I'm using SimpleForm and I wanted to display validation errors as label tags, which has (arguably) accessibility benefits. Here's how to add a custom error_label component that adds correct "for" attribute.

simple_form.rb

module SimpleForm
  module Components
    module ErrorLabel
      def error_label
        if has_errors?
          @builder.label(label_target, error_text, label_html_options)
        end
      end
    end
  end

  Inputs::Base.send(:include, SimpleForm::Components::ErrorLabel)
end