1 files changed, 50 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller/metal/etag_with_template_digest.rb b/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
new file mode 100644
index 0000000000..669cf55bca
--- /dev/null
+++ b/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
@@ -0,0 +1,50 @@
+module ActionController
+  # When our views change, they should bubble up into HTTP cache freshness
+  # and bust browser caches. So the template digest for the current action
+  # is automatically included in the ETag.
+  #
+  # Enabled by default for apps that use Action View. Disable by setting
+  #
+  #   config.action_controller.etag_with_template_digest = false
+  #
+  # Override the template to digest by passing +:template+ to +fresh_when+
+  # and +stale?+ calls. For example:
+  #
+  #   # We're going to render widgets/show, not posts/show
+  #   fresh_when @post, template: 'widgets/show'
+  #
+  #   # We're not going to render a template, so omit it from the ETag.
+  #   fresh_when @post, template: false
+  #
+  module EtagWithTemplateDigest
+    extend ActiveSupport::Concern
+
+    include ActionController::ConditionalGet
+
+    included do
+      class_attribute :etag_with_template_digest
+      self.etag_with_template_digest = true
+
+      ActiveSupport.on_load :action_view, yield: true do
+        etag do |options|
+          determine_template_etag(options) if etag_with_template_digest
+        end
+      end
+    end
+
+    private
+    def determine_template_etag(options)
+      if template = pick_template_for_etag(options)
+        lookup_and_digest_template(template)
+      end
+    end
+
+    def pick_template_for_etag(options)
+      options.fetch(:template) { "#{controller_name}/#{action_name}" }
+    end
+
+    def lookup_and_digest_template(template)
+      ActionView::Digestor.digest name: template, finder: lookup_context
+    end
+  end
+end