Re: [RFC PATCH 0/1] adding user.hideTimezone for setting UTC timezone

From: Jonathan Nieder <jrnieder@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Shengfa Lin <shengfa@google.com>,
	git@vger.kernel.org, nathaniel@google.com,
	rsbecker@nexbridge.com, santiago@nyu.edu
Subject: Re: [RFC PATCH 0/1] adding user.hideTimezone for setting UTC timezone
Date: Wed, 30 Sep 2020 20:43:50 -0700	[thread overview]
Message-ID: <20201001034350.GB2930867@google.com> (raw)
In-Reply-To: <xmqqtuved70y.fsf@gitster.c.googlers.com>

Junio C Hamano wrote:

>                                                Our setenv() may not
> be early enough---before the code that decides to call a setenv()
> is run, there are many things that are outside your control (like
> the tracing subsystem, repository discovery, etc.) will run, and if
> any of them does something that triggers tzset() to be called, it
> will be done with the value of TZ the process started with, and our
> setenv() that happens much later won't have any effect to it.

I thought about this before, but in fact it's okay: when calling a
function like localtime() (though not localetime_r() --- see my other
reply), tzset() is called each time so it is able to reflect any
updates to the TZ envvar from the interim.

[....]
> You can let the existing code produce its natural result and then
> when the "force UTC" flag is set, override the offset part to +0000
> if and only if the timezone was obtained from the current
> environment (this if-and-only-if is necessary, because you do not
> want to rewrite and force UTC when you run "git commit --amend"
> without the "--reset-author" option to update a commit that was
> created somewhere else to UTC).  That way, we do not have to futz
> with TZ environment or tzset.

Yes, I think this is simpler and nicer than the proposal in my other
reply.

In addition to not having to futz with TZ, I think I like the
semantics better.  The motivation that started this thread was not so
much "I want to set a custom timezone to blend in" but rather "why are
we recording the timezone at all here?"  In that context, it makes
sense to me to have a setting such as

	core.recordTimeZone

that I can turn *off* to say that I don't think datestamp() callers
should consider the timezone to be information worth recording (and
instead they should write +0000).  To me that seems a little simpler
to understand than user.hideTimezone since this focuses on turning
some functionality off (recording of the time zone) instead of turning
on a new stealth mode.

Thanks,
Jonathan