stop using class_attribute where methods/inheritance will suffice.

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

 module ActiveRecord::Associations::Builder
   class Association #:nodoc:
-    class_attribute :valid_options
-    self.valid_options = [:class_name, :foreign_key, :select, :conditions, :include, :extend, :readonly, :validate, :references]
+    class << self
+      attr_accessor :valid_options
+    end
 
-    # Set by subclasses
-    class_attribute :macro
+    self.valid_options = [:class_name, :foreign_key, :select, :conditions, :include, :extend, :readonly, :validate, :references]
 
     attr_reader :model, :name, :scope, :options, :reflection
 
@@ -29,17 +29,28 @@ def mixin
       @model.generated_feature_methods
     end
 
+    include Module.new { def build; end }
+
     def build
       validate_options
-      reflection = model.create_reflection(self.class.macro, name, scope, options, model)
       define_accessors
-      reflection
+      @reflection = model.create_reflection(macro, name, scope, options, model)
+      super # provides an extension point
+      @reflection
+    end
+
+    def macro
+      raise NotImplementedError
+    end
+
+    def valid_options
+      Association.valid_options
     end
 
     private
 
       def validate_options
-        options.assert_valid_keys(self.class.valid_options)
+        options.assert_valid_keys(valid_options)
       end
 
       def define_accessors

activerecord/lib/active_record/associations/builder/belongs_to.rb

@@ -2,9 +2,13 @@
 
 module ActiveRecord::Associations::Builder
   class BelongsTo < SingularAssociation #:nodoc:
-    self.macro = :belongs_to
+    def macro
+      :belongs_to
+    end
 
-    self.valid_options += [:foreign_type, :polymorphic, :touch]
+    def valid_options
+      super + [:foreign_type, :polymorphic, :touch]
+    end
 
     def constructable?
       !options[:polymorphic]

activerecord/lib/active_record/associations/builder/collection_association.rb

@@ -2,10 +2,12 @@ module ActiveRecord::Associations::Builder
   class CollectionAssociation < Association #:nodoc:
     CALLBACKS = [:before_add, :after_add, :before_remove, :after_remove]
 
-    self.valid_options += [
-      :table_name, :order, :group, :having, :limit, :offset, :uniq, :finder_sql,
-      :counter_sql, :before_add, :after_add, :before_remove, :after_remove
-    ]
+    def valid_options
+      super + [
+        :table_name, :order, :group, :having, :limit, :offset, :uniq, :finder_sql,
+        :counter_sql, :before_add, :after_add, :before_remove, :after_remove
+      ]
+    end
 
     attr_reader :block_extension
 

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

 module ActiveRecord::Associations::Builder
   class HasAndBelongsToMany < CollectionAssociation #:nodoc:
-    self.macro = :has_and_belongs_to_many
+    def macro
+      :has_and_belongs_to_many
+    end
 
-    self.valid_options += [:join_table, :association_foreign_key, :delete_sql, :insert_sql]
+    def valid_options
+      super + [:join_table, :association_foreign_key, :delete_sql, :insert_sql]
+    end
 
     def build
       reflection = super

activerecord/lib/active_record/associations/builder/has_many.rb

@@ -2,9 +2,13 @@
 
 module ActiveRecord::Associations::Builder
   class HasMany < CollectionAssociation #:nodoc:
-    self.macro = :has_many
+    def macro
+      :has_many
+    end
 
-    self.valid_options += [:primary_key, :dependent, :as, :through, :source, :source_type, :inverse_of]
+    def valid_options
+      super + [:primary_key, :dependent, :as, :through, :source, :source_type, :inverse_of]
+    end
 
     def build
       reflection = super

activerecord/lib/active_record/associations/builder/has_one.rb

@@ -2,12 +2,15 @@
 
 module ActiveRecord::Associations::Builder
   class HasOne < SingularAssociation #:nodoc:
-    self.macro = :has_one
-
-    self.valid_options += [:order, :as]
+    def macro
+      :has_one
+    end
 
-    class_attribute :through_options
-    self.through_options = [:through, :source, :source_type]
+    def valid_options
+      valid = super + [:order, :as]
+      valid += [:through, :source, :source_type] if options[:through]
+      valid
+    end
 
     def constructable?
       !options[:through]
@@ -21,12 +24,6 @@ def build
 
     private
 
-      def validate_options
-        valid_options = self.class.valid_options
-        valid_options += self.class.through_options if options[:through]
-        options.assert_valid_keys(valid_options)
-      end
-
       def configure_dependency
         if options[:dependent]
           unless options[:dependent].in?([:destroy, :delete, :nullify, :restrict])

activerecord/lib/active_record/associations/builder/singular_association.rb

 module ActiveRecord::Associations::Builder
   class SingularAssociation < Association #:nodoc:
-    self.valid_options += [:remote, :dependent, :counter_cache, :primary_key, :inverse_of]
+    def valid_options
+      super + [:remote, :dependent, :counter_cache, :primary_key, :inverse_of]
+    end
 
     def constructable?
       true

activerecord/lib/active_record/autosave_association.rb

@@ -127,23 +127,17 @@ module ActiveRecord
   module AutosaveAssociation
     extend ActiveSupport::Concern
 
-    ASSOCIATION_TYPES = %w{ HasOne HasMany BelongsTo HasAndBelongsToMany }
-
     module AssociationBuilderExtension #:nodoc:
-      def self.included(base)
-        base.valid_options << :autosave
-      end
-
       def build
-        reflection = super
         model.send(:add_autosave_association_callbacks, reflection)
-        reflection
+        super
       end
     end
 
     included do
-      ASSOCIATION_TYPES.each do |type|
-        Associations::Builder.const_get(type).send(:include, AssociationBuilderExtension)
+      Associations::Builder::Association.class_eval do
+        self.valid_options << :autosave
+        include AssociationBuilderExtension
       end
     end
 

activerecord/test/cases/autosave_association_test.rb

@@ -20,22 +20,6 @@
 require 'models/eye'
 
 class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
-  def test_autosave_should_be_a_valid_option_for_has_one
-    assert ActiveRecord::Associations::Builder::HasOne.valid_options.include?(:autosave)
-  end
-
-  def test_autosave_should_be_a_valid_option_for_belongs_to
-    assert ActiveRecord::Associations::Builder::BelongsTo.valid_options.include?(:autosave)
-  end
-
-  def test_autosave_should_be_a_valid_option_for_has_many
-    assert ActiveRecord::Associations::Builder::HasMany.valid_options.include?(:autosave)
-  end
-
-  def test_autosave_should_be_a_valid_option_for_has_and_belongs_to_many
-    assert ActiveRecord::Associations::Builder::HasAndBelongsToMany.valid_options.include?(:autosave)
-  end
-
   def test_should_not_add_the_same_callbacks_multiple_times_for_has_one
     assert_no_difference_when_adding_callbacks_twice_for Pirate, :ship
   end