CODEWITHSUNDEEP
gitgit-mergegit-revert
Toms Mikoss
Toms Mikoss

Reputation: 9457

Re-doing a reverted merge in Git

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:

Git log output

Upvotes: 361

Views: 214137

Answers (10)

Harry
Harry

Reputation: 31

TL;DR

What commands to run (assuming you are creating a PR):

# Starting from main branch
git checkout -b new-fix-branch
git revert <commit-hash-of-revert>
git reset --soft <commit-hash-of-commit-one-before-the-revert-of-revert>
# Gain peace of mind as you check everything is there.
git add -A
git commit -m "fix: brought back old changes"
# Congrats, syncing your branch will no longer remove the reverted changes.

Explanation

  • Revert the revert. This creates a new commit which gives you back all your reverted changes.
  • Reset --soft to before reverting the revert. This puts all the changes you've gotten back into your working tree locally as unstaged files.
  • Stage and commit changes again. As there is no revert associated with your changes anymore thanks to the reset, git thinks these changes are new and you can sync to your hearts content.

Pros

  • Every step can be a PR if you do not have permissions to do stuff on main/develop/prod etc.
  • No scary risks of losing code
  • Any amount of commits can happen between any step
  • Can see all your changes before final step for peace of mind

Cons

  • At least 8 commands total (checkout -b, revert, reset --soft, add, commit, push, merge, push).

Long Visual Explanation:

Check-out to "main-branch" after a revert two commits ago:

main-branch      ---o---o---(merge)---(revert)---o---(cool)*
                            /                      
feature-branch      ---o---o

o = commits
(name) = named commits for clarity
* = head

Create new branch "new-fix-branch":

main-branch      ---o---o---(merge)---(revert)---o---(cool)
                            /                           |
feature-branch      ---o---o                            |
new-fix-branch                                          *

"git revert <hash-of-revert-commit>" giving us the old changes back:

main-branch      ---o---o---(merge)---(revert)---o---(cool)
                            /                             \
feature-branch      ---o---o                               \
new-fix-branch                                             (X-revert)*

X-revert = changes from original feature-branch, marked as revert in git

"git reset --soft <cool-commit-hash>" gives all the changes but un-committed & un-staged:

main-branch      ---o---o---(merge)---(revert)---o---(cool)
                            /                           |
feature-branch      ---o---o                            |
new-fix-branch                                          X*

X = changes from original feature-branch

stage & commit entire working tree, git now thinks changes are new:

main-branch      ---o---o---(merge)---(revert)---o---(cool)
                            /                             \ 
feature-branch      ---o---o                               \ 
new-fix-branch                                              (X)*

Fix & commit problem that caused issue (optional step), then merge:

main-branch      ---o---o---(merge)---(revert)---o---(cool)          (really-cool-merge)*
                            /                             \               / 
feature-branch      ---o---o                               \             /
new-fix-branch                                              (X)---(optional-fix)

No longer an issue where reverted changes disappear:

Sync branch with old reverted changes with main-branch:

main-branch      ---o---(merge)---(revert)---o---(cool)---o---o---o
                        /                             \            \ 
feature-branch      ---o                               \            \ 
new-fix-branch                                          (X)---(get-latest)*

Upvotes: 1

Condemateguadua
Condemateguadua

Reputation: 616

If needed you can create a new branch and cherry-pick the commits (separate the commit SH with space so it will be one command) from the reverted pull request, that way you'll be able to merge again with out losing files/changes.

Upvotes: 1

J-16 SDiZ
J-16 SDiZ

Reputation: 26930

You have to "revert the revert". Depending on you how did the original revert, 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.

Upvotes: 240

Richard
Richard

Reputation: 2635

To revert a revert in GIT:

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

Upvotes: 29

Misha Mostov
Misha Mostov

Reputation: 21

  1. create new branch at commit prior to the original merge - call it it 'develop-base'
  2. perform interactive rebase of 'develop' on top of 'develop-base' (even though it's already on top). During interactive rebase, you'll have the opportunity to remove both the merge commit, and the commit that reversed the merge, i.e. remove both events from git history

At this point you'll have a clean 'develop' branch to which you can merge your feature brach as you regularly do.

Upvotes: 2

Venkataraman R
Venkataraman R

Reputation: 13009

I would suggest you to follow below steps to revert a revert, say SHA1. 

git checkout develop #go to develop branch
git pull             #get the latest from remote/develop branch
git branch users/yourname/revertOfSHA1 #having HEAD referring to develop
git checkout users/yourname/revertOfSHA1 #checkout the newly created branch
git log --oneline --graph --decorate #find the SHA of the revert in the history, say SHA1
git revert SHA1
git push --set-upstream origin users/yourname/revertOfSHA1 #push the changes to remote

Now create PR for the branch users/yourname/revertOfSHA1

Upvotes: 3

Claire
Claire

Reputation: 3785

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.

Upvotes: 2

Sam Dufel
Sam Dufel

Reputation: 17608

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.

Upvotes: 60

Maksim Kotlyar
Maksim Kotlyar

Reputation: 3957

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.

Upvotes: 87

knweiss
knweiss

Reputation: 471

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).

Upvotes: 5

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