Using GDateTime utilities is costly and shows up high in profiling.
That's because GDateTime has to run timezone offset checks for every
comparison. We can amortize this cost by converting these datetimes
to unix timestamps upfront, and using them for comparisons.
A complication is date-only ranges, for which unix timestamps wouldn't
work. For this, add a new kind of timestamp that only accounts for the
dates.
Add a new test case for date-only comparison.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/770>
Zero length ranges, such as for events without a DTEND could be
considered to overlap a range if they were at exactly the end of the
range. The end of a range however is the first date that is supposed to
not overlap, so a zero-length range on exactly this point should not be
considered overlapping.
This fixes cases where all-day events from the next month could show up
on the same day of the current month if they did not have a DTEND.
This also adds tests for all possible cases of such zero-length events
overlapping.
Fixes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/701
Zelda Ahmed