app/views/application/_form_errors.html.erb
<% if target.errors.any? %>
<div class="alert alert-danger">
<p><%= pluralize(target.errors.count, 'error') %> prohibited this <%= target.model_name.human.downcase %> from being saved:</p>
<ul>
<% target.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>