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How to resolve merge conflicts in Git?


Question

How do I resolve merge conflicts in Git?

2020/07/26
1
4842
7/26/2020 10:13:08 AM

Accepted Answer

Try: git mergetool

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 @JoshGlover comment:

The command

doesn't necessarily open a GUI unless you install one. Running git mergetool for me resulted in vimdiff being used. You can install one of the following tools to use it instead: meld, opendiff, kdiff3, tkdiff, xxdiff, tortoisemerge, gvimdiff, diffuse, ecmerge, p4merge, araxis, vimdiff, emerge.

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

git mergetool

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 info about vimdiff navigation here and here

Step 4. You could edit the MERGED view the following way

If you want to get changes from REMOTE

:diffg RE  

If you want to get changes from BASE

:diffg BA  

If you want to get changes from LOCAL

:diffg LO 

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.

2020/04/04
2968
4/4/2020 4:39:29 PM

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:

git mergetool

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.

Ta-da!

2019/06/10

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:

Tip One

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.

Tip Two

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.

Tip Three

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.)

Tip Four

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.

Tip Five

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.

2014/07/23

  1. Identify which files are in conflict (Git should tell you this).

  2. 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.

  3. Once you've resolved the conflict in a file git add the_file.

  4. Once you've resolved all conflicts, do git rebase --continue or whatever command Git said to do when you completed.

2014/08/07

Check out the answers in Stack Overflow question Aborting a merge in Git, especially Charles Bailey's answer which shows how to view the different versions of the file with problems, for example,

# Common base version of the file.
git show :1:some_file.cpp

# 'Ours' version of the file.
git show :2:some_file.cpp

# 'Theirs' version of the file.
git show :3:some_file.cpp
2017/05/23

Merge conflicts happens when changes are made to a file at the same time. Here is how to solve it.

git CLI

Here are simple steps what to do when you get into conflicted state:

  1. Note the list of conflicted files with: git status (under Unmerged paths section).
  2. Solve the conflicts separately for each file by one of the following approaches:

    • Use GUI to solve the conflicts: git mergetool (the easiest way).

    • To accept remote/other version, use: git checkout --theirs path/file. This will reject any local changes you did for that file.

    • To accept local/our version, use: git checkout --ours path/file

      However you've to be careful, as remote changes that conflicts were done for some reason.

      Related: What is the precise meaning of "ours" and "theirs" in git?

    • Edit the conflicted files manually and look for the code block between <<<<</>>>>> then choose the version either from above or below =====. See: How conflicts are presented.

    • Path and filename conflicts can be solved by git add/git rm.

  3. Finally, review the files ready for commit using: git status.

    If you still have any files under Unmerged paths, and you did solve the conflict manually, then let Git know that you solved it by: git add path/file.

  4. If all conflicts were solved successfully, commit the changes by: git commit -a and push to remote as usual.

See also: Resolving a merge conflict from the command line at GitHub

For practical tutorial, check: Scenario 5 - Fixing Merge Conflicts by Katacoda.

DiffMerge

I've successfully used DiffMerge which can visually compare and merge files on Windows, macOS and Linux/Unix.

It graphically can show the changes between 3 files and it allows automatic merging (when safe to do so) and full control over editing the resulting file.

DiffMerge

Image source: DiffMerge (Linux screenshot)

Simply download it and run in repo as:

git mergetool -t diffmerge .

macOS

On macOS you can install via:

brew install caskroom/cask/brew-cask
brew cask install diffmerge

And probably (if not provided) you need the following extra simple wrapper placed in your PATH (e.g. /usr/bin):

#!/bin/sh
DIFFMERGE_PATH=/Applications/DiffMerge.app
DIFFMERGE_EXE=${DIFFMERGE_PATH}/Contents/MacOS/DiffMerge
exec ${DIFFMERGE_EXE} --nosplash "[email protected]"

Then you can use the following keyboard shortcuts:

  • -Alt-Up/Down to jump to previous/next changes.
  • -Alt-Left/Right to accept change from left or right

Alternatively you can use opendiff (part of Xcode Tools) which lets you merge two files or directories together to create a third file or directory.

2019/10/15

Source: https://stackoverflow.com/questions/161813
Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]