In the app I'm currently developing, it has occurred that I want to conditionally wrap a block of ERB in updates_for based on authorization. So typically one would do:

<% if policy(post).edit? %>
  <%= updates_for post ... %>
    <%= post.content %>
  <% end %>
<% else %>
  <%= post.content %>
<% end %>

which, depending on your setup, might lead to a lot of duplication. This PR simplifies it to

<%= updates_for_if policy(post).edit?, post ... %>
  <%= post.content %>
<% end %>

in the spirit of link_to_if etc.