git says "No files need merging" immediately after a merge conflict

Question

For example

> git cherry-pick <hash>
...
error: could not apply <hash>...
Resolved '<file>' using previous resolution.
> git mergetool
No files need merging
> git status
...
Unmerged paths:
  (use "git add <file>..." to mark resolution)

    both modified: <file>

"both modified" and "No files need merging"? liar!

Answer 1

I'm guessing the problem is somehow git rerere got hold of a bad merge. I think this often happens when meld doesn't quite realise I've pressed Ctrl-S and it records conflict markers into the resolution. Why git still says "both modified" and doesn't allow mergetool to run I don't know. Anyway the fix is as follows:

git rerere forget <file>
git checkout -m <file>
git mergetool

I wish git checkout -m would imply git rerere forget or git status was more explicit. Would have saved a whole bunch of time.

Answer 2

You are correct about git rerere, and the clue is this line:

Resolved '<file>' using previous resolution.

I was not aware of this before (in part because I never actually use git mergetool), but:

Why git still says "both modified" and doesn't allow mergetool to run I don't know.

This is because git mergetool uses git rerere remaining to figure out which files to merge.

I re-created your merge conflict with a reused resolution:

$ echo base version > file
$ git config rerere.enabled true
$ git add file && git commit -m 'create base'
[master 8e7a009] create base
 1 file changed, 1 insertion(+)
 create mode 100644 file
$ git checkout -b branch
Switched to a new branch 'branch'
$ echo 'branch conflict' >> file
$ git add file && git commit -m 'enter branch conflict'
[branch 6661ab7] enter branch conflict
 1 file changed, 1 insertion(+)
$ git checkout -b br2 master
Switched to a new branch 'br2'
$ echo 'different, hence conflict' >> file
$ git add file && git commit -m 'create br2 conflict'
[br2 9684589] create br2 conflict
 1 file changed, 1 insertion(+)
$ git merge branch
Auto-merging file
CONFLICT (content): Merge conflict in file
Recorded preimage for 'file'
Automatic merge failed; fix conflicts and then commit the result.

Note the second-to-last line, which indicates that whatever I do now to resolve the conflict, Git will save the result.

$ vim file

Here, I resolved the conflict (in a way that's harder to show, because of full-screen editing).

$ git add file && git commit -m resolution
Recorded resolution for 'file'.
[br2 8b42a26] resolution

Committing recorded the resolution. I now discarded the merge, then ran it again:

$ git reset --hard HEAD^
HEAD is now at 9684589 create br2 conflict
$ git merge branch
Auto-merging file
CONFLICT (content): Merge conflict in file
Resolved 'file' using previous resolution.
Automatic merge failed; fix conflicts and then commit the result.

Note the "using previous resolution" line.

The status is now that there are unmerged paths:

$ git status
On branch br2
You have unmerged paths.
  (fix conflicts and run "git commit")
  (use "git merge --abort" to abort the merge)

Unmerged paths:
  (use "git add <file>..." to mark resolution)

        both modified:   file

no changes added to commit (use "git add" and/or "git commit -a")

and git ls-files --stage confirms that there are three versions of file file:

$ git ls-files --stage
100644 eb2222a53126bfe165c615e816f5ba268f1e628f 0       README
100644 4b9049d6a70d93a7af91b4f6b741b88ba1f1838a 1       file
100644 5974ab850c831f806f950321b08391ccea97efcf 2       file
100644 7a77704a9d365c790f5a24fe87515b8df0b7e91b 3       file

The contents use my saved resolution:

$ cat file
base version
resolved in br2

Running git mergetool with shell tracing enabled reveals the secret:

+ USAGE='[--tool=tool] [--tool-help] [-y|--no-prompt|--prompt] [-O<orderfile>] [file to merge] ...'
+ SUBDIRECTORY_OK=Yes
[mass snippage]
+ git rerere remaining
+ set --
+ test 0 -eq 0
+ print_noop_and_exit
+ echo 'No files need merging'
No files need merging
+ exit 0

It's now up to me to do something, such as your trick of git rerere forget:

$ git rerere forget file
Updated preimage for 'file'
Forgot resolution for file
$ git checkout -m file
$ cat file
base version
<<<<<<< ours
different, hence conflict
||||||| base
=======
branch conflict
>>>>>>> theirs

Note that when I resolve again, add, and commit, the new resolution is recorded:

$ git add file
$ git commit -m 're-resolved'
Recorded resolution for 'file'.
[br2 00c94b1] re-resolved

(Of course, it's also possible to git config rerere.enabled false.)

Answer 3

I had the same outcome as you after having done a merge, then git reset --hard {commit-prior-to-merge} then re-doing the merge: "both modified" and "No files need merging".

In my case, I was happy with the resolutions stored by rerere, so all I needed to do was git add . and then to git commit the merge.

Apparently there is also a switch to git merge --rerere-autoupdate to avoid this extra step:

After the rerere mechanism reuses a recorded resolution on the current conflict to update the files in the working tree, allow it to also update the index with the result of resolution

https://git-scm.com/docs/git-merge#Documentation/git-merge.txt---rerere-autoupdate