Octopus merge

Octopus merge

[Claudia.Ignat]

Hello,

I have problems on understanding the results of octopus merge in the 
following scenario.

Workspaces ws2, ws3, ws4 and ws5 are clones of the workspace ws1. 
Suppose the current workspace is ws3 and some changes are done in 
parallel in all these 4 workspaces. Further suppose that changes of ws2 
and ws3 are conflicting, while the changes in ws4 and ws5 are neither 
conflicting between them nor with ws2 and ws3.

While I am in the current workspace ws3 I perform the merge

git merge ws4 ws2 ws5

Obviously I obtain conflicts between changes in ws3 and ws2 which I fix 
manually and afterwards I commit the new version of ws3. It seems 
strange that the commit object has only one parent, while including the 
changes of ws4.

If instead I perform

git merge ws4 ws5 ws2

and fix manually the conflicts and performing the commit, the commit 
object has 4 parents (ws3,ws4,ws5 and ws2).

I provide below the script illustrating the first scenario:

# !/bin/bash
TEST_NAME="TP1" # name of the working directory
rm -rf ${TEST_NAME} # cleaning working directory
mkdir -p ${TEST_NAME}
cd ${TEST_NAME}

# initialising initial git workspace
mkdir ws1
cd ws1
git init

# adding a file to ws1
# commit changes
echo -e -n "1\n2\n3\n4\n5\n" > file.txt
git add file.txt
git commit -m "ws1 | add 12345"
cd ..

# cloning three times ws1 (as ws2, ws3 and ws4)
git clone ws1 ws2
git clone ws1 ws3
git clone ws1 ws4
git clone ws1 ws5

# updating file.txt in ws2 (insert X at line 3, then write and quit 'ed')
# commit changes
cd ws2
echo -e "3i\nX\n.\nw\nq\n" | ed file.txt
git add file.txt
git commit -m "ws2 | insert 12X345"
cd ..


# updating file.txt in ws3 (insert Y at line 3, then write and quit 'ed')
# commit changes
cd ws3
echo -e "3i\nY\n.\nw\nq\n" | ed file.txt
git add file.txt
git commit -m "ws3 | insert 12Y345"
cd ..

cd ws4
echo -e -n "U1\n2\n3\n4\n5\n" >  u.txt
git add u.txt
git commit -m "ws4 | add u.txt"
cd ..

cd ws5
echo -e -n "W1\n2\n3\n4\n5\n" > w.txt
git add w.txt
git commit -m "ws5 | add w.txt"
cd ..

# ws3 pull from ws2 ws4 ws5
cd ws3
git remote add bws2 ../ws2
git remote add bws4 ../ws4
git remote add bws5 ../ws5
git fetch bws2
git fetch bws4
git fetch bws5
git merge bws4/master bws2/master bws5/master
cd ..

# resolve conflict in ws3
cd ws3
echo -e '7d\n5d\n3d\n.\nw\nq\n' | ed file.txt
git add file.txt
git commit -m "ws3| in file.txt solve conflict (kept XY) "
cd ..

Could somebody please explain me these results? I suspect a bug in 
octopus merge. I am using version 1.6.3.3 of git.
Thank you in advance.

Best regards,
Claudia Ignat

Re: Octopus merge

[Thomas Rast]

Claudia.Ignat@loria.fr wrote:
> 
> While I am in the current workspace ws3 I perform the merge
> 
> git merge ws4 ws2 ws5
> 
> Obviously I obtain conflicts between changes in ws3 and ws2 which I fix 
> manually and afterwards I commit the new version of ws3.

In doing that last step, you ignored the crucial bit of advice printed
by the octopus merge:

  Automated merge did not work.
  Should not be doing an Octopus.		# <<--
  Merge with strategy octopus failed.

You should simply merge and resolve them separately, not least of all
because in doing so, 'git show $merge' will display your merge
resolutions.  An octopus would tangle all resolutions into a single
commit.

AFAIK the only thing that can be considered a bug here is that the
octopus strategy leaves your worktree in need of 'reset --hard'.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch

Re: Octopus merge

[Michael J Gruber]

Claudia.Ignat@loria.fr venit, vidit, dixit 26.11.2009 16:56:
> # !/bin/bash
> TEST_NAME="TP1" # name of the working directory
> rm -rf ${TEST_NAME} # cleaning working directory
> mkdir -p ${TEST_NAME}
> cd ${TEST_NAME}
> 
> # initialising initial git workspace
> mkdir ws1
> cd ws1
> git init
> 
> # adding a file to ws1
> # commit changes
> echo -e -n "1\n2\n3\n4\n5\n" > file.txt
> git add file.txt
> git commit -m "ws1 | add 12345"
> cd ..
> 
> # cloning three times ws1 (as ws2, ws3 and ws4)
> git clone ws1 ws2
> git clone ws1 ws3
> git clone ws1 ws4
> git clone ws1 ws5
> 
> # updating file.txt in ws2 (insert X at line 3, then write and quit 'ed')
> # commit changes
> cd ws2
> echo -e "3i\nX\n.\nw\nq\n" | ed file.txt
> git add file.txt
> git commit -m "ws2 | insert 12X345"
> cd ..
> 
> 
> # updating file.txt in ws3 (insert Y at line 3, then write and quit 'ed')
> # commit changes
> cd ws3
> echo -e "3i\nY\n.\nw\nq\n" | ed file.txt
> git add file.txt
> git commit -m "ws3 | insert 12Y345"
> cd ..
> 
> cd ws4
> echo -e -n "U1\n2\n3\n4\n5\n" >  u.txt
> git add u.txt
> git commit -m "ws4 | add u.txt"
> cd ..
> 
> cd ws5
> echo -e -n "W1\n2\n3\n4\n5\n" > w.txt
> git add w.txt
> git commit -m "ws5 | add w.txt"
> cd ..
> 
> # ws3 pull from ws2 ws4 ws5
> cd ws3
> git remote add bws2 ../ws2
> git remote add bws4 ../ws4
> git remote add bws5 ../ws5
> git fetch bws2
> git fetch bws4
> git fetch bws5
> git merge bws4/master bws2/master bws5/master
> cd ..
> 
> # resolve conflict in ws3
> cd ws3

First of all, thanks for the clear description and test case!

The octopus strategy cannot do merges which need manual resolution. Or
so the doc says. After trying the merge with 4 2 5, Git tells you:

Trying simple merge with 7ff9b5bd514cb600bac935ebd40eae366bba7d19
Trying simple merge with 6872cd350154743d59cb4d313cbdb122ac43e537
Simple merge did not work, trying automatic merge.
Auto-merging file.txt
ERROR: content conflict in file.txt
fatal: merge program failed
Automated merge did not work.
Should not be doing an Octopus.
Merge with strategy octopus failed.

That is, it aborts the merge completely. If you "resolve" it and commit
it's simply a commit that you make.

If, instead, you merge 4 5 2, Git tells you:

Trying simple merge with e4f78f6905bed39bcd96790a4f63e138a455a445
Trying simple merge with 14c1f2a70767334df5d6d3120631752564094699
Trying simple merge with 8540a039d3fc964d097d4f037357668441d1d4f5
Simple merge did not work, trying automatic merge.
Auto-merging file.txt
ERROR: content conflict in file.txt
fatal: merge program failed
Automatic merge failed; fix conflicts and then commit the result.

Admittedly this looks fatal also, but the last line tells you that the
actual merge process is not aborted yet. If you resolve the conflict and
commit without -m you even see the prepared commit message.

So, octopus can deal with manual conflict resolution if the conflicts
appear in the last step only. That is the difference between the two cases.

Now, in the first case the aborted merge leaves some traces in the index
as well as in the worktree. I'm not sure that is how it's supposed to be.

Cheers,
Michael

Re: Octopus merge

[Claudia.Ignat]

Michael and Thomas, thank you for your explanations. The fact that in 
some cases octopus merge fails, but changes of the first merges subparts 
of octopus merge are included in the worktree rests a dilemma.

Further, I have noticed that for the same conflicting changes the 
conflict messages (referring to conflict types) received in the case of 
an octopus merge are not the same as the conflict messages received for 
the corresponding sequential merges.

I slightly changed the scenario I described in my previous message.

Workspaces ws2, ws3 and ws4 are clones of the workspace ws1. Suppose the 
current workspace is ws3 and some changes are done in parallel in all 
these 3 workspaces. Changes of ws2 and ws3 are conflicting: both modify 
the same line of file file1.txt to different values and they rename the 
same file file2.txt to fileWS2.txt and fileWS3.txt respectively. Changes 
in ws4 are not conflicting with changes in ws2 and ws3.

While I am in the current workspace ws3 I perform the merge

git merge ws2

and content conflict in file1.txt as well as rename/rename conflict are 
signaled.

If instead I perform the merge

git merge ws4 ws2

only the content conflict  in file1.txt is raised, while the conflict 
rename/rename of file2.txt is not mentioned.

The script for the second mentioned scenario is given below.

Do you think this should be the normal behavior of octopus merge?

Thanks.
Cheers,
Claudia

# !/bin/bash

TEST_NAME="TP1" # name of the working directory
rm -rf ${TEST_NAME} # cleaning working directory
mkdir -p ${TEST_NAME}
cd ${TEST_NAME}

# initialising initial git workspace
mkdir ws1
cd ws1
git init

# adding 2 files to ws1
# commit changes
echo -e -n "1\n2\n3\n4\n5\n" > file1.txt
echo -e -n "a\nb\nc\nd\ne\n" > file2.txt
git add file1.txt file2.txt
git commit -m "ws1 | add 12345 in file1.txt; add abcde in file2.txt"
cd ..

# cloning three times ws1 (as ws2, ws3 and ws4)
git clone ws1 ws2
git clone ws1 ws3
git clone ws1 ws4

# updating file1.txt in ws2 (insert X at line 3, then write and quit 'ed')
# rename file2.txt to fileWS2.txt
# commit changes
cd ws2
echo -e "3i\nX\n.\nw\nq\n" | ed file1.txt
git add file1.txt
git mv file2.txt fileWS2.txt
git commit -m "ws2 | insert 12X345 in file1.txt; rename file2.txt to 
fileWS2.txt"
cd ..


# updating file1.txt in ws3 (insert Y at line 3, then write and quit 'ed')
# rename file2.txt to fileWS3.txt
# commit changes
cd ws3
echo -e "3i\nY\n.\nw\nq\n" | ed file1.txt
git add file1.txt
git mv file2.txt fileWS3.txt
git commit -m "ws3 | insert 12Y345 in file1.txt; rename file2.txt to 
fileWS3.txt"
cd ..

# add file u.txt in ws4
cd ws4
echo -e -n "U1\n2\n3\n4\n5\n" >  u.txt
git add u.txt
git commit -m "ws4 | add u.txt"
cd ..

# ws3 pull from ws2 ws4
cd ws3
git remote add bws2 ../ws2
git remote add bws4 ../ws4
git fetch bws2
git fetch bws4
git merge bws4/master bws2/master
cd ..



Michael J Gruber wrote:
> Claudia.Ignat@loria.fr venit, vidit, dixit 26.11.2009 16:56:
>> # !/bin/bash
>> TEST_NAME="TP1" # name of the working directory
>> rm -rf ${TEST_NAME} # cleaning working directory
>> mkdir -p ${TEST_NAME}
>> cd ${TEST_NAME}
>>
>> # initialising initial git workspace
>> mkdir ws1
>> cd ws1
>> git init
>>
>> # adding a file to ws1
>> # commit changes
>> echo -e -n "1\n2\n3\n4\n5\n" > file.txt
>> git add file.txt
>> git commit -m "ws1 | add 12345"
>> cd ..
>>
>> # cloning three times ws1 (as ws2, ws3 and ws4)
>> git clone ws1 ws2
>> git clone ws1 ws3
>> git clone ws1 ws4
>> git clone ws1 ws5
>>
>> # updating file.txt in ws2 (insert X at line 3, then write and quit 'ed')
>> # commit changes
>> cd ws2
>> echo -e "3i\nX\n.\nw\nq\n" | ed file.txt
>> git add file.txt
>> git commit -m "ws2 | insert 12X345"
>> cd ..
>>
>>
>> # updating file.txt in ws3 (insert Y at line 3, then write and quit 'ed')
>> # commit changes
>> cd ws3
>> echo -e "3i\nY\n.\nw\nq\n" | ed file.txt
>> git add file.txt
>> git commit -m "ws3 | insert 12Y345"
>> cd ..
>>
>> cd ws4
>> echo -e -n "U1\n2\n3\n4\n5\n" >  u.txt
>> git add u.txt
>> git commit -m "ws4 | add u.txt"
>> cd ..
>>
>> cd ws5
>> echo -e -n "W1\n2\n3\n4\n5\n" > w.txt
>> git add w.txt
>> git commit -m "ws5 | add w.txt"
>> cd ..
>>
>> # ws3 pull from ws2 ws4 ws5
>> cd ws3
>> git remote add bws2 ../ws2
>> git remote add bws4 ../ws4
>> git remote add bws5 ../ws5
>> git fetch bws2
>> git fetch bws4
>> git fetch bws5
>> git merge bws4/master bws2/master bws5/master
>> cd ..
>>
>> # resolve conflict in ws3
>> cd ws3
> 
> First of all, thanks for the clear description and test case!
> 
> The octopus strategy cannot do merges which need manual resolution. Or
> so the doc says. After trying the merge with 4 2 5, Git tells you:
> 
> Trying simple merge with 7ff9b5bd514cb600bac935ebd40eae366bba7d19
> Trying simple merge with 6872cd350154743d59cb4d313cbdb122ac43e537
> Simple merge did not work, trying automatic merge.
> Auto-merging file.txt
> ERROR: content conflict in file.txt
> fatal: merge program failed
> Automated merge did not work.
> Should not be doing an Octopus.
> Merge with strategy octopus failed.
> 
> That is, it aborts the merge completely. If you "resolve" it and commit
> it's simply a commit that you make.
> 
> If, instead, you merge 4 5 2, Git tells you:
> 
> Trying simple merge with e4f78f6905bed39bcd96790a4f63e138a455a445
> Trying simple merge with 14c1f2a70767334df5d6d3120631752564094699
> Trying simple merge with 8540a039d3fc964d097d4f037357668441d1d4f5
> Simple merge did not work, trying automatic merge.
> Auto-merging file.txt
> ERROR: content conflict in file.txt
> fatal: merge program failed
> Automatic merge failed; fix conflicts and then commit the result.
> 
> Admittedly this looks fatal also, but the last line tells you that the
> actual merge process is not aborted yet. If you resolve the conflict and
> commit without -m you even see the prepared commit message.
> 
> So, octopus can deal with manual conflict resolution if the conflicts
> appear in the last step only. That is the difference between the two cases.
> 
> Now, in the first case the aborted merge leaves some traces in the index
> as well as in the worktree. I'm not sure that is how it's supposed to be.
> 
> Cheers,
> Michael