From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@postgresql.org,
        Peter Eisentraut <peter_e@gmx.net>,
        Petr Jelinek <petr@2ndquadrant.com>
Subject: Re: 002_types.pl fails on some timezones on windows
In-reply-to: <f4b9c195-7caa-4849-ba67-49a5d153e203@dunslane.net>
References: <20210930183641.7lh4jhvpipvromca@alap3.anarazel.de>
 <f4b9c195-7caa-4849-ba67-49a5d153e203@dunslane.net>
Comments: In-reply-to Andrew Dunstan <andrew@dunslane.net>
	message dated "Thu, 30 Sep 2021 15:19:30 -0400"
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Date: Thu, 30 Sep 2021 15:38:38 -0400
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Andrew Dunstan <andrew@dunslane.net> writes:
> On 9/30/21 2:36 PM, Andres Freund wrote:
>> CI showed me a failure in 002_types.pl on windows. I only just now noti=
ced
>> that because the subscription tests aren't run by any of the vcregress.=
pl
>> steps :(

> We have windows buildfarm animals running the subscription tests, e.g.
> <https://buildfarm.postgresql.org/cgi-bin/show_stage_log.pl?nm=3Ddrongo&=
dt=3D2021-09-29%2019%3A08%3A23&stg=3Dsubscription-check>
> and they do it by calling vcregress.pl.

But are they running with the prevailing zone set to "Greenwich Standard
Time"?

I dug around to see exactly how we handle that, and was somewhat
gobsmacked to find this mapping in findtimezone.c:

		/* (UTC+00:00) Monrovia, Reykjavik */
		"Greenwich Standard Time", "Greenwich Daylight Time",
		"Africa/Casablanca"

According to current tzdb,

# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
Zone Africa/Casablanca	-0:30:20 -	LMT	1913 Oct 26
			 0:00	Morocco	+00/+01	1984 Mar 16
			 1:00	-	+01	1986
			 0:00	Morocco	+00/+01	2018 Oct 28  3:00
			 1:00	Morocco	+01/+00

Morocco has had weird changes-every-year DST rules since 2008, which'd
go a long way towards explaining funny behavior with this zone, even
without the "reverse DST" since 2018.  And sure enough, 002_types.pl
falls over with TZ=3DAfrica/Casablanca on my Linux machine, too.

I'm inclined to think we ought to be translating that zone name to
Europe/London instead.  Or maybe we should translate to straight-up UTC?
But the option of "Greenwich Daylight Time" suggests that Windows thinks
this means UK civil time, not UTC.

I wonder if findtimezone.c has any other surprising Windows mappings.
I've never dug through that list particularly.

			regards, tom lane