Add deprecation notice

Author: josh

lib/sass/rails/importer.rb

@@ -103,6 +103,33 @@ def extensions
             'css.sass.erb' => :sass_erb
           }.merge(super)
         end
+
+        def find_relative(*args)
+          deprecate_extra_css_extension(super)
+        end
+
+        def find(*args)
+          deprecate_extra_css_extension(super)
+        end
+
+        private
+          def deprecate_extra_css_extension(engine)
+            if engine && filename = engine.options[:filename]
+              if filename.end_with?('.css.scss')
+                msg = "Extra .css in SCSS file is unnecessary. Rename #{filename} to #{filename.sub('.css.scss', '.scss')}."
+              elsif filename.end_with?('.css.sass')
+                msg = "Extra .css in SCSS file is unnecessary. Rename #{filename} to #{filename.sub('.css.sass', '.sass')}."
+              elsif filename.end_with?('.css.scss.erb')
+                msg = "Extra .css in SCSS/ERB file is unnecessary. Rename #{filename} to #{filename.sub('.css.scss.erb', '.scss.erb')}."
+              elsif filename.end_with?('.css.sass.erb')
+                msg = "Extra .css in SASS/ERB file is unnecessary. Rename #{filename} to #{filename.sub('.css.sass.erb', '.sass.erb')}."
+              end
+
+              ActiveSupport::Deprecation.warn(msg) if msg
+            end
+
+            engine
+          end
       end
 
       include Deprecated