Bring back support for callable cache key when rendering collection

actionpack/test/controller/caching_test.rb

@@ -393,9 +393,14 @@ def index_with_comment
    @customers = [Customer.new('david', 1)]
    render partial: 'customers/commented_customer', collection: @customers, as: :customer, cached: true
  end

  def index_with_callable_cache_key
    @customers = [Customer.new('david', 1)]
    render partial: 'customers/customer', collection: @customers, cached: -> customer { 'cached_david' }
  end
end

class AutomaticCollectionCacheTest < ActionController::TestCase
class CollectionCacheTest < ActionController::TestCase
  def setup
    super
    @controller = CollectionCacheController.new
@@ -438,6 +443,11 @@ def test_caching_works_with_beginning_comment
    assert_equal 1, @controller.partial_rendered_times
  end

  def test_caching_with_callable_cache_key
    get :index_with_callable_cache_key
    assert_customer_cached 'cached_david', 'david, 1'
  end

  private
    def assert_customer_cached(key, content)
      assert_match content,

actionview/lib/action_view/helpers/cache_helper.rb

@@ -130,9 +130,10 @@ module CacheHelper
      #
      # 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 CacheHelper
      # 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)

actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb

@@ -25,9 +25,15 @@ def cache_collection_render(instrumentation_payload)
        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