[🍒][cxx-interop] Correctly import fields with type NS_OPTIONS.

lib/ClangImporter/ImportDecl.cpp

@@ -3584,11 +3584,30 @@ namespace {
           return nullptr;
       }
 
-      auto importedType =
-          Impl.importType(decl->getType(), ImportTypeKind::RecordField,
-                          ImportDiagnosticAdder(Impl, decl, decl->getLocation()),
-                          isInSystemModule(dc), Bridgeability::None,
-                          getImportTypeAttrs(decl));
+      ImportedType importedType;
+      auto fieldType = decl->getType();
+      if (auto elaborated = dyn_cast<clang::ElaboratedType>(fieldType))
+        fieldType = elaborated->desugar();
+      if (auto typedefType = dyn_cast<clang::TypedefType>(fieldType)) {
+        if (Impl.isUnavailableInSwift(typedefType->getDecl())) {
+          if (auto clangEnum = findAnonymousEnumForTypedef(Impl.SwiftContext, typedefType)) {
+            // If this fails, it means that we need a stronger predicate for
+            // determining the relationship between an enum and typedef.
+            assert(clangEnum.value()->getIntegerType()->getCanonicalTypeInternal() ==
+                   typedefType->getCanonicalTypeInternal());
+            if (auto swiftEnum = Impl.importDecl(*clangEnum, Impl.CurrentVersion)) {
+              importedType = {cast<TypeDecl>(swiftEnum)->getDeclaredInterfaceType(), false};
+            }
+          }
+        }
+      }
+
+      if (!importedType)
+        importedType =
+            Impl.importType(decl->getType(), ImportTypeKind::RecordField,
+                            ImportDiagnosticAdder(Impl, decl, decl->getLocation()),
+                            isInSystemModule(dc), Bridgeability::None,
+                            getImportTypeAttrs(decl));
       if (!importedType) {
         Impl.addImportDiagnostic(
             decl, Diagnostic(diag::record_field_not_imported, decl),
@@ -5817,6 +5836,13 @@ SwiftDeclConverter::importAsOptionSetType(DeclContext *dc, Identifier name,
                                           const clang::EnumDecl *decl) {
   ASTContext &ctx = Impl.SwiftContext;
 
+  auto Loc = Impl.importSourceLoc(decl->getLocation());
+
+  // Create a struct with the underlying type as a field.
+  auto structDecl = Impl.createDeclWithClangNode<StructDecl>(
+      decl, AccessLevel::Public, Loc, name, Loc, None, nullptr, dc);
+  Impl.ImportedDecls[{decl->getCanonicalDecl(), getVersion()}] = structDecl;
+
   // Compute the underlying type.
   auto underlyingType = Impl.importTypeIgnoreIUO(
       decl->getIntegerType(), ImportTypeKind::Enum,
@@ -5825,12 +5851,6 @@ SwiftDeclConverter::importAsOptionSetType(DeclContext *dc, Identifier name,
   if (!underlyingType)
     return nullptr;
 
-  auto Loc = Impl.importSourceLoc(decl->getLocation());
-
-  // Create a struct with the underlying type as a field.
-  auto structDecl = Impl.createDeclWithClangNode<StructDecl>(
-      decl, AccessLevel::Public, Loc, name, Loc, None, nullptr, dc);
-
   synthesizer.makeStructRawValued(structDecl, underlyingType,
                                   {KnownProtocolKind::OptionSet});
   auto selfType = structDecl->getDeclaredInterfaceType();

test/Interop/Cxx/enum/Inputs/c-enums-NS_OPTIONS.h

@@ -81,6 +81,10 @@ typedef NS_OPTIONS(NSUInteger, Bar) {
 
 typedef NS_OPTIONS(NSUInteger, Baz) { Baz1, Baz2 };
 
+struct HasNSOptionField {
+  Bar bar;
+};
+
 Baz CFunctionReturningNSOption();
 void CFunctionTakingNSOption(Baz);
 

test/Interop/Cxx/enum/c-enums-NS_OPTIONS.swift

@@ -20,3 +20,8 @@ import CenumsNSOptions
 // CHECK-NEXT:   @available(swift, obsoleted: 3, renamed: "insertionIndex")
 // CHECK-NEXT:   static var InsertionIndex: NSBinarySearchingOptions { get }
 // CHECK-NEXT: }
+
+// CHECK: struct Bar : OptionSet, @unchecked Sendable
+// CHECK: struct HasNSOptionField {
+// CHECK:   var bar: Bar
+// CHECK: }

test/Interop/Cxx/enum/ns-option-as-field.swift

@@ -0,0 +1,23 @@
+// RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop)
+
+// REQUIRES: objc_interop
+// REQUIRES: executable_test
+
+import CenumsNSOptions
+import StdlibUnittest
+
+var FieldTestSuite = TestSuite("NS_Option as field")
+
+struct HasNSOptionMember {
+  var member: Bar
+}
+
+FieldTestSuite.test("NSOption as field") {
+  var parent = HasNSOptionMember(member: [.SwiftOptionOneApiNotes, .SwiftOptionTwoApiNotes])
+  expectEqual(parent.member, [.SwiftOptionOneApiNotes, .SwiftOptionTwoApiNotes])
+
+  parent.member = [.SwiftOptionOneApiNotes]
+  expectNotEqual(parent.member, [.SwiftOptionOneApiNotes, .SwiftOptionTwoApiNotes])
+}
+
+runAllTests()