Undeprecate the :extend option

Suggested by @dhh.

It doesn't affect the generated SQL, so seems reasonable to continue to
allow it as an association option.

activerecord/CHANGELOG.md

@@ -985,7 +985,6 @@
 
       * `:conditions` becomes `:where`.
       * `:include` becomes `:includes`.
-      * `:extend` becomes `:extending`.
 
     The code to implement the deprecated features has been moved out to
     the `activerecord-deprecated_finders` gem. This gem is a dependency

activerecord/activerecord.gemspec

@@ -25,5 +25,5 @@ Gem::Specification.new do |s|
   s.add_dependency 'activemodel',   version
 
   s.add_dependency 'arel',                            '~> 3.0.2'
-  s.add_dependency 'activerecord-deprecated_finders', '0.0.1'
+  s.add_dependency 'activerecord-deprecated_finders', '0.0.2'
 end

activerecord/lib/active_record/associations/association_scope.rb

@@ -16,6 +16,7 @@ module ActiveRecord
       def scope
         scope = klass.unscoped
         scope.merge! eval_scope(klass, reflection.scope) if reflection.scope
+        scope.extending! Array(options[:extend])
         add_constraints(scope)
       end
 

activerecord/lib/active_record/associations/builder/collection_association.rb

@@ -6,7 +6,8 @@ module ActiveRecord::Associations::Builder
     CALLBACKS = [:before_add, :after_add, :before_remove, :after_remove]
 
     def valid_options
-      super + [:table_name, :finder_sql, :counter_sql, :before_add, :after_add, :before_remove, :after_remove]
+      super + [:table_name, :finder_sql, :counter_sql, :before_add,
+               :after_add, :before_remove, :after_remove, :extend]
     end
 
     attr_reader :block_extension, :extension_module

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -1717,4 +1717,16 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     author = authors(:mary)
     assert !author.first_posts.exists?
   end
+
+  test "association with extend option" do
+    post = posts(:welcome)
+    assert_equal "lifo",  post.comments_with_extend.author
+    assert_equal "hello", post.comments_with_extend.greeting
+  end
+
+  test "association with extend option with multiple extensions" do
+    post = posts(:welcome)
+    assert_equal "lifo",  post.comments_with_extend_2.author
+    assert_equal "hello", post.comments_with_extend_2.greeting
+  end
 end

activerecord/test/models/post.rb

@@ -5,6 +5,12 @@ class Post < ActiveRecord::Base
     end
   end
 
+  module NamedExtension2
+    def greeting
+      "hello"
+    end
+  end
+
   scope :containing_the_letter_a, -> { where("body LIKE '%a%'") }
   scope :ranked_by_comments,      -> { order("comments_count DESC") }
 
@@ -43,6 +49,14 @@ class Post < ActiveRecord::Base
     end
   end
 
+  has_many :comments_with_extend, extend: NamedExtension, class_name: "Comment", foreign_key: "post_id" do
+    def greeting
+      "hello"
+    end
+  end
+
+  has_many :comments_with_extend_2, extend: [NamedExtension, NamedExtension2], class_name: "Comment", foreign_key: "post_id"
+
   has_many :author_favorites, :through => :author
   has_many :author_categorizations, :through => :author, :source => :categorizations
   has_many :author_addresses, :through => :author