Allow layout fallback when using `layout` method

Rails will now use your default layout (such as "layouts/application") when you specify a layout with `:only` and `:except` condition, and those conditions fail.

For example, consider this snippet:

    class CarsController
      layout 'single_car', :only => :show
    end

Rails will use 'layouts/single_car' when a request comes in `:show` action, and use 'layouts/application' (or 'layouts/cars', if exists) when a request comes in for any other actions.

3 files changed, 93 insertions, 26 deletions

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 6d62d5eeec..8844d6e6f6 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,5 +1,15 @@
 ## Rails 3.2.0 (unreleased) ##
 
+*   Rails will now use your default layout (such as "layouts/application") when you specify a layout with `:only` and `:except` condition, and those conditions fail. *Prem Sichanugrist*
+
+    For example, consider this snippet:
+
+        class CarsController
+          layout 'single_car', :only => :show
+        end
+
+    Rails will use 'layouts/single_car' when a request comes in `:show` action, and use 'layouts/application' (or 'layouts/cars', if exists) when a request comes in for any other actions.
+
 *   form_for with +:as+ option uses "#{action}_#{as}" as css class and id:
 
     Before:
diff --git a/actionpack/lib/abstract_controller/layouts.rb b/actionpack/lib/abstract_controller/layouts.rb
index bbf5efe565..79edd5418e 100644
--- a/actionpack/lib/abstract_controller/layouts.rb
+++ b/actionpack/lib/abstract_controller/layouts.rb
@@ -244,42 +244,51 @@ module AbstractController
       def _write_layout_method
         remove_possible_method(:_layout)
 
-        case defined?(@_layout) ? @_layout : nil
-        when String
-          self.class_eval %{def _layout; #{@_layout.inspect} end}, __FILE__, __LINE__
-        when Symbol
-          self.class_eval <<-ruby_eval, __FILE__, __LINE__ + 1
-            def _layout
+        prefixes = _implied_layout_name =~ /\blayouts/ ? [] : ["layouts"]
+        layout_definition = case defined?(@_layout) ? @_layout : nil
+          when String
+            @_layout.inspect
+          when Symbol
+            <<-RUBY
               #{@_layout}.tap do |layout|
                 unless layout.is_a?(String) || !layout
                   raise ArgumentError, "Your layout method :#{@_layout} returned \#{layout}. It " \
                     "should have returned a String, false, or nil"
                 end
               end
-            end
-          ruby_eval
-        when Proc
-          define_method :_layout_from_proc, &@_layout
-          self.class_eval %{def _layout; _layout_from_proc(self) end}, __FILE__, __LINE__
-        when false
-          self.class_eval %{def _layout; end}, __FILE__, __LINE__
-        when true
-          raise ArgumentError, "Layouts must be specified as a String, Symbol, false, or nil"
-        when nil
-          if name
-            _prefixes = _implied_layout_name =~ /\blayouts/ ? [] : ["layouts"]
-
-            self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
-              def _layout
-                if template_exists?("#{_implied_layout_name}", #{_prefixes.inspect})
+            RUBY
+          when Proc
+            define_method :_layout_from_proc, &@_layout
+            "_layout_from_proc(self)"
+          when false
+            nil
+          when true
+            raise ArgumentError, "Layouts must be specified as a String, Symbol, false, or nil"
+          when nil
+            if name
+              <<-RUBY
+                if template_exists?("#{_implied_layout_name}", #{prefixes.inspect})
                   "#{_implied_layout_name}"
                 else
                   super
                 end
+              RUBY
+            end
+          end
+
+        self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
+          def _layout
+            if action_has_layout?
+              #{layout_definition}
+            elsif self.class.name
+              if template_exists?("#{_implied_layout_name}", #{prefixes.inspect})
+                  "#{_implied_layout_name}"
+              else
+                super
               end
-            RUBY
+            end
           end
-        end
+        RUBY
         self.class_eval { private :_layout }
       end
     end
@@ -337,7 +346,7 @@ module AbstractController
     # * <tt>template</tt> - The template object for the default layout (or nil)
     def _default_layout(require_layout = false)
       begin
-        layout_name = _layout if action_has_layout?
+        layout_name = _layout
       rescue NameError => e
         raise e, "Could not render layout: #{e.message}"
       end
diff --git a/actionpack/test/abstract/layouts_test.rb b/actionpack/test/abstract/layouts_test.rb
index 86208899f8..a5382a730d 100644
--- a/actionpack/test/abstract/layouts_test.rb
+++ b/actionpack/test/abstract/layouts_test.rb
@@ -141,6 +141,30 @@ module AbstractControllerTests
       end
     end
 
+    class WithOnlyConditional < WithStringImpliedChild
+      layout "overwrite", :only => :show
+
+      def index
+        render :template => ActionView::Template::Text.new("Hello index!")
+      end
+
+      def show
+        render :template => ActionView::Template::Text.new("Hello show!")
+      end
+    end
+
+    class WithExceptConditional < WithStringImpliedChild
+      layout "overwrite", :except => :show
+
+      def index
+        render :template => ActionView::Template::Text.new("Hello index!")
+      end
+
+      def show
+        render :template => ActionView::Template::Text.new("Hello show!")
+      end
+    end
+
     class TestBase < ActiveSupport::TestCase
       test "when no layout is specified, and no default is available, render without a layout" do
         controller = Blank.new
@@ -260,6 +284,30 @@ module AbstractControllerTests
           end
         end
       end
+
+      test "when specify an :only option which match current action name" do
+        controller = WithOnlyConditional.new
+        controller.process(:show)
+        assert_equal "Overwrite Hello show!", controller.response_body
+      end
+
+      test "when specify an :only option which does not match current action name" do
+        controller = WithOnlyConditional.new
+        controller.process(:index)
+        assert_equal "With Implied Hello index!", controller.response_body
+      end
+
+      test "when specify an :except option which match current action name" do
+        controller = WithExceptConditional.new
+        controller.process(:show)
+        assert_equal "With Implied Hello show!", controller.response_body
+      end
+
+      test "when specify an :except option which does not match current action name" do
+        controller = WithExceptConditional.new
+        controller.process(:index)
+        assert_equal "Overwrite Hello index!", controller.response_body
+      end
     end
   end
-end
\ No newline at end of file
+end