[cxx-interop] Fix exporting Swift enums with C POD associated data

These types are OK to by copied using memcpy. Previously, the generated
code assumed these types are exported swift types with all the value witness
functions.

rdar://111812577

Author: Gabor Horvath

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -32,6 +32,7 @@
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/SwiftNameTranslation.h"
+#include "swift/AST/Type.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/AST/TypeVisitor.h"
 #include "swift/AST/Types.h"
@@ -45,6 +46,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/Decl.h"
+#include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/SourceManager.h"
@@ -475,6 +477,17 @@ class DeclAndTypePrinter::Implementation
     os << "@end\n";
   }
 
+  static bool isClangPOD(const NominalTypeDecl *ntd) {
+    auto clangDecl = ntd->getClangDecl();
+    if (!clangDecl)
+      return false;
+    if (const auto *rd = dyn_cast<clang::RecordDecl>(clangDecl)) {
+      return !isa<clang::CXXRecordDecl>(rd) ||
+             cast<clang::CXXRecordDecl>(rd)->isPOD();
+    }
+    return false;
+  }
+
   void visitEnumDeclCxx(EnumDecl *ED) {
     assert(owningPrinter.outputLang == OutputLanguageMode::Cxx);
 
@@ -588,7 +601,9 @@ class DeclAndTypePrinter::Implementation
             assert(objectTypeDecl != nullptr || paramType->isOptional());
 
             if (objectTypeDecl &&
-                owningPrinter.typeMapping.getKnownCxxTypeInfo(objectTypeDecl)) {
+                (owningPrinter.typeMapping.getKnownCxxTypeInfo(
+                     objectTypeDecl) ||
+                 isClangPOD(objectTypeDecl))) {
               outOfLineOS << "    " << types[paramType] << " result;\n";
               outOfLineOS << "    "
                              "memcpy(&result, payloadFromDestruction, "
@@ -755,8 +770,9 @@ class DeclAndTypePrinter::Implementation
                   assert(objectTypeDecl != nullptr || paramType->isOptional());
 
                   if (objectTypeDecl &&
-                      owningPrinter.typeMapping.getKnownCxxTypeInfo(
-                          objectTypeDecl)) {
+                      (owningPrinter.typeMapping.getKnownCxxTypeInfo(
+                           objectTypeDecl) ||
+                       isClangPOD(objectTypeDecl))) {
                     outOfLineOS
                         << "    memcpy(result._getOpaquePointer(), &val, "
                            "sizeof(val));\n";

test/Interop/SwiftToCxx/stdlib/core-foundation-types-in-cxx.swift

@@ -3,6 +3,10 @@
 // RUN: %target-swift-frontend %s -module-name UseCoreFoundation -enable-experimental-cxx-interop -clang-header-expose-decls=all-public -typecheck -verify -emit-clang-header-path %t/UseCoreFoundation.h
 // RUN: %FileCheck %s < %t/UseCoreFoundation.h
 
+// RUN: echo "#include <netinet/in.h>" > %t/full-header.h
+// RUN: cat %t/UseCoreFoundation.h >> %t/full-header.h
+// RUN: %target-interop-build-clangxx -std=gnu++20 -fobjc-arc -c -x objective-c++-header %t/full-header.h -o %t/o.o
+
 // REQUIRES: objc_interop
 
 import CoreFoundation
@@ -16,5 +20,9 @@ public func networkThing() -> in_addr? {
     return nil
 }
 
+public enum MyEnum {
+    case value(in_addr)
+}
+
 // CHECK: SWIFT_EXTERN bool $s17UseCoreFoundation6foobarySbSo9CFDataRefaF(CFDataRef _Nonnull a) SWIFT_NOEXCEPT SWIFT_CALL; // foobar(_:)
 // CHECK: SWIFT_INLINE_THUNK swift::Optional<in_addr> networkThing() noexcept SWIFT_SYMBOL("s:17UseCoreFoundation12networkThingSo7in_addrVSgyF") SWIFT_WARN_UNUSED_RESULT {