title: vim diff does not work
body: <p>Somehow my vim (macvim) stops showing me the highlighted differences betweeen two files. </p>
  
  <p>My env: </p>
  
  <ul>
  <li>osx 10.9 with macvim installed</li>
  </ul>
  
  <p>Facts:</p>
  
  <ul>
  <li>The diff works a few months ago when I do either of below:
  <ul>
  <li>vimdiff a b, or </li>
  <li>vim -d a b</li>
  </ul></li>
  </ul>
  
  <p>It shows the color diff</p>
  
  <p>Now, it does not show the color diff, it loads two files to the buff,</p>
  
  <ul>
  <li>either showing the same file(a vs a) in the vsplit windows (a few weeks ago)</li>
  <li>or showing two files (a vs b) in the vsplit windows (current)</li>
  </ul>
  
  <p>then I will have to use :diffThis for both windows to see diff in color</p>
  
  <p>Diagnosis:</p>
  
  <p>I used: vim -d a b -u None to disable all plugins, it shows color diff, I though it's one of the plugins causing issues, then I tried disable one by one(move the plugin out of directory), but even I disabled all plugins I still can not see diff in color.</p>
  
  <p>I have spent a few days on this but no luck.</p>
  
  <p>Please if anyone knows how to resolve it.</p>