[tz] isdst bug Europe/Dublin (tzdb-2019c)

Stefan Rueger stefan.rueger at theblueorange.space
Sat Dec 7 17:21:05 UTC 2019

Looks like zdump claims Dublin has DST during winter, not summer:

$ ./zdump -i -c2020,2021 Europe/Dublin

-	-	+00	GMT	1
2020-03-29	02	+01	IST
2020-10-25	01	+00	GMT	1

Compare with the output for London, which is as I would expect:

$ ./zdump -i -c2020,2021 Europe/London

-	-	+00	GMT
2020-03-29	02	+01	BST	1
2020-10-25	01	+00	GMT

Generally, I think it's neater if the time stretches with the larger GMT values are considered DST. This is almost always true, except for Europe/Dublin, Eire, Africa/Casablanca and Africa/El_Aaiun.

Morocco (and Western Sahara) change the time to have shorter fasts during Ramadan, so to speak to *not* save daylight. I would therefore still argue that the time outside Ramadan should be considered DST and the time during Ramadan the non-DST time.

I am aware that the view "DST means larger GMT value" is not a precise definition (a region that change times zones in quick succession might easily accrue more than two GMT values within a few years). It's therefore not a great candidate for implementation in zic/zdump. However, I hold that periodic *future* annual back-and-forth switches should adopt that principle.

Anyway, over to you


PS: You are providing an *amazing* service - many thanks for that!

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