title: Install stack project extra-deps with stack
body: <p>How can I build project <code>a</code> with dependency <code>b</code> when both are not found in <code>stack</code> indices?</p>
  
  <p>I used <code>stack install</code> on <code>b</code>, added <code>extra-deps</code> but still failed to build <code>a</code>.</p>
  
  <pre><code>Didn't see b in your package indices. Updating and trying again.
  </code></pre>
  
  <p>Why <code>b</code> is not in my "package indices"? How should I build project <code>a</code>? </p>