Re: commit gone after merge - how to debug?

[Matthieu Moy <Matthieu.Moy@grenoble-inp.fr>]

[ Jumping back in time ]

Igor Lautar <igor.lautar@gmail.com> writes:

>> Try this:
>>
>> commit=<sha1 of your merge commit>
>> # Show diff with first parent:
>> git diff "$commit" "$commit"^1
>> # Show diff with second parent:
>> git diff "$commit" "$commit"^2
>
> Yes, change is shown in commit^2, but actual file after merge does not have it.

My commands had the wrong order. It should have been git diff
"$commit"^2 "$commit". So, it showed the reverse of the modification
introduced by the commit. If you see your change here, it means the
change was reverted by the merge.

My understanding of the situation up to now is:

M
|\
A C
|/
B

($commit = M, $commit^1 = A and $commit^2 = B)

Your file had a content (say, "old") at revision B. It changed content
(say, to "new") at revision C, and at some point. A did not change it so
it had the content "old". Then you merged, expected the merge commit M
to get content "new", and actually got "old".

So, your history looks like:

M (old)
| \
|  `---.
|       \
A (old)  C (new)
|       /
|  .---'
| /
|/
B (old)

and "git diff C M" shows the diff between new and old.

Something went wrong during the merge, I guess it used an ancestor (B
above) that had "new" as content. I don't see how this happened (rather
clearly, your history is more complex than my example above), but
"GIT_MERGE_VERBOSITY=5 git merge" will show you which common ancestor
was used, it may help.

What's possible is that someone had already merged the branch containing
"new", got conflicts, and resolved it in favor of "old" somewhere in the
history of your master branch.

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/