add `extend` option on `has_and_belongs_to_many`.

3 files changed, 20 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index a3e2d5bd8e..e90490f8b6 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Pass `:extend` option for `has_and_belongs_to_many` associations to the underlying `has_many :through`.
+
+    *Jaehyun Shin*
+
 *   Deprecate `Relation#uniq` use `Relation#distinct` instead.
 
     See #9683.
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 779a3fbbbd..1ca648d48d 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1737,7 +1737,7 @@ module ActiveRecord
         hm_options[:through] = middle_reflection.name
         hm_options[:source] = join_model.right_reflection.name
 
-        [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name].each do |k|
+        [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name, :extend].each do |k|
           hm_options[k] = options[k] if options.key? k
         end
 
diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index 2ec2bb1754..e584c94ad8 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -83,6 +83,16 @@ class DeveloperWithSymbolClassName < Developer
   has_and_belongs_to_many :projects, class_name: :ProjectWithSymbolsForKeys
 end
 
+class DeveloperWithExtendOption < Developer
+  module NamedExtension
+    def category
+      'sns'
+    end
+  end
+
+  has_and_belongs_to_many :projects, extend: NamedExtension
+end
+
 class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :categories, :posts, :categories_posts, :developers, :projects, :developers_projects,
            :parrots, :pirates, :parrots_pirates, :treasures, :price_estimates, :tags, :taggings, :computers
@@ -577,6 +587,11 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     assert_equal developers(:poor_jamis), projects(:active_record).developers.where("salary < 10000").first
   end
 
+  def test_association_with_extend_option
+    eponine = DeveloperWithExtendOption.create(name: 'Eponine')
+    assert_equal 'sns', eponine.projects.category
+  end
+
   def test_replace_with_less
     david = developers(:david)
     david.projects = [projects(:action_controller)]