What goes in a Stack package.yaml file? : <p>I notice that Stack supports using a <code>package.yaml</code> file that it will use to generate a <code>.cabal</code> file. For example, <a href="https://github.com/yi-editor/yi/blob/2f0c7b738b3a1f79ff149034db2c4392273ee26f/yi-core/package.yaml">yi-core/package.yaml</a>. Its structure seems very similar to a Cabal file, but not quite the same. Some of the keys have been renamed (for example, Stack uses <code>source-dirs</code> instead of <code>hs-source-dirs</code>).</p>

<p>I haven't found any documentation on this feature. <a href="https://docs.haskellstack.org/en/stable/yaml_configuration/">The Stack docs</a> don't seem to mention <code>package.yaml</code> at all. Does a specification exist?</p>
