return vector selector from expressionWithNoMetricName

pkg/validator/expression.go

@@ -403,13 +403,13 @@ func (e expressionWithNoMetricName) String() string {
 
 func (e expressionWithNoMetricName) Validate(rule rulefmt.Rule, _ *prometheus.Client) []error {
 	var errs []error
-	names, err := getExpressionMetricsNames(rule.Expr)
+	vectorsWithNames, err := getExpressionMetricsNames(rule.Expr)
 	if err != nil {
 		return []error{err}
 	}
-	for _, s := range names {
-		if s == "" {
-			errs = append(errs, fmt.Errorf("missing metric name for expression `%s`", rule.Expr))
+	for _, v := range vectorsWithNames {
+		if v.MetricName == "" {
+			errs = append(errs, fmt.Errorf("missing metric name for vector `%s`", v.Vector.String()))
 		}
 	}
 	return errs

pkg/validator/expression_helpers.go

@@ -48,20 +48,26 @@ func getExpressionSelectors(expr string) ([]string, error) {
 	return selectors, nil
 }
 
-func getExpressionMetricsNames(expr string) ([]string, error) {
+type VectorSelectorWithMetricName struct {
+	Vector     *parser.VectorSelector
+	MetricName string
+}
+
+func getExpressionMetricsNames(expr string) ([]VectorSelectorWithMetricName, error) {
 	promQl, err := parser.ParseExpr(expr)
 	if err != nil {
-		return []string{}, fmt.Errorf("failed to parse expression `%s`: %s", expr, err)
+		return []VectorSelectorWithMetricName{}, fmt.Errorf("failed to parse expression `%s`: %s", expr, err)
 	}
-	var names []string
+	var vectors []VectorSelectorWithMetricName
 	parser.Inspect(promQl, func(n parser.Node, ns []parser.Node) error {
 		switch v := n.(type) {
 		case *parser.VectorSelector:
-			names = append(names, getMetricNameFromLabels(v.LabelMatchers))
+			metricName := getMetricNameFromLabels(v.LabelMatchers)
+			vectors = append(vectors, VectorSelectorWithMetricName{Vector: v, MetricName: metricName})
 		}
 		return nil
 	})
-	return names, nil
+	return vectors, nil
 }
 
 func getMetricNameFromLabels(labels []*labels.Matcher) string {