Fix describe enumerators

include/boost/describe/enum.hpp

@@ -66,6 +66,7 @@ template<class... T> auto enum_descriptor_fn_impl( int, T... )
 
 #define BOOST_DESCRIBE_NESTED_ENUM(E, ...) \
     static_assert(std::is_enum<E>::value, "BOOST_DESCRIBE_NESTED_ENUM should only be used with enums"); \
+    friend bool boost_has_nested_enum_descriptor_fn( E** ) { return true; } \
     friend BOOST_DESCRIBE_ENUM_BEGIN(E) \
     BOOST_DESCRIBE_PP_FOR_EACH(BOOST_DESCRIBE_ENUM_ENTRY, E, __VA_ARGS__) \
     BOOST_DESCRIBE_ENUM_END(E)
@@ -81,6 +82,7 @@ template<class... T> auto enum_descriptor_fn_impl( int, T... )
 
 #define BOOST_DESCRIBE_NESTED_ENUM(E, ...) \
     static_assert(std::is_enum<E>::value, "BOOST_DESCRIBE_NESTED_ENUM should only be used with enums"); \
+    friend bool boost_has_nested_enum_descriptor_fn( E** ) { return true; } \
     BOOST_DESCRIBE_MAYBE_UNUSED friend BOOST_DESCRIBE_ENUM_BEGIN(E) \
     BOOST_DESCRIBE_PP_FOR_EACH(BOOST_DESCRIBE_ENUM_ENTRY, E, ##__VA_ARGS__) \
     BOOST_DESCRIBE_ENUM_END(E)

include/boost/describe/enumerators.hpp

@@ -20,6 +20,7 @@ namespace describe
 // describe_enumerators<E>
 
 template<class E> using describe_enumerators = decltype( boost_enum_descriptor_fn( static_cast<E**>(0) ) );
+template<class E> using nested_describe_enumerators = decltype (boost_has_nested_enum_descriptor_fn(static_cast<E**>(0) ) );
 
 // has_describe_enumerators<E>
 
@@ -34,9 +35,21 @@ template<class E> struct has_describe_enumerators<E, void_t<describe_enumerators
 {
 };
 
+template<class E, class En = void> struct has_nested_describe_enumerators: std::false_type
+{
+};
+
+template<class E> struct has_nested_describe_enumerators<E, void_t<nested_describe_enumerators<E>>>: std::true_type
+{
+};
+
+template<class E> struct has_describe_enumerators_or_nested_describe_enumerators : std::integral_constant<bool, 
+    has_nested_describe_enumerators<E>::value || has_describe_enumerators<E>::value>
+{
+};
 } // namespace detail
 
-template<class E> using has_describe_enumerators = detail::has_describe_enumerators<E>;
+template<class E> using has_describe_enumerators = detail::has_describe_enumerators_or_nested_describe_enumerators<E>;
 
 } // namespace describe
 } // namespace boost

test/nested_enum_test.cpp

@@ -27,6 +27,10 @@ class X2
 
     BOOST_DESCRIBE_NESTED_ENUM(E, v1, v2)
 
+#if defined(BOOST_DESCRIBE_CXX14)
+    static_assert(boost::describe::has_describe_enumerators<E>::value, "");
+#endif
+
 public:
 
     typedef E E2;