Revert "Revert "Merge pull request #41831 from hyp/unify-header""

This reverts commit 4c9582c295.

include/swift/AST/DiagnosticsFrontend.def

@@ -118,9 +118,7 @@ ERROR(error_mode_cannot_emit_dependencies,none,
 ERROR(error_mode_cannot_emit_reference_dependencies,none,
       "this mode does not support emitting reference dependency files", ())
 ERROR(error_mode_cannot_emit_header,none,
-      "this mode does not support emitting Objective-C headers", ())
+      "this mode does not support emitting Objective-C or C++ headers", ())
-ERROR(error_mode_cannot_emit_cxx_header,none,
-      "this mode does not support emitting C++ headers", ())
 ERROR(error_mode_cannot_emit_loaded_module_trace,none,
       "this mode does not support emitting the loaded module trace", ())
 ERROR(error_mode_cannot_emit_module,none,

include/swift/Basic/FileTypes.def

@@ -59,8 +59,7 @@ TYPE("raw-sib",             RawSIB,                    "sib",             "")
 TYPE("llvm-ir",             LLVM_IR,                   "ll",              "")
 TYPE("llvm-bc",             LLVM_BC,                   "bc",              "")
 TYPE("diagnostics",         SerializedDiagnostics,     "dia",             "")
-TYPE("objc-header",         ObjCHeader,                "h",               "")
+TYPE("clang-header",        ClangHeader,               "h",               "")
-TYPE("cxx-header",          CXXHeader,                 "h",               "")
 TYPE("swift-dependencies",  SwiftDeps,                 "swiftdeps",       "")
 TYPE("external-swift-dependencies", ExternalSwiftDeps,  "swiftdeps.external",  "")
 TYPE("remap",               Remapping,                 "remap",           "")

include/swift/Basic/SupplementaryOutputPaths.h

@@ -20,7 +20,8 @@
 
 namespace swift {
 struct SupplementaryOutputPaths {
-  /// The path to which we should emit an Objective-C header for the module.
+  /// The path to which we should emit a header file that exposes the Swift
+  /// declarations to C, Objective-C and C++ clients for the module.
   ///
   /// Currently only makes sense when the compiler has whole module knowledge.
   /// The modes for which it makes sense incuide both WMO and the "merge
@@ -28,19 +29,8 @@ struct SupplementaryOutputPaths {
   /// the header is emitted in single-file mode, since it needs whole-module
   /// information.
   ///
-  /// \sa swift::printAsObjC
+  /// \sa swift::printAsClangHeader
-  std::string ObjCHeaderOutputPath;
+  std::string ClangHeaderOutputPath;
-
-  /// The path to which we should emit a C++ header for the module.
-  ///
-  /// Currently only makes sense when the compiler has whole module knowledge.
-  /// The modes for which it makes sense include both WMO and the "merge
-  /// modules" job that happens after the normal compilation jobs. That's where
-  /// the header is emitted in single-file mode, since it needs whole-module
-  /// information.
-  ///
-  /// \sa swift::printAsCXX
-  std::string CxxHeaderOutputPath;
 
   /// The path to which we should emit a serialized module.
   /// It is valid whenever there are any inputs.
@@ -170,10 +160,8 @@ struct SupplementaryOutputPaths {
 
   /// Apply a given function for each existing (non-empty string) supplementary output
   void forEachSetOutput(llvm::function_ref<void(const std::string&)> fn) const {
-    if (!ObjCHeaderOutputPath.empty())
+    if (!ClangHeaderOutputPath.empty())
-      fn(ObjCHeaderOutputPath);
+      fn(ClangHeaderOutputPath);
-    if (!CxxHeaderOutputPath.empty())
-      fn(CxxHeaderOutputPath);
     if (!ModuleOutputPath.empty())
       fn(ModuleOutputPath); 
     if (!ModuleSourceInfoOutputPath.empty())
@@ -209,9 +197,8 @@ struct SupplementaryOutputPaths {
   }
 
   bool empty() const {
-    return ObjCHeaderOutputPath.empty() && CxxHeaderOutputPath.empty() &&
+    return ClangHeaderOutputPath.empty() && ModuleOutputPath.empty() &&
-           ModuleOutputPath.empty() && ModuleDocOutputPath.empty() &&
+           ModuleDocOutputPath.empty() && DependenciesFilePath.empty() &&
-           DependenciesFilePath.empty() &&
            ReferenceDependenciesFilePath.empty() &&
            SerializedDiagnosticsPath.empty() && LoadedModuleTracePath.empty() &&
            TBDPath.empty() && ModuleInterfaceOutputPath.empty() &&

include/swift/Frontend/Frontend.h

@@ -392,8 +392,7 @@ public:
 
   std::string getOutputFilenameForAtMostOnePrimary() const;
   std::string getMainInputFilenameForDebugInfoForAtMostOnePrimary() const;
-  std::string getObjCHeaderOutputPathForAtMostOnePrimary() const;
+  std::string getClangHeaderOutputPathForAtMostOnePrimary() const;
-  std::string getCxxHeaderOutputPathForAtMostOnePrimary() const;
   std::string getModuleOutputPathForAtMostOnePrimary() const;
   std::string
   getReferenceDependenciesFilePathForPrimary(StringRef filename) const;

include/swift/Frontend/FrontendInputsAndOutputs.h

@@ -249,8 +249,7 @@ public:
 
   bool hasDependenciesPath() const;
   bool hasReferenceDependenciesPath() const;
-  bool hasObjCHeaderOutputPath() const;
+  bool hasClangHeaderOutputPath() const;
-  bool hasCxxHeaderOutputPath() const;
   bool hasLoadedModuleTracePath() const;
   bool hasModuleOutputPath() const;
   bool hasModuleDocOutputPath() const;

include/swift/Option/Options.td

@@ -532,13 +532,11 @@ def emit_objc_header_path : Separate<["-"], "emit-objc-header-path">,
          SupplementaryOutput]>,
   MetaVarName<"<path>">, HelpText<"Emit an Objective-C header file to <path>">;
 
-def emit_cxx_header : Flag<["-"], "emit-cxx-header">,
+def emit_clang_header_path : Separate<["-"], "emit-clang-header-path">,
-  Flags<[FrontendOption, NoInteractiveOption, SupplementaryOutput]>,
+  Flags<[FrontendOption, NoDriverOption, NoInteractiveOption, ArgumentIsPath,
-  HelpText<"Emit a C++ header file">;
-def emit_cxx_header_path : Separate<["-"], "emit-cxx-header-path">,
-  Flags<[FrontendOption, NoInteractiveOption, ArgumentIsPath,
          SupplementaryOutput]>,
-  MetaVarName<"<path>">, HelpText<"Emit a C++ header file to <path>">;
+  HelpText<"Emit an Objective-C and C++ header file to <path>">,
+  Alias<emit_objc_header_path>;
 
 def static : Flag<["-"], "static">,
   Flags<[FrontendOption, ModuleInterfaceOption, NoInteractiveOption]>,

include/swift/PrintAsClang/PrintAsClang.h

@@ -21,16 +21,18 @@ namespace swift {
   class ModuleDecl;
   class ValueDecl;
 
-  /// Print the Objective-C-compatible declarations in a module as a Clang
+  /// Print the exposed declarations in a module into a Clang header.
-  /// header.
+  ///
+  /// The Objective-C compatible declarations are printed into a block that
+  /// ensures that those declarations are only usable when the header is
+  /// compiled in Objective-C mode.
+  ///  The C++ compatible declarations are printed into a block that ensures
+  ///  that those declarations are only usable when the header is compiled in
+  ///  C++ mode.
   ///
   /// Returns true on error.
-  bool printAsObjC(raw_ostream &out, ModuleDecl *M, StringRef bridgingHeader);
+  bool printAsClangHeader(raw_ostream &out, ModuleDecl *M,
-
+                          StringRef bridgingHeader);
-  /// Print the C++-compatible declarations in a module as a Clang header.
-  ///
-  /// Returns true on error.
-  bool printAsCXX(raw_ostream &os, ModuleDecl *M);
 }
 
 #endif

lib/Basic/FileTypes.cpp

@@ -73,8 +73,7 @@ bool file_types::isTextual(ID Id) {
   case file_types::TY_ASTDump:
   case file_types::TY_RawSIL:
   case file_types::TY_LLVM_IR:
-  case file_types::TY_ObjCHeader:
+  case file_types::TY_ClangHeader:
-  case file_types::TY_CXXHeader:
   case file_types::TY_AutolinkFile:
   case file_types::TY_ImportedModules:
   case file_types::TY_TBD:
@@ -132,8 +131,7 @@ bool file_types::isAfterLLVM(ID Id) {
   case file_types::TY_Dependencies:
   case file_types::TY_ASTDump:
   case file_types::TY_RawSIL:
-  case file_types::TY_ObjCHeader:
+  case file_types::TY_ClangHeader:
-  case file_types::TY_CXXHeader:
   case file_types::TY_AutolinkFile:
   case file_types::TY_Image:
   case file_types::TY_dSYM:
@@ -183,8 +181,7 @@ bool file_types::isPartOfSwiftCompilation(ID Id) {
   case file_types::TY_LLVM_BC:
   case file_types::TY_Object:
   case file_types::TY_Dependencies:
-  case file_types::TY_ObjCHeader:
+  case file_types::TY_ClangHeader:
-  case file_types::TY_CXXHeader:
   case file_types::TY_AutolinkFile:
   case file_types::TY_PCH:
   case file_types::TY_ImportedModules:

lib/Driver/Driver.cpp

@@ -1981,8 +1981,7 @@ void Driver::buildActions(SmallVectorImpl<const Action *> &TopLevelActions,
       if (Arg *A = Args.getLastArg(options::OPT_import_objc_header)) {
         StringRef Value = A->getValue();
         auto Ty = TC.lookupTypeForExtension(llvm::sys::path::extension(Value));
-        if (Ty == file_types::TY_ObjCHeader ||
+        if (Ty == file_types::TY_ClangHeader) {
-            Ty == file_types::TY_CXXHeader) {
           auto *HeaderInput = C.createAction<InputAction>(*A, Ty);
           StringRef PersistentPCHDir;
           if (const Arg *A = Args.getLastArg(options::OPT_pch_output_dir)) {
@@ -2065,8 +2064,7 @@ void Driver::buildActions(SmallVectorImpl<const Action *> &TopLevelActions,
       case file_types::TY_LLVM_IR:
       case file_types::TY_LLVM_BC:
       case file_types::TY_SerializedDiagnostics:
-      case file_types::TY_ObjCHeader:
+      case file_types::TY_ClangHeader:
-      case file_types::TY_CXXHeader:
       case file_types::TY_ClangModuleFile:
       case file_types::TY_SwiftDeps:
       case file_types::TY_ExternalSwiftDeps:
@@ -3480,12 +3478,12 @@ void Driver::chooseObjectiveCHeaderOutputPath(Compilation &C,
                                               StringRef workingDirectory,
                                               CommandOutput *Output) const {
 
-  if (hasExistingAdditionalOutput(*Output, file_types::TY_ObjCHeader))
+  if (hasExistingAdditionalOutput(*Output, file_types::TY_ClangHeader))
     return;
 
   StringRef ObjCHeaderPath;
   if (OutputMap) {
-    auto iter = OutputMap->find(file_types::TY_ObjCHeader);
+    auto iter = OutputMap->find(file_types::TY_ClangHeader);
     if (iter != OutputMap->end())
       ObjCHeaderPath = iter->second;
   }
@@ -3495,13 +3493,13 @@ void Driver::chooseObjectiveCHeaderOutputPath(Compilation &C,
       ObjCHeaderPath = A->getValue();
 
   if (!ObjCHeaderPath.empty()) {
-    Output->setAdditionalOutputForType(file_types::TY_ObjCHeader,
+    Output->setAdditionalOutputForType(file_types::TY_ClangHeader,
                                        ObjCHeaderPath);
   } else {
     // Put the header next to the primary output file.
     // FIXME: That's not correct if the user /just/ passed -emit-header
     // and not -emit-module.
-    addAuxiliaryOutput(C, *Output, file_types::TY_ObjCHeader,
+    addAuxiliaryOutput(C, *Output, file_types::TY_ClangHeader,
                        /*output file map*/ nullptr, workingDirectory);
   }
 }

lib/Driver/ToolChains.cpp

@@ -675,8 +675,7 @@ const char *ToolChain::JobContext::computeFrontendModeForCompile() const {
   case file_types::TY_Dependencies:
   case file_types::TY_SwiftModuleDocFile:
   case file_types::TY_SerializedDiagnostics:
-  case file_types::TY_ObjCHeader:
+  case file_types::TY_ClangHeader:
-  case file_types::TY_CXXHeader:
   case file_types::TY_Image:
   case file_types::TY_SwiftDeps:
   case file_types::TY_ExternalSwiftDeps:
@@ -815,7 +814,7 @@ void ToolChain::JobContext::addFrontendSupplementaryOutputArguments(
                    file_types::TY_SerializedDiagnostics,
                    "-serialize-diagnostics-path");
 
-  if (addOutputsOfType(arguments, Output, Args, file_types::ID::TY_ObjCHeader,
+  if (addOutputsOfType(arguments, Output, Args, file_types::ID::TY_ClangHeader,
                        "-emit-objc-header-path")) {
     assert(OI.CompilerMode == OutputInfo::Mode::SingleCompile &&
            "The Swift tool should only emit an Obj-C header in single compile"
@@ -936,8 +935,7 @@ ToolChain::constructInvocation(const BackendJobAction &job,
     case file_types::TY_Dependencies:
     case file_types::TY_SwiftModuleDocFile:
     case file_types::TY_SerializedDiagnostics:
-    case file_types::TY_ObjCHeader:
+    case file_types::TY_ClangHeader:
-    case file_types::TY_CXXHeader:
     case file_types::TY_Image:
     case file_types::TY_SwiftDeps:
     case file_types::TY_ExternalSwiftDeps:
@@ -1100,7 +1098,7 @@ ToolChain::constructInvocation(const MergeModuleJobAction &job,
                    file_types::TY_SerializedDiagnostics,
                    "-serialize-diagnostics-path");
   addOutputsOfType(Arguments, context.Output, context.Args,
-                   file_types::TY_ObjCHeader, "-emit-objc-header-path");
+                   file_types::TY_ClangHeader, "-emit-objc-header-path");
   addOutputsOfType(Arguments, context.Output, context.Args, file_types::TY_TBD,
                    "-emit-tbd-path");
 
@@ -1309,7 +1307,7 @@ ToolChain::constructInvocation(const GeneratePCHJobAction &job,
                    file_types::TY_SerializedDiagnostics,
                    "-serialize-diagnostics-path");
 
-  addInputsOfType(Arguments, context.InputActions, file_types::TY_ObjCHeader);
+  addInputsOfType(Arguments, context.InputActions, file_types::TY_ClangHeader);
   context.Args.AddLastArg(Arguments, options::OPT_index_store_path);
 
   if (job.isPersistentPCH()) {

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -625,15 +625,10 @@ bool ArgsToFrontendOptionsConverter::checkUnusedSupplementaryOutputPaths()
     return true;
   }
   if (!FrontendOptions::canActionEmitClangHeader(Opts.RequestedAction) &&
-      Opts.InputsAndOutputs.hasObjCHeaderOutputPath()) {
+      Opts.InputsAndOutputs.hasClangHeaderOutputPath()) {
     Diags.diagnose(SourceLoc(), diag::error_mode_cannot_emit_header);
     return true;
   }
-  if (!FrontendOptions::canActionEmitClangHeader(Opts.RequestedAction) &&
-      Opts.InputsAndOutputs.hasCxxHeaderOutputPath()) {
-    Diags.diagnose(SourceLoc(), diag::error_mode_cannot_emit_cxx_header);
-    return true;
-  }
   if (!FrontendOptions::canActionEmitLoadedModuleTrace(Opts.RequestedAction) &&
       Opts.InputsAndOutputs.hasLoadedModuleTracePath()) {
     Diags.diagnose(SourceLoc(),

lib/Frontend/ArgsToFrontendOutputsConverter.cpp

@@ -308,10 +308,8 @@ Optional<std::vector<SupplementaryOutputPaths>>
 SupplementaryOutputPathsComputer::getSupplementaryOutputPathsFromArguments()
     const {
 
-  auto objCHeaderOutput = getSupplementaryFilenamesFromArguments(
+  auto clangHeaderOutput = getSupplementaryFilenamesFromArguments(
       options::OPT_emit_objc_header_path);
-  auto cxxHeaderOutput =
-      getSupplementaryFilenamesFromArguments(options::OPT_emit_cxx_header_path);
   auto moduleOutput =
       getSupplementaryFilenamesFromArguments(options::OPT_emit_module_path);
   auto moduleDocOutput =
@@ -341,8 +339,8 @@ SupplementaryOutputPathsComputer::getSupplementaryOutputPathsFromArguments()
       options::OPT_emit_module_semantic_info_path);
   auto optRecordOutput = getSupplementaryFilenamesFromArguments(
       options::OPT_save_optimization_record_path);
-  if (!objCHeaderOutput || !cxxHeaderOutput || !moduleOutput ||
+  if (!clangHeaderOutput || !moduleOutput || !moduleDocOutput ||
-      !moduleDocOutput || !dependenciesFile || !referenceDependenciesFile ||
+      !dependenciesFile || !referenceDependenciesFile ||
       !serializedDiagnostics || !fixItsOutput || !loadedModuleTrace || !TBD ||
       !moduleInterfaceOutput || !privateModuleInterfaceOutput ||
       !moduleSourceInfoOutput || !moduleSummaryOutput || !abiDescriptorOutput ||
@@ -355,8 +353,7 @@ SupplementaryOutputPathsComputer::getSupplementaryOutputPathsFromArguments()
       InputsAndOutputs.countOfFilesProducingSupplementaryOutput();
   for (unsigned i = 0; i < N; ++i) {
     SupplementaryOutputPaths sop;
-    sop.ObjCHeaderOutputPath = (*objCHeaderOutput)[i];
+    sop.ClangHeaderOutputPath = (*clangHeaderOutput)[i];
-    sop.CxxHeaderOutputPath = (*cxxHeaderOutput)[i];
     sop.ModuleOutputPath = (*moduleOutput)[i];
     sop.ModuleDocOutputPath = (*moduleDocOutput)[i];
     sop.DependenciesFilePath = (*dependenciesFile)[i];
@@ -437,14 +434,9 @@ SupplementaryOutputPathsComputer::computeOutputPathsForOneInput(
   // There is no non-path form of -emit-fixits-path
   auto fixItsOutputPath = pathsFromArguments.FixItsOutputPath;
 
-  auto objcHeaderOutputPath = determineSupplementaryOutputFilename(
+  auto clangHeaderOutputPath = determineSupplementaryOutputFilename(
-      OPT_emit_objc_header, pathsFromArguments.ObjCHeaderOutputPath,
+      OPT_emit_objc_header, pathsFromArguments.ClangHeaderOutputPath,
-      file_types::TY_ObjCHeader, "",
+      file_types::TY_ClangHeader, "",
-      defaultSupplementaryOutputPathExcludingExtension);
-
-  auto cxxHeaderOutputPath = determineSupplementaryOutputFilename(
-      OPT_emit_cxx_header, pathsFromArguments.CxxHeaderOutputPath,
-      file_types::TY_CXXHeader, "",
       defaultSupplementaryOutputPathExcludingExtension);
 
   auto loadedModuleTracePath = determineSupplementaryOutputFilename(
@@ -500,8 +492,7 @@ SupplementaryOutputPathsComputer::computeOutputPathsForOneInput(
       defaultSupplementaryOutputPathExcludingExtension);
 
   SupplementaryOutputPaths sop;
-  sop.ObjCHeaderOutputPath = objcHeaderOutputPath;
+  sop.ClangHeaderOutputPath = clangHeaderOutputPath;
-  sop.CxxHeaderOutputPath = cxxHeaderOutputPath;
   sop.ModuleOutputPath = moduleOutputPath;
   sop.ModuleDocOutputPath = moduleDocOutputPath;
   sop.DependenciesFilePath = dependenciesFilePath;
@@ -586,8 +577,7 @@ createFromTypeToPathMap(const TypeToPathMap *map) {
   if (!map)
     return paths;
   const std::pair<file_types::ID, std::string &> typesAndStrings[] = {
-      {file_types::TY_ObjCHeader, paths.ObjCHeaderOutputPath},
+      {file_types::TY_ClangHeader, paths.ClangHeaderOutputPath},
-      {file_types::TY_CXXHeader, paths.CxxHeaderOutputPath},
       {file_types::TY_SwiftModuleFile, paths.ModuleOutputPath},
       {file_types::TY_SwiftModuleDocFile, paths.ModuleDocOutputPath},
       {file_types::TY_SwiftSourceInfoFile, paths.ModuleSourceInfoOutputPath},
@@ -615,9 +605,9 @@ createFromTypeToPathMap(const TypeToPathMap *map) {
 
 Optional<std::vector<SupplementaryOutputPaths>>
 SupplementaryOutputPathsComputer::readSupplementaryOutputFileMap() const {
-  if (Arg *A = Args.getLastArg(
+  if (Arg *A = Args.getLastArg(options::OPT_emit_objc_header_path,
-          options::OPT_emit_objc_header_path, options::OPT_emit_cxx_header_path,
+                               options::OPT_emit_module_path,
-          options::OPT_emit_module_path, options::OPT_emit_module_doc_path,
+                               options::OPT_emit_module_doc_path,
                                options::OPT_emit_dependencies_path,
                                options::OPT_emit_reference_dependencies_path,
                                options::OPT_serialize_diagnostics_path,

lib/Frontend/Frontend.cpp

@@ -92,14 +92,9 @@ CompilerInvocation::getMainInputFilenameForDebugInfoForAtMostOnePrimary()
       .MainInputFilenameForDebugInfo;
 }
 std::string
-CompilerInvocation::getObjCHeaderOutputPathForAtMostOnePrimary() const {
+CompilerInvocation::getClangHeaderOutputPathForAtMostOnePrimary() const {
   return getPrimarySpecificPathsForAtMostOnePrimary()
-      .SupplementaryOutputs.ObjCHeaderOutputPath;
+      .SupplementaryOutputs.ClangHeaderOutputPath;
-}
-std::string
-CompilerInvocation::getCxxHeaderOutputPathForAtMostOnePrimary() const {
-  return getPrimarySpecificPathsForAtMostOnePrimary()
-      .SupplementaryOutputs.CxxHeaderOutputPath;
 }
 std::string CompilerInvocation::getModuleOutputPathForAtMostOnePrimary() const {
   return getPrimarySpecificPathsForAtMostOnePrimary()

lib/Frontend/FrontendInputsAndOutputs.cpp

@@ -213,7 +213,7 @@ bool FrontendInputsAndOutputs::shouldTreatAsObjCHeader() const {
   if (hasSingleInput()) {
     StringRef InputExt = llvm::sys::path::extension(getFilenameOfFirstInput());
     switch (file_types::lookupTypeForExtension(InputExt)) {
-    case file_types::TY_ObjCHeader:
+    case file_types::TY_ClangHeader:
       return true;
     default:
       return false;
@@ -461,16 +461,10 @@ bool FrontendInputsAndOutputs::hasReferenceDependenciesPath() const {
         return outs.ReferenceDependenciesFilePath;
       });
 }
-bool FrontendInputsAndOutputs::hasObjCHeaderOutputPath() const {
+bool FrontendInputsAndOutputs::hasClangHeaderOutputPath() const {
   return hasSupplementaryOutputPath(
       [](const SupplementaryOutputPaths &outs) -> const std::string & {
-        return outs.ObjCHeaderOutputPath;
+        return outs.ClangHeaderOutputPath;
-      });
-}
-bool FrontendInputsAndOutputs::hasCxxHeaderOutputPath() const {
-  return hasSupplementaryOutputPath(
-      [](const SupplementaryOutputPaths &outs) -> const std::string & {
-        return outs.CxxHeaderOutputPath;
       });
 }
 bool FrontendInputsAndOutputs::hasLoadedModuleTracePath() const {

lib/Frontend/FrontendOptions.cpp

@@ -234,8 +234,7 @@ void FrontendOptions::forAllOutputPaths(
   const std::string *outputs[] = {
       &outs.ModuleOutputPath,          &outs.ModuleDocOutputPath,
       &outs.ModuleInterfaceOutputPath, &outs.PrivateModuleInterfaceOutputPath,
-      &outs.ObjCHeaderOutputPath,      &outs.CxxHeaderOutputPath,
+      &outs.ClangHeaderOutputPath,     &outs.ModuleSourceInfoOutputPath};
-      &outs.ModuleSourceInfoOutputPath};
   for (const std::string *next : outputs) {
     if (!next->empty())
       fn(*next);

lib/FrontendTool/FrontendTool.cpp

@@ -170,36 +170,22 @@ static bool writeSIL(SILModule &SM, const PrimarySpecificPaths &PSPs,
 
 /// Prints the Objective-C "generated header" interface for \p M to \p
 /// outputPath.
-///
+/// Print the exposed "generated header" interface for \p M to \p
-/// ...unless \p outputPath is empty, in which case it does nothing.
-///
-/// \returns true if there were any errors
-///
-/// \see swift::printAsObjC
-static bool printAsObjCIfNeeded(StringRef outputPath, ModuleDecl *M,
-                                StringRef bridgingHeader) {
-  if (outputPath.empty())
-    return false;
-  return withOutputFile(M->getDiags(), outputPath,
-                        [&](raw_ostream &out) -> bool {
-    return printAsObjC(out, M, bridgingHeader);
-  });
-}
-
-/// Prints the C++  "generated header" interface for \p M to \p
 /// outputPath.
 ///
 /// ...unless \p outputPath is empty, in which case it does nothing.
 ///
 /// \returns true if there were any errors
 ///
-/// \see swift::printAsCXX
+/// \see swift::printAsClangHeader
-static bool printAsCxxIfNeeded(StringRef outputPath, ModuleDecl *M) {
+static bool printAsClangHeaderIfNeeded(StringRef outputPath, ModuleDecl *M,
+                                       StringRef bridgingHeader) {
   if (outputPath.empty())
     return false;
-  return withOutputFile(
+  return withOutputFile(M->getDiags(), outputPath,
-      M->getDiags(), outputPath,
+                        [&](raw_ostream &out) -> bool {
-      [&](raw_ostream &os) -> bool { return printAsCXX(os, M); });
+                          return printAsClangHeader(out, M, bridgingHeader);
+                        });
 }
 
 /// Prints the stable module interface for \p M to \p outputPath.
@@ -824,7 +810,7 @@ static bool emitAnyWholeModulePostTypeCheckSupplementaryOutputs(
   bool hadAnyError = false;
 
   if ((!Context.hadError() || opts.AllowModuleWithCompilerErrors) &&
-      opts.InputsAndOutputs.hasObjCHeaderOutputPath()) {
+      opts.InputsAndOutputs.hasClangHeaderOutputPath()) {
     std::string BridgingHeaderPathForPrint;
     if (!opts.ImplicitObjCHeaderPath.empty()) {
       if (opts.BridgingHeaderDirForPrint.hasValue()) {
@@ -838,16 +824,10 @@ static bool emitAnyWholeModulePostTypeCheckSupplementaryOutputs(
         BridgingHeaderPathForPrint = opts.ImplicitObjCHeaderPath;
       }
     }
-    hadAnyError |= printAsObjCIfNeeded(
+    hadAnyError |= printAsClangHeaderIfNeeded(
-        Invocation.getObjCHeaderOutputPathForAtMostOnePrimary(),
+        Invocation.getClangHeaderOutputPathForAtMostOnePrimary(),
         Instance.getMainModule(), BridgingHeaderPathForPrint);
   }
-  if ((!Context.hadError() || opts.AllowModuleWithCompilerErrors) &&
-      opts.InputsAndOutputs.hasCxxHeaderOutputPath()) {
-    hadAnyError |= printAsCxxIfNeeded(
-        Invocation.getCxxHeaderOutputPathForAtMostOnePrimary(),
-        Instance.getMainModule());
-  }
 
   // Only want the header if there's been any errors, ie. there's not much
   // point outputting a swiftinterface for an invalid module

lib/PrintAsClang/PrintAsClang.cpp

@@ -26,9 +26,8 @@
 
 using namespace swift;
 
-static void writePrologue(raw_ostream &out, ASTContext &ctx,
+static void emitCxxConditional(raw_ostream &out,
-                          StringRef macroGuard) {
+                               llvm::function_ref<void()> cxxCase,
-  auto emitCxxConditional = [&](llvm::function_ref<void()> cxxCase,
                                llvm::function_ref<void()> cCase = {}) {
   out << "#if defined(__cplusplus)\n";
   cxxCase();
@@ -37,8 +36,10 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
     cCase();
   }
   out << "#endif\n";
-  };
+}
-  auto emitObjCConditional = [&](llvm::function_ref<void()> objcCase,
+
+static void emitObjCConditional(raw_ostream &out,
+                                llvm::function_ref<void()> objcCase,
                                 llvm::function_ref<void()> nonObjCCase = {}) {
   out << "#if defined(__OBJC__)\n";
   objcCase();
@@ -47,7 +48,10 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
     nonObjCCase();
   }
   out << "#endif\n";
-  };
+}
+
+static void writePrologue(raw_ostream &out, ASTContext &ctx,
+                          StringRef macroGuard) {
 
   out << "// Generated by "
       << version::getSwiftFullVersion(ctx.LangOpts.EffectiveLanguageVersion)
@@ -77,8 +81,10 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
          "#endif\n"
          "\n"
          "#pragma clang diagnostic ignored \"-Wauto-import\"\n";
-  emitObjCConditional([&] { out << "#include <Foundation/Foundation.h>\n"; });
+  emitObjCConditional(out,
+                      [&] { out << "#include <Foundation/Foundation.h>\n"; });
   emitCxxConditional(
+      out,
       [&] {
         out << "#include <cstdint>\n"
                "#include <cstddef>\n"
@@ -276,7 +282,7 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
          "#else\n"
          "# define SWIFT_DEPRECATED_OBJC(Msg) SWIFT_DEPRECATED_MSG(Msg)\n"
          "#endif\n";
-  emitObjCConditional([&] {
+  emitObjCConditional(out, [&] {
     out << "#if !defined(IBSegueAction)\n"
            "# define IBSegueAction\n"
            "#endif\n";
@@ -295,7 +301,8 @@ static void writePrologue(raw_ostream &out, ASTContext &ctx,
   };
   emitMacro("SWIFT_CALL", "__attribute__((swiftcall))");
   // SWIFT_NOEXCEPT applies 'noexcept' in C++ mode only.
-  emitCxxConditional([&] { emitMacro("SWIFT_NOEXCEPT", "noexcept"); },
+  emitCxxConditional(
+      out, [&] { emitMacro("SWIFT_NOEXCEPT", "noexcept"); },
       [&] { emitMacro("SWIFT_NOEXCEPT"); });
   static_assert(SWIFT_MAX_IMPORTED_SIMD_ELEMENTS == 4,
               "need to add SIMD typedefs here if max elements is increased");
@@ -442,33 +449,33 @@ static std::string computeMacroGuard(const ModuleDecl *M) {
   return (llvm::Twine(M->getNameStr().upper()) + "_SWIFT_H").str();
 }
 
-bool swift::printAsObjC(raw_ostream &os, ModuleDecl *M,
+static std::string getModuleContentsCxxString(ModuleDecl &M) {
+  SmallPtrSet<ImportModuleTy, 8> imports;
+  std::string moduleContentsBuf;
+  llvm::raw_string_ostream moduleContents{moduleContentsBuf};
+  printModuleContentsAsCxx(moduleContents, imports, M);
+  return moduleContents.str();
+}
+
+bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
                                StringRef bridgingHeader) {
-  llvm::PrettyStackTraceString trace("While generating Objective-C header");
+  llvm::PrettyStackTraceString trace("While generating Clang header");
 
   SmallPtrSet<ImportModuleTy, 8> imports;
-  std::string moduleContentsBuf;
+  std::string objcModuleContentsBuf;
-  llvm::raw_string_ostream moduleContents{moduleContentsBuf};
+  llvm::raw_string_ostream objcModuleContents{objcModuleContentsBuf};
-  printModuleContentsAsObjC(moduleContents, imports, *M);
+  printModuleContentsAsObjC(objcModuleContents, imports, *M);
   writePrologue(os, M->getASTContext(), computeMacroGuard(M));
-  writeImports(os, imports, *M, bridgingHeader);
+  emitObjCConditional(os,
+                      [&] { writeImports(os, imports, *M, bridgingHeader); });
   writePostImportPrologue(os, *M);
-  os << moduleContents.str();
+  emitObjCConditional(os, [&] { os << objcModuleContents.str(); });
-  writeEpilogue(os);
+  emitCxxConditional(os, [&] {
-
+    // FIXME: Expose Swift with @expose by default.
-  return false;
+    if (M->getASTContext().LangOpts.EnableCXXInterop) {
-}
+      os << getModuleContentsCxxString(*M);
-
+    }
-bool swift::printAsCXX(raw_ostream &os, ModuleDecl *M) {
+  });
-  llvm::PrettyStackTraceString trace("While generating C++ header");
-
-  SmallPtrSet<ImportModuleTy, 8> imports;
-  std::string moduleContentsBuf;
-  llvm::raw_string_ostream moduleContents{moduleContentsBuf};
-  printModuleContentsAsCxx(moduleContents, imports, *M);
-  writePrologue(os, M->getASTContext(), computeMacroGuard(M));
-  writePostImportPrologue(os, *M);
-  os << moduleContents.str();
   writeEpilogue(os);
 
   return false;

test/Driver/bridging-pch.swift

@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 
 // RUN: %target-build-swift -typecheck -driver-print-actions -import-objc-header %S/Inputs/bridging-header.h %s 2>&1 | %FileCheck %s -check-prefix=YESPCHACT
-// YESPCHACT: 0: input, "{{.*}}Inputs/bridging-header.h", objc-header
+// YESPCHACT: 0: input, "{{.*}}Inputs/bridging-header.h", clang-header
 // YESPCHACT: 1: generate-pch, {0}, pch
 // YESPCHACT: 2: input, "{{.*}}bridging-pch.swift", swift
 // YESPCHACT: 3: compile, {2, 1}, none
@@ -30,13 +30,13 @@
 // Test persistent PCH
 
 // RUN: %target-build-swift -typecheck -driver-print-actions -import-objc-header %S/Inputs/bridging-header.h -pch-output-dir %t/pch %s 2>&1 | %FileCheck %s -check-prefix=PERSISTENT-YESPCHACT
-// PERSISTENT-YESPCHACT: 0: input, "{{.*}}Inputs/bridging-header.h", objc-header
+// PERSISTENT-YESPCHACT: 0: input, "{{.*}}Inputs/bridging-header.h", clang-header
 // PERSISTENT-YESPCHACT: 1: generate-pch, {0}, none
 // PERSISTENT-YESPCHACT: 2: input, "{{.*}}bridging-pch.swift", swift
 // PERSISTENT-YESPCHACT: 3: compile, {2, 1}, none
 
 // RUN: %target-build-swift -c -driver-print-actions -embed-bitcode -import-objc-header %S/Inputs/bridging-header.h -pch-output-dir %t/pch %s 2>&1 | %FileCheck %s -check-prefix=PERSISTENT-YESPCHACTBC
-// PERSISTENT-YESPCHACTBC: 0: input, "{{.*}}Inputs/bridging-header.h", objc-header
+// PERSISTENT-YESPCHACTBC: 0: input, "{{.*}}Inputs/bridging-header.h", clang-header
 // PERSISTENT-YESPCHACTBC: 1: generate-pch, {0}, none
 // PERSISTENT-YESPCHACTBC: 2: input, "{{.*}}bridging-pch.swift", swift
 // PERSISTENT-YESPCHACTBC: 3: compile, {2, 1}, llvm-bc

test/Driver/parseable_output.swift

@@ -94,7 +94,7 @@
 // CHECK-NEXT:       "path": "{{.*[\\/]}}parseable_output.swift.tmp.swiftsourceinfo"
 // CHECK-NEXT:     },
 // CHECK-NEXT:     {
-// CHECK-NEXT:       "type": "objc-header",
+// CHECK-NEXT:       "type": "clang-header",
 // CHECK-NEXT:       "path": "{{.*[\\/]}}parseable_output.swift.tmp.h"
 // CHECK-NEXT:     }
 // CHECK-NEXT:   ],

test/Driver/parseable_output_unicode.swift

@@ -96,7 +96,7 @@
 // CHECK-NEXT:       "path": "{{.*[\\/]}}parseable_output_unicode.swift.tmp.swiftsourceinfo"
 // CHECK-NEXT:     },
 // CHECK-NEXT:     {
-// CHECK-NEXT:       "type": "objc-header",
+// CHECK-NEXT:       "type": "clang-header",
 // CHECK-NEXT:       "path": "{{.*[\\/]}}parseable_output_unicode.swift.tmp.h"
 // CHECK-NEXT:     }
 // CHECK-NEXT:   ],

test/Frontend/supplementary-output-support.swift

@@ -18,18 +18,11 @@
 // RESOLVE_IMPORTS_NO_REFERENCE_DEPS: error: this mode does not support emitting reference dependency files{{$}}
 
 // RUN: not %target-swift-frontend -parse -emit-objc-header %s 2>&1 | %FileCheck -check-prefix=PARSE_NO_OBJC_HEADER %s
-// PARSE_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C headers{{$}}
+// PARSE_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C or C++ headers{{$}}
 // RUN: not %target-swift-frontend -dump-ast -emit-objc-header %s 2>&1 | %FileCheck -check-prefix=DUMP_NO_OBJC_HEADER %s
-// DUMP_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C headers{{$}}
+// DUMP_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C or C++ headers{{$}}
 // RUN: not %target-swift-frontend -resolve-imports -emit-objc-header %s 2>&1 | %FileCheck -check-prefix=RESOLVE_IMPORTS_NO_OBJC_HEADER %s
-// RESOLVE_IMPORTS_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C headers{{$}}
+// RESOLVE_IMPORTS_NO_OBJC_HEADER: error: this mode does not support emitting Objective-C or C++ headers{{$}}
-
-// RUN: not %target-swift-frontend -parse -emit-cxx-header %s 2>&1 | %FileCheck -check-prefix=PARSE_NO_CXX_HEADER %s
-// PARSE_NO_CXX_HEADER: error: this mode does not support emitting C++ headers{{$}}
-// RUN: not %target-swift-frontend -dump-ast -emit-cxx-header %s 2>&1 | %FileCheck -check-prefix=DUMP_NO_CXX_HEADER %s
-// DUMP_NO_CXX_HEADER: error: this mode does not support emitting C++ headers{{$}}
-// RUN: not %target-swift-frontend -resolve-imports -emit-cxx-header %s 2>&1 | %FileCheck -check-prefix=RESOLVE_IMPORTS_NO_CXX_HEADER %s
-// RESOLVE_IMPORTS_NO_CXX_HEADER: error: this mode does not support emitting C++ headers{{$}}
 
 // RUN: not %target-swift-frontend -parse -emit-module-interface-path %t %s 2>&1 | %FileCheck -check-prefix=PARSE_NO_INTERFACE %s
 // PARSE_NO_INTERFACE: error: this mode does not support emitting module interface files{{$}}

test/Interop/SwiftToCxx/functions/cdecl-execution.cpp

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/cdecl.swift -typecheck -module-name CdeclFunctions -emit-cxx-header-path %t/functions.h
+// RUN: %target-swift-frontend %S/cdecl.swift -typecheck -module-name CdeclFunctions -enable-cxx-interop -emit-clang-header-path %t/functions.h
 
 // RUN: %target-interop-build-clangxx -c %s -I %t -o %t/cdecl-execution.o
 // RUN: %target-interop-build-swift %S/cdecl.swift -o %t/cdecl-execution -Xlinker %t/cdecl-execution.o -module-name Functions -Xfrontend -entry-point-function-name -Xfrontend swiftMain

test/Interop/SwiftToCxx/functions/cdecl.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name CdeclFunctions -emit-cxx-header-path %t/cdecl.h
+// RUN: %target-swift-frontend %s -typecheck -module-name CdeclFunctions -enable-cxx-interop -emit-clang-header-path %t/cdecl.h
 // RUN: %FileCheck %s < %t/cdecl.h
 
 // RUN: %check-interop-cxx-header-in-clang(%t/cdecl.h)

test/Interop/SwiftToCxx/functions/function-availability.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Functions -emit-cxx-header-path %t/functions.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -enable-cxx-interop -emit-clang-header-path %t/functions.h
 // RUN: %FileCheck %s < %t/functions.h
 
 // RUN: %check-interop-cxx-header-in-clang(%t/functions.h)

test/Interop/SwiftToCxx/functions/swift-functions-execution.cpp

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/swift-functions.swift -typecheck -module-name Functions -emit-cxx-header-path %t/functions.h
+// RUN: %target-swift-frontend %S/swift-functions.swift -typecheck -module-name Functions -enable-cxx-interop -emit-clang-header-path %t/functions.h
 
 // RUN: %target-interop-build-clangxx -c %s -I %t -o %t/swift-functions-execution.o
 // RUN: %target-interop-build-swift %S/swift-functions.swift -o %t/swift-functions-execution -Xlinker %t/swift-functions-execution.o -module-name Functions -Xfrontend -entry-point-function-name -Xfrontend swiftMain

test/Interop/SwiftToCxx/functions/swift-functions.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Functions -emit-cxx-header-path %t/functions.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -enable-cxx-interop -emit-clang-header-path %t/functions.h
 // RUN: %FileCheck %s < %t/functions.h
 
 // RUN: %check-interop-cxx-header-in-clang(%t/functions.h)

test/Interop/SwiftToCxx/module/module-to-namespace.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -typecheck -module-name Test -emit-cxx-header-path %t/empty.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Test -enable-cxx-interop -emit-clang-header-path %t/empty.h
 // RUN: %FileCheck %s < %t/empty.h
 
 // RUN: %check-interop-cxx-header-in-clang(%t/empty.h)

test/PrintAsCxx/empty.swift

@@ -1,13 +1,7 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -typecheck -emit-cxx-header-path %t/empty.h
+// RUN: %target-swift-frontend %s -typecheck -enable-cxx-interop -emit-clang-header-path %t/empty.h
 // RUN: %FileCheck %s < %t/empty.h
 
-// RUN: %check-cxx-header-in-clang -std=c++14 %t/empty.h
-// RUN: %check-cxx-header-in-clang -std=c++17 %t/empty.h
-
-// CHECK-NOT: @import Swift;
-// CHECK-NOT: IBSegueAction
-
 // CHECK-LABEL: #ifndef EMPTY_SWIFT_H
 // CHECK-NEXT:  #define EMPTY_SWIFT_H
 
@@ -63,7 +57,19 @@
 // CHECK: # define SWIFT_EXTENSION(M)
 // CHECK: # define OBJC_DESIGNATED_INITIALIZER
 
-// CHECK-LABEL: namespace empty {
+// CHECK-LABEL: #if defined(__OBJC__)
+// CHECK-NEXT:  #if !defined(IBSegueAction)
+// CHECK-NEXT:  # define IBSegueAction
+// CHECK-NEXT:  #endif
+
+// CHECK-LABEL: #if defined(__OBJC__)
+// CHECK-NEXT:  #if __has_feature(modules)
+
+// CHECK-LABEL: #if defined(__OBJC__)
+// CHECK-NEXT:  #endif
+// CHECK-NEXT:  #if defined(__cplusplus)
+// CHECK-NEXT:  namespace empty {
 // CHECK:       } // namespace empty
+// CHECK:       #endif
 
 // CHECK-NOT: @

test/PrintAsObjC/Inputs/comments-expected-output.h

@@ -424,6 +424,9 @@ SWIFT_CLASS("_TtC8comments13UnorderedList")
 - (void)f0;
 @end
 
+#endif
+#if defined(__cplusplus)
+#endif
 #if __has_attribute(external_source_symbol)
 # pragma clang attribute pop
 #endif