Re-doing a reverted merge in Git

问题:

I have run into a bit of a problem here: I had a problem-specific branch 28s in Git, that I merged in the general develop branch. Turns out I had done it too fast, so I used git-revert to undo the merge. Now, however, the time has come to merge 28s into develop, but git-merge command sees the original merge, and happily announces that all is well and branches have been already merged. What do I do now? Create a \'Revert \"Revert \"28s -> develop\"\" \' commit? Doesn\'t seem to be a good way to do it, but I can\'t imagine any other at the moment.

What the tree structure looks like:

回答1:

You have to \"revert the revert\". Depends on how did you revert that, it may not be as easy as it sounds. Look at the official document on this topic.

---o---o---o---M---x---x---W---x---Y
              /
      ---A---B-------------------C---D

to allow:

---o---o---o---M---x---x-------x-------*
              /                       /
      ---A---B-------------------C---D

But does it all work? Sure it does. You can revert a merge, and from a purely technical angle, git did it very naturally and had no real troubles.
It just considered it a change from \"state before merge\" to \"state after merge\", and that was it.
Nothing complicated, nothing odd, nothing really dangerous. Git will do it without even thinking about it.

So from a technical angle, there\'s nothing wrong with reverting a merge, but from a workflow angle it\'s something that you generally should try to avoid.

If at all possible, for example, if you find a problem that got merged into the main tree, rather than revert the merge, try really hard to:

• bisect the problem down into the branch you merged, and just fix it,
• or try to revert the individual commit that caused it.

Yes, it\'s more complex, and no, it\'s not always going to work (sometimes the answer is: \"oops, I really shouldn\'t have merged it, because it wasn\'t ready yet, and I really need to undo all of the merge\"). So then you really should revert the merge, but when you want to re-do the merge, you now need to do it by reverting the revert.

回答2:

Let\'s assume you have such history

---o---o---o---M---W---x-------x-------*
              /                      
      ---A---B

Where A, B failed commits and W - is revert of M

So before I start fixing found problems I do cherry-pick of W commit to my branch

git cherry-pick -x W

Then I revert W commit on my branch

git revert W 

After I can continue fixing.

The final history could look like:

---o---o---o---M---W---x-------x-------*
              /                       /     
      ---A---B---W---W`----------C---D

When I send a PR it will clearly shows that PR is undo revert and adds some new commits.

回答3:

To revert the revert without screwing up your workflow too much:

• Create a local trash copy of develop
• Revert the revert commit on the local copy of develop
• Merge that copy into your feature branch, and push your feature branch to your git server.

Your feature branch should now be able to be merged as normal when you\'re ready for it. The only downside here is that you\'ll a have a few extra merge/revert commits in your history.

回答4:

Instead of using git-revert you could have used this command in the devel branch to throw away (undo) the wrong merge commit (instead of just reverting it).

git checkout devel
git reset --hard COMMIT_BEFORE_WRONG_MERGE

This will also adjust the contents of the working directory accordingly. Be careful:

• Save your changes in the develop branch (since the wrong merge) because they too will be erased by the git-reset. All commits after the one you specify as the git reset argument will be gone!
• Also, don\'t do this if your changes were already pulled from other repositories because the reset will rewrite history.

I recommend to study the git-reset man-page carefully before trying this.

Now, after the reset you can re-apply your changes in devel and then do

git checkout devel
git merge 28s

This will be a real merge from 28s into devel like the initial one (which is now erased from git\'s history).

回答5:

I just found this post when facing the same problem. I find above wayyy to scary to do reset hards etc. I\'ll end up deleting something I don\'t want to, and won\'t be able to get it back.

Instead I checked out the commit I wanted the branch to go back to e.g. git checkout 123466t7632723. Then converted to a branch git checkout my-new-branch. I then deleted the branch I didn\'t want any more. Of course this will only work if you are able to throw away the branch you messed up.

回答6:

To revert a revert:

git revert <commit-hash-of-previous-revert>