Add "required" for input tags of fields with "presence" validation and "minlength" / "maxlength" of fields with "length" validation

form_builder.rb

# config/initializers/form_builder.rb

module InputTagsMarkedAsRequiredOrWithMinMaxLengthInHTMLIfValidatedForPresence
  def initialize(object_name, method_name, template_object, options = {})
    return super unless options[:object] # it will be nil when called from #form_with
    
    validators = options[:object].class.validators_on(method_name)

    unless options.has_key? :required # check using has_key? to allow "required: nil"
      if validators.any? ActiveRecord::Validations::PresenceValidator
        options[:required] = true
      end
    end

    # They can be more than one...
    length_validators = validators.select do |validator|
      validator.is_a? ActiveRecord::Validations::LengthValidator
    end

    length_validators.each do |validator|
      if options[:minlength].blank? && validator.options[:minimum]
        options[:minlength] = validator.options[:minimum]
      end

      if options[:maxlength].blank? && validator.options[:maximum]
        options[:maxlength] = validator.options[:maximum]
      end
    end

    return super
  end
end

class ActionView::Helpers::Tags::TextField
  prepend InputTagsMarkedAsRequiredOrWithMinMaxLengthInHTMLIfValidatedForPresence
end