Pass SQL group by values when including scoped association

Fixes problem when added `group()` in association scope was lost
in eager loaded association.

activerecord/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Pass SQL group by values when including scoped association
+
+    Fixes problem when added `group()` in association scope was lost
+    in eager loaded association.
+
+    *Lucjan Suski*
+
 *   Version the API presented to migration classes, so we can change parameter
     defaults without breaking existing migrations, or forcing them to be
     rewritten through a deprecation cycle.

activerecord/lib/active_record/associations/preloader/association.rb

@@ -107,7 +107,7 @@ def load_records
           @preloaded_records = slices.flat_map do |slice|
             records_for(slice)
           end
-          @preloaded_records.group_by do |record| 
+          @preloaded_records.group_by do |record|
             convert_key(record[association_key_name])
           end
         end
@@ -139,6 +139,10 @@ def build_scope
             scope.order!(order_values)
           end
 
+          if group_values = preload_values[:group] || values[:group]
+            scope.group!(group_values)
+          end
+
           if preload_values[:reordering] || values[:reordering]
             scope.reordering_value = true
           end

activerecord/test/cases/associations/eager_test.rb

@@ -1242,6 +1242,19 @@ def test_eager_load_multiple_associations_with_references
     assert_equal projects.last.mentor.developers.first.contracts, projects.last.developers.last.contracts
   end
 
+  def test_eager_load_with_group_clause
+    assert_nothing_raised(ActiveRecord::StatementInvalid) do
+      subclass = Class.new(ActiveRecord::Base) do
+        def self.name; "Author"; end
+        self.table_name = "authors"
+        has_many :posts_ordered_by_comments_tags_count, -> { joins('LEFT JOIN comments ON comments.post_id = posts.id').order("SUM(comments.tags_count)").group('posts.id') }, :class_name => "Post"
+      end
+
+      posts = subclass.includes(:posts_ordered_by_comments_tags_count).first.posts_ordered_by_comments_tags_count
+      assert_equal subclass.first.posts_ordered_by_comments_tags_count, posts
+    end
+  end
+
   test "scoping with a circular preload" do
     assert_equal Comment.find(1), Comment.preload(:post => :comments).scoping { Comment.find(1) }
   end