Switch to vformat_to

Drive-by: reduce the amount of occurences of #ifdef SPDLOG_USE_STD_FORMAT

include/spdlog/details/fmt_helper.h

@@ -23,6 +23,20 @@ inline spdlog::string_view_t to_string_view(const memory_buf_t &buf) SPDLOG_NOEX
     return spdlog::string_view_t{buf.data(), buf.size()};
 }
 
+#ifdef SPDLOG_USE_STD_FORMAT
+template<typename T>
+std::basic_string<T> to_string(const std::basic_string<T> &buf)
+{
+    return buf;
+}
+#else
+template<typename T, size_t Size>
+std::basic_string<T> to_string(const fmt::basic_memory_buffer<T, Size> &buf)
+{
+    return fmt::to_string(buf);
+}
+#endif
+
 inline void append_string_view(spdlog::string_view_t view, memory_buf_t &dest)
 {
     auto *buf_ptr = view.data();

include/spdlog/details/os-inl.h

@@ -388,11 +388,7 @@ SPDLOG_INLINE std::string filename_to_str(const filename_t &filename)
 {
     memory_buf_t buf;
     wstr_to_utf8buf(filename, buf);
-#    ifdef SPDLOG_USE_STD_FORMAT
-    return buf;
-#    else
-    return fmt::to_string(buf);
-#    endif
+    return fmt_helper::to_string(buf);
 }
 #else
 SPDLOG_INLINE std::string filename_to_str(const filename_t &filename)