Add detail::system_error_category_message, use it in error_code::message

include/boost/system/detail/error_code.hpp

@@ -256,7 +256,14 @@ public:
 
 #endif
 
-        return category().message( value() );
+        if( lc_flags_ == 0 )
+        {
+            return detail::system_error_category_message( value() );
+        }
+        else
+        {
+            return category().message( value() );
+        }
     }
 
     char const * message( char * buffer, std::size_t len ) const BOOST_NOEXCEPT
@@ -264,23 +271,33 @@ public:
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
         if( lc_flags_ == 1 )
         {
+            std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
+
 #if !defined(BOOST_NO_EXCEPTIONS)
             try
 #endif
             {
-                std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
                 detail::snprintf( buffer, len, "%s", ec.message().c_str() );
                 return buffer;
             }
 #if !defined(BOOST_NO_EXCEPTIONS)
             catch( ... )
             {
+                detail::snprintf( buffer, len, "No message text available for error std:%s:%d", ec.category().name(), ec.value() );
+                return buffer;
             }
 #endif
         }
 #endif
 
-        return category().message( value(), buffer, len );
+        if( lc_flags_ == 0 )
+        {
+            return detail::system_error_category_message( value(), buffer, len );
+        }
+        else
+        {
+            return category().message( value(), buffer, len );
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR bool failed() const BOOST_NOEXCEPT

include/boost/system/detail/system_category_impl.hpp

@@ -11,6 +11,7 @@
 //  See library home page at http://www.boost.org/libs/system
 
 #include <boost/system/detail/system_category.hpp>
+#include <boost/system/detail/system_category_message.hpp>
 #include <boost/system/detail/error_condition.hpp>
 #include <boost/system/api_config.hpp>
 
@@ -22,7 +23,6 @@
 
 #if defined(BOOST_WINDOWS_API)
 
-#include <boost/system/detail/system_category_message_win32.hpp>
 #include <boost/system/detail/system_category_condition_win32.hpp>
 
 inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
@@ -39,35 +39,23 @@ inline boost::system::error_condition boost::system::detail::system_error_catego
     }
 }
 
-inline std::string boost::system::detail::system_error_category::message( int ev ) const
-{
-    return system_category_message_win32( ev );
-}
-
-inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
-{
-    return system_category_message_win32( ev, buffer, len );
-}
-
 #else // #if defined(BOOST_WINDOWS_API)
 
-#include <boost/system/detail/generic_category_message.hpp>
-
 inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
 {
     return error_condition( boost::system::detail::generic_value_tag( ev ) );
 }
 
+#endif // #if defined(BOOST_WINDOWS_API)
+
 inline std::string boost::system::detail::system_error_category::message( int ev ) const
 {
-    return generic_error_category_message( ev );
+    return system_error_category_message( ev );
 }
 
 inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
 {
-    return generic_error_category_message( ev, buffer, len );
+    return system_error_category_message( ev, buffer, len );
 }
 
-#endif // #if defined(BOOST_WINDOWS_API)
-
 #endif // #ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_IMPL_HPP_INCLUDED

include/boost/system/detail/system_category_message.hpp

@@ -0,0 +1,71 @@
+#ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED
+
+// Implementation of system_error_category_message
+//
+// Copyright 2018, 2022 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/api_config.hpp>
+
+#if !defined(BOOST_POSIX_API) && !defined(BOOST_WINDOWS_API)
+#  error BOOST_POSIX_API or BOOST_WINDOWS_API must be defined
+#endif
+
+#if defined(BOOST_WINDOWS_API)
+
+#include <boost/system/detail/system_category_message_win32.hpp>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+inline std::string system_error_category_message( int ev )
+{
+    return system_category_message_win32( ev );
+}
+
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+{
+    return system_category_message_win32( ev, buffer, len );
+}
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#else // #if defined(BOOST_WINDOWS_API)
+
+#include <boost/system/detail/generic_category_message.hpp>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+inline std::string system_error_category_message( int ev )
+{
+    return generic_error_category_message( ev );
+}
+
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+{
+    return generic_error_category_message( ev, buffer, len );
+}
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // #if defined(BOOST_WINDOWS_API)
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED