Why does git mergetool open 4 windows in vimdiff? (I'd expect 3)

Question

When I met a conflict, I tried to use git-mergetool to solve it. I typed:

>git mergetool -t vimdiff

It opened vimdiff

Answer 1

After lots of research for issuing mergetool with vimdiff and only 3 windows, I came up with this configuration, that allows me to chose when I want 3 windows or the default 4 windows:

git config --global merge.tool vimdiff
git config --global alias.mt mergetool

git config --global mergetool.merge3.cmd 'vim -d -c "wincmd l" "$LOCAL" "$MERGED" "$REMOTE"'
git config --global alias.m3 'mergetool -t merge3'

Now you can start 3 windows just typing:

git m3

And the default (4 windows) will still works as expected with:

git mt

Also, you probably would like to add this lines to the end of your ~/.vimrc or /etc/vim/vimrc

 " shortcuts to vimdiff
 let mapleader=','
 let g:mapleader=','

 if &diff
    map 1 :diffget LOCAL
    map 2 :diffget BASE
    map 3 :diffget REMOTE
 endif

This will create shortcuts like ,1 to grab from left, ,3 to grab from right (in both modes) and also ,2 to grab from base (center window) in the 4 windows mode.

That helps a lot!

My ~/.gitconfig file looks like this:

[user]
        name = Dr Beco
        email = my@email
[merge]
        tool = vimdiff
[mergetool "merge3"]
        cmd = vim -d -c \"wincmd l\" \"$LOCAL\" \"$MERGED\" \"$REMOTE\"
[alias]
        lo = log --pretty=format:\"%h %ce %cd %s\" --graph
        co = checkout
        ci = commit
        cm = commit -a -m
        st = status
        br = branch
        m3 = mergetool -t merge3
        mt = mergetool
[diff]
        tool = vimdiff

I hope this helps you (and those who get to here).