Undo git fast forward merge

Question

I have this situation : Working on some testBranch for some time and I wanted to sync with master so I did git checkout testBranch and git merge master/testBranch

So now my branch is synced with master but then I found out that I want to undo that merge and problem is that merge is done with fast forward and now my commit history is mixed with master commits and testBranch commits and I don't know how to revert to state before merge on my testBranch.

Thanks for any help

Keslie

Are commits merged from master/testBranch located at the tip of your testBranch or you've already managed to record several your own local commits on top of what has been merged? The way to recover heavily depends on this. – Emlynne

Any reason you're not satisfied with my answer? – Garibald

Answer 1

git reflog show testBranch

should show the Fast-forward merge as last item ({0}). After making sure this is the case, checkout testBranch and then just do

git reset --keep testBranch@{1}

to revert to the previous state.

Garibald

This is a good answer. I would add that it's important to make sure you checkout testBranch before running git reset – Cressler

An easy-to-understand and nice approach! This should be marked as an answer – Stain

Note for PowerShell users: You must run last command as git reset --keep 'testBranch@{1}' – Jabiru

Answer 2

If you know of a revision in which you want your local testBranch, it is as simple as:

git checkout testBranch
git reset --hard <revision>

If you have changes mixed in like (oldest on top):

<point>
<your_change_a>
<change_from_someone_else>
<your_change_b>
<testBranch>

You could:

git checkout testBranch
git reset --hard <point>
git cherry-pick <your_change_a>
git cherry-pick <your_change_b>

Demote

This should work. I would also recommend using a Git graphical viewer such as gitg or gitk to get a good overview of the changes you want to undo. – Terrarium

Thanks for your answer, but I have found another solution (I haven't try yours but I suppose it works to). Solution is found in this blog : blog.tplus1.com/blog/2011/09/23/undo-a-fast-forward-git-merge ... hope it helps someone else to :) ... – Keslie