From 1b4399dfe7eaa8dd2a75f35815ea429962c51a29 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafael=20Mendon=C3=A7a=20Fran=C3=A7a?=
 <rafaelmfranca@gmail.com>
Date: Tue, 7 Jul 2015 13:38:54 -0300
Subject: [PATCH] Fix regression caused by a01d164b

When preload is used in a default scope the preload_values were
returning nested arrays and causing the preloader to fail because it
doesn't know how to deal with nested arrays. So before calling preload!
we need to splat the arguments.

This is not needed to includes because it flatten its arguments.
---
 .../lib/active_record/relation/merger.rb      |  4 ++--
 activerecord/test/cases/relations_test.rb     | 19 +++++++++++++++++++
 activerecord/test/models/post.rb              | 16 ++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index dd8f0aa298..0b38666ce9 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -87,8 +87,8 @@ module ActiveRecord
         return if other.preload_values.empty? && other.includes_values.empty?
 
         if other.klass == relation.klass
-          relation.preload! other.preload_values unless other.preload_values.empty?
-          relation.includes! other.includes_values unless other.includes_values.empty?
+          relation.preload!(*other.preload_values) unless other.preload_values.empty?
+          relation.includes!(other.includes_values) unless other.includes_values.empty?
         else
           reflection = relation.klass.reflect_on_all_associations.find do |r|
             r.class_name == other.klass.name
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index acbf85d398..5f48c2b40f 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -647,6 +647,25 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
+  def test_preloading_with_associations_default_scopes_and_merges
+    post = Post.create! title: 'Uhuu', body: 'body'
+    reader = Reader.create! post_id: post.id, person_id: 1
+
+    post_rel = PostWithPreloadDefaultScope.preload(:readers).joins(:readers).where(title: 'Uhuu')
+    result_post = PostWithPreloadDefaultScope.all.merge(post_rel).to_a.first
+
+    assert_no_queries do
+      assert_equal [reader], result_post.readers.to_a
+    end
+
+    post_rel = PostWithIncludesDefaultScope.includes(:readers).where(title: 'Uhuu')
+    result_post = PostWithIncludesDefaultScope.all.merge(post_rel).to_a.first
+
+    assert_no_queries do
+      assert_equal [reader], result_post.readers.to_a
+    end
+  end
+
   def test_loading_with_one_association
     posts = Post.preload(:comments)
     post = posts.find { |p| p.id == 1 }
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 052b1c9690..10f13b67da 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -208,6 +208,22 @@ class PostWithDefaultScope < ActiveRecord::Base
   default_scope { order(:title) }
 end
 
+class PostWithPreloadDefaultScope < ActiveRecord::Base
+  self.table_name = 'posts'
+
+  has_many :readers, foreign_key: 'post_id'
+
+  default_scope { preload(:readers) }
+end
+
+class PostWithIncludesDefaultScope < ActiveRecord::Base
+  self.table_name = 'posts'
+
+  has_many :readers, foreign_key: 'post_id'
+
+  default_scope { includes(:readers) }
+end
+
 class SpecialPostWithDefaultScope < ActiveRecord::Base
   self.table_name = 'posts'
   default_scope { where(:id => [1, 5,6]) }