Preserve context for joins while merging relations

This is a backport of #10164, already merged into
master. The issue is described in lengthy detail
in issues #3002 and #5494.

1 files changed, 8 insertions, 1 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 98fe6b7611..f14eee2eb8 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -4,6 +4,7 @@ require 'models/tagging'
 require 'models/post'
 require 'models/topic'
 require 'models/comment'
+require 'models/rating'
 require 'models/reply'
 require 'models/author'
 require 'models/comment'
@@ -19,7 +20,7 @@ require 'models/minivan'
 
 class RelationTest < ActiveRecord::TestCase
   fixtures :authors, :topics, :entrants, :developers, :companies, :developers_projects, :accounts, :categories, :categorizations, :posts, :comments,
-    :tags, :taggings, :cars, :minivans
+    :ratings, :tags, :taggings, :cars, :minivans
 
   def test_do_not_double_quote_string_id
     van = Minivan.last
@@ -696,6 +697,12 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal 1, comments.count
   end
 
+  def test_relation_merging_with_merged_joins
+    special_comments_with_ratings = SpecialComment.joins(:ratings)
+    posts_with_special_comments_with_ratings = Post.group('posts.id').joins(:special_comments).merge(special_comments_with_ratings)
+    assert_equal 1, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
+  end
+
   def test_count
     posts = Post.scoped