Re: [PATCH] Make display-time-mode time zone configurable

[Mark Oteiza]

On 19/02/16 at 10:02am, Paul Eggert wrote:
> On 02/19/2016 09:14 AM, Mark Oteiza wrote:
> > My first thought of a use-case is simply keeping time zone in the mode
> > line the same regardless of what the system time (or local time) may be,
> > akin to not changing one's watch when travelling.
> 
> That's easily done with (setenv "TZ" "America/Los_Angeles"), or whatever you
> want the mode-line's time zone to be.

Sure, if you want to globally change the time zone in emacs and all the
subprocesses it spawns, which is counter to the purpose of the defcustom
in the first place--to expose convenient fine control of the displayed
time zone in display-time-mode.

> > Alternatively, similar to standardizing on one a particular time zone in
> > time-stamp.el, it may also be desirable in a privacy sense to
> > standardize the rest of Emacs' time displays (e.g. time stamps in email
> > or other network connections) to another time zone but still keep the
> > "wall clock" (meaning display-time-mode) as local time.
> 
> If there's a need to use publish some other time zone for privacy reasons,
> then it would make sense to add a configuration variable for one's "public
> time zone", which Emacs uses for email and other uses intended to be public,
> while continuing to use the current TZ-based approach for the actual time
> zone. Alternatively, Emacs could add a configuration variable for one's
> "private time zone", which would be used for mode lines and for other
> private things, while continuing to use TZ for the time zone announced for
> public uses. The former of these two alternatives sounds more plausible to
> me, as users expect TZ to be the "true" time zone.

Perhaps. However, Emacs already has knobs for time-stamps, knobs for the
modeline, and knobs for calendar-* for the different parts of
displaying/formatting time.  While the fragmentation can be painful,
I don't think the problem will be solved any time soon. There will still
be some desire to customize the time zone in different parts of Emacs.
Adding a global option will just be another layer of indirection.  In
the mean time, let's expose features.