Fall back to comparing by label set when sorting by label

Co-authored-by: Aleks Fazlieva <britishrum@users.noreply.github.com>
Signed-off-by: suntala <arati.rana@grafana.com>

promql/functions.go

@@ -406,10 +406,10 @@ func funcSortDesc(vals []parser.Value, args parser.Expressions, enh *EvalNodeHel
 
 // === sort_by_label(vector parser.ValueTypeVector, label parser.ValueTypeString...) (Vector, Annotations) ===
 func funcSortByLabel(vals []parser.Value, args parser.Expressions, enh *EvalNodeHelper) (Vector, annotations.Annotations) {
-	// In case the labels are the same, NaN should sort to the bottom, so take
-	// ascending sort with NaN first and reverse it.
-	var anno annotations.Annotations
-	vals[0], anno = funcSort(vals, args, enh)
+	slices.SortFunc(vals[0].(Vector), func(a, b Sample) int {
+		return labels.Compare(a.Metric, b.Metric)
+	})
+
 	labels := stringSliceFromArgs(args[1:])
 	slices.SortFunc(vals[0].(Vector), func(a, b Sample) int {
 		// Iterate over each given label
@@ -431,7 +431,7 @@ func funcSortByLabel(vals []parser.Value, args parser.Expressions, enh *EvalNode
 		return 0
 	})
 
-	return vals[0].(Vector), anno
+	return vals[0].(Vector), nil
 }
 
 // === sort_by_label_desc(vector parser.ValueTypeVector, label parser.ValueTypeString...) (Vector, Annotations) ===

promql/promqltest/testdata/functions.test

@@ -523,16 +523,16 @@ load 5m
 	node_uname_info{job="node_exporter", instance="4m1000", release="1.111.3"} 0+10x10
 
 eval_ordered instant at 50m sort_by_label(http_requests, "instance")
-	http_requests{group="production", instance="0", job="api-server"} 100
 	http_requests{group="canary", instance="0", job="api-server"} 300
-	http_requests{group="production", instance="0", job="app-server"} 500
 	http_requests{group="canary", instance="0", job="app-server"} 700
-	http_requests{group="production", instance="1", job="api-server"} 200
+	http_requests{group="production", instance="0", job="api-server"} 100
+	http_requests{group="production", instance="0", job="app-server"} 500
 	http_requests{group="canary", instance="1", job="api-server"} 400
-	http_requests{group="production", instance="1", job="app-server"} 600
 	http_requests{group="canary", instance="1", job="app-server"} 800
-	http_requests{group="production", instance="2", job="api-server"} 100
+	http_requests{group="production", instance="1", job="api-server"} 200
+	http_requests{group="production", instance="1", job="app-server"} 600
 	http_requests{group="canary", instance="2", job="api-server"} NaN
+	http_requests{group="production", instance="2", job="api-server"} 100
 
 eval_ordered instant at 50m sort_by_label(http_requests, "instance", "group")
 	http_requests{group="canary", instance="0", job="api-server"} 300