after_build support in class-based extension

middleman-core/lib/middleman-core/extensions.rb

@@ -165,6 +165,16 @@ module Middleman
           ext.app.sitemap.register_resource_list_manipulator(ext.class.extension_name, ext)
         end
       end
+
+      if ext.respond_to?(:after_build)
+        klass.after_build do |builder|
+          if ext.method(:after_build).arity === 1
+            ext.after_build(builder)
+          else
+            ext.after_build
+          end
+        end
+      end
     end
   end
 end

middleman-core/lib/middleman-more/extensions/gzip.rb

@@ -18,30 +18,28 @@ class Middleman::Extensions::Gzip < ::Middleman::Extension
     require 'zlib'
     require 'stringio'
     require 'find'
+  end
 
-    gzip_ext = self
-
-    app.after_build do |builder|
-      paths = ::Middleman::Util.all_files_under(self.class.inst.build_dir)
+  def after_build(builder)
+    paths = ::Middleman::Util.all_files_under(app.build_dir)
     total_savings = 0
 
     paths.each do |path|
-        next unless gzip_ext.options.exts.include? path.extname
+      next unless options.exts.include? path.extname
 
-        output_filename, old_size, new_size = gzip_ext.gzip_file(path.to_s)
+      output_filename, old_size, new_size = gzip_file(path.to_s)
 
       if output_filename
         total_savings += (old_size - new_size)
         size_change_word = (old_size - new_size) > 0 ? 'smaller' : 'larger'
         old_locale = I18n.locale
         I18n.locale = :en # use the english localizations for printing out file sizes to make sure the localizations exist
-          builder.say_status :gzip, "#{output_filename} (#{number_to_human_size((old_size - new_size).abs)} #{size_change_word})"
+        builder.say_status :gzip, "#{output_filename} (#{app.number_to_human_size((old_size - new_size).abs)} #{size_change_word})"
         I18n.locale = old_locale
       end
     end
 
-      builder.say_status :gzip, "Total gzip savings: #{number_to_human_size(total_savings)}", :blue
-    end
+    builder.say_status :gzip, "Total gzip savings: #{app.number_to_human_size(total_savings)}", :blue
   end
 
   def gzip_file(path)