Fixing invalid argument iwhite on vimdiff

Posted on Thu 07 November 2019 in programming

[Update from 2020-03-27 below]

Vim's diff mode is a lightweight diffing tool that can be used at the command line, in particular with the git diff command. In a previous post, I wrote about configuring vimdiff as the git difftool for use with Matlab development (yes, way back when I was actually writing Matlab code).

Recently, I've been getting errors using vimdiff of the following (showing manual invocation rather than through git diff):

$ vimdiff
Error detected while processing /Users/micahsmith/.vimrc:
line   65:
E474: Invalid argument: diffopt+=iwhite
Press ENTER or type command to continue

The corresponding section of my .vimrc file is as follows:

"Ignore whitespace with vimdiff
if &diff
    set diffopt+=iwhite
endif

Had a new version of vim been released that deprecated this diffopt option? No, iwhite still appeared in the manual under :help diffopt. This error was driving me crazy, as when I ran git diff when there were many changed files, this error message would display for me to acknowledge between every file comparison.

After beating my head against the wall for a while, I finally figured out the issue. Most of my frustration is environment specific, but it does seem like MacOS Catalina bundled a different version of vim that removed support for the iwhite option. I'm not going to dive into it too thoroughly, but if you confirm that Catalina is to blame, let me know in the comments.

I don't use the system version of vim anyway, instead using MacVim installed using Homebrew Cask. So why was this causing me problems? I realized that I had been using an alias to invoke MacVim from the terminal but that my alias did not capture invocation of the form vimdiff which used the system vim. Uninstall MacVim and reinstalling it caused it to re-install symlinks including /usr/local/bin/vim, a command that did not exist as such when I originally installed MacVim.

Before

  • vim aliased to /usr/bin/local/mvim in ~/.bashrc
  • git difftool set to vimdiff which pointed to system /usr/bin/vim and was unaffected by vim alias
  • upgrade to MacOS Catalina involved upgrade of system vim which dropped support for iwhite

After

  • re-install MacVim (brew cask zap macvim && brew cask install macvim) which created a symlink at /usr/local/bin/vim
  • deleted vim alias in ~/.bashrc as /usr/local/bin already higher on my $PATH than /usr/bin
  • git difftool set to vim -d (equivalent to vimdiff but hopefully less likely to cause future path issues)

Update

I dove deeper into the source of the problem on the version of vim provided by MacOS Catalina and I was able to identify the problem more clearly and find a solution. First, the Catalina vim version did not drop support for iwhite. Rather, the problem is that somehow the default setting which includes internal is invalid for the version of vim installed. Here is a log demonstrating the issue.

$ /usr/bin/vim -u NONE
:set diffopt?
  diffopt=internal,filler
:set diffopt+=iwhite
E474: Invalid argument: diffopt+=iwhite
:set diffopt=internal
E474: Invalid argument: diffopt=internal
:set diffopt=filler
:set diffopt+=iwhite
:set diffopt?
  diffopt=filler,iwhite

Summary

  • stock vim with no config defaults to diffopt=internal,filler
  • stock vim does not actually support the option internal (:help diffopt is actually accurate in this regard in that it is not shown as an option, though it is listed as the default)
  • running :set diffopt+=iwhite semantically does :set diffopt=internal,filler,iwhite which contains an invalid option
  • the error message is highly misleading suggesting that the invalid argument is iwhite when it is actually internal

A quick fix

  • first remove internal from the list of options
  • then add your desired options
if &diff
    set diffopt-=internal
    set diffopt+=iwhite
endif

My version of vim FWIW:

$ /usr/bin/vim --version
VIM - Vi IMproved 8.1 (2018 May 18, compiled Dec 13 2019 14:45:40)
Included patches: 1-503, 505-680, 682-1312
Compiled by roo@apple.com

vim macos catalina