Properly handle scoping with has_many :through. Fixes #14537.

activerecord/lib/active_record/associations/through_association.rb

@@ -14,9 +14,14 @@ module ThroughAssociation #:nodoc:
         def target_scope
           scope = super
           chain.drop(1).each do |reflection|
+            relation = if reflection.scope
+              reflection.klass.all.instance_eval(&reflection.scope)
+            else
+              reflection.klass.all
+            end
+            
             scope.merge!(
-              reflection.klass.all.
-                except(:select, :create_with, :includes, :preload, :joins, :eager_load)
+              relation.except(:select, :create_with, :includes, :preload, :joins, :eager_load)
             )
           end
           scope

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -1105,4 +1105,16 @@ def test_has_many_through_obeys_order_on_through_association
   def test_has_many_through_with_includes_in_through_association_scope
     assert_not_empty posts(:welcome).author_address_extra_with_address
   end
+  
+  def test_has_many_through_unscope_default_scope
+    post = Post.create!(:title => 'Beaches', :body => "I like beaches!")
+    Reader.create! :person => people(:david), :post => post
+    LazyReader.create! :person => people(:susan), :post => post
+    
+    assert_equal 2, post.people.to_a.size
+    assert_equal 1, post.lazy_people.to_a.size
+    
+    assert_equal 2, post.lazy_readers_unscope_skimmers.to_a.size
+    assert_equal 2, post.lazy_people_unscope_skimmers.to_a.size
+  end
 end

activerecord/test/models/post.rb

@@ -144,6 +144,10 @@ def add_joins_and_select
 
   has_many :lazy_readers
   has_many :lazy_readers_skimmers_or_not, -> { where(skimmer: [ true, false ]) }, :class_name => 'LazyReader'
+  
+  has_many :lazy_people, :through => :lazy_readers, :source => :person
+  has_many :lazy_readers_unscope_skimmers, -> { skimmers_or_not }, :class_name => 'LazyReader'
+  has_many :lazy_people_unscope_skimmers, :through => :lazy_readers_unscope_skimmers, :source => :person
 
   def self.top(limit)
     ranked_by_comments.limit_by(limit)

activerecord/test/models/reader.rb

@@ -15,6 +15,8 @@ class SecureReader < ActiveRecord::Base
 class LazyReader < ActiveRecord::Base
   self.table_name = "readers"
   default_scope -> { where(skimmer: true) }
+  
+  scope :skimmers_or_not, -> { unscope(:where => :skimmer) }
 
   belongs_to :post
   belongs_to :person