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From: Thomas Guyot-Sionnest <tguyot@gmail.com>
To: Taylor Blau <me@ttaylorr.com>
Cc: git@vger.kernel.org, Thomas Guyot-Sionnest <dermoth@aei.ca>
Subject: Re: [PATCH 1/2] diff: Fix modified lines stats with --stat and --numstat
Date: Fri, 18 Sep 2020 11:10:45 -0400	[thread overview]
Message-ID: <CALqVohfQZu=itUyfU7nubJpgBETh2q7W1TVx=c2E32ey2cFZkA@mail.gmail.com> (raw)
In-Reply-To: <20200918144651.GA1612043@nand.local>

On Fri, 18 Sep 2020 at 10:46, Taylor Blau <me@ttaylorr.com> wrote:
>
> On Fri, Sep 18, 2020 at 07:32:55AM -0400, Thomas Guyot-Sionnest wrote:
> > -     same_contents = oideq(&one->oid, &two->oid);
> > +     if (one->is_stdin && two->is_stdin)
> > +             same_contents = !strcmp(one->data, two->data);
>
> Hmm. A couple of thoughts here:
>
>   - strcmp seems like a slow-down here, since we'll have to go through
>     at worst the smaller of one->data and two->data to compare each of
>     them.
>
>   - strcmp is likely not the right way to do that, since we could be
>     diffing binary content, in which case we'd want to continue over
>     NULs and instead stop at a fixed length (the minimum of the length
>     of one->data and two->data, specifically). I'd have expected memcmp
>     here instead.
>

You're absolutely right - this is a bug I managed to figure out last
night - first real incursion into git C code - and I definitely didn't
think this through. TBH so far I coded mostly with tools dealing in
plaintext and C strings.

>   - Why do we have to do this at all all the way up in
>     'builtin_diffstat'? I would expect these to contain the right
>     OIDs by the time they are given back to us from the call to
>     'diff_fill_oid_info' in 'run_diffstat'.
>
> So, my last point is the most important of the three. I'd expect
> something more along the lines of:
>
>   1. diff_fill_oid_info resolve the link to the pipe, and
>   2. index_path handles the resolved fd.
>
> ...but it looks like that is already what it's doing? I'm confused why
> this doesn't work as-is.

So the idea is to checksum the data and write a valid oid. I'll see if
I can figure that out. Thanks for the hint though else I would likely
have gone with a buffer and memcmp. Your solution seems cleaner, and
there is a few other uses of oideq's that look dubious at best with
the case of null oids / buffered data so it's definitely a better
approach.

> > +     else
> > +             same_contents = oideq(&one->oid, &two->oid);
> >
> >       if (diff_filespec_is_binary(o->repo, one) ||
> >           diff_filespec_is_binary(o->repo, two)) {
> > diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
> > index e024cff65c..4715e75b68 100755
> > --- a/t/t3206-range-diff.sh
> > +++ b/t/t3206-range-diff.sh
> > @@ -258,11 +258,11 @@ test_expect_success 'changed commit with --stat diff option' '
> >            a => b | 0
> >            1 file changed, 0 insertions(+), 0 deletions(-)
> >       3:  $(test_oid t3) ! 3:  $(test_oid c3) s/11/B/
> > -          a => b | 0
> > -          1 file changed, 0 insertions(+), 0 deletions(-)
> > +          a => b | 2 +-
> > +          1 file changed, 1 insertion(+), 1 deletion(-)
> >       4:  $(test_oid t4) ! 4:  $(test_oid c4) s/12/B/
> > -          a => b | 0
> > -          1 file changed, 0 insertions(+), 0 deletions(-)
> > +          a => b | 2 +-
> > +          1 file changed, 1 insertion(+), 1 deletion(-)
>
> The tests definitely demonstrate that the old behavior was wrong,
> though...
>

For the records I verified the actual diffs (I think they're even
hardcoded in the earlier tests) and the remaining 0-add/del's are also
valid.

Regards,

Thomas

  reply	other threads:[~2020-09-18 15:11 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 11:32 Allow passing pipes to diff --no-index + bugfix Thomas Guyot-Sionnest
2020-09-18 11:32 ` [PATCH 1/2] diff: Fix modified lines stats with --stat and --numstat Thomas Guyot-Sionnest
2020-09-18 14:46   ` Taylor Blau
2020-09-18 15:10     ` Thomas Guyot-Sionnest [this message]
2020-09-18 17:37       ` Jeff King
2020-09-18 18:00         ` Thomas Guyot-Sionnest
2020-09-20  4:53       ` Thomas Guyot
2020-09-18 17:27   ` Jeff King
2020-09-18 17:52     ` Thomas Guyot-Sionnest
2020-09-18 18:06       ` Junio C Hamano
2020-09-23 19:16         ` Johannes Schindelin
2020-09-23 19:23           ` Junio C Hamano
2020-09-23 20:44             ` Johannes Schindelin
2020-09-24  4:49               ` Thomas Guyot
2020-09-24  5:24                 ` [PATCH v3] " Thomas Guyot-Sionnest
2020-09-24  7:41                   ` [PATCH v4] " Thomas Guyot-Sionnest
2020-09-24  6:40                 ` [PATCH 1/2] " Junio C Hamano
2020-09-24  7:13                   ` Thomas Guyot
2020-09-24 17:19                     ` Junio C Hamano
2020-09-24 17:38                       ` Junio C Hamano
2020-09-23 15:05     ` Johannes Schindelin
2020-09-20 13:09   ` [PATCH v2] " Thomas Guyot-Sionnest
2020-09-20 15:39     ` Taylor Blau
2020-09-20 16:38       ` Thomas Guyot
2020-09-20 19:11       ` Junio C Hamano
2020-09-20 20:08         ` Junio C Hamano
2020-09-20 20:36         ` Junio C Hamano
2020-09-20 22:15           ` Junio C Hamano
2020-09-21 19:26         ` Jeff King
2020-09-21 21:51           ` Junio C Hamano
2020-09-21 22:20             ` Jeff King
2020-09-21 22:37               ` Junio C Hamano
2020-09-18 11:32 ` [PATCH 2/2] Allow passing pipes for input pipes to diff --no-index Thomas Guyot-Sionnest
2020-09-18 14:36   ` Taylor Blau
2020-09-18 16:34     ` Thomas Guyot-Sionnest
2020-09-18 17:19       ` Jeff King
2020-09-18 17:21         ` Jeff King
2020-09-18 17:39         ` Thomas Guyot-Sionnest
2020-09-18 17:48         ` Junio C Hamano
2020-09-18 18:02           ` Jeff King
2020-09-20 12:54             ` Thomas Guyot
2020-09-21 19:31               ` Jeff King
2020-09-21 20:14                 ` Junio C Hamano
2020-09-18 17:58       ` Taylor Blau
2020-09-18 18:05         ` Jeff King
2020-09-18 17:20     ` Jeff King
2020-09-18 18:00       ` Taylor Blau
2020-09-18 21:56   ` brian m. carlson
2020-09-18 17:51 ` Allow passing pipes to diff --no-index + bugfix Junio C Hamano
2020-09-18 18:24   ` Thomas Guyot-Sionnest

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