title: attribute 'fallthrough' cannot be applied in this context
body: <p>I'm trying to use the c++17 <code>[[fallthrough]]</code> attribute in visual studio 2017:</p>
  
  <pre><code>Qt::ItemFlags flags = Qt::ItemIsSelectable;
  
  switch (index.column())
  {
  case 0:
      flags |= Qt::ItemIsUserCheckable;
      break;
  case 2:
      [[fallthrough]]
  case 3:
      [[fallthrough]]
  case 4:
      flags |= Qt::ItemIsEditable;
      break;
  }
  return flags;
  </code></pre>
  
  <p>but I get the compiler error:</p>
  
  <blockquote>
    <p>attribute 'fallthrough' cannot be applied in this context</p>
  </blockquote>
  
  <p>This seems like the only context where you can use <code>[[fallthrough]]</code>... what am I doing wrong?</p>