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I would like to amend a merge commit which failed a unit test on our continuous integration server, but I don't want to leave a commit which fails tests in the history.

Since this commit was only used by the CI server (and would not have been pulled down by anyone else) I would like to fix up the merge and then --force push it to replace the existing failed merge commit.

My problem is, I can't work out how to easily get back to the state immediately before the original commit was made, so that I can fix the failing test, recommit the merge and then force push that change up.

I don't really want to have to redo the whole merge, since there are quite a few files with conflicts which had to be resolved and all but one was resolved successfully.

What I have tried so far

Attempt 1: git reset

My first attempt was to do a mixed reset back to the commit before the merge commit, fix the bug introduced by the merge and then recommit.

git reset HEAD^ # Fix the failing test git commit

Unfortunately this results in a non-merge commit which silently incorporates all of the branch changes - not really what I want. *8')

Attempt 2: reset, stash, merge & apply

I then attempted to use stash to save the changes I made during my first attempt to merge:

git reset HEAD^ git add . # Since there were untracked files git stash git merge branch git stash apply # Fails git add . git stash apply # Merged but with conflicts

Unfortunately when git stash apply attempts to merge my stashed changes with the existing conflicted merge files it fails with the error

Cannot apply to a dirty working tree, please stage your changes

If I dutifully make my working directory clean by using git add . then the git stash apply runs but now not only do I have conflicts, I have conflicts with conflicts in them and any files which should have been removed have been added back in.

Attempt 3: amend and/or rebase.

I tried the nice simple suggestion by qqx to just fix the problem and git commit --amend the original commit, but without actually going back to the mid-merge state you lose access to the merge tools.

Once I've committed, I lose the ability to run git mergetool {file} as it just returns with the error:

{file}: file does not need merging

When trying to fix up a merge conflict, I really like being able to see my base, left, right and current revisions all together using tools like kdiff3.

using rebase suffers the same issue.

Any hints on a workflow which could allow me to achieve my desired result would be appreciated.

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2 Answers 2

Reset to default
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Since you're just resetting the most recent commit it seems that you haven't done any other commits since the one that is problematic. Because of this you should be able to just fix the code, use git add on the changed files, then use git commit --amend to replace the existing merge commit. That will preserve the merge information.

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and even otherwise, resetting to the offending commit and then rebasing the other history on top of the amended version should work—untested though (git reflog is your friend if you lose track of what you actually want to have as your HEAD afterwards).
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git branch old_merge git checkout -b new_merge HEAD~ git merge branch

Would get you back into pending merge state, where you can use the normal merge tools. Since the old merge is saved as the old_merge branch you can also use git checkout old_merge {file} to use the choices that you made for a particular file on your previous attempt. Once you're done you can commit that as normal, then checkout the branch that you were previously working on and use git reset --hard new_merge to switch to using the new merge commit.

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Thanks for the help qqx, I'll try that out when I get back to work on Tuesday. I ended up using a combination of 2 and 3. A reset to the old head and a merge to get a kdiff3 window up with the file I wanted to re-merge, then a hard reset back to the merge commit, before fixing it up, quitting kdiff3 and amending the existing commit.

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