title: How can I see a "three way diff" for a Git merge conflict?
body: <p>Suppose I'm on Git branch <code>master</code> and I <code>git merge featurebranch</code>. There is a conflict in <code>foo.html</code>.</p>
  
  <p>When I open <code>foo.html</code>, I see, in the area of the conflict, what <code>master</code> has and what <code>featurebranch</code> has. But I can't really tell <strong>what change</strong> was made on <code>master</code> that conflicted with <code>featurebranch</code>; I only know what master has <strong>now</strong>.</p>
  
  <p>I'd like to see the <strong>diff</strong> that each one applied.</p>
  
  <p>Or, to get the same information, I could see:</p>
  
  <ul>
  <li>The version <code>master</code> has now</li>
  <li>The version <code>featurebranch</code> has now</li>
  <li>The version <strong>their common ancestor</strong> had</li>
  </ul>
  
  <p>How can I see this?</p>