The best answers to the question “How to resolve merge conflicts in a Git repository?” in the category Dev.
I want to resolve merge conflicts in my Git repository.
How can I do that?
Here’s a probable use case, from the top:
You’re going to pull some changes, but oops, you’re not up to date:
git fetch origin git pull origin master From ssh://[email protected]:22/projectname * branch master -> FETCH_HEAD Updating a030c3a..ee25213 error: Entry 'filename.c' not uptodate. Cannot merge.
So you get up-to-date and try again, but have a conflict:
git add filename.c git commit -m "made some wild and crazy changes" git pull origin master From ssh://[email protected]:22/projectname * branch master -> FETCH_HEAD Auto-merging filename.c CONFLICT (content): Merge conflict in filename.c Automatic merge failed; fix conflicts and then commit the result.
So you decide to take a look at the changes:
Oh my, oh my, upstream changed some things, but just to use my changes…no…their changes…
git checkout --ours filename.c git checkout --theirs filename.c git add filename.c git commit -m "using theirs"
And then we try a final time
git pull origin master From ssh://[email protected]:22/projectname * branch master -> FETCH_HEAD Already up-to-date.
It opens a GUI that steps you through each conflict, and you get to choose how to merge. Sometimes it requires a bit of hand editing afterwards, but usually it’s enough by itself. It is much better than doing the whole thing by hand certainly.
As per Josh Glover’s comment:
doesn’t necessarily open a GUI unless you install one. Running
git mergetoolfor me resulted in
vimdiffbeing used. You can install
one of the following tools to use it instead:
Below is the sample procedure to use
vimdiff for resolve merge conflicts. Based on this link
Step 1: Run following commands in your terminal
git config merge.tool vimdiff git config merge.conflictstyle diff3 git config mergetool.prompt false
This will set vimdiff as the default merge tool.
Step 2: Run following command in terminal
Step 3: You will see a vimdiff display in following format
╔═══════╦══════╦════════╗ ║ ║ ║ ║ ║ LOCAL ║ BASE ║ REMOTE ║ ║ ║ ║ ║ ╠═══════╩══════╩════════╣ ║ ║ ║ MERGED ║ ║ ║ ╚═══════════════════════╝
These 4 views are
LOCAL – this is file from the current branch
BASE – common ancestor, how file looked before both changes
REMOTE – file you are merging into your branch
MERGED – merge result, this is what gets saved in the repo
You can navigate among these views using ctrl+w. You can directly reach MERGED view using ctrl+w followed by j.
More information about vimdiff navigation is here and here.
Step 4. You could edit the MERGED view the following way
If you want to get changes from REMOTE
If you want to get changes from BASE
If you want to get changes from LOCAL
Step 5. Save, Exit, Commit and Clean up
:wqa save and exit from vi
git commit -m "message"
git clean Remove extra files (e.g. *.orig) created by diff tool.
Identify which files are in conflict (Git should tell you this).
Open each file and examine the diffs; Git demarcates them. Hopefully it will be obvious which version of each block to keep. You may need to discuss it with fellow developers who committed the code.
Once you’ve resolved the conflict in a file
git add the_file.
Once you’ve resolved all conflicts, do
git rebase --continueor whatever command
Git said to do when you completed.
I find merge tools rarely help me understand the conflict or the resolution. I’m usually more successful looking at the conflict markers in a text editor and using git log as a supplement.
Here are a few tips:
The best thing I have found is to use the “diff3” merge conflict style:
git config merge.conflictstyle diff3
This produces conflict markers like this:
<<<<<<< Changes made on the branch that is being merged into. In most cases, this is the branch that I have currently checked out (i.e. HEAD). ||||||| The common ancestor version. ======= Changes made on the branch that is being merged in. This is often a feature/topic branch. >>>>>>>
The middle section is what the common ancestor looked like. This is useful because you can compare it to the top and bottom versions to get a better sense of what was changed on each branch, which gives you a better idea for what the purpose of each change was.
If the conflict is only a few lines, this generally makes the conflict very obvious. (Knowing how to fix a conflict is very different; you need to be aware of what other people are working on. If you’re confused, it’s probably best to just call that person into your room so they can see what you’re looking at.)
If the conflict is longer, then I will cut and paste each of the three sections into three separate files, such as “mine”, “common” and “theirs”.
Then I can run the following commands to see the two diff hunks that caused the conflict:
diff common mine diff common theirs
This is not the same as using a merge tool, since a merge tool will include all of the non-conflicting diff hunks too. I find that to be distracting.
Somebody already mentioned this, but understanding the intention behind each diff hunk is generally very helpful for understanding where a conflict came from and how to handle it.
git log --merge -p <name of file>
This shows all of the commits that touched that file in between the common ancestor and the two heads you are merging. (So it doesn’t include commits that already exist in both branches before merging.) This helps you ignore diff hunks that clearly are not a factor in your current conflict.
Verify your changes with automated tools.
If you have automated tests, run those. If you have a lint, run that. If it’s a buildable project, then build it before you commit, etc. In all cases, you need to do a bit of testing to make sure your changes didn’t break anything. (Heck, even a merge without conflicts can break working code.)
Plan ahead; communicate with co-workers.
Planning ahead and being aware of what others are working on can help prevent merge conflicts and/or help resolve them earlier — while the details are still fresh in mind.
For example, if you know that you and another person are both working on different refactoring that will both affect the same set of files, you should talk to each other ahead of time and get a better sense for what types of changes each of you is making. You might save considerable time and effort if you conduct your planned changes serially rather than in parallel.
For major refactorings that cut across a large swath of code, you should strongly consider working serially: everybody stops working on that area of the code while one person performs the complete refactoring.
If you can’t work serially (due to time pressure, maybe), then communicating about expected merge conflicts at least helps you solve the problems sooner while the details are still fresh in mind. For example, if a co-worker is making a disruptive series of commits over the course of a one-week period, you may choose to merge/rebase on that co-workers branch once or twice each day during that week. That way, if you do find merge/rebase conflicts, you can solve them more quickly than if you wait a few weeks to merge everything together in one big lump.
If you’re unsure of a merge, don’t force it.
Merging can feel overwhelming, especially when there are a lot of conflicting files and the conflict markers cover hundreds of lines. Often times when estimating software projects we don’t include enough time for overhead items like handling a gnarly merge, so it feels like a real drag to spend several hours dissecting each conflict.
In the long run, planning ahead and being aware of what others are working on are the best tools for anticipating merge conflicts and prepare yourself to resolve them correctly in less time.