Revert "Alerting: add template funcs (#38404)" (#39258)

This reverts commit d6fb0181fb.

pkg/services/ngalert/state/cache.go

@@ -1,9 +1,13 @@
 package state
 
 import (
+	"bytes"
 	"fmt"
+	"math"
+	"strconv"
 	"strings"
 	"sync"
+	text_template "text/template"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 
@@ -103,6 +107,70 @@ func (c *cache) expandRuleLabelsAndAnnotations(alertRule *ngModels.AlertRule, la
 	return expand(alertRule.Labels), expand(alertRule.Annotations)
 }
 
+// templateCaptureValue represents each value in .Values in the annotations
+// and labels template.
+type templateCaptureValue struct {
+	Labels map[string]string
+	Value  float64
+}
+
+// String implements the Stringer interface to print the value of each RefID
+// in the template via {{ $values.A }} rather than {{ $values.A.Value }}.
+func (v templateCaptureValue) String() string {
+	return strconv.FormatFloat(v.Value, 'f', -1, 64)
+}
+
+func expandTemplate(name, text string, labels map[string]string, alertInstance eval.Result) (result string, resultErr error) {
+	name = "__alert_" + name
+	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() {
+		if r := recover(); r != nil {
+			var ok bool
+			resultErr, ok = r.(error)
+			if !ok {
+				resultErr = fmt.Errorf("panic expanding template %v: %v", name, r)
+			}
+		}
+	}()
+
+	tmpl, err := text_template.New(name).Option("missingkey=error").Parse(text)
+	if err != nil {
+		return "", fmt.Errorf("error parsing template %v: %s", name, err.Error())
+	}
+	var buffer bytes.Buffer
+	if err := tmpl.Execute(&buffer, struct {
+		Labels map[string]string
+		Values map[string]templateCaptureValue
+		Value  string
+	}{
+		Labels: labels,
+		Values: newTemplateCaptureValues(alertInstance.Values),
+		Value:  alertInstance.EvaluationString,
+	}); err != nil {
+		return "", fmt.Errorf("error executing template %v: %s", name, err.Error())
+	}
+	return buffer.String(), nil
+}
+
+func newTemplateCaptureValues(values map[string]eval.NumberValueCapture) map[string]templateCaptureValue {
+	m := make(map[string]templateCaptureValue)
+	for k, v := range values {
+		var f float64
+		if v.Value != nil {
+			f = *v.Value
+		} else {
+			f = math.NaN()
+		}
+		m[k] = templateCaptureValue{
+			Labels: v.Labels,
+			Value:  f,
+		}
+	}
+	return m
+}
+
 func (c *cache) set(entry *State) {
 	c.mtxStates.Lock()
 	defer c.mtxStates.Unlock()