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Wrong timezone names in strftime/strflocaltime for DST #1912

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trantor opened this issue May 28, 2019 · 7 comments · May be fixed by #2863
Open

Wrong timezone names in strftime/strflocaltime for DST #1912

trantor opened this issue May 28, 2019 · 7 comments · May be fixed by #2863
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@nicowilliams
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@trantor
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trantor commented May 28, 2019

Describe the bug
jq does not print the timezone correctly expanding the %Z in the time format for strftime/strflocaltime when it comes to DST.
To Reproduce
Using the example from the wiki...

$ TZ=Europe/Rome ./jq-linux64 -cn 'now|strflocaltime("%Y-%m-%dT%H:%M:%S %Z")'
"2019-05-28T17:10:54 CET"

$ TZ=Europe/Rome date +"%Y-%m-%dT%H:%M:%S %Z"
2019-05-28T17:10:54 CEST

date reports, correctly, CEST as the timezone taking DST into account. jq does not.

Expected behavior
The output of jq to specify the correct timezone following DST

Environment (please complete the following information):

  • Linux Ubuntu 16.04
  • jq version 1.6
@nicowilliams
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Huh, I think there's no real difference between strftime and strflocaltime...

Also, strftime(3) in glibc should be doing this for us, but evidently it's not, and the date(1) command is not calling strftime(3) either!

This looks like a bug in glibc, honestly, though we might be able to work around it.

To get at the DST TZ name we need to use localtime_r() and expect a tm_zone name from the broken-down time struct (struct tm), then use that in the formatting of time. So to work around this we'll need an autoconf test for tm_zone, and when it's present... use either a private strftime() or a wrapper that replaces %Z with the tm_zone. Ugh.

@krzyk
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krzyk commented Apr 7, 2021

This issue exists also in Debian testing in 2021.

@itchyny itchyny mentioned this issue Aug 11, 2021
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@poettig poettig mentioned this issue May 8, 2022
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@DehanLUO
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DehanLUO commented Jan 8, 2023 •
edited

Same error on MacOS Monterey version 12.6.
This looks like a bug in function static jv tm2jv(struct tm *tm) and function static int jv2tm(jv a, struct tm *tm). The daylight saving time flag (tm_isdst), which is greater than zero if DST is in effect, is lost.
There is a 10-month-old branch 439cf72 there to fix it. I applied this fix locally. And it works on my machine.

@D3vil0p3r D3vil0p3r mentioned this issue Jun 8, 2023
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@trantor
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trantor commented Aug 27, 2023

@nicowilliams could we look back at this issue with new development?

@nicowilliams
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nicowilliams commented Aug 28, 2023 •
edited

Yes this is because the jq representation of broken-down time doesn't have a field for tm_isdst. We also don't look at or set tm_zone nor tm_gmtoff. Should be an easy fix.

@nicowilliams
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Relatedly, mktime drops the fractional part of the seconds.

nicowilliams added a commit that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix #1912)
b7df0ea
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
9cc655f
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
e68efc3
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
f423f70
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
7d7433f
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 28, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
fcbcf5d
@nicowilliams nicowilliams self-assigned this Aug 28, 2023
@nicowilliams nicowilliams linked a pull request Aug 28, 2023 that will close this issue
Open
nicowilliams added a commit to nicowilliams/jq that referenced this issue Aug 29, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
e0ca192
@trantor
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trantor commented Sep 6, 2023

@nicowilliams #2863 seems to properly address the problem I originally reported

nicowilliams added a commit to nicowilliams/jq that referenced this issue Sep 7, 2023
@nicowilliams
Broken down time needs tm_{isdst,gmtoff,zone} too (fix jqlang#1912)
b7e8510
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Time function improvements (fix #1912) nicowilliams/jq
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@trantor @krzyk @itchyny @nicowilliams @DehanLUO