exponentation operator to drop metric name in result of op operation (#5329)

Signed-off-by: Daisy T <daisyts@gmx.com>

promql/engine.go

@@ -1893,7 +1893,7 @@ func btos(b bool) float64 {
 // result of the op operation.
 func shouldDropMetricName(op ItemType) bool {
 	switch op {
-	case itemADD, itemSUB, itemDIV, itemMUL, itemMOD:
+	case itemADD, itemSUB, itemDIV, itemMUL, itemPOW, itemMOD:
 		return true
 	default:
 		return false

promql/testdata/operators.test

@@ -350,6 +350,45 @@ eval instant at 5m node_cpu > on(job, instance) group_left(target) (threshold or
   node_cpu{instance="def",job="node",mode="idle"} 8
   node_cpu{instance="def",job="node",mode="user"} 2
 
+
+# Check that binops drop the metric name.
+eval instant at 5m node_cpu + 2
+  {instance="abc",job="node",mode="idle"} 5
+  {instance="abc",job="node",mode="user"} 3
+  {instance="def",job="node",mode="idle"} 10
+  {instance="def",job="node",mode="user"} 4
+
+eval instant at 5m node_cpu - 2
+  {instance="abc",job="node",mode="idle"} 1
+  {instance="abc",job="node",mode="user"} -1
+  {instance="def",job="node",mode="idle"} 6
+  {instance="def",job="node",mode="user"} 0
+
+eval instant at 5m node_cpu / 2
+  {instance="abc",job="node",mode="idle"} 1.5
+  {instance="abc",job="node",mode="user"} 0.5
+  {instance="def",job="node",mode="idle"} 4
+  {instance="def",job="node",mode="user"} 1
+
+eval instant at 5m node_cpu * 2
+  {instance="abc",job="node",mode="idle"} 6
+  {instance="abc",job="node",mode="user"} 2
+  {instance="def",job="node",mode="idle"} 16
+  {instance="def",job="node",mode="user"} 4
+
+eval instant at 5m node_cpu ^ 2
+  {instance="abc",job="node",mode="idle"} 9
+  {instance="abc",job="node",mode="user"} 1
+  {instance="def",job="node",mode="idle"} 64
+  {instance="def",job="node",mode="user"} 4
+
+eval instant at 5m node_cpu % 2
+  {instance="abc",job="node",mode="idle"} 1
+  {instance="abc",job="node",mode="user"} 1
+  {instance="def",job="node",mode="idle"} 0
+  {instance="def",job="node",mode="user"} 0
+
+	
 clear
 
 load 5m