Union has its associated (nested) tag enum

For each union, a `Tag` enum type is auto-generated.

  union U {
   int a;
   String b;
  }

is equivalent to

  union U {
    int a;
    String b;
    @Backing(type="int") enum Tag { a, b }
  }

Bug: 218912230
Test: aidl_integration_test
Change-Id: Ic0cb8f4ad9a80fe9a301a97d4f061457fc99756a

10 files changed, 353 insertions, 39 deletions

diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ArrayOfInterfaces.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ArrayOfInterfaces.h
index 0265063d..b5c0a6ce 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ArrayOfInterfaces.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ArrayOfInterfaces.h
@@ -2,12 +2,16 @@
 
 #include <android/aidl/tests/ArrayOfInterfaces.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/IBinder.h>
 #include <binder/IInterface.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
 #include <cassert>
+#include <cstdint>
 #include <optional>
+#include <string>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -136,12 +140,17 @@ public:
   };  // class MyParcelable
   class MyUnion : public ::android::Parcelable {
   public:
-    enum Tag : int32_t {
-      iface = 0,  // android.aidl.tests.ArrayOfInterfaces.IEmptyInterface iface;
-      nullable_iface,  // android.aidl.tests.ArrayOfInterfaces.IEmptyInterface nullable_iface;
-      iface_array,  // android.aidl.tests.ArrayOfInterfaces.IEmptyInterface[] iface_array;
-      nullable_iface_array,  // android.aidl.tests.ArrayOfInterfaces.IEmptyInterface[] nullable_iface_array;
+    enum class Tag : int32_t {
+      iface = 0,
+      nullable_iface = 1,
+      iface_array = 2,
+      nullable_iface_array = 3,
     };
+    // Expose tag symbols for legacy code
+    static const inline Tag iface = Tag::iface;
+    static const inline Tag nullable_iface = Tag::nullable_iface;
+    static const inline Tag iface_array = Tag::iface_array;
+    static const inline Tag nullable_iface_array = Tag::nullable_iface_array;
 
     template<typename _Tp>
     static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, MyUnion>;
@@ -263,3 +272,37 @@ public:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+[[nodiscard]] static inline std::string toString(ArrayOfInterfaces::MyUnion::Tag val) {
+  switch(val) {
+  case ArrayOfInterfaces::MyUnion::Tag::iface:
+    return "iface";
+  case ArrayOfInterfaces::MyUnion::Tag::nullable_iface:
+    return "nullable_iface";
+  case ArrayOfInterfaces::MyUnion::Tag::iface_array:
+    return "iface_array";
+  case ArrayOfInterfaces::MyUnion::Tag::nullable_iface_array:
+    return "nullable_iface_array";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag, 4> enum_values<::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag> = {
+  ::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag::iface,
+  ::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag::nullable_iface,
+  ::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag::iface_array,
+  ::android::aidl::tests::ArrayOfInterfaces::MyUnion::Tag::nullable_iface_array,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BnTestService.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BnTestService.h
index 2d2a8648..3cb8ad0d 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BnTestService.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BnTestService.h
@@ -71,8 +71,9 @@ public:
   static constexpr uint32_t TRANSACTION_ReverseNullableIBinderArray = ::android::IBinder::FIRST_CALL_TRANSACTION + 60;
   static constexpr uint32_t TRANSACTION_GetOldNameInterface = ::android::IBinder::FIRST_CALL_TRANSACTION + 61;
   static constexpr uint32_t TRANSACTION_GetNewNameInterface = ::android::IBinder::FIRST_CALL_TRANSACTION + 62;
-  static constexpr uint32_t TRANSACTION_GetCppJavaTests = ::android::IBinder::FIRST_CALL_TRANSACTION + 63;
-  static constexpr uint32_t TRANSACTION_getBackendType = ::android::IBinder::FIRST_CALL_TRANSACTION + 64;
+  static constexpr uint32_t TRANSACTION_GetUnionTags = ::android::IBinder::FIRST_CALL_TRANSACTION + 63;
+  static constexpr uint32_t TRANSACTION_GetCppJavaTests = ::android::IBinder::FIRST_CALL_TRANSACTION + 64;
+  static constexpr uint32_t TRANSACTION_getBackendType = ::android::IBinder::FIRST_CALL_TRANSACTION + 65;
   explicit BnTestService();
   ::android::status_t onTransact(uint32_t _aidl_code, const ::android::Parcel& _aidl_data, ::android::Parcel* _aidl_reply, uint32_t _aidl_flags) override;
 };  // class BnTestService
@@ -270,6 +271,9 @@ public:
   ::android::binder::Status GetNewNameInterface(::android::sp<::android::aidl::tests::INewName>* _aidl_return) override {
     return _aidl_delegate->GetNewNameInterface(_aidl_return);
   }
+  ::android::binder::Status GetUnionTags(const ::std::vector<::android::aidl::tests::Union>& input, ::std::vector<::android::aidl::tests::Union::Tag>* _aidl_return) override {
+    return _aidl_delegate->GetUnionTags(input, _aidl_return);
+  }
   ::android::binder::Status GetCppJavaTests(::android::sp<::android::IBinder>* _aidl_return) override {
     return _aidl_delegate->GetCppJavaTests(_aidl_return);
   }
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BpTestService.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BpTestService.h
index c1cbaa8d..3829d9b9 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BpTestService.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/BpTestService.h
@@ -75,6 +75,7 @@ public:
   ::android::binder::Status ReverseNullableIBinderArray(const ::std::optional<::std::vector<::android::sp<::android::IBinder>>>& input, ::std::optional<::std::vector<::android::sp<::android::IBinder>>>* repeated, ::std::optional<::std::vector<::android::sp<::android::IBinder>>>* _aidl_return) override;
   ::android::binder::Status GetOldNameInterface(::android::sp<::android::aidl::tests::IOldName>* _aidl_return) override;
   ::android::binder::Status GetNewNameInterface(::android::sp<::android::aidl::tests::INewName>* _aidl_return) override;
+  ::android::binder::Status GetUnionTags(const ::std::vector<::android::aidl::tests::Union>& input, ::std::vector<::android::aidl::tests::Union::Tag>* _aidl_return) override;
   ::android::binder::Status GetCppJavaTests(::android::sp<::android::IBinder>* _aidl_return) override;
   ::android::binder::Status getBackendType(::android::aidl::tests::BackendType* _aidl_return) override;
 };  // class BpTestService
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/FixedSize.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/FixedSize.h
index f94a3b88..65f67117 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/FixedSize.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/FixedSize.h
@@ -3,10 +3,13 @@
 #include <android/aidl/tests/FixedSize.h>
 #include <android/aidl/tests/LongEnum.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
 #include <cassert>
 #include <cstdint>
+#include <string>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -24,16 +27,25 @@ class FixedSize : public ::android::Parcelable {
 public:
   class FixedUnion : public ::android::Parcelable {
   public:
-    enum Tag : uint8_t {
-      booleanValue = 0,  // boolean booleanValue;
-      byteValue,  // byte byteValue;
-      charValue,  // char charValue;
-      intValue,  // int intValue;
-      longValue,  // long longValue;
-      floatValue,  // float floatValue;
-      doubleValue,  // double doubleValue;
-      enumValue,  // android.aidl.tests.LongEnum enumValue;
+    enum class Tag : int8_t {
+      booleanValue = 0,
+      byteValue = 1,
+      charValue = 2,
+      intValue = 3,
+      longValue = 4,
+      floatValue = 5,
+      doubleValue = 6,
+      enumValue = 7,
     };
+    // Expose tag symbols for legacy code
+    static const inline Tag booleanValue = Tag::booleanValue;
+    static const inline Tag byteValue = Tag::byteValue;
+    static const inline Tag charValue = Tag::charValue;
+    static const inline Tag intValue = Tag::intValue;
+    static const inline Tag longValue = Tag::longValue;
+    static const inline Tag floatValue = Tag::floatValue;
+    static const inline Tag doubleValue = Tag::doubleValue;
+    static const inline Tag enumValue = Tag::enumValue;
 
     template <Tag _Tag>
     using _at = typename std::tuple_element<static_cast<size_t>(_Tag), std::tuple<bool, int8_t, char16_t, int32_t, int64_t, float, double, ::android::aidl::tests::LongEnum>>::type;
@@ -119,7 +131,7 @@ public:
       return os.str();
     }
   private:
-    Tag _tag __attribute__((aligned (1))) = booleanValue;
+    Tag _tag = booleanValue;
     union _value_t {
       _value_t() {}
       ~_value_t() {}
@@ -220,3 +232,49 @@ public:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+[[nodiscard]] static inline std::string toString(FixedSize::FixedUnion::Tag val) {
+  switch(val) {
+  case FixedSize::FixedUnion::Tag::booleanValue:
+    return "booleanValue";
+  case FixedSize::FixedUnion::Tag::byteValue:
+    return "byteValue";
+  case FixedSize::FixedUnion::Tag::charValue:
+    return "charValue";
+  case FixedSize::FixedUnion::Tag::intValue:
+    return "intValue";
+  case FixedSize::FixedUnion::Tag::longValue:
+    return "longValue";
+  case FixedSize::FixedUnion::Tag::floatValue:
+    return "floatValue";
+  case FixedSize::FixedUnion::Tag::doubleValue:
+    return "doubleValue";
+  case FixedSize::FixedUnion::Tag::enumValue:
+    return "enumValue";
+  default:
+    return std::to_string(static_cast<int8_t>(val));
+  }
+}
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::FixedSize::FixedUnion::Tag, 8> enum_values<::android::aidl::tests::FixedSize::FixedUnion::Tag> = {
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::booleanValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::byteValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::charValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::intValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::longValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::floatValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::doubleValue,
+  ::android::aidl::tests::FixedSize::FixedUnion::Tag::enumValue,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ITestService.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ITestService.h
index dd0e7f1c..9246a87e 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ITestService.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ITestService.h
@@ -10,6 +10,7 @@
 #include <android/aidl/tests/LongEnum.h>
 #include <android/aidl/tests/RecursiveList.h>
 #include <android/aidl/tests/StructuredParcelable.h>
+#include <android/aidl/tests/Union.h>
 #include <android/aidl/tests/extension/ExtendableParcelable.h>
 #include <android/binder_to_string.h>
 #include <binder/IBinder.h>
@@ -272,6 +273,7 @@ public:
   virtual ::android::binder::Status ReverseNullableIBinderArray(const ::std::optional<::std::vector<::android::sp<::android::IBinder>>>& input, ::std::optional<::std::vector<::android::sp<::android::IBinder>>>* repeated, ::std::optional<::std::vector<::android::sp<::android::IBinder>>>* _aidl_return) = 0;
   virtual ::android::binder::Status GetOldNameInterface(::android::sp<::android::aidl::tests::IOldName>* _aidl_return) = 0;
   virtual ::android::binder::Status GetNewNameInterface(::android::sp<::android::aidl::tests::INewName>* _aidl_return) = 0;
+  virtual ::android::binder::Status GetUnionTags(const ::std::vector<::android::aidl::tests::Union>& input, ::std::vector<::android::aidl::tests::Union::Tag>* _aidl_return) = 0;
   virtual ::android::binder::Status GetCppJavaTests(::android::sp<::android::IBinder>* _aidl_return) = 0;
   virtual ::android::binder::Status getBackendType(::android::aidl::tests::BackendType* _aidl_return) = 0;
 };  // class ITestService
@@ -470,6 +472,9 @@ public:
   ::android::binder::Status GetNewNameInterface(::android::sp<::android::aidl::tests::INewName>* /*_aidl_return*/) override {
     return ::android::binder::Status::fromStatusT(::android::UNKNOWN_TRANSACTION);
   }
+  ::android::binder::Status GetUnionTags(const ::std::vector<::android::aidl::tests::Union>& /*input*/, ::std::vector<::android::aidl::tests::Union::Tag>* /*_aidl_return*/) override {
+    return ::android::binder::Status::fromStatusT(::android::UNKNOWN_TRANSACTION);
+  }
   ::android::binder::Status GetCppJavaTests(::android::sp<::android::IBinder>* /*_aidl_return*/) override {
     return ::android::binder::Status::fromStatusT(::android::UNKNOWN_TRANSACTION);
   }
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ListOfInterfaces.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ListOfInterfaces.h
index e9dcb2b0..455bf4b6 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ListOfInterfaces.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/ListOfInterfaces.h
@@ -2,12 +2,16 @@
 
 #include <android/aidl/tests/ListOfInterfaces.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/IBinder.h>
 #include <binder/IInterface.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
 #include <cassert>
+#include <cstdint>
 #include <optional>
+#include <string>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -136,12 +140,17 @@ public:
   };  // class MyParcelable
   class MyUnion : public ::android::Parcelable {
   public:
-    enum Tag : int32_t {
-      iface = 0,  // android.aidl.tests.ListOfInterfaces.IEmptyInterface iface;
-      nullable_iface,  // android.aidl.tests.ListOfInterfaces.IEmptyInterface nullable_iface;
-      iface_list,  // List<android.aidl.tests.ListOfInterfaces.IEmptyInterface> iface_list;
-      nullable_iface_list,  // List<android.aidl.tests.ListOfInterfaces.IEmptyInterface> nullable_iface_list;
+    enum class Tag : int32_t {
+      iface = 0,
+      nullable_iface = 1,
+      iface_list = 2,
+      nullable_iface_list = 3,
     };
+    // Expose tag symbols for legacy code
+    static const inline Tag iface = Tag::iface;
+    static const inline Tag nullable_iface = Tag::nullable_iface;
+    static const inline Tag iface_list = Tag::iface_list;
+    static const inline Tag nullable_iface_list = Tag::nullable_iface_list;
 
     template<typename _Tp>
     static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, MyUnion>;
@@ -263,3 +272,37 @@ public:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+[[nodiscard]] static inline std::string toString(ListOfInterfaces::MyUnion::Tag val) {
+  switch(val) {
+  case ListOfInterfaces::MyUnion::Tag::iface:
+    return "iface";
+  case ListOfInterfaces::MyUnion::Tag::nullable_iface:
+    return "nullable_iface";
+  case ListOfInterfaces::MyUnion::Tag::iface_list:
+    return "iface_list";
+  case ListOfInterfaces::MyUnion::Tag::nullable_iface_list:
+    return "nullable_iface_list";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::ListOfInterfaces::MyUnion::Tag, 4> enum_values<::android::aidl::tests::ListOfInterfaces::MyUnion::Tag> = {
+  ::android::aidl::tests::ListOfInterfaces::MyUnion::Tag::iface,
+  ::android::aidl::tests::ListOfInterfaces::MyUnion::Tag::nullable_iface,
+  ::android::aidl::tests::ListOfInterfaces::MyUnion::Tag::iface_list,
+  ::android::aidl::tests::ListOfInterfaces::MyUnion::Tag::nullable_iface_list,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/Union.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/Union.h
index 44284019..a82300f7 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/Union.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/Union.h
@@ -2,6 +2,8 @@
 
 #include <android/aidl/tests/ByteEnum.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/IBinder.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
@@ -23,15 +25,23 @@ namespace aidl {
 namespace tests {
 class Union : public ::android::Parcelable {
 public:
-  enum Tag : int32_t {
-    ns = 0,  // int[] ns;
-    n,  // int n;
-    m,  // int m;
-    s,  // String s;
-    ibinder,  // IBinder ibinder;
-    ss,  // List<String> ss;
-    be,  // android.aidl.tests.ByteEnum be;
+  enum class Tag : int32_t {
+    ns = 0,
+    n = 1,
+    m = 2,
+    s = 3,
+    ibinder = 4,
+    ss = 5,
+    be = 6,
   };
+  // Expose tag symbols for legacy code
+  static const inline Tag ns = Tag::ns;
+  static const inline Tag n = Tag::n;
+  static const inline Tag m = Tag::m;
+  static const inline Tag s = Tag::s;
+  static const inline Tag ibinder = Tag::ibinder;
+  static const inline Tag ss = Tag::ss;
+  static const inline Tag be = Tag::be;
 
   template<typename _Tp>
   static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, Union>;
@@ -125,3 +135,46 @@ private:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+[[nodiscard]] static inline std::string toString(Union::Tag val) {
+  switch(val) {
+  case Union::Tag::ns:
+    return "ns";
+  case Union::Tag::n:
+    return "n";
+  case Union::Tag::m:
+    return "m";
+  case Union::Tag::s:
+    return "s";
+  case Union::Tag::ibinder:
+    return "ibinder";
+  case Union::Tag::ss:
+    return "ss";
+  case Union::Tag::be:
+    return "be";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::Union::Tag, 7> enum_values<::android::aidl::tests::Union::Tag> = {
+  ::android::aidl::tests::Union::Tag::ns,
+  ::android::aidl::tests::Union::Tag::n,
+  ::android::aidl::tests::Union::Tag::m,
+  ::android::aidl::tests::Union::Tag::s,
+  ::android::aidl::tests::Union::Tag::ibinder,
+  ::android::aidl::tests::Union::Tag::ss,
+  ::android::aidl::tests::Union::Tag::be,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/UnionWithFd.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/UnionWithFd.h
index 06ae2a60..c97edf1f 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/UnionWithFd.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/UnionWithFd.h
@@ -1,11 +1,14 @@
 #pragma once
 
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/Parcel.h>
 #include <binder/ParcelFileDescriptor.h>
 #include <binder/Status.h>
 #include <cassert>
 #include <cstdint>
+#include <string>
 #include <type_traits>
 #include <utility>
 #include <utils/String16.h>
@@ -20,10 +23,13 @@ namespace aidl {
 namespace tests {
 class UnionWithFd : public ::android::Parcelable {
 public:
-  enum Tag : int32_t {
-    num = 0,  // int num;
-    pfd,  // ParcelFileDescriptor pfd;
+  enum class Tag : int32_t {
+    num = 0,
+    pfd = 1,
   };
+  // Expose tag symbols for legacy code
+  static const inline Tag num = Tag::num;
+  static const inline Tag pfd = Tag::pfd;
 
   template<typename _Tp>
   static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, UnionWithFd>;
@@ -111,3 +117,31 @@ private:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+[[nodiscard]] static inline std::string toString(UnionWithFd::Tag val) {
+  switch(val) {
+  case UnionWithFd::Tag::num:
+    return "num";
+  case UnionWithFd::Tag::pfd:
+    return "pfd";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::UnionWithFd::Tag, 2> enum_values<::android::aidl::tests::UnionWithFd::Tag> = {
+  ::android::aidl::tests::UnionWithFd::Tag::num,
+  ::android::aidl::tests::UnionWithFd::Tag::pfd,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/EnumUnion.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/EnumUnion.h
index 3898fbcf..a65f9f0b 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/EnumUnion.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/EnumUnion.h
@@ -3,9 +3,13 @@
 #include <android/aidl/tests/IntEnum.h>
 #include <android/aidl/tests/LongEnum.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
 #include <cassert>
+#include <cstdint>
+#include <string>
 #include <type_traits>
 #include <utility>
 #include <utils/String16.h>
@@ -21,10 +25,13 @@ namespace tests {
 namespace unions {
 class EnumUnion : public ::android::Parcelable {
 public:
-  enum Tag : int32_t {
-    intEnum = 0,  // android.aidl.tests.IntEnum intEnum;
-    longEnum,  // android.aidl.tests.LongEnum longEnum;
+  enum class Tag : int32_t {
+    intEnum = 0,
+    longEnum = 1,
   };
+  // Expose tag symbols for legacy code
+  static const inline Tag intEnum = Tag::intEnum;
+  static const inline Tag longEnum = Tag::longEnum;
 
   template<typename _Tp>
   static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, EnumUnion>;
@@ -113,3 +120,33 @@ private:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+namespace unions {
+[[nodiscard]] static inline std::string toString(EnumUnion::Tag val) {
+  switch(val) {
+  case EnumUnion::Tag::intEnum:
+    return "intEnum";
+  case EnumUnion::Tag::longEnum:
+    return "longEnum";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace unions
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::unions::EnumUnion::Tag, 2> enum_values<::android::aidl::tests::unions::EnumUnion::Tag> = {
+  ::android::aidl::tests::unions::EnumUnion::Tag::intEnum,
+  ::android::aidl::tests::unions::EnumUnion::Tag::longEnum,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android
diff --git a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/UnionInUnion.h b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/UnionInUnion.h
index 9adbbe96..9badc3af 100644
--- a/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/UnionInUnion.h
+++ b/tests/golden_output/aidl-test-interface-cpp-source/gen/include/android/aidl/tests/unions/UnionInUnion.h
@@ -2,10 +2,13 @@
 
 #include <android/aidl/tests/unions/EnumUnion.h>
 #include <android/binder_to_string.h>
+#include <array>
+#include <binder/Enums.h>
 #include <binder/Parcel.h>
 #include <binder/Status.h>
 #include <cassert>
 #include <cstdint>
+#include <string>
 #include <type_traits>
 #include <utility>
 #include <utils/String16.h>
@@ -21,10 +24,13 @@ namespace tests {
 namespace unions {
 class UnionInUnion : public ::android::Parcelable {
 public:
-  enum Tag : int32_t {
-    first = 0,  // android.aidl.tests.unions.EnumUnion first;
-    second,  // int second;
+  enum class Tag : int32_t {
+    first = 0,
+    second = 1,
   };
+  // Expose tag symbols for legacy code
+  static const inline Tag first = Tag::first;
+  static const inline Tag second = Tag::second;
 
   template<typename _Tp>
   static constexpr bool _not_self = !std::is_same_v<std::remove_cv_t<std::remove_reference_t<_Tp>>, UnionInUnion>;
@@ -113,3 +119,33 @@ private:
 }  // namespace tests
 }  // namespace aidl
 }  // namespace android
+namespace android {
+namespace aidl {
+namespace tests {
+namespace unions {
+[[nodiscard]] static inline std::string toString(UnionInUnion::Tag val) {
+  switch(val) {
+  case UnionInUnion::Tag::first:
+    return "first";
+  case UnionInUnion::Tag::second:
+    return "second";
+  default:
+    return std::to_string(static_cast<int32_t>(val));
+  }
+}
+}  // namespace unions
+}  // namespace tests
+}  // namespace aidl
+}  // namespace android
+namespace android {
+namespace internal {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc++17-extensions"
+template <>
+constexpr inline std::array<::android::aidl::tests::unions::UnionInUnion::Tag, 2> enum_values<::android::aidl::tests::unions::UnionInUnion::Tag> = {
+  ::android::aidl::tests::unions::UnionInUnion::Tag::first,
+  ::android::aidl::tests::unions::UnionInUnion::Tag::second,
+};
+#pragma clang diagnostic pop
+}  // namespace internal
+}  // namespace android