[interop][SwiftToCxx] ensure all emitted 'swift' namespaces are marked as swift_private

Author: hyp

lib/PrintAsClang/PrintClangValueType.cpp

@@ -544,7 +544,7 @@ void ClangValueTypePrinter::printTypePrecedingGenericTraits(
   ClangSyntaxPrinter printer(os);
   // FIXME: avoid popping out of the module's namespace here.
   os << "} // end namespace \n\n";
-  os << "namespace swift {\n";
+  os << "namespace swift SWIFT_PRIVATE_ATTR {\n";
 
   os << "#pragma clang diagnostic push\n";
   os << "#pragma clang diagnostic ignored \"-Wc++17-extensions\"\n";
@@ -570,7 +570,7 @@ void ClangValueTypePrinter::printTypeGenericTraits(
   ClangSyntaxPrinter printer(os);
   // FIXME: avoid popping out of the module's namespace here.
   os << "} // end namespace \n\n";
-  os << "namespace swift {\n";
+  os << "namespace swift SWIFT_PRIVATE_ATTR {\n";
 
   if (typeDecl->hasClangNode()) {
     /// Print a reference to the type metadata fucntion for a C++ type.

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

@@ -9,7 +9,7 @@
 
 // RUN: %check-interop-cxx-header-in-clang(%t/swiftMod2.h -DSWIFT_CXX_INTEROP_HIDE_STL_OVERLAY  -Wno-error)
 
-// RUN: %target-swift-ide-test -print-module -module-to-print=SwiftToCxxTest -I %t -source-filename=x -enable-experimental-cxx-interop -Xcc -DSWIFT_CXX_INTEROP_HIDE_SWIFT_ERROR
+// RUN: %target-swift-ide-test -print-module -module-to-print=SwiftToCxxTest -I %t -source-filename=x -enable-experimental-cxx-interop -Xcc -DSWIFT_CXX_INTEROP_HIDE_SWIFT_ERROR | %FileCheck --check-prefix=INTERFACE %s
 
 // XFAIL: OS=linux-android, OS=linux-androideabi
 
@@ -37,3 +37,5 @@ public func testFunction() -> String {
 // CHECK: namespace swift SWIFT_PRIVATE_ATTR SWIFT_SYMBOL_MODULE("swift") {
 // CHECK: namespace SwiftMod SWIFT_PRIVATE_ATTR SWIFT_SYMBOL_MODULE("SwiftMod") {
 // CHECK-NOT: namespace swift {
+
+// INTERFACE-NOT: enum swift