Expand the value string in annotations and labels of alerts (#37051)

This commit makes it possible to use the value string in
annotations and labels for alerts with "{{ $value }}"

docs/sources/alerting/unified-alerting/alerting-rules/create-grafana-managed-rule.md

@@ -109,8 +109,9 @@ The following template variables are available when expanding annotations and la
 
 | Name    | Description     |
 | ------- | --------------- |
-| $labels | Labels contains the labels from the query or condition. For example, `{{ $labels.instance }}` and `{{ $labels.job }}`. |
-| $values | Values contains the values of all reduce and math expressions that were evaluated for this alert rule. For example, `{{ $values.A }}`, `{{ $values.A.Labels }}` and `{{ $values.A.Value }}` where `A` is the `refID` of the expression. |
+| $labels | The labels from the query or condition. For example, `{{ $labels.instance }}` and `{{ $labels.job }}`. |
+| $values | The values of all reduce and math expressions that were evaluated for this alert rule. For example, `{{ $values.A }}`, `{{ $values.A.Labels }}` and `{{ $values.A.Value }}` where `A` is the `refID` of the expression. |
+| $value  | The value string of the alert instance. For example, `[ var='A' labels={instance=foo} value=10 ]`. |
 
 ## Preview alerts
 

pkg/services/ngalert/state/cache.go

@@ -39,7 +39,7 @@ func (c *cache) getOrCreate(alertRule *ngModels.AlertRule, result eval.Result) *
 	// clone the labels so we don't change eval.Result
 	labels := result.Instance.Copy()
 	attachRuleLabels(labels, alertRule)
-	ruleLabels, annotations := c.expandRuleLabelsAndAnnotations(alertRule, labels, result.Values)
+	ruleLabels, annotations := c.expandRuleLabelsAndAnnotations(alertRule, labels, result)
 
 	// if duplicate labels exist, alertRule label will take precedence
 	lbs := mergeLabels(ruleLabels, result.Instance)
@@ -88,11 +88,11 @@ func attachRuleLabels(m map[string]string, alertRule *ngModels.AlertRule) {
 	m[prometheusModel.AlertNameLabel] = alertRule.Title
 }
 
-func (c *cache) expandRuleLabelsAndAnnotations(alertRule *ngModels.AlertRule, labels map[string]string, values map[string]eval.NumberValueCapture) (map[string]string, map[string]string) {
+func (c *cache) expandRuleLabelsAndAnnotations(alertRule *ngModels.AlertRule, labels map[string]string, alertInstance eval.Result) (map[string]string, map[string]string) {
 	expand := func(original map[string]string) map[string]string {
 		expanded := make(map[string]string, len(original))
 		for k, v := range original {
-			ev, err := expandTemplate(alertRule.Title, v, labels, values)
+			ev, err := expandTemplate(alertRule.Title, v, labels, alertInstance)
 			expanded[k] = ev
 			if err != nil {
 				c.log.Error("error in expanding template", "name", k, "value", v, "err", err.Error())
@@ -122,9 +122,9 @@ func (v templateCaptureValue) String() string {
 	return "null"
 }
 
-func expandTemplate(name, text string, labels map[string]string, values map[string]eval.NumberValueCapture) (result string, resultErr error) {
+func expandTemplate(name, text string, labels map[string]string, alertInstance eval.Result) (result string, resultErr error) {
 	name = "__alert_" + name
-	text = "{{- $labels := .Labels -}}{{- $values := .Values -}}" + text
+	text = "{{- $labels := .Labels -}}{{- $values := .Values -}}{{- $value := .Value -}}" + text
 	// It'd better to have no alert description than to kill the whole process
 	// if there's a bug in the template.
 	defer func() {
@@ -145,11 +145,12 @@ func expandTemplate(name, text string, labels map[string]string, values map[stri
 	if err := tmpl.Execute(&buffer, struct {
 		Labels map[string]string
 		Values map[string]templateCaptureValue
+		Value  string
 	}{
 		Labels: labels,
 		Values: func() map[string]templateCaptureValue {
 			m := make(map[string]templateCaptureValue)
-			for k, v := range values {
+			for k, v := range alertInstance.Values {
 				m[k] = templateCaptureValue{
 					Labels: v.Labels,
 					Value:  v.Value,
@@ -157,6 +158,7 @@ func expandTemplate(name, text string, labels map[string]string, values map[stri
 			}
 			return m
 		}(),
+		Value: alertInstance.EvaluationString,
 	}); err != nil {
 		return "", fmt.Errorf("error executing template %v: %s", name, err.Error())
 	}

pkg/services/ngalert/state/cache_test.go

@@ -1,9 +1,13 @@
 package state
 
 import (
+	"errors"
 	"testing"
 
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	ptr "github.com/xorcare/pointer"
 )
 
@@ -32,3 +36,65 @@ func TestTemplateCaptureValueStringer(t *testing.T) {
 		})
 	}
 }
+
+func TestExpandTemplate(t *testing.T) {
+	cases := []struct {
+		name          string
+		text          string
+		alertInstance eval.Result
+		labels        data.Labels
+		expected      string
+		expectedError error
+	}{{
+		name:     "instance labels are expanded into $labels",
+		text:     "{{ $labels.instance }} is down",
+		labels:   data.Labels{"instance": "foo"},
+		expected: "foo is down",
+	}, {
+		name:          "missing instance label returns error",
+		text:          "{{ $labels.instance }} is down",
+		labels:        data.Labels{},
+		expectedError: errors.New("error executing template __alert_test: template: __alert_test:1:86: executing \"__alert_test\" at <$labels.instance>: map has no entry for key \"instance\""),
+	}, {
+		name: "values are expanded into $values",
+		text: "{{ $values.A.Labels.instance }} has value {{ $values.A }}",
+		alertInstance: eval.Result{
+			Values: map[string]eval.NumberValueCapture{
+				"A": {
+					Var:    "A",
+					Labels: data.Labels{"instance": "foo"},
+					Value:  ptr.Float64(10),
+				},
+			},
+		},
+		expected: "foo has value 10",
+	}, {
+		name: "missing label in $values returns error",
+		text: "{{ $values.A.Labels.instance }} has value {{ $values.A }}",
+		alertInstance: eval.Result{
+			Values: map[string]eval.NumberValueCapture{
+				"A": {
+					Var:    "A",
+					Labels: data.Labels{},
+					Value:  ptr.Float64(10),
+				},
+			},
+		},
+		expectedError: errors.New("error executing template __alert_test: template: __alert_test:1:86: executing \"__alert_test\" at <$values.A.Labels.instance>: map has no entry for key \"instance\""),
+	}, {
+		name: "value string is expanded into $value",
+		text: "{{ $value }}",
+		alertInstance: eval.Result{
+			EvaluationString: "[ var='A' labels={instance=foo} value=10 ]",
+		},
+		expected: "[ var='A' labels={instance=foo} value=10 ]",
+	}}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			v, err := expandTemplate("test", c.text, c.labels, c.alertInstance)
+			require.Equal(t, c.expectedError, err)
+			require.Equal(t, c.expected, v)
+		})
+	}
+}