title: Scope with joins in Rails 4.2
body: <p>I've got code similar to</p>
  
  <pre><code>class Article &lt; ActiveRecord::Base
    has_many :comments
    scope :with_comments, joins(:comments)
  end
  </code></pre>
  
  <p>based on <a href="https://stackoverflow.com/a/18082147/38765">this answer</a>, but when I use it in Rails 4.2, I get </p>
  
  <pre><code>/Users/agrimm/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/activerecord-4.2.0/lib/active_record/scoping/named.rb:143:in `scope': The scope body needs to be callable. (ArgumentError)
  </code></pre>
  
  <p>Have the rules with regards to allowing joins in scope changed between Rails 4 and Rails 4.2? I can see mention of joins in the <a href="http://guides.rubyonrails.org/4_2_release_notes.html" rel="nofollow noreferrer">4.2 release notes</a>, but I can't tell if it's applicable here.</p>