Re: show all merge conflicts

[Michael J Gruber <git@drmicha.warpmail.net>]

G. Sylvie Davies venit, vidit, dixit 29.01.2017 07:45:
> On Sat, Jan 28, 2017 at 6:28 AM, Jeff King <peff@peff.net> wrote:
>> On Fri, Jan 27, 2017 at 09:42:41PM -0800, G. Sylvie Davies wrote:
>>
>>> Aside from the usual "git log -cc", I think this should work (replace
>>> HEAD with whichever commit you are analyzing):
>>>
>>> git diff --name-only HEAD^2...HEAD^1 > m1
>>> git diff --name-only HEAD^1...HEAD^2 > b1
>>> git diff --name-only HEAD^1..HEAD    > m2
>>> git diff --name-only HEAD^2..HEAD    > b2
>>>
>>> If files listed between m1 and b2 differ, then the merge is dirty.
>>> Similarly for m2 and b1.
>>>
>>> More information here:
>>>
>>> http://stackoverflow.com/questions/27683077/how-do-you-detect-an-evil-merge-in-git/41356308#41356308
>>
>> I don't think that can reliably find evil merges, since it looks at the
>> file level. If you had one hunk resolved for "theirs" and one hunk for
>> "ours" in a given file, then the file will be listed in each diff,
>> whether it has evil hunks or not.
>>
> 
> Well, you have to do both.  Do "git show -c" to catch that one
> ("theirs" for one hunk, "ours" for the other, same file).
> 
> And then do that sequence of the 4 "git diff" commands to identify
> dirty merges where "theirs" or "ours" was applied to entire files, and
> thus not showing up in the "git show -c".
> 
>> I don't think this is just about evil merges, though. For instance,
>> try:
>>
>>   seq 1 10 >file
>>   git add file
>>   git commit -m base
>>
>>   sed s/4/master/ <file >tmp && mv tmp file
>>   git commit -am master
>>
>>   git checkout -b other HEAD^
>>   sed s/4/other/ <file >tmp && mv tmp file
>>   git commit -am other
>>
>>   git merge master
>>   git checkout --ours file
>>   git commit -am merged
>>
>>   merge=$(git rev-parse HEAD)
>>
>> The question is: were there conflicts in $merge, and how were they
>> resolved?
>>
>> That isn't an evil merge, but there's still something interesting to
>> show that "git log --cc" won't display.
>>
>> Replaying the merge like:
>>
>>   git checkout $merge^1
>>   git merge $merge^2
>>   git diff -R $merge
>>
>> shows you the patch to go from the conflict state to the final one.
>>
> 
> I know the stackoverflow question asks "how to detect evil merges",
> and I go along with that in my answer.  But honestly I prefer to call
> them dirty rather than evil, and by "dirty" I just mean merges that
> did not resolve cleanly via "git merge", and had some form of user
> intervention, be it conflict resolution, or other strange things.
> 
> The trick I propose with the sequence of 4 "git diff" commands
> identifies that merge from your example as dirty:
> 
> $ cat b1 m2
> file
> 
> $ cat b2 m1
> file
> file
> 
> The trick doesn't really tell you much except that the merge is dirty.
> If you notice that the "m2" file is empty, I think that's one way to
> realize that master's edit was dropped, and therefore "other" won.
> 
> Maybe it even merged cleanly but someone did a "git commit --amend" to
> make it the merge dirty after the fact.
> 
> I do like your approach, it's very simple and reliable.  But in my
> situation I'm writing pre-receive hooks for bare repos, so I don't
> think I can actually do "git merge"!
> 
> I think my suggestion would work for OP, as long as they also run "git
> show -c" alongside it.   (And your suggestion would work, too, of
> course).

If you're curious, I kept rebasing Thomas' remerge-diff (on top of our
next) so far. You can find it at

https://github.com/mjg/git/tree/remerge-diff

if you're interested. I don't know what problems were found back then,
or what it would take to get this in-tree now.

Michael