title: How do I add Platforms to an Existing Flutter App/Project?
body: <p>I created a Flutter app with mobile support only:</p>
  <pre class="lang-sh prettyprint-override"><code>flutter create --platforms=ios,android foo
  </code></pre>
  <p>I also have another Flutter project that I created before web was supported by Flutter, which is why it only contains support for mobile.</p>
  <hr />
  <p>Now, I want to run my app on web and macOS, but I receive the following error when trying to use <code>flutter run -d macos</code>:</p>
  <pre><code>Exception: No macOS desktop project configured. See https://flutter.dev/desktop#add-desktop-support-to-an-existing-app to learn about adding macOS support to a project.
  </code></pre>