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

[Martin Apel]

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.


In GNU Emacs 28.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo 
version 1.16.0)
 of 2022-04-05 built on LP5-MAL1-CEM
Repository revision: 5a223c7f2ef4c31abbd46367b6ea83cd19d30aa7
Repository branch: HEAD
Windowing system distributor 'HC-Consult', version 11.0.12009000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure --program-suffix=-28 --with-x-toolkit=gtk3 --with-json 
--with-native-compilation --with-xwidgets CC=gcc-10
 PKG_CONFIG_PATH=/opt/rh/devtoolset-8/root/usr/lib64/pkgconfig'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON LIBOTF 
LIBSELINUX LIBXML2 MODULES NATIVE_COMP
NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 
XDBE XIM XPM XWIDGETS GTK3 ZLIB

Important settings:
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Major mode: Diary

Minor modes in effect:
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  transient-mark-mode: t

Load-path shadows:
/home/martin/.emacs.d/el-get/transient/lisp/transient hides 
/usr/local/share/emacs/28.1/lisp/transient
/home/martin/.emacs.d/el-get/gdb-mi/gdb-mi hides 
/usr/local/share/emacs/28.1/lisp/progmodes/gdb-mi

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calendar_issue.ical
Description: Binary data