Clean up dependent option validation.

We don't need the complexity of to_sentence, and it shouldn't be a bang
method.

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

@@ -77,16 +77,12 @@ def define_writers
         end
       end
 
-      def check_valid_dependent!(dependent, valid_options)
-        unless valid_options.include?(dependent)
-          valid_options_message = valid_options.map(&:inspect).to_sentence(
-            words_connector: ', ', two_words_connector: ' or ', last_word_connector: ' or ')
-
-          raise ArgumentError, "The :dependent option expects either " \
-            "#{valid_options_message} (#{dependent.inspect})"
+      def validate_dependent_option(valid_options)
+        unless valid_options.include? options[:dependent]
+          raise ArgumentError, "The :dependent option must be one of #{valid_options}, but is :#{options[:dependent]}"
         end
 
-        if dependent == :restrict
+        if options[:dependent] == :restrict
           ActiveSupport::Deprecation.warn(
             "The :restrict option is deprecated. Please use :restrict_with_exception instead, which " \
             "provides the same functionality."

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

@@ -72,7 +72,7 @@ def add_touch_callbacks(reflection)
 
       def configure_dependency
         if dependent = options[:dependent]
-          check_valid_dependent! dependent, [:destroy, :delete]
+          validate_dependent_option [:destroy, :delete]
 
           method_name = "belongs_to_dependent_#{dependent}_for_#{name}"
           model.send(:class_eval, <<-eoruby, __FILE__, __LINE__ + 1)

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

@@ -19,9 +19,7 @@ def build
 
       def configure_dependency
         if dependent = options[:dependent]
-          check_valid_dependent! dependent, [:destroy, :delete_all, :nullify, :restrict,
-                                             :restrict_with_error, :restrict_with_exception]
-
+          validate_dependent_option [:destroy, :delete_all, :nullify, :restrict, :restrict_with_error, :restrict_with_exception]
           send("define_#{dependent}_dependency_method")
           model.before_destroy dependency_method_name
         end

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

@@ -25,8 +25,7 @@ def build
 
       def configure_dependency
         if dependent = options[:dependent]
-          check_valid_dependent! dependent, [:destroy, :delete, :nullify, :restrict, :restrict_with_error, :restrict_with_exception]
-
+          validate_dependent_option [:destroy, :delete, :nullify, :restrict, :restrict_with_error, :restrict_with_exception]
           send("define_#{dependent}_dependency_method")
           model.before_destroy dependency_method_name
         end