[interop][SwiftToCxx] add support for emitting Swift stdlib dependenc…

include/swift/Frontend/FrontendOptions.h

@@ -19,6 +19,7 @@
 #include "swift/Frontend/FrontendInputsAndOutputs.h"
 #include "swift/Frontend/InputFile.h"
 #include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringMap.h"
 
 #include <string>
@@ -388,9 +389,16 @@ class FrontendOptions {
   /// '.../lib/swift', otherwise '.../lib/swift_static'.
   bool UseSharedResourceFolder = true;
 
-  /// Indicates whether to expose all public declarations in the generated clang
+  enum class ClangHeaderExposeBehavior {
+    /// Expose all public declarations in the generated header.
+    AllPublic,
+    /// Expose declarations only when they have expose attribute.
+    HasExposeAttr
+  };
+
+  /// Indicates which declarations should be exposed in the generated clang
   /// header.
-  bool ExposePublicDeclsInClangHeader = false;
+  llvm::Optional<ClangHeaderExposeBehavior> ClangHeaderExposedDecls;
 
   /// Emit C++ bindings for the exposed Swift declarations in the generated
   /// clang header.

include/swift/Option/FrontendOptions.td

@@ -1081,11 +1081,12 @@ def skip_import_in_public_interface:
   HelpText<"Skip the import statement corresponding to a module name "
            "when printing the public interface.">;
 
-def clang_header_expose_public_decls:
-  Flag<["-"], "clang-header-expose-public-decls">,
-  HelpText<"Expose all public declarations in the generated clang header">,
-  Flags<[FrontendOption, HelpHidden]>;
-
+def clang_header_expose_decls:
+  Joined<["-"], "clang-header-expose-decls=">,
+  HelpText<"Which declarations should be exposed in the generated clang header.">,
+  Flags<[FrontendOption, HelpHidden]>,
+  MetaVarName<"all-public|has-expose-attr">;
+
 def weak_link_at_target :
   Flag<["-"], "weak-link-at-target">,
   HelpText<"Weakly link symbols for declarations that were introduced at the "

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -284,8 +284,13 @@ bool ArgsToFrontendOptionsConverter::convert(
   Opts.EnableIncrementalDependencyVerifier |= Args.hasArg(OPT_verify_incremental_dependencies);
   Opts.UseSharedResourceFolder = !Args.hasArg(OPT_use_static_resource_dir);
   Opts.DisableBuildingInterface = Args.hasArg(OPT_disable_building_interface);
-  Opts.ExposePublicDeclsInClangHeader =
-      Args.hasArg(OPT_clang_header_expose_public_decls);
+  if (const Arg *A = Args.getLastArg(options::OPT_clang_header_expose_decls)) {
+      Opts.ClangHeaderExposedDecls =
+          llvm::StringSwitch<llvm::Optional<FrontendOptions::ClangHeaderExposeBehavior>>(A->getValue())
+              .Case("all-public", FrontendOptions::ClangHeaderExposeBehavior::AllPublic)
+              .Case("has-expose-attr", FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr)
+              .Default(llvm::None);
+  }
   Opts.EnableExperimentalCxxInteropInClangHeader =
       Args.hasArg(OPT_enable_experimental_cxx_interop_in_clang_header);
 

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -134,6 +134,7 @@ class ModuleWriter {
   llvm::raw_string_ostream outOfLineDefinitionsOS;
   DeclAndTypePrinter printer;
   OutputLanguageMode outputLangMode;
+  bool dependsOnStdlib = false;
 
 public:
   ModuleWriter(raw_ostream &os, raw_ostream &prologueOS,
@@ -149,6 +150,11 @@ class ModuleWriter {
 
   PrimitiveTypeMapping &getTypeMapping() { return typeMapping; }
 
+  /// Returns true if a Stdlib dependency was seen during the emission of this module.
+  bool isStdlibRequired() const {
+    return dependsOnStdlib;
+  }
+
   /// Returns true if we added the decl's module to the import set, false if
   /// the decl is a local decl.
   ///
@@ -159,8 +165,10 @@ class ModuleWriter {
 
     if (otherModule == &M)
       return false;
-    if (otherModule->isStdlibModule() ||
-        otherModule->isBuiltinModule())
+    if (otherModule->isStdlibModule()) {
+      dependsOnStdlib = true;
+      return true;
+    } else if (otherModule->isBuiltinModule())
       return true;
     // Don't need a module for SIMD types in C.
     if (otherModule->getName() == M.getASTContext().Id_simd)
@@ -734,20 +742,22 @@ void swift::printModuleContentsAsObjC(
       .write();
 }
 
-void swift::printModuleContentsAsCxx(
-    raw_ostream &os, llvm::SmallPtrSetImpl<ImportModuleTy> &imports,
+EmittedClangHeaderDependencyInfo swift::printModuleContentsAsCxx(
+    raw_ostream &os,
     ModuleDecl &M, SwiftToClangInteropContext &interopContext,
     bool requiresExposedAttribute) {
   std::string moduleContentsBuf;
   llvm::raw_string_ostream moduleOS{moduleContentsBuf};
   std::string modulePrologueBuf;
   llvm::raw_string_ostream prologueOS{modulePrologueBuf};
+  EmittedClangHeaderDependencyInfo info;
 
   // FIXME: Use getRequiredAccess once @expose is supported.
-  ModuleWriter writer(moduleOS, prologueOS, imports, M, interopContext,
+  ModuleWriter writer(moduleOS, prologueOS, info.imports, M, interopContext,
                       AccessLevel::Public, requiresExposedAttribute,
                       OutputLanguageMode::Cxx);
   writer.write();
+  info.dependsOnStandardLibrary = writer.isStdlibRequired();
 
   os << "#ifndef SWIFT_PRINTED_CORE\n";
   os << "#define SWIFT_PRINTED_CORE\n";
@@ -778,4 +788,5 @@ void swift::printModuleContentsAsCxx(
   ClangSyntaxPrinter(os).printNamespace(
       [&](raw_ostream &os) { M.ValueDecl::getName().print(os); },
       [&](raw_ostream &os) { os << moduleOS.str(); });
+  return info;
 }

lib/PrintAsClang/ModuleContentsWriter.h

@@ -36,10 +36,17 @@ void printModuleContentsAsObjC(raw_ostream &os,
                                ModuleDecl &M,
                                SwiftToClangInteropContext &interopContext);
 
-/// Prints the declarations of \p M to \p os in C++ language mode and collects
-/// imports in \p imports along the way.
-void printModuleContentsAsCxx(raw_ostream &os,
-                              llvm::SmallPtrSetImpl<ImportModuleTy> &imports,
+struct EmittedClangHeaderDependencyInfo {
+    /// The set of imported modules used by this module.
+    SmallPtrSet<ImportModuleTy, 8> imports;
+    /// True if the printed module depends on types from the Stdlib module.
+    bool dependsOnStandardLibrary = false;
+};
+
+/// Prints the declarations of \p M to \p os in C++ language mode.
+///
+/// \returns Dependencies required by this module.
+EmittedClangHeaderDependencyInfo printModuleContentsAsCxx(raw_ostream &os,
                               ModuleDecl &M,
                               SwiftToClangInteropContext &interopContext,
                               bool requiresExposedAttribute);

lib/PrintAsClang/PrintAsClang.cpp

@@ -495,16 +495,6 @@ static std::string computeMacroGuard(const ModuleDecl *M) {
   return (llvm::Twine(M->getNameStr().upper()) + "_SWIFT_H").str();
 }
 
-static std::string getModuleContentsCxxString(
-    ModuleDecl &M, SmallPtrSet<ImportModuleTy, 8> &imports,
-    SwiftToClangInteropContext &interopContext, bool requiresExposedAttribute) {
-  std::string moduleContentsBuf;
-  llvm::raw_string_ostream moduleContents{moduleContentsBuf};
-  printModuleContentsAsCxx(moduleContents, imports, M, interopContext,
-                           requiresExposedAttribute);
-  return std::move(moduleContents.str());
-}
-
 bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
                                StringRef bridgingHeader,
                                const FrontendOptions &frontendOpts,
@@ -524,18 +514,30 @@ bool swift::printAsClangHeader(raw_ostream &os, ModuleDecl *M,
   emitObjCConditional(os, [&] { os << objcModuleContents.str(); });
   emitCxxConditional(os, [&] {
     // FIXME: Expose Swift with @expose by default.
-    bool enableCxx = frontendOpts.ExposePublicDeclsInClangHeader ||
+    bool enableCxx = frontendOpts.ClangHeaderExposedDecls.hasValue() ||
                      frontendOpts.EnableExperimentalCxxInteropInClangHeader ||
                      M->DeclContext::getASTContext().LangOpts.EnableCXXInterop;
     if (enableCxx) {
-      SmallPtrSet<ImportModuleTy, 8> imports;
-      auto contents = getModuleContentsCxxString(
-          *M, imports, interopContext,
-          /*requiresExposedAttribute=*/
-          !frontendOpts.ExposePublicDeclsInClangHeader);
+      bool requiresExplicitExpose = !frontendOpts.ClangHeaderExposedDecls.hasValue() ||
+        *frontendOpts.ClangHeaderExposedDecls == FrontendOptions::ClangHeaderExposeBehavior::HasExposeAttr;
+      // Default dependency behavior is used when the -clang-header-expose-decls flag is not specified.
+      bool defaultDependencyBehavior = !frontendOpts.ClangHeaderExposedDecls.hasValue();
+
+      std::string moduleContentsBuf;
+      llvm::raw_string_ostream moduleContents{moduleContentsBuf};
+      auto deps = printModuleContentsAsCxx(moduleContents, *M, interopContext,
+                               /*requiresExposedAttribute=*/requiresExplicitExpose);
       // FIXME: In ObjC++ mode, we do not need to reimport duplicate modules.
-      writeImports(os, imports, *M, bridgingHeader, /*useCxxImport=*/true);
-      os << contents;
+      writeImports(os, deps.imports, *M, bridgingHeader, /*useCxxImport=*/true);
+
+      // Embed the standard library directly.
+      if (defaultDependencyBehavior && deps.dependsOnStandardLibrary) {
+        assert(!M->isStdlibModule());
+        SwiftToClangInteropContext interopContext(*M->getASTContext().getStdlibModule(), irGenOpts);
+        printModuleContentsAsCxx(os, *M->getASTContext().getStdlibModule(), interopContext, /*requiresExposedAttribute=*/true);
+      }
+
+      os << moduleContents.str();
     }
   });
   writeEpilogue(os);

test/Interop/CxxToSwiftToCxx/bridge-cxx-struct-back-to-cxx-execution.cpp

@@ -3,7 +3,7 @@
 
 // RUN: %target-swift-frontend -parse-as-library %platform-module-dir/Swift.swiftmodule/%module-target-triple.swiftinterface -enable-library-evolution -disable-objc-attr-requires-foundation-module -typecheck -module-name Swift -parse-stdlib -enable-experimental-cxx-interop -emit-clang-header-path %t/Swift.h  -experimental-skip-all-function-bodies
 
-// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxx -emit-clang-header-path %t/UseCxx.h -I %t -enable-experimental-cxx-interop -clang-header-expose-public-decls
+// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxx -emit-clang-header-path %t/UseCxx.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=all-public
 
 // RUN: %target-interop-build-clangxx -std=c++20 -c %t/use-swift-cxx-types.cpp -I %t -o %t/swift-cxx-execution.o -g
 // RUN: %target-interop-build-swift %t/use-cxx-types.swift -o %t/swift-cxx-execution -Xlinker %t/swift-cxx-execution.o -module-name UseCxx -Xfrontend -entry-point-function-name -Xfrontend swiftMain -I %t -g

test/Interop/CxxToSwiftToCxx/bridge-cxx-struct-back-to-cxx.swift

@@ -1,11 +1,11 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
-// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxxTy -emit-clang-header-path %t/UseCxxTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-public-decls
+// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxxTy -emit-clang-header-path %t/UseCxxTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=all-public
 
 // RUN: %FileCheck %s < %t/UseCxxTy.h
 
-// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxxTy -emit-clang-header-path %t/UseCxxTyExposeOnly.h -I %t -enable-experimental-cxx-interop
+// RUN: %target-swift-frontend -typecheck %t/use-cxx-types.swift -typecheck -module-name UseCxxTy -emit-clang-header-path %t/UseCxxTyExposeOnly.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=has-expose-attr
 
 // RUN: %FileCheck %s < %t/UseCxxTyExposeOnly.h
 

test/Interop/ObjCToSwiftToObjCxx/bridge-objc-types-back-to-objcxx-execution.mm

@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
-// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-public-decls
+// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=all-public
 
 // RUN: %target-interop-build-clangxx -std=c++20 -fobjc-arc -c %t/use-swift-objc-types.mm -I %t -o %t/swift-objc-execution.o
 // RUN: %target-interop-build-swift %t/use-objc-types.swift -o %t/swift-objc-execution -Xlinker %t/swift-objc-execution.o -module-name UseObjCTy -Xfrontend -entry-point-function-name -Xfrontend swiftMain -I %t

test/Interop/ObjCToSwiftToObjCxx/bridge-objc-types-back-to-objcxx.swift

@@ -1,11 +1,11 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
-// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-public-decls
+// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTy.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=all-public
 
 // RUN: %FileCheck %s < %t/UseObjCTy.h
 
-// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTyExposeOnly.h -I %t -enable-experimental-cxx-interop
+// RUN: %target-swift-frontend -typecheck %t/use-objc-types.swift -typecheck -module-name UseObjCTy -emit-clang-header-path %t/UseObjCTyExposeOnly.h -I %t -enable-experimental-cxx-interop -clang-header-expose-decls=has-expose-attr
 
 // RUN: %FileCheck %s < %t/UseObjCTyExposeOnly.h
 

test/Interop/SwiftToC/functions/swift-function-argument-keyword-in-c.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Functions -clang-header-expose-public-decls -emit-clang-header-path %t/functions.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -clang-header-expose-decls=all-public -emit-clang-header-path %t/functions.h
 // RUN: %FileCheck %s < %t/functions.h
 
 // CHECK: SWIFT_EXTERN void $s9Functions19testKeywordArgument8registerySi_tF(ptrdiff_t register_) SWIFT_NOEXCEPT SWIFT_CALL;

test/Interop/SwiftToC/functions/swift-primitive-functions-c-bridging-long-lp64.swift

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

test/Interop/SwiftToC/functions/swift-primitive-functions-c-bridging.swift

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

test/Interop/SwiftToC/functions/swift-primitive-functions-execution-long-lp64.c

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/swift-primitive-functions-c-bridging-long-lp64.swift -typecheck -module-name Functions -clang-header-expose-public-decls -emit-clang-header-path %t/functions.h
+// RUN: %target-swift-frontend %S/swift-primitive-functions-c-bridging-long-lp64.swift -typecheck -module-name Functions -clang-header-expose-decls=all-public -emit-clang-header-path %t/functions.h
 
 // RUN: %target-interop-build-clang -c %s -I %t -o %t/swift-functions-execution.o
 // RUN: %target-interop-build-swift %S/swift-primitive-functions-c-bridging-long-lp64.swift -o %t/swift-functions-execution -Xlinker %t/swift-functions-execution.o -module-name Functions -Xfrontend -entry-point-function-name -Xfrontend swiftMain

test/Interop/SwiftToC/functions/swift-primitive-functions-execution.c

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

test/Interop/SwiftToC/structs/large-structs-pass-return-indirect-in-c-execution.c

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/large-structs-pass-return-indirect-in-c.swift -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %S/large-structs-pass-return-indirect-in-c.swift -typecheck -module-name Structs -clang-header-expose-decls=all-public -emit-clang-header-path %t/structs.h
 
 // RUN: %target-interop-build-clang -c %s -I %t -o %t/swift-structs-execution.o
 // RUN: %target-interop-build-swift %S/large-structs-pass-return-indirect-in-c.swift -o %t/swift-structs-execution -Xlinker %t/swift-structs-execution.o -module-name Structs -Xfrontend -entry-point-function-name -Xfrontend swiftMain

test/Interop/SwiftToC/structs/large-structs-pass-return-indirect-in-c.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-decls=all-public -emit-clang-header-path %t/structs.h
 // RUN: %FileCheck %s < %t/structs.h
 
 // RUN: %check-interop-c-header-in-clang(%t/structs.h)

test/Interop/SwiftToC/structs/small-structs-64-bit-pass-return-direct-in-c.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-decls=all-public -emit-clang-header-path %t/structs.h
 // RUN: %FileCheck %s < %t/structs.h
 
 // RUN: %check-interop-c-header-in-clang(%t/structs.h -Wno-unused-function)

test/Interop/SwiftToC/structs/small-structs-pass-return-direct-in-c-execution.c

@@ -2,7 +2,7 @@
 
 // RUN: cat %S/small-structs-pass-return-direct-in-c.swift %S/small-structs-64-bit-pass-return-direct-in-c.swift > %t/full-small-structs-pass-return-direct-in-c.swift
 
-// RUN: %target-swift-frontend %t/full-small-structs-pass-return-direct-in-c.swift -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %t/full-small-structs-pass-return-direct-in-c.swift -typecheck -module-name Structs -clang-header-expose-decls=all-public -emit-clang-header-path %t/structs.h
 
 // RUN: %target-interop-build-clang -c %s -I %t -o %t/swift-structs-execution.o -Wno-incompatible-pointer-types
 // RUN: %target-interop-build-swift %t/full-small-structs-pass-return-direct-in-c.swift -o %t/swift-structs-execution -Xlinker %t/swift-structs-execution.o -module-name Structs -Xfrontend -entry-point-function-name -Xfrontend swiftMain

test/Interop/SwiftToC/structs/small-structs-pass-return-direct-in-c.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-public-decls -emit-clang-header-path %t/structs.h
+// RUN: %target-swift-frontend %s -typecheck -module-name Structs -clang-header-expose-decls=all-public -emit-clang-header-path %t/structs.h
 // RUN: %FileCheck %s < %t/structs.h
 
 // RUN: %check-interop-c-header-in-clang(%t/structs.h -Wno-unused-function)

test/Interop/SwiftToCxx/class/class-api-prohibited.cpp

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend %S/swift-class-in-cxx.swift -typecheck -module-name Class -clang-header-expose-public-decls -emit-clang-header-path %t/class.h
+// RUN: %target-swift-frontend %S/swift-class-in-cxx.swift -typecheck -module-name Class -clang-header-expose-decls=all-public -emit-clang-header-path %t/class.h
 
 // RUN: not %target-interop-build-clangxx -c %s -I %t -o %t/swift-class-execution.o