1 files changed, 57 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..640c75536e
--- /dev/null
+++ b/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+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, default: 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
+
+      # Pick the template digest to include in the ETag. If the +:template+ option
+      # is present, use the named template. If +:template+ is +nil+ or absent, use
+      # the default controller/action template. If +:template+ is false, omit the
+      # template digest from the ETag.
+      def pick_template_for_etag(options)
+        unless options[:template] == false
+          options[:template] || "#{controller_path}/#{action_name}"
+        end
+      end
+
+      def lookup_and_digest_template(template)
+        ActionView::Digestor.digest name: template, finder: lookup_context
+      end
+  end
+end