From 2e63564776291cc484ea221e0be861812067bfec Mon Sep 17 00:00:00 2001
From: Quentin Chateau <quentin.chateau@gmail.com>
Date: Fri, 22 Mar 2024 22:23:06 +0100
Subject: [PATCH] Support parameter packs for bases in BOOST_DESCRIBE_CLASS

---
 include/boost/describe/detail/bases.hpp | 24 +++++++++---------------
 test/bases_test.cpp                     | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/include/boost/describe/detail/bases.hpp b/include/boost/describe/detail/bases.hpp
index 3a08064..d4fe494 100644
--- a/include/boost/describe/detail/bases.hpp
+++ b/include/boost/describe/detail/bases.hpp
@@ -30,24 +30,18 @@ template<class C, class B> struct base_descriptor
 template<class C, class B> constexpr unsigned base_descriptor<C, B>::modifiers;
 #endif
 
-template<class... T> auto base_descriptor_fn_impl( int, T... )
-{
-    return list<T...>();
-}
-
-#define BOOST_DESCRIBE_BASE_IMPL(C, B) , boost::describe::detail::base_descriptor<C, B>()
-
-#if defined(_MSC_VER) && !defined(__clang__)
-
-#define BOOST_DESCRIBE_BASES(C, ...) inline auto boost_base_descriptor_fn( C** ) \
-{ return boost::describe::detail::base_descriptor_fn_impl( 0 BOOST_DESCRIBE_PP_FOR_EACH(BOOST_DESCRIBE_BASE_IMPL, C, __VA_ARGS__) ); }
+// bases_descriptor
+template<typename ...>
+struct bases_descriptor_impl;
 
-#else
+template<class C, class ...Bs>
+struct bases_descriptor_impl<C, list<Bs...>>
+{
+    using type = list<base_descriptor<C, Bs>...>;
+};
 
 #define BOOST_DESCRIBE_BASES(C, ...) inline auto boost_base_descriptor_fn( C** ) \
-{ return boost::describe::detail::base_descriptor_fn_impl( 0 BOOST_DESCRIBE_PP_FOR_EACH(BOOST_DESCRIBE_BASE_IMPL, C, ##__VA_ARGS__) ); }
-
-#endif
+{ return typename boost::describe::detail::bases_descriptor_impl<C, boost::describe::detail::list<__VA_ARGS__>>::type(); }
 
 } // namespace detail
 } // namespace describe
diff --git a/test/bases_test.cpp b/test/bases_test.cpp
index 09ed845..4c7b646 100644
--- a/test/bases_test.cpp
+++ b/test/bases_test.cpp
@@ -62,6 +62,14 @@ int main() {}
 
 #include <boost/mp11.hpp>
 
+template<typename ...Bases>
+struct ZT: Bases...
+{
+    BOOST_DESCRIBE_CLASS(ZT, (Bases...), (), (), ());
+};
+
+using Z = ZT<X1, X2, X3>;
+
 int main()
 {
     using namespace boost::describe;
@@ -151,6 +159,21 @@ int main()
         BOOST_TEST_EQ( (mp_at_c<L, 1>::modifiers), mod_private | mod_virtual );
     }
 
+    {
+        using L = describe_bases<Z, mod_any_access>;
+
+        BOOST_TEST_EQ( mp_size<L>::value, 3 );
+
+        BOOST_TEST_TRAIT_SAME( typename mp_at_c<L, 0>::type, X1 );
+        BOOST_TEST_EQ( (mp_at_c<L, 0>::modifiers), mod_public );
+
+        BOOST_TEST_TRAIT_SAME( typename mp_at_c<L, 1>::type, X2 );
+        BOOST_TEST_EQ( (mp_at_c<L, 1>::modifiers), mod_public );
+
+        BOOST_TEST_TRAIT_SAME( typename mp_at_c<L, 2>::type, X3 );
+        BOOST_TEST_EQ( (mp_at_c<L, 2>::modifiers), mod_public );
+    }
+
     return boost::report_errors();
 }