handle validates_length_of :is option

lib/simple_form/components/maxlength.rb

@@ -12,7 +12,7 @@ module SimpleForm
       def maximum_length_from_validation
         if options[:maxlength] == true
           if (length_validator = find_length_validator) && !length_validator.options[:tokenizer]
-            length_validator.options[:maximum]
+            length_validator.options[:is] || length_validator.options[:maximum]
           end
         else
           options[:maxlength]

test/form_builder/error_notification_test.rb

@@ -11,6 +11,7 @@ class ErrorNotificationTest < ActionView::TestCase
 
   test 'error notification is not generated when the object has no error' do
     assert @validating_user.valid?
+
     with_error_notification_for @validating_user
     assert_no_select 'p.error_notification'
   end

test/inputs/string_input_test.rb

@@ -52,6 +52,11 @@ class StringInputTest < ActionView::TestCase
     assert_no_select 'input.string[maxlength]'
   end
 
+  test 'input should get maxlength from validation when :is option present' do
+    with_input_for @validating_user, :home_picture, :string
+    assert_select 'input.string[maxlength=12]'
+  end
+
   test 'input should not generate placeholder by default' do
     with_input_for @user, :name, :string
     assert_no_select 'input[placeholder]'

test/support/models.rb

@@ -156,6 +156,7 @@ class ValidatingUser < User
   validates_length_of :name, :maximum => 25
   validates_length_of :description, :maximum => 50
   validates_length_of :action, :maximum => 10, :tokenizer => lambda { |str| str.scan(/\w+/) }
+  validates_length_of :home_picture, :is => 12
 
   def min_amount
     10

test/test_helper.rb

@@ -62,6 +62,7 @@ class ActionView::TestCase
       :id => 1,
       :name => 'New in Simple Form!',
       :description => 'Hello!',
+      :home_picture => 'Home picture',
       :created_at => Time.now,
       :age => 19,
       :amount => 15,