How do you revert a faulty git merge commit

Question

So one of my coworkers accidentally made a merge that actually only kept one side of the tree. So he started a merge, deleted all the changes introduced by the merge, and then committed the merge.

Here is a simple test case I did on a test repo. This repo has three branches. idx is the topic branch that was accidentally merged, and master is the mainline. dev is just a test of how revert -m works so you can ignore it.

What I want to do is revert the faulty merge. So from master I try to run git revert -m 1 <sha1sum of faulty merge> but then git responds with:

# On branch master                               
nothing to commit (working directory clean)

So it doesn't actually create a revert commit that undoes the merge. I believe that this happens because the merge didn't actually contain any real changes.

Is this a git bug, or am I missing something?

Answer 1

The best rule of thumb here is to never ever change the history of your repo after it has been made public. It really screws things up. I don't think this case can avoid it though.

I think there are a couple of options here but the simplest is to do a rebase. Using your repo, these are the commands I used:

git rebase -i ead3646

Then, when the interactive shell comes up, remove the entire line of the faulty commit. Save that and you should wind up with a new history like this:

* f0ab6d5 more normal work on dev
* ebb5103 idx commit
* ead3646 master change
* 582c38c dev commits
* f4b8bc6 initial commit

Getting you two (and others) back in sync is going to take some branching, pushing, emailing and lunch buying.