select can have required option, closes #340

lib/simple_form/inputs/collection_input.rb

@@ -33,15 +33,19 @@ module SimpleForm
         end
       end
 
-      # Select components does not allow the required html tag.
+      # Checkbox components does not use the required html tag.
+      # See more info here - https://github.com/plataformatec/simple_form/issues/340#issuecomment-2871956
       def has_required?
-        super && input_type != :select
+        super && (input_options[:include_blank] || multiple?) && input_type != :check_boxes
       end
 
       # Check if :include_blank must be included by default.
       def skip_include_blank?
-        (options.keys & [:prompt, :include_blank, :default, :selected]).any? ||
-          options[:input_html].try(:[], :multiple)
+        (options.keys & [:prompt, :include_blank, :default, :selected]).any? || multiple?
+      end
+
+      def multiple?
+        !!options[:input_html].try(:[], :multiple)
       end
 
       # Detect the right method to find the label and value for a collection.

test/inputs/collection_input_test.rb

@@ -259,12 +259,36 @@ class CollectionInputTest < ActionView::TestCase
     end
   end
 
-  test 'collection input with select type should not generate invalid required html attribute' do
-    with_input_for @user, :name, :select, :collection => ['Jose' , 'Carlos']
+  test 'collection input with select type should generate required html attribute only with blank option' do
+    with_input_for @user, :name, :select, :include_blank => true, :collection => ['Jose' , 'Carlos']
+    assert_select 'select.required'
+    assert_select 'select[required]'
+  end
+
+  test 'collection input with select type should not generate required html attribute without blank option' do
+    with_input_for @user, :name, :select, :include_blank => false, :collection => ['Jose' , 'Carlos']
     assert_select 'select.required'
     assert_no_select 'select[required]'
   end
 
+  test 'collection input with select type with multiple attribute should generate required html attribute without blank option' do
+    with_input_for @user, :name, :select, :include_blank => true, :input_html => {:multiple => true}, :collection => ['Jose' , 'Carlos']
+    assert_select 'select.required'
+    assert_select 'select[required]'
+  end
+
+  test 'collection input with select type with multiple attribute should generate required html attribute with blank option' do
+    with_input_for @user, :name, :select, :include_blank => true, :input_html => {:multiple => true}, :collection => ['Jose' , 'Carlos']
+    assert_select 'select.required'
+    assert_select 'select[required]'
+  end
+
+  test 'collection input with check_boxes type should not generate required html attribute' do
+    with_input_for @user, :name, :check_boxes, :collection => ['Jose' , 'Carlos']
+    assert_select 'input.required'
+    assert_no_select 'input[required]'
+  end
+
   test 'input should allow disabled options with a lambda for collection select' do
     with_input_for @user, :name, :select, :collection => ["Carlos", "Antonio"],
       :disabled => lambda { |x| x == "Carlos" }