Update the diff view automatically
From Vim Tips Wiki
created October 29, 2001 · complexity intermediate · author Douglas Potts · version 6.0
When trying to reconcile differences between files, and using the new 'diff' functionality in Vim 6.0 you may want to automatically update the differences as you are working along. A convienent time is when you write out either of the files you are diff'ing. This autocmd will take care of doing that for you.
" If doing a diff. Upon writing changes to file, automatically update the " differences autocmd BufWritePost * if &diff == 1 | diffupdate | endif
A more aggressive auto-diffupdate is discussed on vim_use and should probably be merged into this tip.