title: "git push" works, but "@{push}" gives the error "cannot resolve"
body: <p>I'm trying to use the <code>@{push}</code> notation. I have <code>branch.&lt;branchname&gt;.pushRemote</code> set. If I use <code>git push -v</code>, it correctly works, and prints:</p>
  
  <pre><code>Pushing to git@github.com:&lt;my-repo&gt;
  </code></pre>
  
  <p>However, if I try to use <code>git diff @{push}</code> I get the error:</p>
  
  <blockquote>
    <p>fatal: cannot resolve 'simple' push to a single destination</p>
  </blockquote>
  
  <p>As far as I understand, this should work, according to the manual:</p>
  
  <pre><code>[&lt;branchname&gt;]@{push}, e.g. master@{push}, @{push}
         The suffix @{push} reports the branch "where we would push to" if git push were run 
         while branchname was checked out (or the current HEAD if no branchname is specified). 
  </code></pre>
  
  <p><code>git rev-parse --symbolic-full-name @{push}</code> prints the same "cannot resolve" error message.</p>
  
  <p>Is this a git bug, or did I setup something incorrectly? Any tips what to try?</p>