daily file sink - daylight saving time

[MarioPoneder]

Hello,

it seems like there is a problem with daylight saving time, because the method spdlog::sinks::daily_file_sink::next_rotation_tp_() just adds 24 hours on return.

Kind regards
Mario

[gabime]

I can't find a reliable and fast way to handle dst. mktime might fail detecting it, and it is not well defined what to do anyway if the rotation time is same as dst.

[USAFrenzy]

I don't know if this has already been addressed in other issues, but with the addition of C++20's date time functionalities, std::chrono::time_zone's get_info() function returns a variable save which gives the daylight savings offset which could be helpful here. That being said, I'm not sure if this is worth looking into and providing a feature flag check to include or not based on C++20 requirements for this specific case, but the upside might be the fact that you would only have to pay the cost once initially and maybe whenever there was a check before rotating the log file.

The only other thing I can think of is bundling a form of Howard's date library with date/tz.h similar to how spdlog currently bundles a subsection of fmtlib, and optimizing some wrappers around the base calls that the C++20 additions call for the get_info().save variable, but I understand if adding dependencies is something that isn't wanted here.

It might take some time to do, especially as I'm still learning my way around programming as a whole, but I would be happy to try to put something together for this if either case sounds like a plausible solution? If not, I totally understand.