runtime/ftplugin/git.vim

" Vim filetype plugin
" Language:	generic git output
" Maintainer:	Tim Pope <vimNOSPAM@tpope.org>

" Only do this when not done yet for this buffer
if (exists("b:did_ftplugin"))
  finish
endif
let b:did_ftplugin = 1

if !exists('b:git_dir')
  if expand('%:p') =~# '[\/]\.git[\/]modules[\/]'
    " Stay out of the way
  elseif expand('%:p') =~# '\.git\>'
    let b:git_dir = matchstr(expand('%:p'),'.*\.git\>')
  elseif $GIT_DIR != ''
    let b:git_dir = $GIT_DIR
  endif
  if (has('win32') || has('win64')) && exists('b:git_dir')
    let b:git_dir = substitute(b:git_dir,'\\','/','g')
  endif
endif

if exists('*shellescape') && exists('b:git_dir') && b:git_dir != ''
  if b:git_dir =~# '/\.git$' " Not a bare repository
    let &l:path = escape(fnamemodify(b:git_dir,':h'),'\, ').','.&l:path
  endif
  let &l:path = escape(b:git_dir,'\, ').','.&l:path
  let &l:keywordprg = 'git --git-dir='.shellescape(b:git_dir).' show'
else
  setlocal keywordprg=git\ show
endif
if has('gui_running')
  let &l:keywordprg = substitute(&l:keywordprg,'^git\>','git --no-pager','')
endif

setlocal includeexpr=substitute(v:fname,'^[^/]\\+/','','')
let b:undo_ftplugin = "setl keywordprg< path< includeexpr<"