func funcHistogramQuantile(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	q := vals[0].(Vector)[0].V
	inVec := vals[1].(Vector)
	sigf := enh.signatureFunc(false, excludedLabels...)

	if enh.signatureToMetricWithBuckets == nil {
		enh.signatureToMetricWithBuckets = map[uint64]*metricWithBuckets{}
	} else {
		for _, v := range enh.signatureToMetricWithBuckets {
			v.buckets = v.buckets[:0]
		}
	}
	for _, el := range inVec {
		upperBound, err := strconv.ParseFloat(
			el.Metric.Get(model.BucketLabel), 64,
		)
		if err != nil {
			// Oops, no bucket label or malformed label value. Skip.
			// TODO(beorn7): Issue a warning somehow.
			continue
		}
		hash := sigf(el.Metric)

		mb, ok := enh.signatureToMetricWithBuckets[hash]
		if !ok {
			el.Metric = labels.NewBuilder(el.Metric).
				Del(labels.BucketLabel, labels.MetricName).
				Labels()

			mb = &metricWithBuckets{el.Metric, nil}
			enh.signatureToMetricWithBuckets[hash] = mb
		}
		mb.buckets = append(mb.buckets, bucket{upperBound, el.V})
	}

	for _, mb := range enh.signatureToMetricWithBuckets {
		if len(mb.buckets) > 0 {
			enh.out = append(enh.out, Sample{
				Metric: mb.metric,
				Point:  Point{V: bucketQuantile(q, mb.buckets)},
			})
		}
	}

	return enh.out
}
func funcHistogramQuantile(vals []Value, args Expressions, enh *EvalNodeHelper) Vector {
	q := vals[0].(Vector)[0].V
	inVec := vals[1].(Vector)
	sigf := enh.signatureFunc(false, excludedLabels...)

	if enh.signatureToMetricWithBuckets == nil {
		enh.signatureToMetricWithBuckets = map[uint64]*metricWithBuckets{}
	} else {
		for _, v := range enh.signatureToMetricWithBuckets {
			v.buckets = v.buckets[:0]
		}
	}
	for _, el := range inVec {
		upperBound, err := strconv.ParseFloat(
			el.Metric.Get(model.BucketLabel), 64,
		)
		if err != nil {
			// Oops, no bucket label or malformed label value. Skip.
			// TODO(beorn7): Issue a warning somehow.
			continue
		}
		hash := sigf(el.Metric)

		mb, ok := enh.signatureToMetricWithBuckets[hash]
		if !ok {
			el.Metric = labels.NewBuilder(el.Metric).
				Del(labels.BucketLabel, labels.MetricName).
				Labels()

			mb = &metricWithBuckets{el.Metric, nil}
			enh.signatureToMetricWithBuckets[hash] = mb
		}
		mb.buckets = append(mb.buckets, bucket{upperBound, el.V})
	}

	for _, mb := range enh.signatureToMetricWithBuckets {
		if len(mb.buckets) > 0 {
			enh.out = append(enh.out, Sample{
				Metric: mb.metric,
				Point:  Point{V: bucketQuantile(q, mb.buckets)},
			})
		}
	}

	return enh.out
}
// === histogram_quantile(k ValueTypeScalar, Vector ValueTypeVector) Vector ===