[cxx-interop] Support nested classes in reverse interop

Turns out we already had most of the building blocks given we already
support nested structs.

rdar://143343490

include/swift/AST/SwiftNameTranslation.h

@@ -84,7 +84,6 @@ enum RepresentationError {
   UnrepresentableEnumCaseTuple,
   UnrepresentableProtocol,
   UnrepresentableMoveOnly,
-  UnrepresentableNested,
   UnrepresentableMacro,
   UnrepresentableZeroSizedValueType,
 };

lib/AST/SwiftNameTranslation.cpp

@@ -249,11 +249,6 @@ swift::cxx_translation::getDeclRepresentation(
         return {Unsupported, UnrepresentableGeneric};
       genericSignature = typeDecl->getGenericSignature();
     }
-    // Nested classes are not yet supported.
-    if (isa<ClassDecl>(VD) && !typeDecl->hasClangNode() &&
-        isa_and_nonnull<NominalTypeDecl>(
-            typeDecl->getDeclContext()->getAsDecl()))
-      return {Unsupported, UnrepresentableNested};
     if (!isa<ClassDecl>(typeDecl) && isZeroSized && (*isZeroSized)(typeDecl))
       return {Unsupported, UnrepresentableZeroSizedValueType};
   }
@@ -392,8 +387,6 @@ swift::cxx_translation::diagnoseRepresenationError(RepresentationError error,
     return Diagnostic(diag::expose_protocol_to_cxx_unsupported, vd);
   case UnrepresentableMoveOnly:
     return Diagnostic(diag::expose_move_only_to_cxx, vd);
-  case UnrepresentableNested:
-    return Diagnostic(diag::expose_nested_type_to_cxx, vd);
   case UnrepresentableMacro:
     return Diagnostic(diag::expose_macro_to_cxx, vd);
   case UnrepresentableZeroSizedValueType:

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -260,9 +260,6 @@ private:
         auto VD = dyn_cast<ValueDecl>(member);
         if (!VD || !shouldInclude(VD))
           continue;
-        // TODO: support nested classes.
-        if (isa<ClassDecl>(member))
-          continue;
         if (const auto *TD = dyn_cast<NominalTypeDecl>(member))
           printUsingForNestedType(TD, TD->getModuleContext());
       }

lib/PrintAsClang/PrintClangClassType.cpp

@@ -116,9 +116,12 @@ void ClangClassTypePrinter::printClassTypeDecl(
 void ClangClassTypePrinter::printClassTypeReturnScaffold(
     raw_ostream &os, const ClassDecl *type, const ModuleDecl *moduleContext,
     llvm::function_ref<void(void)> bodyPrinter) {
+  ClangSyntaxPrinter printer(type->getASTContext(), os);
   os << "  return ";
-  ClangSyntaxPrinter(type->getASTContext(), os).printModuleNamespaceQualifiersIfNeeded(
+  printer.printModuleNamespaceQualifiersIfNeeded(type->getModuleContext(),
-      type->getModuleContext(), moduleContext);
+                                                 moduleContext);
+  if (!printer.printNestedTypeNamespaceQualifiers(type))
+    os << "::";
   os << cxx_synthesis::getCxxImplNamespaceName() << "::";
   ClangValueTypePrinter::printCxxImplClassName(os, type);
   os << "::makeRetained(";

lib/PrintAsClang/PrintClangFunction.cpp

@@ -348,7 +348,8 @@ public:
     if (typeUseKind == FunctionSignatureTypeUse::ParamType && !isInOutParam)
       os << "const ";
     printOptional(optionalKind, [&]() {
-      ClangSyntaxPrinter(CT->getASTContext(), os).printBaseName(CT->getDecl());
+      ClangSyntaxPrinter(CT->getASTContext(), os)
+          .printPrimaryCxxTypeName(cd, moduleContext);
     });
     if (typeUseKind == FunctionSignatureTypeUse::ParamType)
       os << "&";

test/Interop/SwiftToCxx/class/nested-classes-in-cxx-execution.cpp

@@ -0,0 +1,26 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend %S/nested-classes-in-cxx.swift -enable-library-evolution -typecheck -module-name Classes -clang-header-expose-decls=all-public -emit-clang-header-path %t/classes.h
+
+// RUN: %target-interop-build-clangxx -std=c++17 -c %s -I %t -o %t/swift-classes-execution.o
+
+// RUN: %target-interop-build-swift %S/nested-classes-in-cxx.swift -enable-library-evolution -o %t/swift-classes-execution -Xlinker %t/swift-classes-execution.o -module-name Classes -Xfrontend -entry-point-function-name -Xfrontend swiftMain
+
+// RUN: %target-codesign %t/swift-classes-execution
+// RUN: %target-run %t/swift-classes-execution
+
+// REQUIRES: executable_test
+
+#include "classes.h"
+#include <cassert>
+
+int main() {
+  using namespace Classes;
+  auto x = makeRecordConfig();
+  RecordConfig::File::Gate y = x.getGate();
+  assert(y.getProp() == 80);
+  assert(y.computeValue() == 160);
+  RecordConfig::AudioFormat z = x.getFile().getFormat();
+  assert(z == RecordConfig::AudioFormat::ALAC);
+  RecordConfig::File::Gate g = RecordConfig::File::Gate::init();
+}

test/Interop/SwiftToCxx/class/nested-classes-in-cxx.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -enable-library-evolution -typecheck -module-name Classes -clang-header-expose-decls=all-public -emit-clang-header-path %t/classes.h
+
+// RUN: %check-interop-cxx-header-in-clang(%t/classes.h -DSWIFT_CXX_INTEROP_HIDE_STL_OVERLAY -std=c++17)
+
+public class RecordConfig {
+    public enum AudioFormat {
+        case PCM, ALAC, AAC
+    }
+
+    public struct Directory {
+        public var path: String?
+    }
+
+    public class File {
+        public var format: AudioFormat = .ALAC
+
+        public class Gate {
+            public init() {}
+            public var prop: Int32 = 80
+
+            public func computeValue() -> Int32 {
+                return prop * 2
+            }
+        }
+    }
+
+    public var directory = Directory()
+    public var file = File()
+    public var gate = File.Gate()
+}
+
+public func makeRecordConfig() -> RecordConfig {
+    return RecordConfig()
+}