Add support of Formtastic::String input_html

lib/active_admin_datetimepicker/base.rb

@@ -14,13 +14,14 @@ def input_html_data
     end
 
     def input_html_options(input_name = nil, placeholder = nil)
-      options = {}
-      options[:class] = [self.options[:class], html_class].compact.join(' ')
-      options[:data] ||= input_html_data
-      options[:data].merge!(datepicker_options: datetime_picker_options)
-      options[:value] ||= input_value(input_name)
-      options[:maxlength] = 19
-      options
+      super().tap do |options|
+        options[:class] = [self.options[:class], html_class].compact.join(' ')
+        options[:data] ||= input_html_data
+        options[:data].merge!(datepicker_options: datetime_picker_options)
+        options[:value] ||= input_value(input_name)
+        options[:maxlength] = 19
+        options[:placeholder] = placeholder unless placeholder.nil?
+      end
     end
 
     def input_value(input_name = nil)

spec/filters_and_edit_form_spec.rb

@@ -38,6 +38,8 @@
 
       expect(page.find('input#q_birthday_gteq').value).to start_with(date_from)
       expect(page.find('input#q_birthday_lteq').value).to start_with(date_to)
+      expect(page).to have_css('input#q_birthday_gteq[placeholder="From"]')
+      expect(page).to have_css('input#q_birthday_lteq[placeholder="To"]')
     end
   end
 
@@ -59,6 +61,7 @@
     it 'can set birthday'  do
       date_birthday = Date.today.beginning_of_month.strftime("%Y-%m-%d")
       expect(page.find('#author_birthday').value).to start_with(date_birthday)
+      expect(page).to have_css('#author_birthday[placeholder="Formtastic placeholder"]')
     end
   end
 

spec/support/admin.rb

@@ -10,7 +10,7 @@ def add_author_resource(options = {}, &block)
 
       f.inputs 'General' do
         f.input :name
-        f.input :birthday, as: :date_time_picker
+        f.input :birthday, as: :date_time_picker, input_html: { placeholder: 'Formtastic placeholder' }
       end
 
       f.actions