Debugging CanCanCan abilities

abilities_debug.rb

def audit_ability(ability:, action:, subject:)
  begin
    ability.authorize!(action, subject)
    puts "CanCanCan: User has ability to #{action} for #{subject.inspect}"
  rescue CanCanCan::AccessDenied => exception
    failed_rules = ability.send(:relevant_rules_for_match, exception.action, exception.subject).reject do |rule|
      rule.matches_conditions?(exception.action, exception.subject)
    end

    if failed_rules.any?
      puts "CanCanCan::AccessDenied: User does not have ability to #{exception.action} for #{exception.subject.inspect} due to the following conditions:\n"
      
      failed_rules.map do |rule|
        pp { conditions: rule.conditions, block: rule.instance_variable_get(:@block) }
        puts ""
      end
    else
      puts "CanCanCan::AccessDenied: User does not have ability to #{exception.action} for #{exception.subject.inspect} for indeterminate reasons"
    end
  end
end

user = User.find(...)
action = :some_action
subject = SomeThing
ability = Ability.new(user, ...)

audit_ability(ability:, action:, subject:)