bug#11281: DST has not effect on windows XP when system DST adjustment is disabled

bug#11281: DST has not effect on windows XP when system DST adjustment is disabled

[Shuguang Sun]

I'm using GNU Emacs 24.0.95.1 (i386-mingw-nt5.1.2600) of 2012-04-02 on
MARVIN on WindowsXP SP3. I believe the issue exists in other version
as well.

In windows,
1. If I select the time zone GMP-5 EST (East Standard Time) and  check
the enable Daylight Saving Time checkbox, the command
display-time-world in emacs can show the time of New York correctly
with DST.
2. If I select the time zone GMP-5 EST (East Standard Time) and
UNCHECK the enable Daylight Saving Time checkbox, or if I select a
time zone without DST, the command display-time-world in emacs can not
show the time of New York correctly with DST.
But actually the display-time-world-list for New York is ("EST5EDT"
"New York"), which (EST5EDT) supposes to enable the Daylight Saving
Time to show the time.

I try the following code to trace the issue:
(setq old-tz (getenv "TZ"))
(setenv "TZ" "EST+5EDT")
(message (format "%s" (getenv "TZ")))
(message (format-time-string "%A %d %B %R %Z"))
(decode-time)
(setenv "TZ" "EST+5")
(message (format "%s" (getenv "TZ")))
(message (format-time-string "%A %d %B %R %Z"))
(decode-time)
(setenv "TZ" old-tz)

The output is (Because I select a timezone without DST in windows, the
time in the outputs is no DST as I described above):
"EST+5EDT"
"Thursday 19 April 11:27 EDT"
(26 27 11 19 4 2012 4 t -18000)

"EST+5"
"Thursday 19 April 11:27 EST"
(34 27 11 19 4 2012 4 nil -18000)

(DST is t if daylight saving time is in effect,otherwise nil.from the
doc of decode-time) From the output of decode-time, it is clear that
if the TZ is set to "EST+5EDT", the DST is effect. So it is most
likely the function format-time-string can not catch this information.
But it is still weird that it DOES has effect if I enable the DST in
the Windows system.

bug#11281: DST has not effect on windows XP when system DST adjustment is disabled

[Stefan Kangas]

Shuguang Sun <shuguang@gmail.com> writes:

> I'm using GNU Emacs 24.0.95.1 (i386-mingw-nt5.1.2600) of 2012-04-02 on
> MARVIN on WindowsXP SP3. I believe the issue exists in other version
> as well.
>
> In windows,
> 1. If I select the time zone GMP-5 EST (East Standard Time) and  check
> the enable Daylight Saving Time checkbox, the command
> display-time-world in emacs can show the time of New York correctly
> with DST.
> 2. If I select the time zone GMP-5 EST (East Standard Time) and
> UNCHECK the enable Daylight Saving Time checkbox, or if I select a
> time zone without DST, the command display-time-world in emacs can not
> show the time of New York correctly with DST.
> But actually the display-time-world-list for New York is ("EST5EDT"
> "New York"), which (EST5EDT) supposes to enable the Daylight Saving
> Time to show the time.
>
> I try the following code to trace the issue:
> (setq old-tz (getenv "TZ"))
> (setenv "TZ" "EST+5EDT")
> (message (format "%s" (getenv "TZ")))
> (message (format-time-string "%A %d %B %R %Z"))
> (decode-time)
> (setenv "TZ" "EST+5")
> (message (format "%s" (getenv "TZ")))
> (message (format-time-string "%A %d %B %R %Z"))
> (decode-time)
> (setenv "TZ" old-tz)
>
> The output is (Because I select a timezone without DST in windows, the
> time in the outputs is no DST as I described above):
> "EST+5EDT"
> "Thursday 19 April 11:27 EDT"
> (26 27 11 19 4 2012 4 t -18000)
>
> "EST+5"
> "Thursday 19 April 11:27 EST"
> (34 27 11 19 4 2012 4 nil -18000)
>
> (DST is t if daylight saving time is in effect,otherwise nil.from the
> doc of decode-time) From the output of decode-time, it is clear that
> if the TZ is set to "EST+5EDT", the DST is effect. So it is most
> likely the function format-time-string can not catch this information.
> But it is still weird that it DOES has effect if I enable the DST in
> the Windows system.

This was reported 7 years ago, but unfortunately never got a reply at
the time.

Is this still an issue on modern versions of Emacs?

Best regards,
Stefan Kangas

bug#11281: DST has not effect on windows XP when system DST adjustment is disabled

[Stefan Kangas]

Stefan Kangas <stefan@marxist.se> writes:

> This was reported 7 years ago, but unfortunately never got a reply at
> the time.
>
> Is this still an issue on modern versions of Emacs?

More information was requested, but none was given within 39 weeks, so
I'm closing this bug.  If this is still an issue, please reply to this
email (use "Reply to all" in your email client) and we can reopen the
bug report.

Best regards,
Stefan Kangas