Eliminate internal render stack since we only need its head and tail

actionpack/lib/action_view/base.rb

@@ -221,10 +221,12 @@ def include(*args)
     def initialize(view_paths = [], assigns_for_first_render = {}, controller = nil)#:nodoc:
       @assigns = assigns_for_first_render
       @assigns_added = nil
-      @_render_stack = []
       @controller = controller
       @helpers = ProxyModule.new(self)
       self.view_paths = view_paths
+
+      @_first_template = nil
+      @_current_template = nil
     end
 
     attr_reader :view_paths
@@ -286,7 +288,19 @@ def template_format
     # Access the current template being rendered.
     # Returns a ActionView::Template object.
     def template
-      @_render_stack.last
+      @_current_template
+    end
+
+    def template=(template) #:nodoc:
+      @_first_template ||= template
+      @_current_template = template
+    end
+
+    def with_template(current_template)
+      last_template, self.template = template, current_template
+      yield
+    ensure
+      self.template = last_template
     end
 
     private

actionpack/lib/action_view/renderable.rb

@@ -27,23 +27,19 @@ def method_name_without_locals
     def render(view, local_assigns = {})
       compile(local_assigns)
 
-      stack = view.instance_variable_get(:@_render_stack)
-      stack.push(self)
-
-      view.send(:_evaluate_assigns_and_ivars)
-      view.send(:_set_controller_content_type, mime_type) if respond_to?(:mime_type)
-
-      result = view.send(method_name(local_assigns), local_assigns) do |*names|
-        ivar = :@_proc_for_layout
-        if !view.instance_variable_defined?(:"@content_for_#{names.first}") && view.instance_variable_defined?(ivar) && (proc = view.instance_variable_get(ivar))
-          view.capture(*names, &proc)
-        elsif view.instance_variable_defined?(ivar = :"@content_for_#{names.first || :layout}")
-          view.instance_variable_get(ivar)
+      view.with_template self do
+        view.send(:_evaluate_assigns_and_ivars)
+        view.send(:_set_controller_content_type, mime_type) if respond_to?(:mime_type)
+
+        view.send(method_name(local_assigns), local_assigns) do |*names|
+          ivar = :@_proc_for_layout
+          if !view.instance_variable_defined?(:"@content_for_#{names.first}") && view.instance_variable_defined?(ivar) && (proc = view.instance_variable_get(ivar))
+            view.capture(*names, &proc)
+          elsif view.instance_variable_defined?(ivar = :"@content_for_#{names.first || :layout}")
+            view.instance_variable_get(ivar)
+          end
         end
       end
-
-      stack.pop
-      result
     end
 
     def method_name(local_assigns)