Fix merge conflicts for #19938

This is a separate commit, as it is not just a changelog conflict. Want
to point out the changes in the code

activerecord/lib/active_record/associations/join_dependency.rb

@@ -131,9 +131,9 @@ module ActiveRecord
       def instantiate(result_set, aliases)
         primary_key = aliases.column_alias(join_root, join_root.primary_key)
 
-        seen = Hash.new { |h,parent_klass|
-          h[parent_klass] = Hash.new { |i,parent_id|
-            i[parent_id] = Hash.new { |j,child_klass| j[child_klass] = {} }
+        seen = Hash.new { |i, object_id|
+          i[object_id] = Hash.new { |j, child_class|
+            j[child_class] = {}
           }
         }
 
@@ -233,7 +233,6 @@ module ActiveRecord
 
       def construct(ar_parent, parent, row, rs, seen, model_cache, aliases)
         return if ar_parent.nil?
-        primary_id  = ar_parent.id
 
         parent.children.each do |node|
           if node.reflection.collection?
@@ -253,14 +252,14 @@ module ActiveRecord
             next
           end
 
-          model = seen[parent.base_klass][primary_id][node.base_klass][id]
+          model = seen[ar_parent.object_id][node.base_klass][id]
 
           if model
             construct(model, node, row, rs, seen, model_cache, aliases)
           else
             model = construct_model(ar_parent, node, row, model_cache, id, aliases)
             model.readonly!
-            seen[parent.base_klass][primary_id][node.base_klass][id] = model
+            seen[ar_parent.object_id][node.base_klass][id] = model
             construct(model, node, row, rs, seen, model_cache, aliases)
           end
         end

activerecord/test/cases/associations/eager_test.rb

@@ -24,6 +24,8 @@ require 'models/membership'
 require 'models/club'
 require 'models/categorization'
 require 'models/sponsor'
+require 'models/mentor'
+require 'models/contract'
 
 class EagerAssociationTest < ActiveRecord::TestCase
   fixtures :posts, :comments, :authors, :essays, :author_addresses, :categories, :categories_posts,
@@ -1218,6 +1220,16 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_no_queries { assert_equal 2, posts[1].categories[0].categorizations.length }
   end
 
+  def test_eager_load_multiple_associations_with_references
+    mentor = Mentor.create!(name: "Barış Can DAYLIK")
+    developer = Developer.create!(name: "Mehmet Emin İNAÇ", mentor: mentor)
+    Contract.create!(developer: developer)
+    project = Project.create!(name: "VNGRS", mentor: mentor)
+    project.developers << developer
+    projects = Project.references(:mentors).includes(mentor: { developers: :contracts }, developers: :contracts)
+    assert_equal projects.last.mentor.developers.first.contracts, projects.last.developers.last.contracts
+  end
+
   test "scoping with a circular preload" do
     assert_equal Comment.find(1), Comment.preload(:post => :comments).scoping { Comment.find(1) }
   end

activerecord/test/models/developer.rb

@@ -15,6 +15,8 @@ class Developer < ActiveRecord::Base
     end
   end
 
+  belongs_to :mentor
+
   accepts_nested_attributes_for :projects
 
   has_and_belongs_to_many :shared_computers, class_name: "Computer"

activerecord/test/models/mentor.rb

@@ -0,0 +1,3 @@
+class Mentor < ActiveRecord::Base
+  has_many :developers
+end

activerecord/test/models/project.rb

@@ -1,4 +1,5 @@
 class Project < ActiveRecord::Base
+  belongs_to :mentor
   has_and_belongs_to_many :developers, -> { distinct.order 'developers.name desc, developers.id desc' }
   has_and_belongs_to_many :readonly_developers, -> { readonly }, :class_name => "Developer"
   has_and_belongs_to_many :non_unique_developers, -> { order 'developers.name desc, developers.id desc' }, :class_name => 'Developer'

activerecord/test/schema/schema.rb

@@ -253,6 +253,7 @@ ActiveRecord::Schema.define do
     t.string   :first_name
     t.integer  :salary, default: 70000
     t.integer :firm_id
+    t.integer :mentor_id
     if subsecond_precision_supported?
       t.datetime :created_at, precision: 6
       t.datetime :updated_at, precision: 6
@@ -452,6 +453,10 @@ ActiveRecord::Schema.define do
     t.string :name
   end
 
+  create_table :mentors, force: true do |t|
+    t.string :name
+  end
+
   create_table :minivans, force: true, id: false do |t|
     t.string :minivan_id
     t.string :name
@@ -660,6 +665,7 @@ ActiveRecord::Schema.define do
     t.string :name
     t.string :type
     t.integer :firm_id
+    t.integer :mentor_id
   end
 
   create_table :randomly_named_table1, force: true do |t|