Substitute value into validates_format_of message

Signed-off-by: Michael Koziarski <michael@koziarski.com>

activerecord/lib/active_record/validations.rb

@@ -692,7 +692,7 @@ module ActiveRecord
         raise(ArgumentError, "A regular expression must be supplied as the :with option of the configuration hash") unless configuration[:with].is_a?(Regexp)
 
         validates_each(attr_names, configuration) do |record, attr_name, value|
-          record.errors.add(attr_name, configuration[:message]) unless value.to_s =~ configuration[:with]
+          record.errors.add(attr_name, configuration[:message] % value) unless value.to_s =~ configuration[:with]
         end
       end
 

activerecord/test/cases/validations_test.rb

@@ -583,6 +583,12 @@ class ValidationsTest < ActiveRecord::TestCase
     assert_nil t.errors.on(:title)
   end
 
+  def test_validate_format_with_formatted_message
+    Topic.validates_format_of(:title, :with => /^Valid Title$/, :message => "can't be %s")
+    t = Topic.create(:title => 'Invalid title')
+    assert_equal "can't be Invalid title", t.errors.on(:title)
+  end
+
   def test_validates_inclusion_of
     Topic.validates_inclusion_of( :title, :in => %w( a b c d e f g ) )