Support native histogram values in template functions

Co-authored-by: Aleks Fazlieva <britishrum@users.noreply.github.com>
Signed-off-by: suntala <arati.rana@grafana.com>

docs/configuration/template_reference.md

@@ -18,7 +18,7 @@ The primary data structure for dealing with time series data is the sample, defi
 ```go
 type sample struct {
         Labels map[string]string
-        Value  float64
+        Value  interface{}
 }
 ```
 
@@ -44,7 +44,7 @@ If functions are used in a pipeline, the pipeline value is passed as the last ar
 | query         | query string  | []sample | Queries the database, does not support returning range vectors.  |
 | first         | []sample      | sample   | Equivalent to `index a 0`  |
 | label         | label, sample | string   | Equivalent to `index sample.Labels label`  |
-| value         | sample        | float64  | Equivalent to `sample.Value`  |
+| value         | sample        | interface{}  | Equivalent to `sample.Value`  |
 | sortByLabel   | label, []samples | []sample | Sorts the samples by the given label. Is stable.  |
 
 `first`, `label` and `value` are intended to make query results easily usable in pipelines.

template/template.go

@@ -57,7 +57,7 @@ func init() {
 // A version of vector that's easier to use from templates.
 type sample struct {
 	Labels map[string]string
-	Value  float64
+	Value  interface{}
 }
 type queryResult []*sample
 
@@ -96,6 +96,9 @@ func query(ctx context.Context, q string, ts time.Time, queryFn QueryFunc) (quer
 			Value:  v.F,
 			Labels: v.Metric.Map(),
 		}
+		if v.H != nil {
+			s.Value = v.H
+		}
 		result[n] = &s
 	}
 	return result, nil
@@ -160,7 +163,7 @@ func NewTemplateExpander(
 			"label": func(label string, s *sample) string {
 				return s.Labels[label]
 			},
-			"value": func(s *sample) float64 {
+			"value": func(s *sample) interface{} {
 				return s.Value
 			},
 			"strvalue": func(s *sample) string {

template/template_test.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/promql"
 )
@@ -39,6 +40,12 @@ func TestTemplateExpansion(t *testing.T) {
 			text:   "{{ 1 }}",
 			output: "1",
 		},
+		{
+			// Native histogram value.
+			text:   "{{ . | value }}",
+			input:  &sample{Value: &histogram.FloatHistogram{Count: 3, Sum: 10}},
+			output: (&histogram.FloatHistogram{Count: 3, Sum: 10}).String(),
+		},
 		{
 			// Non-ASCII space (not allowed in text/template, see https://github.com/golang/go/blob/master/src/text/template/parse/lex.go#L98)
 			text:       "{{ }}",
@@ -84,6 +91,18 @@ func TestTemplateExpansion(t *testing.T) {
 			},
 			output: "11",
 		},
+		{
+			// Get value of a native histogram from query.
+			text: "{{ query \"metric{instance='a'}\" | first | value }}",
+			queryResult: promql.Vector{
+				{
+					Metric: labels.FromStrings(labels.MetricName, "metric", "instance", "a"),
+					T:      0,
+					H:      &histogram.FloatHistogram{Count: 3, Sum: 10},
+				},
+			},
+			output: (&histogram.FloatHistogram{Count: 3, Sum: 10}).String(),
+		},
 		{
 			// Get label from query.
 			text: "{{ query \"metric{instance='a'}\" | first | label \"instance\" }}",