On Sat, Jan 28, 2017 at 6:28 AM, Jeff King <p...@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).
- Sylvie
