QFE: Fix @ modifier for subquery

CHANGELOG.md

@@ -57,6 +57,7 @@
 * [BUGFIX] Ring: update ring with new ip address when instance is lost, rejoins, but heartbeat is disabled.  #6271
 * [BUGFIX] Ingester: Fix regression on usage of cortex_ingester_queried_chunks. #6398
 * [BUGFIX] Ingester: Fix possible race condition when `active series per LabelSet` is configured. #6409
+* [BUGFIX] Query Frontend: Fix @ modifier not being applied correctly on sub queries. #6450
 
 ## 1.18.1 2024-10-14
 

pkg/querier/tripperware/queryrange/split_by_interval.go

@@ -110,6 +110,15 @@ func evaluateAtModifierFunction(query string, start, end int64) (string, error)
 			}
 			selector.StartOrEnd = 0
 		}
+		if selector, ok := n.(*parser.SubqueryExpr); ok {
+			switch selector.StartOrEnd {
+			case parser.START:
+				selector.Timestamp = &start
+			case parser.END:
+				selector.Timestamp = &end
+			}
+			selector.StartOrEnd = 0
+		}
 		return nil
 	})
 	return expr.String(), err

pkg/querier/tripperware/queryrange/split_by_interval_test.go

@@ -377,6 +377,14 @@ func Test_evaluateAtModifier(t *testing.T) {
 				[2m:])
 			[10m:])`,
 		},
+		{
+			in:       `irate(kube_pod_info{namespace="test"}[1h:1m] @ start())`,
+			expected: `irate(kube_pod_info{namespace="test"}[1h:1m] @ 1546300.800)`,
+		},
+		{
+			in:       `irate(kube_pod_info{namespace="test"} @ end()[1h:1m] @ start())`,
+			expected: `irate(kube_pod_info{namespace="test"} @ 1646300.800 [1h:1m] @ 1546300.800)`,
+		},
 		{
 			// parse error: @ modifier must be preceded by an instant vector selector or range vector selector or a subquery
 			in:                "sum(http_requests_total[5m]) @ 10.001",