title: datastore-indexes.xml doesn't work, creates no index after deploy
body: <p>I have created a Kind called User in Google App Engine datastore, and I am trying to add an index for this kind.</p>
  
  <p>Firstly, I followed <a href="https://cloud.google.com/appengine/docs/standard/java/config/indexconfig" rel="nofollow noreferrer">https://cloud.google.com/appengine/docs/standard/java/config/indexconfig</a> to create index by adding datastore-indexes.xml inside war/WEB-INF, but it doesn't work, no index is created after I deploy to app engine.</p>
  
  <p>code in my datastore-indexes.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;datastore-indexes autoGenerate="false"&gt;
      &lt;datastore-index kind="User" ancestor="false" source="manual"&gt;
          &lt;property name="area" direction="asc"/&gt;
          &lt;property name="coins_balance" direction="asc"/&gt;
      &lt;/datastore-index&gt;
  &lt;/datastore-indexes&gt;
  </code></pre>
  
  <p>Then I followed <a href="https://cloud.google.com/appengine/docs/standard/python/config/indexref" rel="nofollow noreferrer">https://cloud.google.com/appengine/docs/standard/python/config/indexref</a>, I created an index.yaml and run <code>gcloud app deploy index.yaml</code>, this time index is actually created.</p>
  
  <p>So can anyone help me understand why datastore-indexes.xml in my case doesn't work, thanks.</p>