title: How to create a Mix task at the root of an umbrella project?
body: <p>I have an <code>Elixir</code> umbrella project. Each apps in this project can be compiled into executable file using <code>mix escript.build</code>. </p>
  
  <p>I am trying to run this command from the root of umbrella project and got the following error</p>
  
  <pre><code>** (RuntimeError) Trying to access Mix.Project.app_path for an umbrella project but umbrellas have no app
  </code></pre>
  
  <p>I understand why this won't work. So tried to create a custom mix task at the root of the umbrella project. Since the root don't have a <code>lib</code> directory, I added one and created a mix task inside it. But that is not listed in <code>mix help</code>. </p>
  
  <p>How can I define a custom mix task at the root of an umbrella project?</p>