bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Martin Apel via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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When importing the attached minimal ical file using icalendar-import-file, the resulting time is off by one hour. The problem probably lies somewhere in icalendar--convert-recurring-to-diary, but I couldn't pinpoint the exact location.
The only meeting in the attached icalendar file is defined in timezone 'America/New_York' at 10 am. It shows up in my diary (which is timezone 'Europe/Berlin') at 3pm, even though the time difference between the two timezones is 6 hours.

To reproduce, save the attached file somewhere and execute the following command:

(icalendar-import-file "~/calendar_issue.ical" "~/test.diary")

after adjusting the paths as necessary.


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[-- Attachment #2.1.2: Type: text/html, Size: 571 bytes --]

[-- Attachment #2.2: calendar_issue.ical --]
[-- Type: application/octet-stream, Size: 1311 bytes --]

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//davmail.sf.net/NONSGML DavMail Calendar V1.1//EN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART:16010101T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=1SU;BYMONTH=11
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:-0500
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ORGANIZER;CN="Someone":MAILTO:Someone@somewhere.com
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UID:040000008200E00074C5B7101A82E0080000000000C2199FEA2ED80100000000000000001
 0000000A5B64C1A3F56FA46BE19A6956606D137
SUMMARY;LANGUAGE=en-US:Dummy
DTSTART;TZID="America/New_York":20220317T100000
DTEND;TZID="America/New_York":20220317T103000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20220303T153703Z
TRANSP:OPAQUE
STATUS:CONFIRMED
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bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Lars Ingebrigtsen]

Martin Apel <martin.apel@3ds.com> writes:

> When importing the attached minimal ical file using
> icalendar-import-file, the resulting time is off by one hour. The
> problem probably lies somewhere in
> icalendar--convert-recurring-to-diary, but I couldn't pinpoint the
> exact location.  The only meeting in the attached icalendar file is
> defined in timezone 'America/New_York' at 10 am. It shows up in my
> diary (which is timezone 'Europe/Berlin') at 3pm, even though the time
> difference between the two timezones is 6 hours.

No, the difference varies -- Daylight Savings started on March 13 in the
US but on March 27 in the EU, and in that period there was a five hour
difference.

And:

DTSTART;TZID="America/New_York":20220317T100000
DTEND;TZID="America/New_York":20220317T103000

This was in the middle of that period.  So this seems like it's working
as it should?

But if I'm reading the ical file right, this is a recurring (weekly?)
event, so it should be at 4pm after March 27...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Phil Sainty]

[-- Attachment #1: Type: text/plain, Size: 1081 bytes --]

I've also had some issues with ical->diary times, but it's
a feature I've barely started using, so I don't have much
input and I'd not tried to debug it.

I'm using the mu4e email client as the UI for importing these
from email attachments, but AFAICS that's using icalendar.el
via: (icalendar-import-file path diary-file)

In my case the issue isn't restricted to recurring events,
and in general the times imported into the diary seem to be
0.5 hours later than they ought to be.  The example below
(full file attached) is for a meeting from 15:30 to 16:00
on the 20th, and it showed up in my diary as 16:00 to 16:30.

DTSTART;TZID=/freeassociation.sourceforge.net/Pacific/Auckland:
  20220620T153000
DTEND;TZID=/freeassociation.sourceforge.net/Pacific/Auckland:
  20220620T160000

Something noteworthy about the full attached file is just how
many entries there are for daylight savings vs standard time
within the VTIMEZONE block.  This seems to be a history of
daylight savings variations for the timezone, so I did wonder
whether that could be causing any confusion.


-Phil

[-- Attachment #2: example.ics.gz --]
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bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Martin Apel via Bug reports for GNU Emacs, the Swiss army knife of text editors]

[-- Attachment #1: Type: text/plain, Size: 3259 bytes --]

Hi Lars,


Lars Ingebrigtsen <larsi@gnus.org> writes:

> EXTERNAL EMAIL : The sender of this email is external to 3DS. Be wary of the content and do not open unexpected
> attachments or links. If you consider this email as spam, you can click the following link
> <https://spam-report.3ds.com/?linktext=https://www.mailcontrol.com/sr/YVso8k_J-_nGX2PQPOmvUtvW5gv9VGgLuRYdU8YNcKA2_t9cJ1amT5dPw1_hrXq58cEWYV4_gjYfmF8UmgH1OQ>==
> (no login or additional action will be requested).
>
>
> Martin Apel <martin.apel@3ds.com> writes:
>
>> When importing the attached minimal ical file using
>> icalendar-import-file, the resulting time is off by one hour. The
>> problem probably lies somewhere in
>> icalendar--convert-recurring-to-diary, but I couldn't pinpoint the
>> exact location.  The only meeting in the attached icalendar file is
>> defined in timezone 'America/New_York' at 10 am. It shows up in my
>> diary (which is timezone 'Europe/Berlin') at 3pm, even though the time
>> difference between the two timezones is 6 hours.
>
> No, the difference varies -- Daylight Savings started on March 13 in the
> US but on March 27 in the EU, and in that period there was a five hour
> difference.
>
> And:
>
> DTSTART;TZID="America/New_York":20220317T100000
> DTEND;TZID="America/New_York":20220317T103000
>
> This was in the middle of that period.  So this seems like it's working
> as it should?
>
> But if I'm reading the ical file right, this is a recurring (weekly?)
> event, so it should be at 4pm after March 27...

I thought that it might have something to do with the different start dates for daylight savings time. However it should
show up at 4pm, but it shows up at 3pm after March 27.

Maybe this is a more general problem, that the diary does not consider timezones at all. I think, that the conversion
functionality would need to convert each date of a recurring event separately, as the daylight savings time might have
changed between consecutive repetitions.  However the diary syntax does not allow to specify this, as far as I
understand. So maybe this is more of a shortcoming in the diary syntax than a conversion problem.  Probably instead of
diary-cyclic another sexp would be needed, which also takes the time of day into account, which diary-cyclic does not
do.

Thanks,

Martin
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bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Lars Ingebrigtsen]

Martin Apel <martin.apel@3ds.com> writes:

> Maybe this is a more general problem, that the diary does not consider
> timezones at all. I think, that the conversion functionality would
> need to convert each date of a recurring event separately, as the
> daylight savings time might have changed between consecutive
> repetitions.

Yes, for repeating events, diary has to keep track of what the original
time zone (and time) is, and convert from that time each day.  I've
skimmed the diary functions, and it doesn't seem like that's something
the diary functions have taken into accound, so patches welcome.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Martin Apel via Bug reports for GNU Emacs, the Swiss army knife of text editors]

[-- Attachment #1: Type: text/plain, Size: 2524 bytes --]

Hallo Lars,


Lars Ingebrigtsen <larsi@gnus.org> writes:

> EXTERNAL EMAIL : The sender of this email is external to 3DS. Be wary of the content and do not open unexpected
> attachments or links. If you consider this email as spam, you can click the following link
> <https://spam-report.3ds.com/?linktext=https://www.mailcontrol.com/sr/kra54IrKYHHGX2PQPOmvUiOFufhVdryLdnNqnQjMvSqaqSk_Vs5yB6Bl580EfnElME0E4c2ZJnGzbAWAmKJQAw>==
> (no login or additional action will be requested).
>
>
> Martin Apel <martin.apel@3ds.com> writes:
>
>> Maybe this is a more general problem, that the diary does not consider
>> timezones at all. I think, that the conversion functionality would
>> need to convert each date of a recurring event separately, as the
>> daylight savings time might have changed between consecutive
>> repetitions.
>
> Yes, for repeating events, diary has to keep track of what the original
> time zone (and time) is, and convert from that time each day.  I've
> skimmed the diary functions, and it doesn't seem like that's something
> the diary functions have taken into accound, so patches welcome.

I suppose, that it would be a major undertaking to teach the diary about timezones. As this is a personal diary it
probably also doesn't make too much sense. Therefore I wonder, if it wouldn't be the better approach, to split a
recurring event from ical into separate events in the diary. This way the conversion functionality could convert each
event separately. When I find the time, I can try to improve this, but for now I don't fully understand the details of
the code.
This email and any attachments are intended solely for the use of the individual or entity to whom it is addressed and may be confidential and/or privileged.

If you are not one of the named recipients or have received this email in error,

(i) you should not read, disclose, or copy it,

(ii) please notify sender of your receipt by reply email and delete this email and all attachments,

(iii) Dassault Systèmes does not accept or assume any liability or responsibility for any use of or reliance on this email.


Please be informed that your personal data are processed according to our data privacy policy as described on our website. Should you have any questions related to personal data protection, please contact 3DS Data Protection Officer at 3DS.compliance-privacy@3ds.com<mailto:3DS.compliance-privacy@3ds.com>


For other languages, go to https://www.3ds.com/terms/email-disclaimer

bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Lars Ingebrigtsen]

Martin Apel <martin.apel@3ds.com> writes:

> I suppose, that it would be a major undertaking to teach the diary
> about timezones. As this is a personal diary it probably also doesn't
> make too much sense. Therefore I wonder, if it wouldn't be the better
> approach, to split a recurring event from ical into separate events in
> the diary.

If you have an event that repeats yearly, that's a lot of entries.  But
more importantly, you don't know a year in advance what the actual time
is going to be until much later -- gummints change time zone rules on a
whim, and a 4:00 PM event in New York time may or may not be 22:00
German time in five months time -- you can't tell in advance.

The only way to make this work reliably is to store the actual time zone
of the event.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#56125: 28.1; Timezone conversion sometimes wrong for recurring events, when importing ical to diary

[Martin Apel via Bug reports for GNU Emacs, the Swiss army knife of text editors]

[-- Attachment #1: Type: text/plain, Size: 2473 bytes --]

Hi Lars,


Lars Ingebrigtsen <larsi@gnus.org> writes:

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> Martin Apel <martin.apel@3ds.com> writes:
>
>> I suppose, that it would be a major undertaking to teach the diary
>> about timezones. As this is a personal diary it probably also doesn't
>> make too much sense. Therefore I wonder, if it wouldn't be the better
>> approach, to split a recurring event from ical into separate events in
>> the diary.
>
> If you have an event that repeats yearly, that's a lot of entries.  But
> more importantly, you don't know a year in advance what the actual time
> is going to be until much later -- gummints change time zone rules on a
> whim, and a 4:00 PM event in New York time may or may not be 22:00
> German time in five months time -- you can't tell in advance.
>
> The only way to make this work reliably is to store the actual time zone
> of the event.

You are right, I thought that these times are fairly fixed. I think for the time being I have to be careful with
appointments created in different timezones, because extending the diary package is beyond my ELisp skills and also
beyond my free time.
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