Make templateData a struct

Signed-off-by: Dimitar Dimitrov <dimitar.dimitrov@grafana.com>

rules/alerting.go

@@ -380,7 +380,7 @@ func (r *AlertingRule) Eval(ctx context.Context, queryOffset time.Duration, ts t
 			result, err := tmpl.Expand()
 			if err != nil {
 				result = fmt.Sprintf("<error expanding template: %s>", err)
-				r.logger.Warn("Expanding alert template failed", "err", err, "data", fmt.Sprintf("%#v", tmplData))
+				r.logger.Warn("Expanding alert template failed", "err", err, "data", tmplData)
 			}
 			return result
 		}

template/template.go

@@ -280,14 +280,30 @@ func NewTemplateExpander(
 	}
 }
 
+type templateData struct {
+	Labels         map[string]string
+	ExternalLabels map[string]string
+	ExternalURL    string
+	Value          interface{}
+}
+
+// String implements fmt.Stringer interface.
+func (t templateData) String() string {
+	labelsString := func(labels map[string]string) string {
+		// model.LabelSet has a ready String() method, that we can use.
+		labelSet := make(model.LabelSet, len(t.Labels))
+		for k, v := range t.Labels {
+			labelSet[model.LabelName(k)] = model.LabelValue(v)
+		}
+		return labelSet.String()
+	}
+
+	return fmt.Sprintf("<Labels: %s, ExternalLabels: %s, ExternalURL: %s, Value: %v>", labelsString(t.Labels), labelsString(t.ExternalLabels), t.ExternalURL, t.Value)
+}
+
 // AlertTemplateData returns the interface to be used in expanding the template.
 func AlertTemplateData(labels, externalLabels map[string]string, externalURL string, smpl promql.Sample) interface{} {
-	res := struct {
-		Labels         map[string]string
-		ExternalLabels map[string]string
-		ExternalURL    string
-		Value          interface{}
-	}{
+	res := templateData{
 		Labels:         labels,
 		ExternalLabels: externalLabels,
 		ExternalURL:    externalURL,