title: Syntax for a Homebrew formula depending on a cask
body: <p>I'm writing a homebrew formula for a project (<a href="https://www.cryfs.org" rel="noreferrer">https://www.cryfs.org</a>).
  Since it is a file system, it depends on osxfuse, which is unfortunately only available as a cask. That is, the formula should have the cask as a dependency.</p>
  
  <p>I tried the following</p>
  
  <pre><code>depends_on :cask =&gt; "osxfuse"
  </code></pre>
  
  <p>but I got the error message</p>
  
  <pre><code>Unsupported special dependency :cask
  </code></pre>
  
  <p>What is the syntax for adding casks as dependencies to a formula?</p>