app/validators/leading_whitespace_validator.rb

   1 class LeadingWhitespaceValidator < ActiveModel::EachValidator
   2   def validate_each(record, attribute, value)
   3     if value =~ /\A\s/
   4       record.errors[attribute] << (options[:message] || I18n.t("validations.leading whitespace"))
   5     end
   6   end
   7 end