Re: [PATCH] xdiff: implement a zealous diff3

[Felipe Contreras <felipe.contreras@gmail.com>]

Jeff King wrote:
> On Sun, Jun 13, 2021 at 09:31:55AM -0500, Felipe Contreras wrote:
> 
> > From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > 
> > "zdiff3" is identical to ordinary diff3, only it allows more aggressive
> > compaction than diff3. This way the displayed base isn't necessary
> > technically correct, but still this mode might help resolving merge
> > conflicts between two near identical additions.
> > 
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > ---
> > 
> > I'm re-sending this patch from 2013 because I do think it provides value
> > and we might want to make it the default.
> 
> I take it you didn't investigate the segfault I mentioned.

I don't know how I was supposed to investigate the few segfaults you
mentioned. All you said is that you never tracked the bug.

> Try this:
> 
>    commit=a5170794372cf1325710a3419473c91ec4af53bf
>    for style in merge diff3 zdiff3; do
>      git reset --hard
>      git checkout $commit^1
>      git -c merge.conflictstyle=$style merge $commit^2
>    done
> 
> The first two are fine; the zdiff3 one segfaults within the xmerge.c
> code.

I can reproduct the segfault, and here is a simpler way to reproduce it:

(I have a hacked version of diff3 until merge-file learns how to use
merge.conflictstyle)

  cat >b <<EOF
  A
  EOF

  cat >l <<EOF
  A

  B
  C
  D
  E
  F
  GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
  H
  I
  EOF

  cat >r <<EOF
  A

  b
  C
  D
  E
  F
  GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
  H
  i
  EOF

  $git merge-file --diff3 -p l b r

-- 
Felipe Contreras