Return rendered template information instead of just strings

This commit introduces "rendered template" and "rendered collection"
objects.  The template renderers can now return a more complex object
than just strings.  This allows the framework to get more information
about the templates that were rendered.  In this commit we use the
rendered template object to set the "rendered_format" on the lookup
context in the controller rather than all the way in the template renderer.
That means we don't need to check the "rendered_format" every time we
render a template, we just do it once after all templates have been
rendered.

7 files changed, 92 insertions, 31 deletions

diff --git a/actionview/lib/action_view/renderer/abstract_renderer.rb b/actionview/lib/action_view/renderer/abstract_renderer.rb
index ae366ce54a..2a51f2ef99 100644
--- a/actionview/lib/action_view/renderer/abstract_renderer.rb
+++ b/actionview/lib/action_view/renderer/abstract_renderer.rb
@@ -27,6 +27,46 @@ module ActionView
       raise NotImplementedError
     end
 
+    class RenderedCollection # :nodoc:
+      attr_reader :rendered_templates
+
+      def initialize(rendered_templates, spacer)
+        @rendered_templates = rendered_templates
+        @spacer = spacer
+      end
+
+      def body
+        @rendered_templates.map(&:body).join(@spacer.body).html_safe
+      end
+
+      def format
+        rendered_templates.first.format
+      end
+
+      class EmptyCollection
+        def format; nil; end
+        def body; nil; end
+      end
+
+      EMPTY = EmptyCollection.new
+    end
+
+    class RenderedTemplate # :nodoc:
+      attr_reader :body, :layout, :template
+
+      def initialize(body, layout, template)
+        @body = body
+        @layout = layout
+        @template = template
+      end
+
+      def format
+        template.formats.first
+      end
+
+      EMPTY_SPACER = Struct.new(:body).new
+    end
+
     private
 
       def extract_details(options) # :doc:
@@ -49,5 +89,13 @@ module ActionView
 
         @lookup_context.formats = formats | @lookup_context.formats
       end
+
+      def build_rendered_template(content, layout, template)
+        RenderedTemplate.new content, layout, template
+      end
+
+      def build_rendered_collection(templates, spacer)
+        RenderedCollection.new(templates, spacer)
+      end
   end
 end
diff --git a/actionview/lib/action_view/renderer/partial_renderer.rb b/actionview/lib/action_view/renderer/partial_renderer.rb
index f8a6f13ae9..f4319b8528 100644
--- a/actionview/lib/action_view/renderer/partial_renderer.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer.rb
@@ -314,14 +314,6 @@ module ActionView
         template = nil
       end
 
-      @lookup_context.rendered_format ||= begin
-        if template && template.formats.first
-          template.formats.first
-        else
-          formats.first
-        end
-      end
-
       if @collection
         render_collection(context, template)
       else
@@ -334,10 +326,13 @@ module ActionView
       def render_collection(view, template)
         identifier = (template && template.identifier) || @path
         instrument(:collection, identifier: identifier, count: @collection.size) do |payload|
-          return nil if @collection.blank?
+          return RenderedCollection::EMPTY if @collection.blank?
 
-          if @options.key?(:spacer_template)
-            spacer = find_template(@options[:spacer_template], @locals.keys).render(view, @locals)
+          spacer = if @options.key?(:spacer_template)
+            spacer_template = find_template(@options[:spacer_template], @locals.keys)
+            build_rendered_template(spacer_template.render(view, @locals), nil, spacer_template)
+          else
+            RenderedTemplate::EMPTY_SPACER
           end
 
           collection_body = if template
@@ -347,7 +342,7 @@ module ActionView
           else
             collection_without_template(view)
           end
-          collection_body.join(spacer).html_safe
+          build_rendered_collection(collection_body, spacer)
         end
       end
 
@@ -369,7 +364,7 @@ module ActionView
 
           content = layout.render(view, locals) { content } if layout
           payload[:cache_hit] = view.view_renderer.cache_hits[template.virtual_path]
-          content
+          build_rendered_template(content, layout, template)
         end
       end
 
@@ -460,7 +455,7 @@ module ActionView
           content = template.render(view, locals)
           content = layout.render(view, locals) { content } if layout
           partial_iteration.iterate!
-          content
+          build_rendered_template(content, layout, template)
         end
       end
 
@@ -482,7 +477,7 @@ module ActionView
           template = (cache[path] ||= find_template(path, keys + [as, counter, iteration]))
           content = template.render(view, locals)
           partial_iteration.iterate!
-          content
+          build_rendered_template(content, nil, template)
         end
       end
 
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 9f1de5a397..401391290f 100644
--- a/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
+++ b/actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb
@@ -40,7 +40,7 @@ module ActionView
         rendered_partials = @collection.empty? ? [] : yield
 
         index = 0
-        fetch_or_cache_partial(cached_partials, order_by: keyed_collection.each_key) do
+        fetch_or_cache_partial(cached_partials, template, order_by: keyed_collection.each_key) do
           # This block is called once
           # for every cache miss while preserving order.
           rendered_partials[index].tap { index += 1 }
@@ -81,11 +81,13 @@ module ActionView
       #
       # If the partial is not already cached it will also be
       # written back to the underlying cache store.
-      def fetch_or_cache_partial(cached_partials, order_by:)
+      def fetch_or_cache_partial(cached_partials, template, order_by:)
         order_by.map do |cache_key|
-          cached_partials.fetch(cache_key) do
+          if content = cached_partials[cache_key]
+            build_rendered_template(content, nil, template)
+          else
             yield.tap do |rendered_partial|
-              collection_cache.write(cache_key, rendered_partial)
+              collection_cache.write(cache_key, rendered_partial.body)
             end
           end
         end
diff --git a/actionview/lib/action_view/renderer/renderer.rb b/actionview/lib/action_view/renderer/renderer.rb
index 3f3a97529d..485eb1a5b4 100644
--- a/actionview/lib/action_view/renderer/renderer.rb
+++ b/actionview/lib/action_view/renderer/renderer.rb
@@ -19,10 +19,14 @@ module ActionView
 
     # Main render entry point shared by Action View and Action Controller.
     def render(context, options)
+      render_to_object(context, options).body
+    end
+
+    def render_to_object(context, options) # :nodoc:
       if options.key?(:partial)
-        render_partial(context, options)
+        render_partial_to_object(context, options)
       else
-        render_template(context, options)
+        render_template_to_object(context, options)
       end
     end
 
@@ -41,16 +45,24 @@ module ActionView
 
     # Direct access to template rendering.
     def render_template(context, options) #:nodoc:
-      TemplateRenderer.new(@lookup_context).render(context, options)
+      render_template_to_object(context, options).body
     end
 
     # Direct access to partial rendering.
     def render_partial(context, options, &block) #:nodoc:
-      PartialRenderer.new(@lookup_context).render(context, options, block)
+      render_partial_to_object(context, options, &block).body
     end
 
     def cache_hits # :nodoc:
       @cache_hits ||= {}
     end
+
+    def render_template_to_object(context, options) #:nodoc:
+      TemplateRenderer.new(@lookup_context).render(context, options)
+    end
+
+    def render_partial_to_object(context, options, &block) #:nodoc:
+      PartialRenderer.new(@lookup_context).render(context, options, block)
+    end
   end
 end
diff --git a/actionview/lib/action_view/renderer/streaming_template_renderer.rb b/actionview/lib/action_view/renderer/streaming_template_renderer.rb
index f414620923..279ef3c680 100644
--- a/actionview/lib/action_view/renderer/streaming_template_renderer.rb
+++ b/actionview/lib/action_view/renderer/streaming_template_renderer.rb
@@ -44,7 +44,7 @@ module ActionView
     # object that responds to each. This object is initialized with a block
     # that knows how to render the template.
     def render_template(view, template, layout_name = nil, locals = {}) #:nodoc:
-      return [super] unless layout_name && template.supports_streaming?
+      return [super.body] unless layout_name && template.supports_streaming?
 
       locals ||= {}
       layout   = layout_name && find_layout(layout_name, locals.keys, [formats.first])
diff --git a/actionview/lib/action_view/renderer/template_renderer.rb b/actionview/lib/action_view/renderer/template_renderer.rb
index c36baeffcd..7052fe0961 100644
--- a/actionview/lib/action_view/renderer/template_renderer.rb
+++ b/actionview/lib/action_view/renderer/template_renderer.rb
@@ -10,8 +10,6 @@ module ActionView
 
       prepend_formats(template.formats)
 
-      @lookup_context.rendered_format ||= (template.formats.first || formats.first)
-
       render_template(context, template, options[:layout], options[:locals] || {})
     end
 
@@ -46,23 +44,24 @@ module ActionView
       # Renders the given template. A string representing the layout can be
       # supplied as well.
       def render_template(view, template, layout_name, locals)
-        render_with_layout(view, layout_name, locals) do |layout|
+        render_with_layout(view, layout_name, template, locals) do |layout|
           instrument(:template, identifier: template.identifier, layout: layout.try(:virtual_path)) do
             template.render(view, locals) { |*name| view._layout_for(*name) }
           end
         end
       end
 
-      def render_with_layout(view, path, locals)
+      def render_with_layout(view, path, template, locals)
         layout  = path && find_layout(path, locals.keys, [formats.first])
         content = yield(layout)
 
-        if layout
+        body = if layout
           view.view_flow.set(:layout, content)
           layout.render(view, locals) { |*name| view._layout_for(*name) }
         else
           content
         end
+        build_rendered_template(body, layout, template)
       end
 
       # This is the method which actually finds the layout using details in the lookup
diff --git a/actionview/lib/action_view/rendering.rb b/actionview/lib/action_view/rendering.rb
index b798e80b04..699ccb0ca8 100644
--- a/actionview/lib/action_view/rendering.rb
+++ b/actionview/lib/action_view/rendering.rb
@@ -109,10 +109,15 @@ module ActionView
         context = view_context
 
         context.assign assigns if assigns
-        lookup_context.rendered_format = nil if options[:formats]
         lookup_context.variants = variant if variant
 
-        context.view_renderer.render(context, options)
+        rendered_template = context.in_rendering_context(options) do |renderer|
+          renderer.render_to_object(context, options)
+        end
+
+        lookup_context.rendered_format = rendered_template.format || lookup_context.formats.first
+
+        rendered_template.body
       end
 
       # Assign the rendered format to look up context.