4 files changed, 21 insertions, 9 deletions
diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index d11243c4c0..ca04f48c1c 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -219,7 +219,7 @@ module ActiveModel
         rescue TypeError, NoMethodError
         end
 
-        changed_attributes[attr] = value
+        set_attribute_was(attr, value)
       end
 
       # Handle <tt>reset_*!</tt> for +method_missing+.
@@ -233,8 +233,22 @@ module ActiveModel
       def restore_attribute!(attr)
         if attribute_changed?(attr)
           __send__("#{attr}=", changed_attributes[attr])
-          changed_attributes.delete(attr)
+          clear_attribute_changes([attr])
         end
       end
+
+      # This is necessary because `changed_attributes` might be overridden in
+      # other implemntations (e.g. in `ActiveRecord`)
+      alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:
+
+      # Force an attribute to have a particular "before" value
+      def set_attribute_was(attr, old_value)
+        attributes_changed_by_setter[attr] = old_value
+      end
+
+      # Remove changes information for the provided attributes.
+      def clear_attribute_changes(attributes)
+        attributes_changed_by_setter.except!(*attributes)
+      end
   end
 end
diff --git a/activemodel/lib/active_model/naming.rb b/activemodel/lib/active_model/naming.rb
index 86f5c96af9..241e88deeb 100644
--- a/activemodel/lib/active_model/naming.rb
+++ b/activemodel/lib/active_model/naming.rb
@@ -215,10 +215,8 @@ module ActiveModel
   # provided method below, or rolling your own is required.
   module Naming
     def self.extended(base) #:nodoc:
-      base.class_eval do
-        remove_possible_method(:model_name)
-        delegate :model_name, to: :class
-      end
+      base.remove_possible_method :model_name
+      base.delegate :model_name, to: :class
     end
 
     # Returns an ActiveModel::Name object for module. It can be
diff --git a/activemodel/lib/active_model/secure_password.rb b/activemodel/lib/active_model/secure_password.rb
index 7e179cf4b7..f6ad35769f 100644
--- a/activemodel/lib/active_model/secure_password.rb
+++ b/activemodel/lib/active_model/secure_password.rb
@@ -105,7 +105,7 @@ module ActiveModel
       attr_reader :password
 
       # Encrypts the password into the +password_digest+ attribute, only if the
-      # new password is not blank.
+      # new password is not empty.
       #
       #   class User < ActiveRecord::Base
       #     has_secure_password validations: false
@@ -119,7 +119,7 @@ module ActiveModel
       def password=(unencrypted_password)
         if unencrypted_password.nil?
           self.password_digest = nil
-        elsif unencrypted_password.present?
+        elsif !unencrypted_password.empty?
           @password = unencrypted_password
           cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST : BCrypt::Engine.cost
           self.password_digest = BCrypt::Password.create(unencrypted_password, cost: cost)
diff --git a/activemodel/lib/active_model/validator.rb b/activemodel/lib/active_model/validator.rb
index 65cb1e5a88..0116de68ab 100644
--- a/activemodel/lib/active_model/validator.rb
+++ b/activemodel/lib/active_model/validator.rb
@@ -79,7 +79,7 @@ module ActiveModel
   #     include ActiveModel::Validations
   #     attr_accessor :title
   #
-  #     validates :title, presence: true
+  #     validates :title, presence: true, title: true
   #   end
   #
   # It can be useful to access the class that is using that validator when there are prerequisites such