title: Condition on template with v-if using v-slot prop
body: <p>I'm trying to make a condition to enable a named slot like this:</p>
  
  <pre><code>&lt;template v-slot:item="{ item }" v-if="item.loading"&gt;
    &lt;v-progress-circular indeterminate color="primary"&gt;&lt;/v-progress-circular&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>My use case is a Vuetify datatable: each item has a "loading" property, and I'd like to activate "item" slot only if the row is loading ("item" slot is Slot to replace the default rendering of a row)</p>
  
  <p>The error is that <code>item</code> is undefined in the <code>v-if</code>, which seems logic : item is only defined for <code>template</code> children tag.</p>
  
  <p>Is there a way to solve this problem?</p>