Normalise 'le' and 'quantile' labels in queries

Signed-off-by: Ganesh Vernekar <ganesh.vernekar@reddit.com>

cmd/prometheus/main.go

@@ -253,6 +253,9 @@ func (c *flagConfig) setFeatureListOptions(logger *slog.Logger) error {
 			case "promql-duration-expr":
 				parser.ExperimentalDurationExpr = true
 				logger.Info("Experimental duration expression parsing enabled.")
+			case "promql-normalise-le-quantile-labels":
+				parser.NormaliseLeAndQuantileMatchers = true
+				logger.Info("Experimental normalising of 'le' and 'quantile' labels for PromQL enabled.")
 			case "native-histograms":
 				c.tsdb.EnableNativeHistograms = true
 				c.scrape.EnableNativeHistogramsIngestion = true

model/textparse/openmetricsparse.go

@@ -773,7 +773,7 @@ func normalizeFloatsInLabelValues(t model.MetricType, l, v string) string {
 	if (t == model.MetricTypeSummary && l == model.QuantileLabel) || (t == model.MetricTypeHistogram && l == model.BucketLabel) {
 		f, err := strconv.ParseFloat(v, 64)
 		if err == nil {
-			return formatOpenMetricsFloat(f)
+			return FormatOpenMetricsFloat(f)
 		}
 	}
 	return v

model/textparse/protobufparse.go

@@ -34,7 +34,7 @@ import (
 	"github.com/prometheus/prometheus/schema"
 )
 
-// floatFormatBufPool is exclusively used in formatOpenMetricsFloat.
+// floatFormatBufPool is exclusively used in FormatOpenMetricsFloat.
 var floatFormatBufPool = sync.Pool{
 	New: func() any {
 		// To contain at most 17 digits and additional syntax for a float64.
@@ -632,7 +632,7 @@ func (p *ProtobufParser) getMagicLabel() (bool, string, string) {
 		qq := p.dec.GetSummary().GetQuantile()
 		q := qq[p.fieldPos]
 		p.fieldsDone = p.fieldPos == len(qq)-1
-		return true, model.QuantileLabel, formatOpenMetricsFloat(q.GetQuantile())
+		return true, model.QuantileLabel, FormatOpenMetricsFloat(q.GetQuantile())
 	case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
 		bb := p.dec.GetHistogram().GetBucket()
 		if p.fieldPos >= len(bb) {
@@ -641,15 +641,15 @@ func (p *ProtobufParser) getMagicLabel() (bool, string, string) {
 		}
 		b := bb[p.fieldPos]
 		p.fieldsDone = math.IsInf(b.GetUpperBound(), +1)
-		return true, model.BucketLabel, formatOpenMetricsFloat(b.GetUpperBound())
+		return true, model.BucketLabel, FormatOpenMetricsFloat(b.GetUpperBound())
 	}
 	return false, "", ""
 }
 
-// formatOpenMetricsFloat works like the usual Go string formatting of a float
+// FormatOpenMetricsFloat works like the usual Go string formatting of a float
 // but appends ".0" if the resulting number would otherwise contain neither a
 // "." nor an "e".
-func formatOpenMetricsFloat(f float64) string {
+func FormatOpenMetricsFloat(f float64) string {
 	// A few common cases hardcoded.
 	switch {
 	case f == 1:

promql/parser/parse.go

@@ -28,6 +28,7 @@ import (
 
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/model/textparse"
 	"github.com/prometheus/prometheus/model/timestamp"
 	"github.com/prometheus/prometheus/promql/parser/posrange"
 	"github.com/prometheus/prometheus/util/strutil"
@@ -42,6 +43,11 @@ var parserPool = sync.Pool{
 // ExperimentalDurationExpr is a flag to enable experimental duration expression parsing.
 var ExperimentalDurationExpr bool
 
+// NormaliseLeAndQuantileMatchers is a flag to enable experimental conversion of matchers like
+// le="2" and quantile="2" to le=~"2|2.0" and quantile=~"2|2.0" to match the normalisation
+// of these labels during scrape time.
+var NormaliseLeAndQuantileMatchers bool
+
 type Parser interface {
 	ParseExpr() (Expr, error)
 	Close()
@@ -839,6 +845,31 @@ func (p *parser) checkAST(node Node) (typ ValueType) {
 		p.checkAST(n.VectorSelector)
 
 	case *VectorSelector:
+		if NormaliseLeAndQuantileMatchers {
+			for i, m := range n.LabelMatchers {
+				// Rewrite the matchers of type le="2" and quantile="2".
+				if m == nil || m.Type != labels.MatchEqual || (m.Name != model.QuantileLabel && m.Name != model.BucketLabel) {
+					continue
+				}
+				f, err := strconv.ParseFloat(m.Value, 64)
+				if err != nil {
+					continue
+				}
+				omFloat := textparse.FormatOpenMetricsFloat(f)
+				if omFloat == m.Value {
+					// The label value is already in the OpenMetric format, example le="2.0".
+					continue
+				}
+				// Example: changes the matcher from le="2" to le=~"2|2.0".
+				mat, err := labels.NewMatcher(labels.MatchRegexp, m.Name, fmt.Sprintf("%s|%s", m.Value, omFloat))
+				if err == nil {
+					n.LabelMatchers[i] = mat
+				} else {
+					p.addParseErrf(n.PositionRange(), "rewrite of matcher failed: %s", err.Error())
+				}
+			}
+		}
+
 		if n.Name != "" {
 			// In this case the last LabelMatcher is checking for the metric name
 			// set outside the braces. This checks if the name has already been set