title: How do I create a custom Diesel query using SQL functions with user-provided inputs?
body: <p>I want to perform a query that uses custom SQL functions of PostGIS bundles. For instance, I can run the subsequent query with psql:</p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT * FROM places 
  WHERE earth_box(ll_to_earth(40.6333125,-8.659492), 20)
  @&gt; ll_to_earth(places.lat, places.lng);
  </code></pre>
  
  <p><code>ll_to_earth</code> and <code>earth_box</code> are PostGIS functions. How can I make this query with Diesel with those values of <code>lat</code> and <code>lng</code> as input?</p>
  
  <p>I browsed the documentation but I can't wrap my head around it.</p>