Bring back support for callable cache_key on collection rendering

2 files changed, 19 insertions, 4 deletions

diff --git a/actionview/lib/action_view/helpers/cache_helper.rb b/actionview/lib/action_view/helpers/cache_helper.rb
index 4eaaa239e2..e28b02f015 100644
--- a/actionview/lib/action_view/helpers/cache_helper.rb
+++ b/actionview/lib/action_view/helpers/cache_helper.rb
@@ -130,9 +130,10 @@ module ActionView
       #
       # When rendering a collection of objects that each use the same partial, a `cached`
       # option can be passed.
+      #
       # For collections rendered such:
       #
-      #   <%= render partial: 'notifications/notification', collection: @notifications, cached: true %>
+      #   <%= render partial: 'projects/project', collection: @projects, cached: true %>
       #
       # The `cached: true` will make Action View's rendering read several templates
       # from cache at once instead of one call per template.
@@ -142,13 +143,21 @@ module ActionView
       # Works great alongside individual template fragment caching.
       # For instance if the template the collection renders is cached like:
       #
-      #   # notifications/_notification.html.erb
-      #   <% cache notification do %>
+      #   # projects/_project.html.erb
+      #   <% cache project do %>
       #     <%# ... %>
       #   <% end %>
       #
       # Any collection renders will find those cached templates when attempting
       # to read multiple templates at once.
+      #
+      # If your collection cache depends on multiple sources (try to avoid this to keep things simple),
+      # you can name all these dependencies as part of a block that returns an array:
+      #
+      #   <%= render partial: 'projects/project', collection: @projects, cached: -> project { [ project, current_user ] } %>
+      #
+      # This will include both records as part of the cache key and updating either of them will
+      # expire the cache.
       def cache(name = {}, options = {}, &block)
         if controller.respond_to?(:perform_caching) && controller.perform_caching
           name_options = options.slice(:skip_digest, :virtual_path)
diff --git a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
index f7deba94ce..1fbe209200 100644
--- a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -25,9 +25,15 @@ module ActionView
         end
       end
 
+      def callable_cache_key?
+        @options[:cached].respond_to?(:call)
+      end
+
       def collection_by_cache_keys
+        seed = callable_cache_key? ? @options[:cached] : ->(i) { i }
+
         @collection.each_with_object({}) do |item, hash|
-          hash[expanded_cache_key(item)] = item
+          hash[expanded_cache_key(seed.call(item))] = item
         end
       end