Time zones!

Publication dates are are like a lot of things normally specified as dates, where some action happens at a particular moment in time. Mismiy treats publication dates as datetimes, defaulting to midnight if you do not specify the time of day. It also defaulted to the local time zone, which is probably fine, but caused trouble when I tried to set up a build & test action on GitHub.

GitHub Actions are run on a Ubuntu server whose time zone is set to UTC. During northern-hemisphere summer my computer is running on British Summer Time. It follows that my tests failed on CI as soon as they they tried to do anything with dates.

The fix for this was to get more serious about working out the time zone of a blog, and ensuring that all the ways we acquire datetimes deal with time zones correctly. This has become easier with newer versions of Python, where the datetime module has more and clearer operations for setting and adjusting time zones, and the relatively new zoneinfo module provides support for modern Zone info specifications.

Thus the META.yaml file we introduced to set blog ID and title can also set tz. This specifies the time zone using IANA tz database codes like Europe/London. Datetimes supplied without time zone will be assumed to be in the specified time zone. We have tests now to check that we deal with this on the way in, so that the Atom-feed-generating code can assume that the datetimes it is working with are time-zone-aware.