How do I use vimdiff to resolve a git merge conflict?

Question

I just merged a branch into my master in git and I got Automatic merge failed; fix conflicts and then commit the result. Now I ran git mergetool and vimdiff opened with the image below. I don't know how to use vimdiff. What does each panel here mean and how should I proceed to fix the merge conflict?

Boomer

See this page. If that's what you mean by "correct", the current state of your code is on the top left. – Allaround

@Allaround I am still confused after reading that, what are the shortcuts and how do I choose which file to use as the main branch? – Boomer

@Danny http://www.rosipov.com/blog/use-vimdiff-as-git-mergetool/ is a good one. – Noellenoellyn

Also see: this – Lint

Use fugitive as per this accepted answer: https://mcmap.net/q/16758/-why-does-git-mergetool-open-4-windows-in-vimdiff-i-39-d-expect-3 – Siddra

Answer 1

All four buffers provide a different view of the same file. The top left buffer (LOCAL) is how the file looked in your target branch (what you are merging into). The top right buffer (REMOTE) is how the file looked in your source branch (where you are merging from). The middle buffer (BASE) is the common ancestor of the two (so you can compare how the left and right versions have diverged from each other).

I may be mistaken on the following point. I think the source of the merge conflict is that both files have changed the same portion of the file since BASE; LOCAL has changed the quotes from double to single, and REMOTE has made the same change but also changed the background value from a color to a URL. (I think the merge is not smart enough to notice that all the changes to LOCAL are also present in REMOTE; it just knows that LOCAL has made changes since BASE in the same places that REMOTE has).

In any case, the bottom buffer contains the file you can actually edit—the one sitting in your working directory. You can make any changes you like; vim is showing you how it differs from each of the top views, which are the areas that the automatic merge couldn't not handle. Pull changes from LOCAL if you don't want the REMOTE changes. Pull changes from REMOTE if you prefer those to the LOCAL changes. Pull from BASE if you think both REMOTE and LOCAL are wrong. Do something completely different if you have a better idea! In the end, the changes you make here are the ones that will actually be committed.

Shewmaker

Quick question how do I save in vim? – Boomer

:x or :w (:x exits too) plus 'return'. – Tirol

Anders: there are other merge tools you can use if you are not familiar with how to use vim. – Shewmaker

@Shewmaker is there one you reccomend? – Boomer

@AndersKitson, since you are on Mac OS X, FileMerge is perfect, free and comes with XCode. – Allaround

Why the downvote? If there is something factually incorrect, please fix it, or at least point it out. – Shewmaker

Can FileMerge be started off the command line with git, @romainl? If so, how? – Corse

Do $ git mergetool -t opendiff but I'm not in front of my Mac right now so I can't explain from memory. I think that I use a wrapper shell script. – Allaround

i normally use kdiff3 and the view is similar, so i understand it, but over a remote connection, when i try to use vimdiff, i have no idea what the shortcut keys are – Monostrophe

Quick question, is there a way to 'pull from remote, local or base' without manually editing the bottom window and re-typing in it all over? – Mazonson

I think there is an option for git merge that selects one branch or the other to resolve all conflicts. – Shewmaker

The comment would be more usefull with key bindings. What I have found so far elsewhere is do and dp, but that's only usefull with two window pane. – Prase

Answer 2

@chepner's answer is great, I would like to add some details on "how should I proceed to fix the merge conflict" part of the question. If you look into how to actually use vimdiff in this case, it goes below.

---

First, to address the "abort everything" option - if you do not want to use "vimdiff" and want to abort the merge: press Esc, then type :qa! and hit Enter. (see also How do I exit the Vim editor?). Git will ask you if the merge was complete, reply with n.

---

If you want to use vimdiff, here are some useful shortcuts. This assumes you know basics of Vim (navigation and insert/normal mode):

• navigate to the bottom buffer (merge result): Ctrl-W j
• navigate to next diff with j/k; or, better, use ] c and [ c to navigate to the next and previous diff respectively
• use z o while on a fold to open it, if you want to see more context
• for each diff, as per @chepner's answer, you can either get the code from a local, remote or base version, or edit it and redo as you see fit
  • to get it from the local version, use :diffget LO
  • from remote: :diffget RE
  • from base: :diffget BA
  • or, if you want to edit code yourself, get a version from local/remote/base first, and then go to the insert mode and edit the rest
• once done, save the merge result, and quit all windows :wqa
  • if you want to abort merging the current file and not mark it as resolved, quit with :cquit instead: How do you cancel an external git diff?
• normally, git detects that the merge was made and creates the merge commit

It does not appear to be possible to add both local and remote conflict hunks without copy pasting or custom shortcuts: https://vi.stackexchange.com/questions/10534/is-there-a-way-to-take-both-when-using-vim-as-merge-tool which is a shame since add add is such a common conflict type.

To prevent vimdiff from asking you to press enter every time it starts, add to your .vimrc:

set shortmess=Ot

as mentioned at: https://vi.stackexchange.com/questions/771/how-can-i-suppress-the-press-enter-prompt-when-opening-files-in-diff-mode

You can search the Internet for other vimdiff shortcuts. I have found this one useful: https://gist.github.com/hyamamoto/7783966

Lion

This should be upvoted x1000 times and accepted as a better answer. – Solberg

to quick jump to next conflict, just do search for === . do " /===" and enter – Henghold

See this post (stackoverflow.com/questions/51520705/…) if more than one match found using :diffget. – Crux

It seems something has changed since this was written: "press Esc, then type :qa! and hit Enter. Git will ask you if the merge was complete, reply with n." git is not asking me anything, it is assuming the merge was completed. To successfully abort, I need to use the other command provided later, ":cquit". Is this a change in git's behavior? Or vimdiff's? – Waggon

Is there no shortcut to navigate between conflict ? – Denson

Answer 3

The ultimate mergetool to replace vimdiff

This is kind of tongue-in-cheek, but it is what I ended up converging to as a vimmer after trying vimdiff.

To resolve a merge conflict, what I almost always need is to see:

• REMOTE
• LOCAL
• two diffs:
  • diff BASE REMOTE
  • diff BASE LOCAL

to then try to put both of them together.

While vimdiff does show BASE, LOCAL and REMOTE in the screen:

    +--------------------------------+
    | LOCAL  |     BASE     | REMOTE |
    +--------------------------------+
    |             MERGED             |
    +--------------------------------+

I don't know how to make it clearly show those two diffs that I need besides by looking right left right left a bunch of times.

Furthermore, LOCAL and REMOTE are already visible in the git merge conflict markers, so I don't gain that much from a tool that shows them again.

Therefore, I instead created my own tiny "difftool" that actually shows the diffs that I was missing:

~/bin/cirosantilli-mergetool

#!/usr/bin/env bash
BASE="$1"
LOCAL="$2"
REMOTE="$3"
diff --color -u "$BASE" "$LOCAL"
diff --color -u "$BASE" "$REMOTE"
exit 1

GitHub upstream.

And install it with:

git config --global mergetool.cirosantilli-mergetool.cmd 'cirosantilli-mergetool $BASE $LOCAL $REMOTE'
git config --global mergetool.cirosantilli-mergetool.trustExitCode true
# If you want this to become your default mergetool.
#git config --global merge.tool 'cirosantilli-mergetool'

Now, when you do:

git mergetool -t cirosantilli-mergetool

it shows the two diffs that I want on the terminal, e.g. something along:

--- ./src/dev/arm/RealView_BASE_15560.py        2019-12-27 13:46:41.967021591 +0000
+++ ./src/dev/arm/RealView_LOCAL_15560.py       2019-12-27 13:46:41.979021479 +0000
@@ -994,7 +994,7 @@                                                              
                                       
     def setupBootLoader(self, cur_sys, loc):
         if not cur_sys.boot_loader:                           
-            cur_sys.boot_loader = [ loc('boot_emm.arm64'), loc('boot_emm.arm') ]
+            cur_sys.boot_loader = [ loc('boot.arm64'), loc('boot.arm') ]
         cur_sys.atags_addr = 0x8000000                  
         cur_sys.load_offset = 0x80000000                    

@@ -1054,7 +1054,7 @@                                           
             ]                                                     
                       
     def setupBootLoader(self, cur_sys, loc):
-        cur_sys.boot_loader = [ loc('boot_emm_v2.arm64') ]
+        cur_sys.boot_loader = [ loc('boot_v2.arm64') ]
         super(VExpress_GEM5_V2_Base,self).setupBootLoader(
                 cur_sys, loc)                             
                                                           
--- ./src/dev/arm/RealView_BASE_15560.py        2019-12-27 13:46:41.967021591 +0000
+++ ./src/dev/arm/RealView_REMOTE_15560.py      2019-12-27 13:46:41.991021366 +0000
@@ -610,10 +610,10 @@           
     def attachIO(self, *args, **kwargs):              
         self._attach_io(self._off_chip_devices(), *args, **kwargs)
                                      
-    def setupBootLoader(self, cur_sys, loc):
-        cur_sys.boot_loader = loc('boot.arm') 
-        cur_sys.atags_addr = 0x100                           
-        cur_sys.load_offset = 0       
+    def setupBootLoader(self, cur_sys, boot_loader, atags_addr, load_offset):
+        cur_sys.boot_loader = boot_loader      
+        cur_sys.atags_addr = atags_addr     
+        cur_sys.load_offset = load_offset

So you can see here the two diffs dumped into the terminal:

• RealView_BASE_15560.py vs RealView_LOCAL_15560.py
• RealView_BASE_15560.py vs RealView_REMOTE_15560.py

If the diffs are big, I'll just search up with my tmux superpowers.

TODO: to achieve Nirvana the last thing left would be a way to show only diffs for the conflicting hunk. Because if the diffs are large but only a small hunk conflicts, it is annoying to find it.

Yes, you you do lose some shortcuts that vimdiff provides, but in general solving conflicts requires careful copy paste from both versions, which I can do fine inside a normal vim session with the git conflict markers.

Observing and diffing files while vimdiff is running

Before I sat down and automated my perfect setup with cirosantilli-mergetool, this is what I was doing to get the two diffs I needed.

While git mergetool is running vimdiff, if there is a conflict on a file named, say, main.py, git generates files for each of the versions, named as:

main_BASE_1367.py
main_LOCAL_1367.py
main_REMOTE_1367.py

in the same directory as main.py where 1367 is the PID of git mergetool, and therefore a "random" integer, as mentioned at: In a git merge conflict, what are the BACKUP, BASE, LOCAL, and REMOTE files that are generated?

So, to see the diffs that I want, I first find the generated files with git status, and then open new terminals and do a vimdiff between the pairs of files that I care about:

vim -d main_BASE_1367.py main_LOCAL_1367.py
vim -d main_BASE_1367.py main_REMOTE_1367.py

Together with git mergetool, this information helps A LOT to figure out what is going on quickly!

Also, even while mergetool is running, you can just open the file:

vim main.py

directly and edit it there if you feel that it is going to be easier with a larger editor window.

Jump directly to merge conflicts

While ]c jumps to the next diff point inside vimdiff, there isn't always a merge conflict there.

To help with this, I have in my ~/.vimrc:

# Git Merge conflict
nnoremap <leader>gm /\v^\<\<\<\<\<\<\< \|\=\=\=\=\=\=\=$\|\>\>\>\>\>\>\> /<cr>

which finds the conflicts directly.

git imerge

Maybe the best option is to just give up on using vimdiff and rely on regular vim + git imerge which was mentioned at: How can I find out which Git commits cause conflicts? since vimdiff's learning curve is annoying, and it doesn't do the functions we need the most.

Burrstone

@VonC yes, I think you won this one! XD – Burrstone

My vimdiff does not show the MERGED pane...only the 3 at the top. How can i get it to show the merged pane? – Dullard

this help greatly – Nyhagen

you could even do something like, instead of searching terminal window, pipe the diff outputs to files by appending this to the end of the diff cmds > base_remote.diff etc and then script it to open the files in Vim panes with the two diffs at the top and the merge file at the bottom – Nyhagen

@Nyhagen searching the terminal is not a huge problem once you have: superuser.com/questions/231002/… As of late I've gotten a bit lazy and try to use git checkout --conflict=diff3 and visually find the diffs. Risky life. – Burrstone