Introduce String.comma constant for join separators

Sources/JExtractSwiftLib/CTypes/CFunction.swift

@@ -55,7 +55,7 @@ extension CFunction: CustomStringConvertible {
 
     // Function parameters.
     result += "("
-    result += parameters.map { $0.description }.joined(separator: ", ")
+    result += parameters.map { $0.description }.joined(separator: .comma)
     CType.printFunctionParametersSuffix(
       isVariadic: isVariadic,
       hasZeroParameters: parameters.isEmpty,

Sources/JExtractSwiftLib/CTypes/CType.swift

@@ -216,7 +216,7 @@ extension CType: CustomStringConvertible {
       result += "("
 
       // Render the parameter types.
-      result += parameters.map { $0.description }.joined(separator: ", ")
+      result += parameters.map { $0.description }.joined(separator: .comma)
 
       CType.printFunctionParametersSuffix(
         isVariadic: variadic,

Sources/JExtractSwiftLib/Convenience/JavaType+Extensions.swift

@@ -196,7 +196,7 @@ extension JavaType {
         }
       let genericClause: String =
         if !typeParameters.isEmpty {
-          "<\(typeParameters.map(\.boxedName).joined(separator: ", "))>"
+          "<\(typeParameters.map(\.boxedName).joined(separator: .comma))>"
         } else {
           ""
         }

Sources/JExtractSwiftLib/Convenience/String+Extensions.swift

@@ -0,0 +1,18 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+extension String {
+  /// Comma-space separator; Convenience to avoid having to escape the string when joining inside other strings.
+  public static let comma: String = ", "
+}

Sources/JExtractSwiftLib/FFM/CDeclLowering/FFMSwift2JavaGenerator+FunctionLowering.swift

@@ -976,7 +976,7 @@ extension LoweredFunctionSignature {
     as apiKind: SwiftAPIKind,
   ) -> FunctionDeclSyntax {
 
-    let cdeclParams = allLoweredParameters.map(\.description).joined(separator: ", ")
+    let cdeclParams = allLoweredParameters.map(\.description).joined(separator: .comma)
     let cdeclReturnType = cdeclReturnTypeForThunk
     let returnClause = !cdeclReturnType.isVoid ? " -> \(cdeclReturnType.description)" : ""
 
@@ -1036,7 +1036,7 @@ extension LoweredFunctionSignature {
           let argExpr = original.parameters[i].convention == .inout ? "&\(argument)" : argument
           return LabeledExprSyntax(label: original.parameters[i].argumentLabel, expression: argExpr).description
         }
-        .joined(separator: ", ")
+        .joined(separator: .comma)
       resultExpr = "\(callee)(\(raw: arguments))"
 
     case .getter:
@@ -1056,7 +1056,7 @@ extension LoweredFunctionSignature {
         .map { (i, argument) -> String in
           LabeledExprSyntax(label: original.parameters[i].argumentLabel, expression: argument).description
         }
-        .joined(separator: ", ")
+        .joined(separator: .comma)
       resultExpr = "\(callee)[\(raw: parameters)]"
     case .subscriptSetter:
       assert(paramExprs.count >= 1)
@@ -1068,7 +1068,7 @@ extension LoweredFunctionSignature {
         .map { (i, argument) -> String in
           LabeledExprSyntax(label: original.parameters[i].argumentLabel, expression: argument).description
         }
-        .joined(separator: ", ")
+        .joined(separator: .comma)
       resultExpr = "\(callee)[\(raw: parameters)] = \(newValueArgument)"
     }
 

Sources/JExtractSwiftLib/FFM/ConversionStep.swift

@@ -135,7 +135,7 @@ enum ConversionStep: Equatable {
 
       // FIXME: Should be able to use structured initializers here instead
       // of splatting out text.
-      let renderedArgumentList = renderedArguments.joined(separator: ", ")
+      let renderedArgumentList = renderedArguments.joined(separator: .comma)
       return "\(raw: type.description)(\(raw: renderedArgumentList))"
 
     case .tuplify(let elements):
@@ -145,7 +145,7 @@ enum ConversionStep: Equatable {
 
       // FIXME: Should be able to use structured initializers here instead
       // of splatting out text.
-      let renderedElementList = renderedElements.joined(separator: ", ")
+      let renderedElementList = renderedElements.joined(separator: .comma)
       return "(\(raw: renderedElementList))"
 
     case .populatePointer(name: let pointer, assumingType: let type, to: let step):
@@ -185,7 +185,7 @@ enum ConversionStep: Equatable {
       }
 
       // FIXME: Should be able to use structured initializers here instead of splatting out text.
-      let renderedArgumentList = renderedArguments.joined(separator: ", ")
+      let renderedArgumentList = renderedArguments.joined(separator: .comma)
 
       let methodApply: String =
         if let methodName {
@@ -240,7 +240,7 @@ enum ConversionStep: Equatable {
       }
 
       // Call the lowered closure with lowered parameters.
-      let loweredResult = "\(placeholder)(\(args.map(\.description).joined(separator: ", ")))"
+      let loweredResult = "\(placeholder)(\(args.map(\.description).joined(separator: .comma)))"
 
       // Raise the lowered result.
       let result = resultStep.asExprSyntax(placeholder: loweredResult.description, bodyItems: &body)
@@ -249,7 +249,7 @@ enum ConversionStep: Equatable {
       // Construct the closure expression.
       var closure = ExprSyntax(
         """
-        { (\(raw: params.joined(separator: ", "))) in
+        { (\(raw: params.joined(separator: .comma))) in
           }
         """
       ).cast(ClosureExprSyntax.self)

Sources/JExtractSwiftLib/FFM/FFMSwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -136,8 +136,8 @@ extension FFMSwift2JavaGenerator {
       params.append("\(annotationsStr)\(param.type.javaType) \(name)")
       args.append(name)
     }
-    let paramsStr = params.joined(separator: ", ")
-    let argsStr = args.joined(separator: ", ")
+    let paramsStr = params.joined(separator: .comma)
+    let argsStr = args.joined(separator: .comma)
 
     printer.print(
       """
@@ -236,7 +236,7 @@ extension FFMSwift2JavaGenerator {
         """
         @FunctionalInterface
         public interface Function {
-          \(cResultType.javaType) apply(\(paramDecls.joined(separator: ", ")));
+          \(cResultType.javaType) apply(\(paramDecls.joined(separator: .comma)));
         }
         """
       )
@@ -246,7 +246,7 @@ extension FFMSwift2JavaGenerator {
           """
           public final static class Function$Impl implements Function {
             \(impl.members.joinedJavaStatements(indent: 2))
-            public \(cResultType.javaType) apply(\(paramDecls.joined(separator: ", "))) {
+            public \(cResultType.javaType) apply(\(paramDecls.joined(separator: .comma))) {
               \(impl.body)
             }
           }
@@ -319,7 +319,7 @@ extension FFMSwift2JavaGenerator {
         """
         @FunctionalInterface
         public interface \(functionType.name) {
-          \(functionType.result.javaResultType) apply(\(apiParams.joined(separator: ", ")));
+          \(functionType.result.javaResultType) apply(\(apiParams.joined(separator: .comma)));
         }
         """
       )
@@ -333,7 +333,7 @@ extension FFMSwift2JavaGenerator {
       ) { printer in
         printer.print(
           """
-          return \(cdeclDescriptor).toUpcallStub((\(cdeclParams.joined(separator: ", "))) -> {
+          return \(cdeclDescriptor).toUpcallStub((\(cdeclParams.joined(separator: .comma))) -> {
           """
         )
         printer.indent()
@@ -343,7 +343,7 @@ extension FFMSwift2JavaGenerator {
           convertedArgs.append(arg)
         }
 
-        let call = "fi.apply(\(convertedArgs.joined(separator: ", ")))"
+        let call = "fi.apply(\(convertedArgs.joined(separator: .comma)))"
         let result = functionType.result.conversion.render(&printer, call)
         if functionType.result.javaResultType == .void {
           printer.print("\(result);")
@@ -394,7 +394,7 @@ extension FFMSwift2JavaGenerator {
     if translatedSignature.canThrowSwiftIntegerOverflowException {
       throwsClauses.append(JavaType.swiftIntegerOverflowException.className!)
     }
-    let throwsClause = throwsClauses.isEmpty ? "" : " throws \(throwsClauses.joined(separator: ", "))"
+    let throwsClause = throwsClauses.isEmpty ? "" : " throws \(throwsClauses.joined(separator: .comma))"
 
     TranslatedDocumentation.printDocumentation(
       importedFunc: decl,
@@ -404,7 +404,7 @@ extension FFMSwift2JavaGenerator {
     )
     printer.printBraceBlock(
       """
-      \(annotationsStr)\(modifiers) \(returnTy) \(methodName)(\(paramDecls.joined(separator: ", ")))\(throwsClause)
+      \(annotationsStr)\(modifiers) \(returnTy) \(methodName)(\(paramDecls.joined(separator: .comma)))\(throwsClause)
       """
     ) { printer in
       if case .instance = decl.functionSignature.selfParameter {
@@ -516,7 +516,7 @@ extension FFMSwift2JavaGenerator {
     }
 
     //=== Part 3: Downcall.
-    let downCall = "\(thunkName).call(\(downCallArguments.joined(separator: ", ")))"
+    let downCall = "\(thunkName).call(\(downCallArguments.joined(separator: .comma)))"
 
     /// Helper to emit the error check after a downcall
     func printErrorCheck(_ printer: inout JavaPrinter) {
@@ -813,7 +813,7 @@ extension FFMSwift2JavaGenerator.JavaConversionStep {
           placeholderForDowncall: placeholderForDowncall,
         )
       }
-      return "\(tupleClassName)(\(args.joined(separator: ", ")))"
+      return "\(tupleClassName)(\(args.joined(separator: .comma)))"
     }
   }
 }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -180,7 +180,7 @@ extension JNISwift2JavaGenerator {
     if !self.interfaceProtocolWrappers.keys.contains(decl) && !extends.contains("JNISwiftInstance") {
       extends.append("JNISwiftInstance")
     }
-    let extendsString = extends.isEmpty ? "" : " extends \(extends.joined(separator: ", "))"
+    let extendsString = extends.isEmpty ? "" : " extends \(extends.joined(separator: .comma))"
 
     printer.printBraceBlock("public interface \(decl.effectiveJavaSimpleName)\(extendsString)") { printer in
       for initializer in decl.initializers {
@@ -270,7 +270,7 @@ extension JNISwift2JavaGenerator {
       if isEffectivelyGeneric {
         swiftPointerParams.append("selfTypePointer")
       }
-      let swiftPointerArg = swiftPointerParams.map { "long \($0)" }.joined(separator: ", ")
+      let swiftPointerArg = swiftPointerParams.map { "long \($0)" }.joined(separator: .comma)
       printer.printBraceBlock("private \(decl.effectiveJavaSimpleName)(\(swiftPointerArg), SwiftArena swiftArena)") { printer in
         for param in swiftPointerParams {
           printer.print(
@@ -304,11 +304,11 @@ extension JNISwift2JavaGenerator {
          * </ul>
          */
         public static\(genericClause) \(javaName)\(genericClause) wrapMemoryAddressUnsafe(\(swiftPointerArg), SwiftArena swiftArena) {
-          return new \(javaName)\(genericClause)(\(swiftPointerParams.joined(separator: ", ")), swiftArena);
+          return new \(javaName)\(genericClause)(\(swiftPointerParams.joined(separator: .comma)), swiftArena);
         }
 
         public static\(genericClause) \(javaName)\(genericClause) wrapMemoryAddressUnsafe(\(swiftPointerArg)) {
-          return new \(javaName)\(genericClause)(\(swiftPointerParams.joined(separator: ", ")), SwiftMemoryManagement.DEFAULT_SWIFT_JAVA_AUTO_ARENA);
+          return new \(javaName)\(genericClause)(\(swiftPointerParams.joined(separator: .comma)), SwiftMemoryManagement.DEFAULT_SWIFT_JAVA_AUTO_ARENA);
         }
         """
       )
@@ -458,7 +458,7 @@ extension JNISwift2JavaGenerator {
       .compactMap(\.asNominalTypeDeclaration)
       .filter { $0.kind == .protocol }
       .map(\.name)
-    let implementsClause = implements.joined(separator: ", ")
+    let implementsClause = implements.joined(separator: .comma)
     // Specialized types are concrete — no generic clause on the Java side
     let genericClause = decl.javaGenericClause
     printer.printBraceBlock(
@@ -510,7 +510,7 @@ extension JNISwift2JavaGenerator {
       if decl.genericParameterNames.isEmpty {
         ""
       } else {
-        "<\(decl.genericParameterNames.joined(separator: ", "))>"
+        "<\(decl.genericParameterNames.joined(separator: .comma))>"
       }
 
     printer.printBraceBlock("public sealed interface Case\(caseGenericClause)") { printer in
@@ -524,7 +524,7 @@ extension JNISwift2JavaGenerator {
         }
 
         // Print record
-        printer.print("record \(translatedCase.name)\(caseGenericClause)(\(members.joined(separator: ", "))) implements Case\(caseGenericClause) {}")
+        printer.print("record \(translatedCase.name)\(caseGenericClause)(\(members.joined(separator: .comma))) implements Case\(caseGenericClause) {}")
       }
     }
     printer.println()
@@ -591,7 +591,7 @@ extension JNISwift2JavaGenerator {
           } else {
             (0..<enumCase.parameters.count).map { i in
               "t.$\(i)"
-            }.joined(separator: ", ")
+            }.joined(separator: .comma)
           }
         let translatedResult = getAsCaseFunction.translatedFunctionSignature.result
         getAsCaseFunction.translatedFunctionSignature.result.conversion = .method(
@@ -679,7 +679,7 @@ extension JNISwift2JavaGenerator {
       """
       @FunctionalInterface
       public interface \(functionType.name) {
-        \(functionType.result.javaType) apply(\(apiParams.joined(separator: ", ")));
+        \(functionType.result.javaType) apply(\(apiParams.joined(separator: .comma)));
       }
       """
     )
@@ -732,7 +732,7 @@ extension JNISwift2JavaGenerator {
       generics.append((name, extends))
     }
     .map { "\($0) extends \($1.compactMap(\.className).joined(separator: " & "))" }
-    .joined(separator: ", ")
+    .joined(separator: .comma)
 
     if !generics.isEmpty {
       modifiers.append("<" + generics + ">")
@@ -741,7 +741,7 @@ extension JNISwift2JavaGenerator {
     var annotationsStr = translatedSignature.annotations.map({ $0.render() }).joined(separator: "\n")
     if !annotationsStr.isEmpty { annotationsStr += "\n" }
 
-    let parametersStr = parameters.joined(separator: ", ")
+    let parametersStr = parameters.joined(separator: .comma)
 
     // Print default global arena variation
     // If we have enabled javaCallbacks we must emit default
@@ -772,7 +772,7 @@ extension JNISwift2JavaGenerator {
       ) { printer in
         let globalArenaName = "SwiftMemoryManagement.DEFAULT_SWIFT_JAVA_AUTO_ARENA"
         let arguments = translatedDecl.translatedFunctionSignature.parameters.map(\.parameter.name) + [globalArenaName]
-        let call = "\(translatedDecl.name)(\(arguments.joined(separator: ", ")))"
+        let call = "\(translatedDecl.name)(\(arguments.joined(separator: .comma)))"
         if translatedDecl.translatedFunctionSignature.result.javaType.isVoid {
           printer.print("\(call);")
         } else {
@@ -794,7 +794,7 @@ extension JNISwift2JavaGenerator {
       )
     }
     let signature =
-      "\(annotationsStr)\(modifiers.joined(separator: " ")) \(resultType) \(translatedDecl.name)(\(parameters.joined(separator: ", ")))\(throwsClause)"
+      "\(annotationsStr)\(modifiers.joined(separator: " ")) \(resultType) \(translatedDecl.name)(\(parameters.joined(separator: .comma)))\(throwsClause)"
     if skipMethodBody {
       printer.print("\(signature);")
     } else {
@@ -820,7 +820,7 @@ extension JNISwift2JavaGenerator {
 
     let renderedParameters = parameters.map { javaParameter in
       "\(javaParameter.type) \(javaParameter.name)"
-    }.joined(separator: ", ")
+    }.joined(separator: .comma)
 
     printer.print("private static native \(resultType) \(translatedDecl.nativeFunctionName)(\(renderedParameters));")
   }
@@ -862,7 +862,7 @@ extension JNISwift2JavaGenerator {
     // TODO: If we always generate a native method and a "public" method, we can actually choose our own thunk names
     // using the registry?
     let downcall =
-      "\(translatedDecl.parentName).\(translatedDecl.nativeFunctionName)(\(arguments.joined(separator: ", ")))"
+      "\(translatedDecl.parentName).\(translatedDecl.nativeFunctionName)(\(arguments.joined(separator: .comma)))"
 
     //=== Part 4: Convert the return value.
     if translatedFunctionSignature.result.javaType.isVoid {