[interop][SwiftToCxxToSwift] hide reverse interop module namespaces from forward interop

Author: hyp

lib/ClangImporter/ImportDecl.cpp

@@ -1089,6 +1089,9 @@ namespace {
 
     Decl *VisitNamespaceDecl(const clang::NamespaceDecl *decl) {
       DeclContext *dc = nullptr;
+      // Do not import namespace declarations marked as 'swift_private'.
+      if (decl->hasAttr<clang::SwiftPrivateAttr>())
+        return nullptr;
       // If this is a top-level namespace, don't put it in the module we're
       // importing, put it in the "__ObjC" module that is implicitly imported.
       if (!decl->getParent()->isNamespace())

lib/PrintAsClang/ClangSyntaxPrinter.cpp

@@ -50,13 +50,13 @@ bool ClangSyntaxPrinter::isClangKeyword(Identifier name) {
   return ClangSyntaxPrinter::isClangKeyword(name.str());
 }
 
-void ClangSyntaxPrinter::printIdentifier(StringRef name) {
+void ClangSyntaxPrinter::printIdentifier(StringRef name) const {
   os << name;
   if (ClangSyntaxPrinter::isClangKeyword(name))
     os << '_';
 }
 
-void ClangSyntaxPrinter::printBaseName(const ValueDecl *decl) {
+void ClangSyntaxPrinter::printBaseName(const ValueDecl *decl) const {
   assert(decl->getName().isSimpleName());
   printIdentifier(cxx_translation::getNameForCxx(decl));
 }
@@ -136,12 +136,23 @@ void ClangSyntaxPrinter::printNominalTypeQualifier(
   os << "::";
 }
 
+void ClangSyntaxPrinter::printModuleNamespaceStart(
+    const ModuleDecl &moduleContext) const {
+  os << "namespace ";
+  printBaseName(&moduleContext);
+  os << " __attribute__((swift_private))";
+  os << " {\n";
+}
+
 /// Print a C++ namespace declaration with the give name and body.
 void ClangSyntaxPrinter::printNamespace(
     llvm::function_ref<void(raw_ostream &OS)> namePrinter,
-    llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const {
+    llvm::function_ref<void(raw_ostream &OS)> bodyPrinter,
+    NamespaceTrivia trivia) const {
   os << "namespace ";
   namePrinter(os);
+  if (trivia == NamespaceTrivia::AttributeSwiftPrivate)
+    os << " __attribute__((swift_private))";
   os << " {\n\n";
   bodyPrinter(os);
   os << "\n} // namespace ";
@@ -150,9 +161,9 @@ void ClangSyntaxPrinter::printNamespace(
 }
 
 void ClangSyntaxPrinter::printNamespace(
-    StringRef name,
-    llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const {
-  printNamespace([&](raw_ostream &os) { os << name; }, bodyPrinter);
+    StringRef name, llvm::function_ref<void(raw_ostream &OS)> bodyPrinter,
+    NamespaceTrivia trivia) const {
+  printNamespace([&](raw_ostream &os) { os << name; }, bodyPrinter, trivia);
 }
 
 void ClangSyntaxPrinter::printExternC(

lib/PrintAsClang/ClangSyntaxPrinter.h

@@ -50,10 +50,10 @@ class ClangSyntaxPrinter {
 
   /// Print a given identifier. If the identifer conflicts with a keyword, add a
   /// trailing underscore.
-  void printIdentifier(StringRef name);
+  void printIdentifier(StringRef name) const;
 
   /// Print the base name of the given declaration.
-  void printBaseName(const ValueDecl *decl);
+  void printBaseName(const ValueDecl *decl) const;
 
   /// Print the C-style prefix for the given module name, that's used for
   /// C type names inside the module.
@@ -118,14 +118,18 @@ class ClangSyntaxPrinter {
   void printNominalTypeQualifier(const NominalTypeDecl *typeDecl,
                                  const ModuleDecl *moduleContext);
 
+  enum class NamespaceTrivia { None, AttributeSwiftPrivate };
+
+  void printModuleNamespaceStart(const ModuleDecl &moduleContext) const;
+
   /// Print a C++ namespace declaration with the give name and body.
-  void
-  printNamespace(llvm::function_ref<void(raw_ostream &OS)> namePrinter,
-                 llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const;
+  void printNamespace(llvm::function_ref<void(raw_ostream &OS)> namePrinter,
+                      llvm::function_ref<void(raw_ostream &OS)> bodyPrinter,
+                      NamespaceTrivia trivia = NamespaceTrivia::None) const;
 
-  void
-  printNamespace(StringRef name,
-                 llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const;
+  void printNamespace(StringRef name,
+                      llvm::function_ref<void(raw_ostream &OS)> bodyPrinter,
+                      NamespaceTrivia trivia = NamespaceTrivia::None) const;
 
   /// Print an extern C block with given body.
   void

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -783,6 +783,7 @@ EmittedClangHeaderDependencyInfo swift::printModuleContentsAsCxx(
     os << "#ifdef __cplusplus\n";
     os << "namespace ";
     M.ValueDecl::getName().print(os);
+    os << " __attribute__((swift_private))";
     os << " {\n";
     os << "namespace " << cxx_synthesis::getCxxImplNamespaceName() << " {\n";
     os << "extern \"C\" {\n";
@@ -800,6 +801,7 @@ EmittedClangHeaderDependencyInfo swift::printModuleContentsAsCxx(
   // Construct a C++ namespace for the module.
   ClangSyntaxPrinter(os).printNamespace(
       [&](raw_ostream &os) { M.ValueDecl::getName().print(os); },
-      [&](raw_ostream &os) { os << moduleOS.str(); });
+      [&](raw_ostream &os) { os << moduleOS.str(); },
+      ClangSyntaxPrinter::NamespaceTrivia::AttributeSwiftPrivate);
   return info;
 }

lib/PrintAsClang/PrintClangValueType.cpp

@@ -496,9 +496,8 @@ void ClangValueTypePrinter::printTypePrecedingGenericTraits(
   }
   os << "#pragma clang diagnostic pop\n";
   os << "} // namespace swift\n";
-  os << "\nnamespace ";
-  printer.printBaseName(moduleContext);
-  os << " {\n";
+  os << "\n";
+  printer.printModuleNamespaceStart(*moduleContext);
 }
 
 void ClangValueTypePrinter::printTypeGenericTraits(
@@ -592,7 +591,6 @@ void ClangValueTypePrinter::printTypeGenericTraits(
   os << "} // namespace\n";
   os << "#pragma clang diagnostic pop\n";
   os << "} // namespace swift\n";
-  os << "\nnamespace ";
-  printer.printBaseName(moduleContext);
-  os << " {\n";
+  os << "\n";
+  printer.printModuleNamespaceStart(*moduleContext);
 }

test/Interop/SwiftToCxxToSwift/hide-swift-module-namespace-in-swift.swift

@@ -0,0 +1,34 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: touch %t/swiftMod.h
+// RUN: %target-swift-frontend -typecheck %t/swiftMod.swift -typecheck -module-name SwiftMod -emit-clang-header-path %t/swiftMod.h -I %t -enable-experimental-cxx-interop
+
+// RUN: %FileCheck %s < %t/swiftMod.h
+
+// RUN: %target-swift-frontend -typecheck %t/swiftMod.swift -typecheck -module-name SwiftMod -emit-clang-header-path %t/swiftMod2.h -I %t -enable-experimental-cxx-interop
+
+// RUN: %check-interop-cxx-header-in-clang(%t/swiftMod2.h -Wno-error)
+
+//--- header.h
+#include "swiftMod.h"
+
+//--- module.modulemap
+module SwiftToCxxTest {
+    header "header.h"
+    requires cplusplus
+}
+
+//--- swiftMod.swift
+import SwiftToCxxTest
+
+@_expose(Cxx)
+public func testFunction() -> String {
+    let arr = Swift.Array<Int>()
+    let rng = Swift.SystemRandomNumberGenerator()
+    return ""
+}
+
+// CHECK: namespace Swift __attribute__((swift_private)) {
+// CHECK: namespace SwiftMod __attribute__((swift_private)) {
+// CHECK-NOT: namespace Swift {