https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114240
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- > using __format::_ChronoParts; > auto __need = _ChronoParts::_Year | _ChronoParts::_Month > - | _ChronoParts::_Day | _ChronoParts::_TimeOfDay; > + | _ChronoParts::_Day; > + if constexpr (ratio_less_v<typename _Duration::period, days::period>) > + __need |= _ChronoParts::_TimeOfDay; This condition's not right. If we have a period of days, but a floating-point rep, we probably do want to parse and use a time if one is present in the input. "2024-03-07 00:05" can be represented by sys_time<duration<double, days::period>> and is not the same time as "2024-03-07". And if we have a period like ratio<days::period::num+1, 1> then it's greater than days, but not using the time of day in the result will lose accuracy. I'm leaning towards Howard's approach of just assuming 00:00:00 if no time is present, rather than making it depend on the period in any way.
