|
From: | Paul Eggert |
Subject: | bug#55635: `make-decoded-time' incorrectly sets DST to nil, it should be -1 (guess) |
Date: | Fri, 27 May 2022 12:26:56 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 |
On 5/27/22 03:40, Lars Ingebrigtsen wrote:
This looks wrong. Shouldn't it leave the DST flag alone? I.e., just this: (unless (decoded-time-zone time) (setf (decoded-time-zone-time) default-zone)) That is, if we assume that for the DST component -1 means "unknown" and nil means "standard time", it should be OK for decoded-time-set-defaults to leave the DST component alone, for the same reason that it leaves the DOW component alone.
Yes, I think so. But you changed this in a391ffa2f03, and you usually have a good reason for changes like this, so I thought there must be something subtle going on here I didn't quite get. 😀
Thanks for the compliment, not sure it's deserved here....
The old code doesn't look quite right, either, I think... - ;; When we don't have a time zone and we don't have a DST, then mark - ;; it as unknown. - (when (and (not (decoded-time-zone time)) - (not (decoded-time-dst time))) - (setf (decoded-time-dst time) -1)) - - (when (and (not (decoded-time-zone time)) - default-zone) - (setf (decoded-time-zone time) 0))
Yes, that old code was wrong because it incorrectly assumeed that (not (decoded-time-dst time)) means the DST flag is unspecified, whereas it really means that the DST flag is specifying standard time.
It also looked odd because default-zone was used only as a boolean, even though its name suggests that it's the default time zone. This usage dates back to commit fa648a59c9818ae284209ac7ae4f3700aebd92c9 which you installed in July 2019. The only call using default-zone in Emacs is in newsticker--decode-iso8601-date, which passes 0 so that the oddity in the implementation makes no difference there.
Part of the confusion here is that nil doesn't mean "no time zone is known"; it means "use the Emacs default time zone". In other words, nil has the same interpretation problem in time zones that it has in DST flags - it doesn't mean "unknown".
To try to lessen the confusion I installed the attached, which fixes the reported bug so I'll close the bug report. Please feel free to revert if you see a problem with it (I'm just trying to save time here by being bold).
0001-decoded-time-set-defaults-now-leaves-DST-alone.patch
Description: Text Data
[Prev in Thread] | Current Thread | [Next in Thread] |