Fix Promtool showing false duplicate rule warnings (#6270)

Alert rules do not use the Record field, so any alerts with the same
labels and different names would be counted as being duplicates.
Promtool will now consider either field when finding duplicates.

Signed-off-by: Chris Marchbanks <csmarchbanks@gmail.com>

cmd/promtool/main.go

@@ -324,19 +324,19 @@ type compareRuleType struct {
 	label  map[string]string
 }
 
-func checkDuplicates(r []rulefmt.RuleGroup) []compareRuleType {
+func checkDuplicates(groups []rulefmt.RuleGroup) []compareRuleType {
 	var duplicates []compareRuleType
 
-	for rindex := range r {
+	for _, group := range groups {
-		for index, props := range r[rindex].Rules {
+		for index, rule := range group.Rules {
 			inst := compareRuleType{
-				metric: props.Record,
+				metric: ruleMetric(rule),
-				label:  props.Labels,
+				label:  rule.Labels,
 			}
 			for i := 0; i < index; i++ {
 				t := compareRuleType{
-					metric: r[rindex].Rules[i].Record,
+					metric: ruleMetric(group.Rules[i]),
-					label:  r[rindex].Rules[i].Labels,
+					label:  group.Rules[i].Labels,
 				}
 				if reflect.DeepEqual(t, inst) {
 					duplicates = append(duplicates, t)
@@ -347,6 +347,13 @@ func checkDuplicates(r []rulefmt.RuleGroup) []compareRuleType {
 	return duplicates
 }
 
+func ruleMetric(rule rulefmt.Rule) string {
+	if rule.Alert != "" {
+		return rule.Alert
+	}
+	return rule.Record
+}
+
 var checkMetricsUsage = strings.TrimSpace(`
 Pass Prometheus metrics over stdin to lint them for consistency and correctness.