DateTime::create() takes a date/time in local time, but it set
tm_isdst to 0, which meant it was in local winter time always.
Set tm_isdst to -1 so that times during summer time are treated
in summer time, and times in winter time are treated as winter
time (when appropriate). When the time is adjusted backward by
one hour, the same time can be in winter time or summer time,
so this isn't 100% reliable, but for most of the year it should
work fine.
Since LibJS uses DateTime, this means that the Date tuple
ctor (which creates a timestamp from year/month/day/hours/etc
in local time) and getTime() should now have consistent (and
correct) output, which should fix#3327.
In Serenity itself, dst handling (and timezones) are unimplemented
and this doens't have any effect yet, but in Lagom this has an effect.
The implementation in LibC did a timestamp->day-of-week conversion
which looks like a valuable thing to have. But we only need it in
time_to_tm, where we already computed year/month/day -- so let's
consolidate on the day_of_week function in DateTime (which is
getting extracted to AK).
The JS tests pointed out that the implementation in DateTime
had an off-by-one in the month when doing the leap year check,
so this change fixes that bug.
Set member variables after calling mktime(), which canonicalizes
out-of-range values.
With this, DateTime::create(2020, 13, ...) will return a DateTime
on Jan 2021 (assuming the other parameters are in range).
This is just to have a pleasant way to print the current time for now:
dbg() << Core::DateTime::now();
Or if you want it as a string:
Core::DateTime::now().to_string();
