UsingEnum.h - mozsearch

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/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_UsingEnum_h

#define mozilla_UsingEnum_h

#include "mozilla/MacroForEach.h"

// C++20 `using enum` declaration isn't supported in GCC 10. Provide a simple

// macro until our minimum supported GCC has been upgraded to GCC 11. We can

// remove this header and `MOZ_USING_ENUM` after we desupport GCC 10.

//

// Since few developers will be using GCC locally, they may forget to list all

// of the enum's enumerator values and only realize they broke the GCC build

// after their patch is backed out of autoland. To catch this error sooner, use

// the GCC macro in DEBUG builds on all platforms.

//

// Usage:

// ```

// enum class MyEnum { Foo, Bar, Baz };

// MOZ_USING_ENUM(MyEnum, Foo, Bar, Baz);

//

// class MyClass {

//   enum class MyEnum { Foo, Bar, Baz };

//   // Use MOZ_USING_ENUM_STATIC in class declarations because the constexpr

//   // member variables need to be static. This isn't needed for `using enum`.

//   MOZ_USING_ENUM_STATIC(MyEnum, Foo, Bar, Baz);

// };

// ```

#if defined(__cpp_using_enum) && !defined(DEBUG)

#  define MOZ_USING_ENUM(ENUM, ...) using enum ENUM

#  define MOZ_USING_ENUM_STATIC(ENUM, ...) using enum ENUM

#else

#  define MOZ_USING_ENUM_DECLARE(ENUM, NAME) constexpr auto NAME = ENUM::NAME;

#  define MOZ_USING_ENUM(ENUM, ...) \

    MOZ_FOR_EACH(MOZ_USING_ENUM_DECLARE, (ENUM, ), (__VA_ARGS__))

#  define MOZ_USING_ENUM_DECLARE_STATIC(ENUM, NAME) \

    static constexpr auto NAME = ENUM::NAME;

#  define MOZ_USING_ENUM_STATIC(ENUM, ...) \

    MOZ_FOR_EACH(MOZ_USING_ENUM_DECLARE_STATIC, (ENUM, ), (__VA_ARGS__))

#endif

#endif  // mozilla_UsingEnum_h