What time is it?

Feed readers sort posts by their date. Until now a q.e.d. post had a day but no time, so every feed said 00:00:00 and readers put the posts of one day in any order they liked. On a day with five posts that looked random. Now a post can say when it was written:

date = 2026-10-31T18:17:00

TOML already knew

PageDate in crates/qed-core/src/page.rs wraps TOML's own date type, and TOML has four kinds of them:

Written	TOML calls it
2026-10-31	local date
18:17:00	local time
2026-10-31T18:17:00	local date-time
2026-10-31T18:17:00+01:00	offset date-time

So reading a time already worked; only nothing used it. Local means "no time zone written": 18:17 somewhere. RSS, though, wants a moment in time, Sat, 31 Oct 2026 18:17:00 +0100, and for that the time needs its offset from UTC.

The computer's time zone

We decided that a time without a zone is in the computer's time zone when the site is built. That sounds simple, but the offset isn't one number: Vienna is +0100 in winter and +0200 in summer, and which one applies depends on the date of the post, not on today. A post from July built in November must still say +0200.

That needs the time zone rules (the tz database), which q.e.d.'s small calendar.rs deliberately doesn't have. jiff does, and it was already in the dependency tree through another library, so adding it cost nothing new:

let civil = jiff::civil::DateTime::new(2026, 7, 5, 14, 30, 0, 0)?;
let offset = civil.to_zoned(jiff::tz::TimeZone::system())?.offset();
// +02:00 in Vienna: summer time on 5 July

TimeZone::system() is the computer's zone (on Linux from /etc/localtime or the TZ variable). The test uses TimeZone::get("Europe/Vienna") instead, so it gives the same result on every computer. A time written with its own offset (+01:00) keeps it. A date without a time stays midnight UTC, as before, so old feeds don't change.

"Today" moved to the computer's zone as well. It decides whether a post is still in the future; in UTC, a post written at 00:30 in Vienna would have counted as tomorrow's for an hour.

In Elixir you'd reach for DateTime.from_naive(naive, "Europe/Vienna") with a time zone database like tz or tzdata; the idea is the same: a naive date-time plus a zone gives a moment.

Sorting

Posts were sorted by day, then by weight. Now PageDate::sort_key gives a pair, the day and the second of the day, and pairs compare element by element (see Six thousand icons):

pub fn sort_key(&self) -> Option<(Date, u32)>

A post without a time counts as midnight, so it comes after the later posts of its day.

Where the docs posts' times came from

The 75 posts on this site needed times, in the order they were written. The first idea was the files' own timestamps, but the posts were moved into one folder this morning, and 64 of them had the same timestamp since. Git knows better: for each file, the commit that added it.

git log --diff-filter=A --follow --format=%ad \
  --date=format-local:%Y-%m-%d\ %H:%M -- docs/pages/blog/…

--diff-filter=A keeps only the commit that added the file, --follow looks past renames, and format-local prints the time in the computer's zone. Six pairs were added in the same commit; those got a minute apart, in the order of their weight. A one-off script in the scratchpad wrote the times; it isn't part of q.e.d.