attr_accessible and attr_protected raise an exception pointing to use plugin or new protection model

activemodel/lib/active_model.rb

@@ -37,6 +37,7 @@ module ActiveModel
   autoload :ForbiddenAttributesProtection
   autoload :Lint
   autoload :Model
+  autoload :DeprecatedMassAssignmentSecurity
   autoload :Name, 'active_model/naming'
   autoload :Naming
   autoload :Observer, 'active_model/observing'

activemodel/lib/active_model/deprecated_mass_assignment_security.rb

@@ -0,0 +1,19 @@
+module ActiveModel
+  module DeprecatedMassAssignmentSecurity
+    extend ActiveSupport::Concern
+
+     module ClassMethods
+       def attr_protected(*args)
+         raise "`attr_protected` is extracted out of Rails into a gem. " \
+           "Please use new recommended protection model for params " \
+           "or add `protected_attributes` to your Gemfile to use old one."
+       end
+
+       def attr_accessible(*args)
+         raise "`attr_accessible` is extracted out of Rails into a gem. " \
+           "Please use new recommended protection model for params " \
+           "or add `protected_attributes` to your Gemfile to use old one."
+       end
+     end
+  end
+end

activemodel/test/cases/deprecated_mass_assignment_security_test.rb

@@ -0,0 +1,16 @@
+require 'cases/helper'
+require 'models/project'
+
+class DeprecatedMassAssignmentSecurityTest < ActiveModel::TestCase
+  def test_attr_accessible_raise_error
+    assert_raise RuntimeError, /protected_attributes/ do
+      Project.attr_accessible :username
+    end
+  end
+
+  def test_attr_protected_raise_error
+    assert_raise RuntimeError, /protected_attributes/ do
+      Project.attr_protected :username
+    end
+  end
+end

activemodel/test/models/project.rb

@@ -0,0 +1,3 @@
+class Project
+  include ActiveModel::DeprecatedMassAssignmentSecurity
+end

activerecord/lib/active_record/attribute_assignment.rb

@@ -1,6 +1,8 @@
 
 module ActiveRecord
   module AttributeAssignment
+    extend ActiveSupport::Concern
+    include ActiveModel::DeprecatedMassAssignmentSecurity
     include ActiveModel::ForbiddenAttributesProtection
 
     # Allows you to set all the attributes at once by passing in a hash with keys