Re: [PATCH 2/2] pickaxe: use textconv for -S counting

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Tue, Nov 13, 2012 at 03:13:19PM -0800, Junio C Hamano wrote:
>
>> >  static int has_changes(struct diff_filepair *p, struct diff_options *o,
>> >  		       regex_t *regexp, kwset_t kws)
>> >  {
>> > +	struct userdiff_driver *textconv_one = get_textconv(p->one);
>> > +	struct userdiff_driver *textconv_two = get_textconv(p->two);
>> > +	mmfile_t mf1, mf2;
>> > +	int ret;
>> > +
>> >  	if (!o->pickaxe[0])
>> >  		return 0;
>> >  
>> > -	if (!DIFF_FILE_VALID(p->one)) {
>> > -		if (!DIFF_FILE_VALID(p->two))
>> > -			return 0; /* ignore unmerged */
>> 
>> What happened to this part that avoids showing nonsense for unmerged
>> paths?
>
> It's moved down. fill_one will return an empty mmfile if
> !DIFF_FILE_VALID, so we end up here:
>
>         fill_one(p->one, &mf1, &textconv_one);
>         fill_one(p->two, &mf2, &textconv_two);
>
>         if (!mf1.ptr) {
>                 if (!mf2.ptr)
>                         ret = 0; /* ignore unmerged */
>
> Prior to this change, we didn't use fill_one, so we had to check manually.
>
>> > +	/*
>> > +	 * If we have an unmodified pair, we know that the count will be the
>> > +	 * same and don't even have to load the blobs. Unless textconv is in
>> > +	 * play, _and_ we are using two different textconv filters (e.g.,
>> > +	 * because a pair is an exact rename with different textconv attributes
>> > +	 * for each side, which might generate different content).
>> > +	 */
>> > +	if (textconv_one == textconv_two && diff_unmodified_pair(p))
>> > +		return 0;
>> 
>> I am not sure about this part that cares about the textconv.
>> 
>> Wouldn't the normal "git diff A B" skip the filepair that are
>> unmodified in the first place at the object name level without even
>> looking at the contents (see e.g. diff_flush_patch())?
>
> Hmph. The point was to find the case when the paths are different (e.g.,
> in a rename), and therefore the textconvs might be different. But I
> think I missed the fact that diff_unmodified_pair will note the
> difference in paths. So just calling diff_unmodified_pair would be
> sufficient, as the code prior to my patch does.
>
> I thought the point was an optimization to avoid comparing contains() on
> the same data (which we can know will match without looking at it).

Yes.

> Exact renames are the obvious one, but they are not handled here.

That is half true.  Before this change, we will find the same number
of needles and this function would have said "no differences" in a
very inefficient way.  After this change, we may apply different
textconv filters and this function will say "there is a difference",
even though we wouldn't see such a difference at the content level
if there wasn't any rename.