1 files changed, 70 insertions, 0 deletions
diff --git a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
new file mode 100644
index 0000000000..1147963882
--- /dev/null
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -0,0 +1,70 @@
+require 'active_support/core_ext/object/try'
+
+module ActionView
+  module CollectionCaching # :nodoc:
+    extend ActiveSupport::Concern
+
+    included do
+      # Fallback cache store if Action View is used without Rails.
+      # Otherwise overridden in Railtie to use Rails.cache.
+      mattr_accessor(:collection_cache) { ActiveSupport::Cache::MemoryStore.new }
+    end
+
+    private
+      def cache_collection_render
+        return yield unless cache_collection?
+
+        keyed_collection = collection_by_cache_keys
+        partial_cache = collection_cache.read_multi(*keyed_collection.keys)
+
+        @collection = keyed_collection.reject { |key, _| partial_cache.key?(key) }.values
+        rendered_partials = @collection.any? ? yield.dup : []
+
+        fetch_or_cache_partial(partial_cache, order_by: keyed_collection.each_key) do
+          rendered_partials.shift
+        end
+      end
+
+      def cache_collection?
+        @options.fetch(:cache, automatic_cache_eligible?)
+      end
+
+      def automatic_cache_eligible?
+        single_template_render? && !callable_cache_key? &&
+          @template.eligible_for_collection_caching?(as: @options[:as])
+      end
+
+      def single_template_render?
+        @template # Template is only set when a collection renders one template.
+      end
+
+      def callable_cache_key?
+        @options[:cache].respond_to?(:call)
+      end
+
+      def collection_by_cache_keys
+        seed = callable_cache_key? ? @options[:cache] : ->(i) { i }
+
+        @collection.each_with_object({}) do |item, hash|
+          hash[expanded_cache_key(seed.call(item))] = item
+        end
+      end
+
+      def expanded_cache_key(key)
+        key = @view.fragment_cache_key(@view.cache_fragment_name(key, virtual_path: @template.virtual_path))
+        key.frozen? ? key.dup : key # #read_multi & #write may require mutability, Dalli 2.6.0.
+      end
+
+      def fetch_or_cache_partial(cached_partials, order_by:)
+        cache_options = @options[:cache_options] || @locals[:cache_options] || {}
+
+        order_by.map do |key|
+          cached_partials.fetch(key) do
+            yield.tap do |rendered_partial|
+              collection_cache.write(key, rendered_partial, cache_options)
+            end
+          end
+        end
+      end
+  end
+end