Deprecation warning on module doesn't have a required_fields method

app/controllers/devise_controller.rb

@@ -161,4 +161,4 @@ MESSAGE
       super
     end
   end
-end
+end

lib/devise/models.rb

@@ -55,8 +55,12 @@ module Devise
       klass.devise_modules.each do |mod|
         instance = klass.new
 
-        const_get(mod.to_s.classify).required_fields(klass).each do |field|
-          failed_attributes << field unless instance.respond_to?(field)
+        if const_get(mod.to_s.classify).respond_to?(:required_fields)
+          const_get(mod.to_s.classify).required_fields(klass).each do |field|
+            failed_attributes << field unless instance.respond_to?(field)
+          end
+        else
+          ActiveSupport::Deprecation.warn "The module #{mod} doesn't implement self.required_fields(klass). Devise uses required_fields to warn developers of any missing fields in their models. Please implement #{mod}.required_fields(klass) that returns an array of symbols with the required fields."
         end
       end
 
@@ -114,4 +118,4 @@ module Devise
   end
 end
 
-require 'devise/models/authenticatable'
+require 'devise/models/authenticatable'

test/models_test.rb

@@ -108,6 +108,27 @@ class ActiveRecordTest < ActiveSupport::TestCase
   end
 end
 
+def swap_module_method_existence(klass, method)
+  klass.module_eval %Q[
+    class << self
+      alias #{method}_referenced #{method}
+      undef #{method}
+    end
+  ]
+
+  begin
+    yield if block_given?
+  ensure
+
+    klass.module_eval %Q[
+      class << self
+        alias #{method} #{method}_referenced
+        undef #{method}_referenced
+      end
+    ]
+  end
+end
+
 class CheckFieldsTest < ActiveSupport::TestCase
   test 'checks if the class respond_to the required fields' do
     Player = Class.new do
@@ -157,4 +178,21 @@ class CheckFieldsTest < ActiveSupport::TestCase
       Devise::Models.check_fields!(Magician)
     end
   end
+
+  test "doesn't raises a NoMethodError exception when the module doesn't have a required_field(klass) class method" do
+     Driver = Class.new do
+      extend Devise::Models
+
+      def self.before_validation(instance)
+      end
+
+      devise :database_authenticatable
+    end
+
+    swap_module_method_existence Devise::Models::DatabaseAuthenticatable, :required_fields do
+      assert_deprecated "DEPRECATION WARNING: The module database_authenticatable doesn't implement self.required_fields(klass). Devise uses required_fields to warn developers of any missing fields in their models. Please implement database_authenticatable.required_fields(klass) that returns an array of symbols with the required fields." do
+        Devise::Models.check_fields!(Driver)
+      end
+    end
+  end
 end