Check for uninitialized instance variables

actionpack/lib/action_controller/base.rb

@@ -453,7 +453,7 @@ def view_paths=(value)
       #   ArticleController.prepend_view_path(["views/default", "views/custom"])
       #
       def prepend_view_path(path)
-        @view_paths = superclass.view_paths.dup if @view_paths.nil?
+        @view_paths = superclass.view_paths.dup if !defined?(@view_paths) || @view_paths.nil?
         @view_paths.unshift(*path)
       end
 

actionpack/lib/action_view/base.rb

@@ -278,9 +278,9 @@ def render(options = {}, local_assigns = {}, &block) #:nodoc:
     # the same name but differing formats.  See +Request#template_format+
     # for more details.
     def template_format
-      return @template_format if @template_format
-
-      if controller && controller.respond_to?(:request)
+      if defined? @template_format
+        @template_format
+      elsif controller && controller.respond_to?(:request)
         @template_format = controller.request.template_format
       else
         @template_format = :html
@@ -366,7 +366,9 @@ def _render_with_layout(options, local_assigns, &block) #:nodoc:
           end
         else
           begin
-            original_content_for_layout, @content_for_layout = @content_for_layout, render(options)
+            original_content_for_layout = @content_for_layout if defined?(@content_for_layout)
+            @content_for_layout = render(options)
+
             if (options[:inline] || options[:file] || options[:text])
               @cached_content_for_layout = @content_for_layout
               render(:file => partial_layout, :locals => local_assigns)

actionpack/lib/action_view/renderable.rb

 module ActionView
-  module Renderable
-    # NOTE: The template that this mixin is beening include into is frozen
-    # So you can not set or modify any instance variables
-
+  # NOTE: The template that this mixin is being included into is frozen
+  # so you cannot set or modify any instance variables
+  module Renderable #:nodoc:
     extend ActiveSupport::Memoizable
 
     def self.included(base)
@@ -33,10 +32,11 @@ def render(view, local_assigns = {})
       view.send(:_set_controller_content_type, mime_type) if respond_to?(:mime_type)
 
       view.send(method_name(local_assigns), local_assigns) do |*names|
-        if proc = view.instance_variable_get("@_proc_for_layout")
+        ivar = :@_proc_for_layout
+        if view.instance_variable_defined?(ivar) and proc = view.instance_variable_get(ivar)
           view.capture(*names, &proc)
-        else
-          view.instance_variable_get("@content_for_#{names.first || 'layout'}")
+        elsif view.instance_variable_defined?(ivar = :"@content_for_#{names.first || :layout}")
+          view.instance_variable_get(ivar)
         end
       end
     end

actionpack/lib/action_view/renderable_partial.rb

 module ActionView
-  module RenderablePartial
-    # NOTE: The template that this mixin is beening include into is frozen
-    # So you can not set or modify any instance variables
-
+  # NOTE: The template that this mixin is being included into is frozen
+  # so you cannot set or modify any instance variables
+  module RenderablePartial #:nodoc:
     extend ActiveSupport::Memoizable
 
     def variable_name
@@ -30,10 +29,13 @@ def render_partial(view, object = nil, local_assigns = {}, as = nil)
         local_assigns[variable_name]
 
       if view.respond_to?(:controller)
-        object ||= ActiveSupport::Deprecation::DeprecatedObjectProxy.new(
-          view.controller.instance_variable_get("@#{variable_name}"),
-          "@#{variable_name} will no longer be implicitly assigned to #{variable_name}"
-        )
+        ivar = :"@#{variable_name}"
+        object ||=
+          if view.controller.instance_variable_defined?(ivar)
+            ActiveSupport::Deprecation::DeprecatedObjectProxy.new(
+              view.controller.instance_variable_get(ivar),
+              "#{ivar} will no longer be implicitly assigned to #{variable_name}")
+          end
       end
 
       # Ensure correct object is reassigned to other accessors