Windows – Can’t run Vimdiff (7.4) on Windows 7

gvimvimvimdiffwindows 7

I recently installed the 7.4 version of gVim on a Windows 7 machine. Trying to diff two files from the context-sensitive menu on Windows Explorer, I keep getting the error messages:

E810: Cannot read or write temp files
E97: Cannot create diffs

The two selected files are opened in the two-pane gVim view, and the editor seems to be in diff mode, but the actual differences are not highlighted.

The %TEMP% and %TMP% environment variables are populated with a valid directory name.

I get the same response when opening the files in a regular gVim session and typing :diffthis in the command prompt.

This used to work properly with Vim 7.3, but it looked like something was changed in v7.4.

How can I diff the two files?

Best Answer

This issue can be caused by the default _vimrc file created by the installer on Windows. If you're still using that default file, or if you copied it at some point, then check the function you've assigned to the diffexpr option. One of the patches between Vim 7.3 and 7.4 introduced new default quoting rules for the cmd.exe shell on Windows. This patch broke the workaround in the MyDiff() function designed to fix the same issue solved by the patch.

The MyDiff() function was fixed by version 7.4.103 by fixing the installer. Here is the MyDiff() function which the latest installer will create for you if you just want to copy it to your _vimrc:

 function MyDiff()
   let opt = '-a --binary '
   if &diffopt =~ 'icase' | let opt = opt . '-i ' | endif
   if &diffopt =~ 'iwhite' | let opt = opt . '-b ' | endif
   let arg1 = v:fname_in
   if arg1 =~ ' ' | let arg1 = '"' . arg1 . '"' | endif
   let arg2 = v:fname_new
   if arg2 =~ ' ' | let arg2 = '"' . arg2 . '"' | endif
   let arg3 = v:fname_out
   if arg3 =~ ' ' | let arg3 = '"' . arg3 . '"' | endif
   if $VIMRUNTIME =~ ' '
     if &sh =~ '\<cmd'
       if empty(&shellxquote)
         let l:shxq_sav = ''
         set shellxquote&
       endif
       let cmd = '"' . $VIMRUNTIME . '\diff"'
     else
       let cmd = substitute($VIMRUNTIME, ' ', '" ', '') . '\diff"'
     endif
   else
     let cmd = $VIMRUNTIME . '\diff'
   endif
   silent execute '!' . cmd . ' ' . opt . arg1 . ' ' . arg2 . ' > ' . arg3
   if exists('l:shxq_sav')
     let &shellxquote=l:shxq_sav
   endif
 endfunction

You can see your full version in Vim using the :version or :intro commands, or at the splash screen at startup.

Unfortunately if you want an official installer, you will either need to wait until 8.0, or install a nightly build. Nevertheless, you can install Vim from other places or build your own Vim.

Duplicated on Stack Overflow (unusually, on-topic on both sites), if this answer is updated so should the other.

Related Solutions

Change color scheme when calling vimdiff inside Vim

Vim reads your vimrc once, at startup. The if &diff statement is executed when it is read, not every time the state of 'diff' changes. One way to have those color commands executed when you execute :VCSVimDiff is to put them in an autocommand in your vimrc, like this.

au FilterWritePre * if &diff | set t_Co=256 | set bg=dark | colorscheme peaksea | endif

where the FilterWritePre event is one that is triggered when Vim performs a diff.

[The comment didn't work well, so I'll add to my original answer.]

If you want to end VimDiff with :q, what you could do is set up another autocommand, maybe using the BufWinLeave event, again testing &diff and executing the commands to set your default colorscheme.

What I do is use the following command to delete the buffer I had diff'd against, turn off diff mode and restore some saved settings.

command! -bar -bang Nodiff wincmd l <bar> only<bang> <bar> set nodiff noscrollbind scrollopt-=hor wrap foldcolumn=0 virtualedit= foldlevel=99 <bar> if exists("b:fdm") <bar> let &fdm = b:fdm <bar> endif <bar> if exists("b:syn") <bar> let &syn = b:syn <bar> endif

To make and/or save those settings when diff mode is entered, I use the following autocommands.

au FilterWritePre * if &diff | set virtualedit=all | endif
au FilterWritePre * exe 'let b:syn = &syn | if &diff | set syn=OFF | endif'
au BufWinEnter * if &fdm != "diff" | let b:fdm = &fdm | endif

Those commands have evolved over the years, which is my excuse for their inconsistencies.

Windows – Overriding HOMEDRIVE and HOMEPATH as a Windows 7 user

Below are some hacks I've developed. They are not elegant, but may be functional in your corporate environment.

HOMEDRIVE Only

It seems that many applications only use HOMEDRIVE / HOMEPATH. In that case, you can create a startup script that remaps the base drive letter to your local user path via the UNC drive admin path:

set HOME
HOMEDRIVE=G:
HOMEPATH=\
HOMESHARE=\\Server\Users\username

net use g: /delete
net use g: \\localhost\C$\Users\username

HOMEDRIVE Local Default

If you do not need to access "Server" by name at all, you can cause the group policy setting to fail and fall back to your local machine. The easiest way to do this is to add an entry to C:\Windows\System32\drivers\etc\hosts like:

127.0.0.1   Server

After rebooting, you should see something like:

set HOME
HOMEDRIVE=C:
HOMEPATH=\Users\username

HOMEDRIVE/SHARE with Hybrid Local/Remote UNC Paths

If you want access to "Server" by name for some UNC paths, but override others with local paths, I have developed the following abomination. Note: direct server connections to "Server" will still resolve to your local machine. I recommend this solution only if "Server" is only a file server:

Modify C:\Windows\System32\drivers\etc\hosts to redirect "Server" to your local machine:
```
127.0.0.1   Server
```
Add the following Multi-String registry value to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0 to allow credentials to be passed to the local UNC path:
```
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0\
BackConnectionHostNames = Server
```

Create a dummy directory that will serve as the root of Server:

set DUMMY_LOC=C:\Server_Dummy

mkdir %DUMMY_LOC%
cd /D %DUMMY_LOC%

For each UNC path you want to direct to the real Server:

rem Alternatively you can use an IP below, but it is more likely to break if DNS changes
set SERVER_FQDN=Server.network.blah.com

rem Take a look at what's available...
net view \\%SERVER_FQDN%\

mklink /D Remote_Example \\%SERVER_FQDN%\Remote_Example
net share Remote_Example=%DUMMY_LOC%\Remote_Example /grant:everyone,FULL

For each UNC share you want to define locally (such as Users):

rem The link isn't really necessary for the share, I just find it easier to manage when all of these hacks are in the same directory

mklink /D Users C:\Users
net share Users=%DUMMY_LOC%\Users /grant:everyone,FULL

Reboot

For the example, this would allow the following UNC paths to be resolved:

\\Server\Remote_Example => \\Server.network.blah.com\Remote_Example
\\Server\Users          => C:\Users

This path resolution should occur prior to drive mappings. As long as the UNC paths associated with the mappings are valid (be they local or remote), drive letters should behave as expected.

For example, in my setup the following variables are forced by the domain:

set HOME
HOMEDRIVE=G:
HOMEPATH=\
HOMESHARE=\\Server\Users\username

But due to my mappings, the result is:

G: => \\Server\Users\username => C:\Users\username