Collections automatically cache and fetch partials.

Collections can take advantage of `multi_read` if they render one template
and their partials begin with a cache call.

The cache call must correspond to either what the collections elements are
rendered as, or match the inferred name of the partial.

So with a notifications/_notification.html.erb template like:

```ruby
<% cache notification %>
  <%# ... %>
<% end %>
```

A collection would be able to use `multi_read` if rendered like:

```ruby
<%= render @notifications %>
<%= render partial: 'notifications/notification', collection: @notifications, as: :notification %>
```

1 files changed, 18 insertions, 0 deletions

diff --git a/actionview/lib/action_view/template/handlers/erb.rb b/actionview/lib/action_view/template/handlers/erb.rb
index 85a100ed4c..88a8570706 100644
--- a/actionview/lib/action_view/template/handlers/erb.rb
+++ b/actionview/lib/action_view/template/handlers/erb.rb
@@ -123,6 +123,24 @@ module ActionView
           ).src
         end
 
+        # Returns Regexp to extract a cached resource's name from a cache call at the
+        # first line of a template.
+        # The extracted cache name is expected in $1.
+        #
+        #   <% cache notification do %> # => notification
+        #
+        # The pattern should support templates with a beginning comment:
+        #
+        #   <%# Still extractable even though there's a comment %>
+        #   <% cache notification do %> # => notification
+        #
+        # But fail to extract a name if a resource association is cached.
+        #
+        #   <% cache notification.event do %> # => nil
+        def resource_cache_call_pattern
+          /\A(?:<%#.*%>\n?)?<% cache\(?\s*(\w+\.?)/
+        end
+
       private
 
         def valid_encoding(string, encoding)