Junio C Hamano <gitster@xxxxxxxxx> writes:
> Thomas Rast <trast@xxxxxxxxxxx> 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
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