Set the min attribute when there's a >= validation

lib/simple_form/inputs/numeric_input.rb

@@ -9,12 +9,32 @@ module SimpleForm
         input_options = super
         input_options[:type] ||= "number"
         input_options[:size] ||= SimpleForm.default_input_size
+
+        infer_attrs_from_validations(input_options)
+
         input_options
       end
 
       def input_html_classes
         super.unshift("numeric")
       end
+
+    protected
+
+      def infer_attrs_from_validations(input_options)
+        obj = @builder.object
+
+        return unless obj.class.respond_to?(:validators_on)
+
+        validators = obj.class.validators_on(attribute_name)
+        num_validator = validators.find {|v| v.is_a?(ActiveModel::Validations::NumericalityValidator) }
+
+        return if num_validator.nil?
+
+        options = num_validator.__send__(:options)
+
+        input_options[:min] ||= options[:greater_than_or_equal_to]
+      end
     end
   end
-end
+end

test/inputs_test.rb

@@ -54,6 +54,11 @@ class InputTest < ActionView::TestCase
     assert_select 'input[type=number].integer#user_age'
   end
 
+  test 'input should generate a min attribute when such a validation exists in the model' do
+    with_input_for @validating_user, :age, :integer
+    assert_select 'input[min=18]'
+  end
+
   test 'input should generate a float text field for float attributes ' do
     with_input_for @user, :age, :float
     assert_select 'input[type=number].float#user_age'

test/support/models.rb

@@ -118,4 +118,5 @@ class ValidatingUser < User
   include ActiveModel::Validations
   validates :name, :presence => true
   validates :company, :presence => true
+  validates_numericality_of :age, :greater_than_or_equal_to => 18
 end

test/test_helper.rb

@@ -60,6 +60,7 @@ class ActionView::TestCase
       :name => 'New in Simple Form!',
       :description => 'Hello!',
       :created_at => Time.now,
+      :age => 19,
       :company => 1
     }.merge(options))
   end