Re: [PATCH 7/7] xdiff: make diff3 the default conflictStyle

From: Felipe Contreras <felipe.contreras@gmail.com>
To: Sergey Organov <sorganov@gmail.com>, Junio C Hamano <gitster@pobox.com>
Cc: "Johannes Sixt" <j6t@kdbg.org>, "Jeff King" <peff@peff.net>,
	"Felipe Contreras" <felipe.contreras@gmail.com>,
	"David Aguilar" <davvid@gmail.com>,
	"Bagas Sanjaya" <bagasdotme@gmail.com>,
	"Elijah Newren" <newren@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Denton Liu" <liu.denton@gmail.com>,
	git@vger.kernel.org
Subject: Re: [PATCH 7/7] xdiff: make diff3 the default conflictStyle
Date: Fri, 11 Jun 2021 10:32:21 -0500	[thread overview]
Message-ID: <60c38205cdbf8_3ad92084@natae.notmuch> (raw)
In-Reply-To: <875yykipq2.fsf@osv.gnss.ru>

Sergey Organov wrote:
> Junio C Hamano <gitster@pobox.com> writes:

> > I notice that "git merge --help" tells what each part separated by
> > conflict markers mean in both output styles, but does not make a
> > specific recommendation as to which one to use in what situation,
> > and it might benefit a few additional sentences to help readers
> > based on what you said, i.e. the "RCS merge" style that hides the
> > original is succinct and easier to work with when you are familiar
> > with what both sides did, while a more verbose "diff3" style helps
> > when you are unfamiliar with what one side (or both sides) did.
> 
> I don't get it. Once you have diff3 output, and you want something
> simpler, you just kill the inner section, right? RCS merge output style
> is simply inferior.

The issue here is not a mere inner section, it's a nested inner section
due to a recursive merge.

Personally I've never encountered these in real life, but you can
trigger them with the following synthetic example, and the output with
diff3 is:

--- a/content
+++ b/content
@@@ -1,1 -1,1 +1,13 @@@
++<<<<<<< HEAD
 +D
++||||||| merged common ancestors
++<<<<<<<<< Temporary merge branch 1
++B
++||||||||| 2c9519d
++1
++=========
++A
++>>>>>>>>> Temporary merge branch 2
++=======
+ C
++>>>>>>> C

While with merge is:

--- a/content
+++ b/content
@@@ -1,1 -1,1 +1,5 @@@
++<<<<<<< HEAD
 +D
++=======
+ C
++>>>>>>> C

I don't see why diff3 triggers the output of this temporary merge, that
is a bug in my book.

I would expect the output to simply be:

--- a/content
+++ b/content
@@@ -1,1 -1,1 +1,13 @@@
++<<<<<<< HEAD
 +D
++||||||| 2c9519d
++1
++=======
+ C
++>>>>>>> C

Cheers.

  git init repo &&
  cd repo &&

  echo 1 > content &&
  git add content &&
  git commit -m 1 content &&

  git checkout -b A master &&
  echo A > content &&
  git commit -m A content &&

  git checkout -b B master &&
  echo B > content &&
  git commit -m B content &&

  git checkout -b C A &&
  git rev-parse B >.git/MERGE_HEAD &&
  echo C > content &&
  git commit -m C -a &&

  git checkout -b D A &&
  git rev-parse B >.git/MERGE_HEAD &&
  echo D > content &&
  git commit -m D -a &&

  git -c merge.conflictstyle=diff3 merge -m final C &&
  cat content

-- 
Felipe Contreras
