .target(
-      name: "CodePrinting"
+      name: "CodePrinting",
+      dependencies: ["SwiftJavaConfigurationShared"]
     ),
 
     .target(

Sources/CodePrinting/CodePrinter+Java.swift

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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
+//
+//===----------------------------------------------------------------------===//
+
+// ==== -----------------------------------------------------------------------
+// MARK: CodePrinter - Java-language helpers
+
+extension CodePrinter where Language == JavaLanguage {
+
+  /// Print a Java `if (<condition>) { ... }` block.
+  public mutating func printIfBlock(
+    _ condition: Any,
+    function: String = #function,
+    file: String = #fileID,
+    line: UInt = #line,
+    body: (inout CodePrinter) throws -> Void
+  ) rethrows {
+    try printBraceBlock("if (\(condition))", function: function, file: file, line: line, body: body)
+  }
+
+  /// Print a Javadoc comment.
+  ///
+  /// Shape depends on `options.sourceVersion`:
+  /// - Java 23+: Markdown-style line comments (`///`) based on https://openjdk.org/jeps/467
+  /// - Earlier versions: classic `/** ... */` block, with each body line
+  ///   prefixed by ` * ` (just ` *` for blank paragraph separators).
+  ///
+  /// Pass paragraph breaks as blank lines (`\n\n`) inside `text`.
+  public mutating func printJavadocComment(_ text: String) {
+    let lines = text.split(separator: "\n", omittingEmptySubsequences: false)
+    if options.sourceVersion >= 23 {
+      for line in lines {
+        print(line.isEmpty ? "///" : "/// \(line)")
+      }
+    } else {
+      print("/**")
+      for line in lines {
+        print(line.isEmpty ? " *" : " * \(line)")
+      }
+      print(" */")
+    }
+  }
+}

Sources/CodePrinting/CodePrinter+Swift.swift

@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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
+//
+//===----------------------------------------------------------------------===//
+
+// ==== -----------------------------------------------------------------------
+// MARK: CodePrinter - Swift-language helpers
+
+extension CodePrinter where Language == SwiftLanguage {
+
+  /// Print a Swift `if <condition> { ... }` block.
+  /// The condition is emitted verbatim, without surrounding parentheses
+  /// (Swift convention).
+  public mutating func printIfBlock(
+    _ condition: Any,
+    function: String = #function,
+    file: String = #fileID,
+    line: UInt = #line,
+    body: (inout CodePrinter) throws -> Void
+  ) rethrows {
+    try printBraceBlock("if \(condition)", function: function, file: file, line: line, body: body)
+  }
+
+  /// Print a Swift `guard <condition> else { ... }` block.
+  public mutating func printGuardBlock(
+    _ condition: Any,
+    function: String = #function,
+    file: String = #fileID,
+    line: UInt = #line,
+    body: (inout CodePrinter) throws -> Void
+  ) rethrows {
+    try printBraceBlock("guard \(condition) else", function: function, file: file, line: line, body: body)
+  }
+}

Sources/CodePrinting/CodePrinter.swift

@@ -21,7 +21,7 @@ import Foundation
 // ==== -----------------------------------------------------------------------
 // MARK: CodePrinter
 
-public struct CodePrinter: Sendable {
+public struct CodePrinter<Language: CodePrinterLanguage>: Sendable {
   public var contents: String = ""
 
   public var verbose: Bool = false
@@ -32,11 +32,10 @@ public struct CodePrinter: Sendable {
   /// terminator equivalent to `.newLine`.
   public var emitSourceLocations: Bool = true
 
-  /// Token used to start an inline comment. Defaults to `//` for Swift- and
-  /// Java-style output. Hash-comment languages can flip this to `.hash` so
-  /// source-location trailers, `printSeparator` banners, and echo-mode
-  /// headers render with the right comment lead.
-  public var inlineCommentStyle: InlineCommentStyle = .slashSlash
+  /// Token used to start an inline comment. Defaults to the language's
+  /// `defaultInlineCommentStyle`; can be overridden per instance for
+  /// special cases (e.g. testing the alternative style).
+  public var inlineCommentStyle: InlineCommentStyle
 
   public var indentationDepth: Int = 0 {
     didSet {
@@ -65,12 +64,19 @@ public struct CodePrinter: Sendable {
     case accumulateAll
     case flushToFileOnWrite
   }
+
+  /// Per-language options (e.g. Java source version). Languages without
+  /// options use `Void`. Read by language-constrained extensions.
+  public var options: Language.Options
+
   public init(
     mode: PrintMode = .flushToFileOnWrite,
-    inlineCommentStyle: InlineCommentStyle = .slashSlash
+    inlineCommentStyle: InlineCommentStyle? = nil,
+    options: Language.Options = Language.defaultOptions
   ) {
     self.mode = mode
-    self.inlineCommentStyle = inlineCommentStyle
+    self.inlineCommentStyle = inlineCommentStyle ?? Language.defaultInlineCommentStyle
+    self.options = options
   }
 
   public mutating func append(_ text: String) {
@@ -124,27 +130,6 @@ public struct CodePrinter: Sendable {
     print("}", terminator, function: function, file: file, line: line)
   }
 
-  public mutating func printIfBlock(
-    _ condition: Any,
-    function: String = #function,
-    file: String = #fileID,
-    line: UInt = #line,
-    body: (inout CodePrinter) throws -> Void
-  ) rethrows {
-    try printBraceBlock("if (\(condition))", function: function, file: file, line: line, body: body)
-  }
-
-  /// Print a Swift `guard <condition> else { … }` block.
-  public mutating func printGuardBlock(
-    _ condition: Any,
-    function: String = #function,
-    file: String = #fileID,
-    line: UInt = #line,
-    body: (inout CodePrinter) throws -> Void
-  ) rethrows {
-    try printBraceBlock("guard \(condition) else", function: function, file: file, line: line, body: body)
-  }
-
   public mutating func printParts(
     _ parts: String...,
     terminator: PrinterTerminator = .newLine,

Sources/CodePrinting/CodePrinterLanguage.swift

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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 SwiftJavaConfigurationShared
+
+// ==== -----------------------------------------------------------------------
+// MARK: CodePrinterLanguage
+
+/// Phantom-type tag identifying the language a `CodePrinter` emits.
+/// Generators pick a concrete language so language-specific helpers
+/// (e.g. `printGuardBlock` for Swift, `printIfBlock` shaped for Java)
+/// resolve at compile time via constrained extensions.
+public protocol CodePrinterLanguage: Sendable {
+  /// Per-language printer options. Defaults to `Void` for languages
+  /// that don't need any (e.g. Swift today). Java carries the targeted
+  /// source version so helpers can pick the right syntax shape.
+  associatedtype Options: Sendable = Void
+
+  /// Default lead used for inline comments (source-location trailers,
+  /// `printSeparator` banners). May be overridden at the printer instance
+  /// via `CodePrinter.inlineCommentStyle`.
+  static var defaultInlineCommentStyle: InlineCommentStyle { get }
+
+  /// Default value for `CodePrinter.options`.
+  static var defaultOptions: Options { get }
+}
+
+extension CodePrinterLanguage where Options == Void {
+  public static var defaultOptions: Void { () }
+}
+
+// ==== -----------------------------------------------------------------------
+// MARK: Concrete languages
+
+/// Swift output.
+public enum SwiftLanguage: CodePrinterLanguage {
+  public static let defaultInlineCommentStyle: InlineCommentStyle = .slashSlash
+}
+
+/// Java output.
+public enum JavaLanguage: CodePrinterLanguage {
+  public struct Options: Sendable {
+    /// Targeted Java source version.
+    public var sourceVersion: JavaVersion
+
+    public init(sourceVersion: JavaVersion = 8) {
+      self.sourceVersion = sourceVersion
+    }
+  }
+
+  public static let defaultInlineCommentStyle: InlineCommentStyle = .slashSlash
+  public static let defaultOptions = Options()
+}
+
+// ==== -----------------------------------------------------------------------
+// MARK: Typealiases
+
+/// Convenience for `CodePrinter<SwiftLanguage>`. Use this everywhere a
+/// printer's output is Swift code.
+public typealias SwiftPrinter = CodePrinter<SwiftLanguage>
+
+/// Convenience for `CodePrinter<JavaLanguage>`. Use this everywhere a
+/// printer's output is Java code.
+public typealias JavaPrinter = CodePrinter<JavaLanguage>

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+FoundationData.swift

@@ -24,7 +24,7 @@ import struct Foundation.URL
 extension FFMSwift2JavaGenerator {
 
   /// Print Java helper methods for Foundation.Data type
-  package func printFoundationDataHelpers(_ printer: inout CodePrinter, _ decl: ExtractedNominalType) {
+  package func printFoundationDataHelpers(_ printer: inout JavaPrinter, _ decl: ExtractedNominalType) {
     let typeName = decl.swiftNominal.name
     let thunkNameCopyBytes = "swiftjava_\(swiftModuleName)_\(typeName)_copyBytes__"