How can I make git difftool to use gvim (gvimdiff)?

Question

There seems to have been a change in git which makes it no longer work correctly with gvim as the diff tool. Specifically, I always used to use the gvim -geometry flag to maximize the window. Now, I end up with one of the windows blank (empty/zero line file).

Answer 1

OK, I found the answer. In order to work correctly, gvim must stay in the foreground and NOT fork a new process as usual. This is accomplished by using the -f or --nofork flag when starting gvim (or gvimdiff).

I have now setup the following alias which works:

alias gitdg='git difftool --noprompt --extcmd="gvim -d --nofork -geometry 220x80+2000+40" '

Please be careful to note the placement of single- vs. double-quotes to keep the zsh shell happy.

I used the gvim option -geometry to configure the diff windows to have 220 lines x 80 columns. The "+2000+40" means the upper left corner of window to be offset of 2000 pixels horizontally and 80 pixels vertically from the top-left corner of all monitors, so the window appears on the right monitor of my 2-monitor setup. Try setting it to -geometry 160x40+60+20 to see the effect of changes.

Answer 2

On Windows Server 2012R2, adding the following to my .gitconfig worked for me as well. My experience was that the -d and -f were not necessary for my setup. Even though this is Windows, assure you use forward slashes '/' for the path information.

[alias]
    d = difftool
[diff]
    tool = gvimdiff
[difftool]
    prompt = false
[difftool "gvimdiff"]
    path = "C:/Program Files (x86)/Vim/vim81/gvim.exe"

Sample Run ...

c:\>git d index.html

I also discovered I had defined a function for diffexpr in my _vimrc, this needed commented out like so ...

"set diffexpr=MyDiff()

... which allows the 'new' built-in diff to work within gVim. With those changes, everything worked in gui vim.