Extract commit message setup function

plugin/rhubarb.vim

@@ -11,25 +11,25 @@ if !exists('g:dispatch_compilers')
 endif
 let g:dispatch_compilers['hub'] = 'git'
 
-function! s:Config() abort
-  if exists('*FugitiveFind')
-    let dir = FugitiveFind('.git/config')[0:-8]
-    return filereadable(dir . '/config') ? readfile(dir . '/config') : []
-  else
-    return []
+function! s:SetUpMessage(filename) abort
+  if &omnifunc !~# '^\%(syntaxcomplete#Complete\)\=$' ||
+        \ a:filename !~# '\.git[\/].*MSG$' ||
+        \ !exists('*FugitiveFind') || empty(FugitiveGitDir())
+    return
+  endif
+  let config_file = FugitiveFind('.git/config')
+  let config = filereadable(config_file) ? readfile(config_file) : []
+  if !empty(filter(config,
+        \ '!empty(rhubarb#HomepageForUrl(matchstr(v:val, ''^\s*url\s*=\s*"\=\zs\S*'')))'))
+    setlocal omnifunc=rhubarb#Complete
   endif
 endfunction
 
 augroup rhubarb
   autocmd!
-  autocmd User Fugitive
-        \ if expand('%:p') =~# '\.git[\/].*MSG$' &&
-        \   exists('+omnifunc') &&
-        \   &omnifunc =~# '^\%(syntaxcomplete#Complete\)\=$' &&
-        \   !empty(filter(s:Config(),
-        \     '!empty(rhubarb#HomepageForUrl(matchstr(v:val, ''^\s*url\s*=\s*"\=\zs\S*'')))')) |
-        \   setlocal omnifunc=rhubarb#Complete |
-        \ endif
+  if exists('+omnifunc')
+    autocmd User Fugitive call s:SetUpMessage(expand('%:p'))
+  endif
   autocmd BufEnter *
         \ if expand('%') ==# '' && &previewwindow && pumvisible() && getbufvar('#', '&omnifunc') ==# 'rhubarb#omnifunc' |
         \    setlocal nolist linebreak filetype=markdown |