Override default_render's behavior with a block

In 0de4a23 the behavior when there is a missing template was changed to
not raise an error, but instead head :no_content.  This is a breaking
change and some gems rely on this happening.

To allow gems and other code to work around this, allow
`default_render` to take a block which, if provided, will
execute the contents of that block instead of doing the `head :no_content`.

1 files changed, 17 insertions, 2 deletions

diff --git a/actionpack/lib/action_controller/metal/implicit_render.rb b/actionpack/lib/action_controller/metal/implicit_render.rb
index d66b2214ce..17fcc2fa02 100644
--- a/actionpack/lib/action_controller/metal/implicit_render.rb
+++ b/actionpack/lib/action_controller/metal/implicit_render.rb
@@ -3,12 +3,27 @@ module ActionController
 
     include BasicImplicitRender
 
+    # Renders the template corresponding to the controller action, if it exists.
+    # The action name, format, and variant are all taken into account.
+    # For example, the "new" action with an HTML format and variant "phone" 
+    # would try to render the <tt>new.html+phone.erb</tt> template.
+    #
+    # If no template is found <tt>ActionController::BasicImplicitRender</tt>'s implementation is called, unless
+    # a block is passed. In that case, it will override the super implementation.
+    #
+    #   default_render do
+    #     head 404 # No template was found
+    #   end
     def default_render(*args)
       if template_exists?(action_name.to_s, _prefixes, variants: request.variant)
         render(*args)
       else
-        logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content" if logger
-        super
+        if block_given?
+          yield(*args)
+        else
+          logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content" if logger
+          super
+        end
       end
     end