code: func findMetricWithLabels(
  	desc *Desc, metrics []metricWithLabelValues, labels Labels, curry []curriedLabelValue,
  ) int {
  	for i, metric := range metrics {
  		if matchLabels(desc, metric.values, labels, curry) {
  			return i
  		}
  	}
  	return len(metrics)
  }
docs: // findMetricWithLabels returns the index of the matching metric or len(metrics)
  // if not found.