From: Thomas Rast <trast@inf.ethz.ch>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Subject: Re: [PATCH] log: use true parents for diff even when rewriting
Date: Tue, 23 Jul 2013 09:27:06 +0200 [thread overview]
Message-ID: <87k3khpwhh.fsf@linux-k42r.v.cablecom.net> (raw)
In-Reply-To: <7v61w2clli.fsf@alter.siamese.dyndns.org> (Junio C. Hamano's message of "Mon, 22 Jul 2013 14:48:25 -0700")
Junio C Hamano <gitster@pobox.com> writes:
> Thomas Rast <trast@inf.ethz.ch> writes:
>
>> When using pathspec filtering in combination with diff-based log
>> output, parent simplification happens before the diff is computed.
>> The diff is therefore against the *simplified* parents.
>>
>> This works okay, arguably by accident, in the normal case: the pruned
>> commits did not affect the paths being filtered, so the diff against
>> the prune-result is the same as against the diff against the true
>> parents.
>>
>> However, --full-diff breaks this guarantee, and indeed gives pretty
>> spectacular results when comparing the output of
>>
>> git log --graph --stat ...
>> git log --graph --full-diff --stat ...
>>
>> (--graph internally kicks in parent simplification, much like
>> --parents).
Hmm, I stopped writing the message midway through. There should be
another two paragraphs here about storing the original parent list on
the side for later use when showing the diff.
>> Perhaps like this. It's getting a bit late, so I'm not sure if I'm
>> missing another user of the "true" parent list, but it does fix the
>> issue you reported.
>
> Conceptually I can see how this will change the history
> simplification in the vertical direction (skipping the ancestry
> chain and jumping directly to the closest grandparent that touched
> the specified path), but I am not sure how well this interacts with
> history simplification in the horizontal direciton (culling
> irrelevant side branches from the merge).
But isn't that similarly confusing for the user as Uwe's original
problem? Suddenly we'd be showing a merge commit as an ordinary one,
simply because the merged history did not affect the filtered
pathspecs. Thus we would show everything that has been merged on the
*other* files as a big diff. Would that be useful? It would certainly
be a big difference in how the commit is shown.
> I also have to wonder if we always want to incur this save-parents
> overhead, or we are better off limiting it to only when --full-diff
> is in effect.
I haven't quite convinced myself that it is 100% safe to use the
rewritten parents when --full-diff is not in effect...
--
Thomas Rast
trast@{inf,student}.ethz.ch
next prev parent reply other threads:[~2013-07-23 7:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-22 9:08 git log anomalities Uwe Kleine-König
2013-07-22 10:40 ` Thomas Rast
2013-07-22 21:22 ` [PATCH] log: use true parents for diff even when rewriting Thomas Rast
2013-07-22 21:48 ` Junio C Hamano
2013-07-23 7:27 ` Thomas Rast [this message]
2013-07-23 7:49 ` Uwe Kleine-König
2013-07-23 19:55 ` Junio C Hamano
2013-07-31 20:13 ` [PATCH v2] " Thomas Rast
2013-07-31 22:55 ` Jeff King
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