Merge branch 'docs-render_if_exists-opts-caveat' into 'master'

Explain render_if_exists opts caveat

See merge request gitlab-org/gitlab-ce!28366

doc/development/ee_features.md

@@ -446,16 +446,28 @@ The disadvantage of this:
   port `render_if_exists` to CE.
 - If we have typos in the partial name, it would be silently ignored.
 
+
+##### Caveats
+
 The `render_if_exists` view path argument must be relative to `app/views/` and `ee/app/views`.
 Resolving an EE template path that is relative to the CE view path will not work.
 
 ```haml
 - # app/views/projects/index.html.haml
 
-= render_if_exists 'button' # Will not render `ee/app/views/projects/_button` and quietly fail
+= render_if_exists 'button' # Will not render `ee/app/views/projects/_button` and will quietly fail
 = render_if_exists 'projects/button' # Will render `ee/app/views/projects/_button`
 ```
 
+You should not explicitly set render options like `partial` or provide a `locals` hash.
+The first argument should be a path string and the second can be a hash replacing `locals`.
+
+```ruby
+render partial: 'projects/button', locals: { project: project }
+# becomes
+render_if_exists 'projects/button', project: project
+```
+
 #### Using `render_ce`
 
 For `render` and `render_if_exists`, they search for the EE partial first,