rules/alerting.go
func (r *AlertingRule) LastError() error {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.lastError
}
func (r *AlertingRule) LastError() error {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.lastError
}
// LastError returns the last error seen by the alerting rule.