Added SPDLOG_FMT_RUNTIME macro for compatibilty with fmt prior 8

include/spdlog/common.h

@@ -37,9 +37,12 @@
 
 // backward compatibility with fmt versions older than 8
 #if FMT_VERSION >= 80000
+#    define SPDLOG_FMT_RUNTIME(format_string) fmt::runtime(format_string)
 #    if defined(SPDLOG_WCHAR_FILENAMES) || defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT)
 #        include <spdlog/fmt/xchar.h>
 #    endif
+#else
+#    define SPDLOG_FMT_RUNTIME(format_string) format_string
 #endif
 
 // visual studio upto 2013 does not support noexcept nor constexpr

include/spdlog/logger.h

@@ -268,8 +268,7 @@ protected:
     err_handler custom_err_handler_{nullptr};
     details::backtracer tracer_;
 
-    // common implementation for after templated public api has been resolved
-   
+    // common implementation for after templated public api has been resolved   
     template<typename FormatString, typename... Args, typename Char = fmt::char_t<FormatString>,
         typename std::enable_if<!std::is_same<Char, wchar_t>::value, Char>::type * = nullptr>
     void log_(source_loc loc, level::level_enum lvl, const FormatString &fmt, Args &&...args)

include/spdlog/sinks/daily_file_sink.h

@@ -53,7 +53,7 @@ struct daily_filename_format_calculator
 #if defined(_MSC_VER) && defined(SPDLOG_WCHAR_FILENAMES) // for some reason msvc doesnt allow fmt::runtime(..) with wchar here
         return fmt::format(fmt_filename, now_tm);
 #else
-        return fmt::format(fmt::runtime(fmt_filename), now_tm);
+        return fmt::format(SPDLOG_FMT_RUNTIME(fmt_filename), now_tm);
 #endif
     }
 };