Merging adjacent deleted lines?

Merging adjacent deleted lines?

[Jonathan del Strother]

Say I have a file that started out with the following content :

line1
line2
line3
line4


I create a branch, which deletes line2.  Someone else's branch deletes line 3.

When I merge those two branches, the conflict looks like :

line1
<<<<<<< HEAD:lines
line3
=======
line2
>>>>>>> SomeoneElse:lines
line4



Which in my cursory overview, looked an awful lot like the obvious
merge resolution ought to be

line1
line3
line4

After all - I know I want to delete line 2, and wasn't aware of the
other person deleting line 3.

It was only later that we discovered that the merge was broken and
both lines should have been deleted.  Thinking about it, I guess that
the conflict if the other branch _hadn't_ deleted line 3 would have
looked something like

line1
<<<<<<< HEAD:lines
=======
line2
>>>>>>> SomeoneElse:lines
line3
line4

 - which wouldn't have resulted in a conflict anyway.


So, it looks like I need to be way more careful when merging
conflicts.  Which leads me to - what tools do you use when studying
conflicts like that?  git blame seems the obvious one, for getting the
context of each deletion, but it seems like I need to run it once as
git blame HEAD lines, and once as git blame MERGE_HEAD lines.  Is
there something a little more integrated for comparing the origin of
each change from both merge branches simultaneously?

Would welcome any thoughts on how you guys approach conflict-resolution
-Jon

Re: Merging adjacent deleted lines?

[Robin Rosenberg]

onsdag 21 januari 2009 20:20:50 skrev Jonathan del Strother:
[...]
> So, it looks like I need to be way more careful when merging
> conflicts.  Which leads me to - what tools do you use when studying
> conflicts like that?  git blame seems the obvious one, for getting the
> context of each deletion, but it seems like I need to run it once as
> git blame HEAD lines, and once as git blame MERGE_HEAD lines.  Is
> there something a little more integrated for comparing the origin of
> each change from both merge branches simultaneously?
> 
> Would welcome any thoughts on how you guys approach conflict-resolution

I think you've illustrated a case for graphical merge resolution tools, i.e.
run git mergetool to help resolve the conlicts. It will run a graphical tool
for you.

The list seems to be: kdiff3 kdiff3 tkdiff xxdiff meld gvimdiff opendiff emerge vimdiff

None of the tools can run blame in the merge tool also. That would be nice.

-- robin

Re: Merging adjacent deleted lines?

[Junio C Hamano]

Jonathan del Strother <maillist@steelskies.com> writes:

> Say I have a file that started out with the following content :
>
> line1
> line2
> line3
> line4
>
>
> I create a branch, which deletes line2.  Someone else's branch deletes line 3.
>
> When I merge those two branches, the conflict looks like :
>
> line1
> <<<<<<< HEAD:lines
> line3
> =======
> line2
>>>>>>>> SomeoneElse:lines
> line4
>
>
>
> Which in my cursory overview, looked an awful lot like the obvious
> merge resolution ought to be
>
> line1
> line3
> line4

Why?  The obvious resolution would be:

    line1
    line4

as it is obvious that you do not want line2 and the other does not want
line3.

But that is only true if it is obvious to you.  When you cannot remember
what each side did since they forked, there are two ways you can use to
understand the history better without resorting to graphical merge tools.

  $ git log -p --merge <path>

which shows you the commits involved in the conflict, what they did, and
why they did what they did (of course, this assumes that your project
participant did their commits properly).

  $ git checkout --conflict=diff3 <path>

This will add an extra block to the conflicted output to show the common
ancestor's version, after showing yours.  The conflicts left in <path>
would look like this:

    line1
    <<<<<<< ours
    line3
    |||||||
    line2
    line3
    =======
    line2
    >>>>>>> theirs
    line4

which may make it clearer that you deleted line2 and they deleted line3.

Re: Merging adjacent deleted lines?

[Jonathan del Strother]

On Wed, Jan 21, 2009 at 7:49 PM, Robin Rosenberg
<robin.rosenberg.lists@dewire.com> wrote:
> onsdag 21 januari 2009 20:20:50 skrev Jonathan del Strother:
> [...]
> I think you've illustrated a case for graphical merge resolution tools, i.e.
> run git mergetool to help resolve the conlicts. It will run a graphical tool
> for you.
>

Mmm.  I use opendiff, which is generally ok, but in this case produced
a merge looking like this :
http://pastie.org/paste/asset/367587/Picture_6.png
Which, in my mind, isn't any clearer about the fact that both lines
ought to be deleted than the text conflict markers are.  Do any of the
other graphical tools present conflicts like that differently?


On Wed, Jan 21, 2009 at 9:08 PM, Junio C Hamano <gitster@pobox.com> wrote:
> But that is only true if it is obvious to you.  When you cannot remember
> what each side did since they forked, there are two ways you can use to
> understand the history better without resorting to graphical merge tools.
>
>  $ git log -p --merge <path>
>

Ahh, that's very helpful - thanks.

Re: Merging adjacent deleted lines?

[Robin Rosenberg]

torsdag 22 januari 2009 11:57:41 skrev Jonathan del Strother:
> On Wed, Jan 21, 2009 at 7:49 PM, Robin Rosenberg
> <robin.rosenberg.lists@dewire.com> wrote:
> > onsdag 21 januari 2009 20:20:50 skrev Jonathan del Strother:
> > [...]
> > I think you've illustrated a case for graphical merge resolution tools, i.e.
> > run git mergetool to help resolve the conlicts. It will run a graphical tool
> > for you.
> >
> 
> Mmm.  I use opendiff, which is generally ok, but in this case produced
> a merge looking like this :
> http://pastie.org/paste/asset/367587/Picture_6.png
> Which, in my mind, isn't any clearer about the fact that both lines
> ought to be deleted than the text conflict markers are.  Do any of the
> other graphical tools present conflicts like that differently?

Try a three-way merge tool instead like, e.g. xxdiff.

-- robin

Re: Merging adjacent deleted lines?

[Jay Soffian]

On Thu, Jan 22, 2009 at 3:13 PM, Robin Rosenberg
<robin.rosenberg.lists@dewire.com> wrote:
> torsdag 22 januari 2009 11:57:41 skrev Jonathan del Strother:
>> Mmm.  I use opendiff, which is generally ok, but in this case produced
>> a merge looking like this :
>>
>> http://pastie.org/paste/asset/367587/Picture_6.png
>>
>> Which, in my mind, isn't any clearer about the fact that both lines
>> ought to be deleted than the text conflict markers are.  Do any of the
>> other graphical tools present conflicts like that differently?
>
> Try a three-way merge tool instead like, e.g. xxdiff.

opendiff (aka FileMerge) *is* a three-way merge tool. If the
screenshot above is not clear, I'm not sure what would be. The left
pane shows your copy of the file with only line1, line3, and line4.
The right pane shows the other copy, with only line1, line2, and
line4.

The lower pane shows the merge resolution, which currently has the
single conflict highlighted, and is being resolved toward the right.
You can use the Action drop down menu to resolve the conflict one of
five ways: left, right, both (left first), both (right first),
neither. You've currently got "right" selected. The appropriate
resolution is "neither", which keeps neither line3 from the left, nor
line2 from the right.

Shrug.

j.

Re: Merging adjacent deleted lines?

[Robin Rosenberg]

fredag 23 januari 2009 08:18:15 skrev Jay Soffian:
> On Thu, Jan 22, 2009 at 3:13 PM, Robin Rosenberg
> <robin.rosenberg.lists@dewire.com> wrote:
[...]
> > Try a three-way merge tool instead like, e.g. xxdiff.
> 
> opendiff (aka FileMerge) *is* a three-way merge tool. If the
> screenshot above is not clear, I'm not sure what would be. The left
> pane shows your copy of the file with only line1, line3, and line4.
> The right pane shows the other copy, with only line1, line2, and
> line4.

Where's the ancestor? I'm used to having four panes for doing three-way 
merges, but your screenshot showed only three.

> 
> Shrug.

You have the option to ignore me....

-- robin

Re: Merging adjacent deleted lines?

[Jay Soffian]

On Fri, Jan 23, 2009 at 5:32 AM, Robin Rosenberg
<robin.rosenberg.lists@dewire.com> wrote:
> Where's the ancestor? I'm used to having four panes for doing three-way
> merges, but your screenshot showed only three.

I installed xxdiff to compare w/opendiff, meld, and vimdiff and I see
what you mean with xxdiff.

opendiff/meld/vimdiff don't show the ancestor directly, but they are
still using it in order to show how one version differs from the
ancestor in the left pane, and how the other version differs in the
right pane.

>> Shrug.
>
> You have the option to ignore me....

Doh, I meant only "I don't understand." My apologies.

j.

Re: Merging adjacent deleted lines?

[Jay Soffian]

On Fri, Jan 23, 2009 at 10:51 AM, Jay Soffian <jaysoffian@gmail.com> wrote:
> opendiff/meld/vimdiff don't show the ancestor directly, but they are
> still using it in order to show how one version differs from the
> ancestor in the left pane, and how the other version differs in the
> right pane.

Hmm, okay. I see that meld/vimdiff are apparently not doing a 3-way
merge. So I guess after all this, I don't have an explanation about
opendiff. It claims to do a 3-way diff and mergetool is passing it the
ancestor as an argument. Sorry for the confusion.

j.