Re: [WIP v2 1/2] Adding a record-time-zone command option for commit

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 21, 2020, 18:55 UTC
Message-ID: <xmqqzh4f76jr.fsf@gitster.c.googlers.com>
In-Reply-To: <20201021050146.3001222-1-shengfa@google.com>

Shengfa Lin <shengfa@google.com> writes:

> Thanks for the comments and sorry for not describing the design.
> I will add it here.

Thanks. Please do not forget to add it to the updated patch, too. That's where it matters most---you do not necessarily have to explain things to _me_, but you should, to everybody who will read "git log" in the future in order to understand what we did and why.

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> First, I would like to use a "global" variable to keep track of whether
> record-time-zone is set and default to true. Then in various places such
> as commit, pull, merge and rebase; we can add command option that can
> modify this value.
>
> Then in datestamp in date.c, we can check this value; offset would be
> initialized to 0 and only be set if record_time_zone is true. Additionally,
> date_string from the same file would take an extra argument to indicate if
> we want to use nagative sign for zero offset. Then the timestamp along with
> sign and 4 digits offset would be stored in "git_default_date" as buf
> "1603255519 -0000". I think of this as the "encoding" step.

Yes, we could check it in datestamp(), but ...

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> Initially, I thought this would be sufficient to show "-0000" in commit log
> message. However, I found that the show_date function is used for "decoding";
> converting timestamp and tz to more readable format. Then I realize the
> function won't distinguish between +0 and -0 as it only takes in a tz as
> argument. As a result,...

... I would have imagined that you do not have to deal with all those complications if you don't hook this to such a low level of the call graph. That is why I wondered:

>> I may be totally off, ... but wouldn't it be just the
>> matter of touching the single callsite of datestamp() in ident.c, so
>> that after it gets git_default_date string filled, null out the last
>> 5 bytes in it with "-0000" if record_tz is off?

Without any change to datestamp() you made in the patch, the call to the function from ident.c may give us back a string that ends with the integer that is the number of seconds since epoch, and sign plus 4 digits, e.g. +0900 or -0800, that would reveal the true timezone. I would have thought that these five bytes can be replaced with -0000 under some condition (including "the global is set" which is a sign that the feature is being used, but not limited to that one--- we may need to make sure the call to ident_default_date() to fill git_default_date.buf is done on behalf of the user to get a new timestamp to record the user's activity, not doing something like "git commit -C <existing commit>"). I do not immediately see a reason why such a change near the surface level, which does not disrupt the workings of the code at lower levels, would not work.

Thanks.