fix: cleanup dangling route status conditions

internal/provider/kubernetes/status.go

@@ -104,7 +104,7 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 							panic(err)
 						}
 						hCopy := h.DeepCopy()
-						hCopy.Status.Parents = mergeRouteParentStatus(h.Namespace, h.Status.Parents, val.Parents)
+						hCopy.Status.Parents = mergeRouteParentStatus(h.Namespace, r.envoyGateway.Gateway.ControllerName, h.Status.Parents, val.Parents)
 						return hCopy
 					}),
 				})
@@ -134,7 +134,7 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 							panic(err)
 						}
 						gCopy := g.DeepCopy()
-						gCopy.Status.Parents = mergeRouteParentStatus(g.Namespace, g.Status.Parents, val.Parents)
+						gCopy.Status.Parents = mergeRouteParentStatus(g.Namespace, r.envoyGateway.Gateway.ControllerName, g.Status.Parents, val.Parents)
 						return gCopy
 					}),
 				})
@@ -166,7 +166,7 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 							panic(err)
 						}
 						tCopy := t.DeepCopy()
-						tCopy.Status.Parents = mergeRouteParentStatus(t.Namespace, t.Status.Parents, val.Parents)
+						tCopy.Status.Parents = mergeRouteParentStatus(t.Namespace, r.envoyGateway.Gateway.ControllerName, t.Status.Parents, val.Parents)
 						return tCopy
 					}),
 				})
@@ -198,7 +198,7 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 							panic(err)
 						}
 						tCopy := t.DeepCopy()
-						tCopy.Status.Parents = mergeRouteParentStatus(t.Namespace, t.Status.Parents, val.Parents)
+						tCopy.Status.Parents = mergeRouteParentStatus(t.Namespace, r.envoyGateway.Gateway.ControllerName, t.Status.Parents, val.Parents)
 						return tCopy
 					}),
 				})
@@ -230,7 +230,7 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 							panic(err)
 						}
 						uCopy := u.DeepCopy()
-						uCopy.Status.Parents = mergeRouteParentStatus(u.Namespace, u.Status.Parents, val.Parents)
+						uCopy.Status.Parents = mergeRouteParentStatus(u.Namespace, r.envoyGateway.Gateway.ControllerName, u.Status.Parents, val.Parents)
 						return uCopy
 					}),
 				})
@@ -501,21 +501,41 @@ func (r *gatewayAPIReconciler) subscribeAndUpdateStatus(ctx context.Context, ext
 
 // mergeRouteParentStatus merges the old and new RouteParentStatus.
 // This is needed because the RouteParentStatus doesn't support strategic merge patch yet.
-func mergeRouteParentStatus(ns string, old, new []gwapiv1.RouteParentStatus) []gwapiv1.RouteParentStatus {
-	merged := make([]gwapiv1.RouteParentStatus, len(old))
-	_ = copy(merged, old)
-	for _, parent := range new {
+func mergeRouteParentStatus(ns, controllerName string, old, new []gwapiv1.RouteParentStatus) []gwapiv1.RouteParentStatus {
+	// Allocating with worst-case capacity to avoid reallocation.
+	merged := make([]gwapiv1.RouteParentStatus, 0, len(old)+len(new))
+
+	// Range over old status parentRefs in order:
+	// 1. The parentRef exists in the new status: append the new one to the final status.
+	// 2. The parentRef doesn't exist in the new status and it's not our controller: append it to the final status.
+	// 3. The parentRef doesn't exist in the new status, and it is our controller: don't append it to the final status.
+	for _, oldP := range old {
 		found := -1
-		for i, existing := range old {
-			if isParentRefEqual(parent.ParentRef, existing.ParentRef, ns) {
-				found = i
+		for newI, newP := range new {
+			if isParentRefEqual(oldP.ParentRef, newP.ParentRef, ns) {
+				found = newI
 				break
 			}
 		}
 		if found >= 0 {
-			merged[found] = parent
-		} else {
-			merged = append(merged, parent)
+			merged = append(merged, new[found])
+		} else if oldP.ControllerName != gwapiv1.GatewayController(controllerName) {
+			merged = append(merged, oldP)
+		}
+	}
+
+	// Range over new status parentRefs and make sure every parentRef exists in the final status. If not, append it.
+	for _, newP := range new {
+		found := false
+		for _, mergedP := range merged {
+			if isParentRefEqual(newP.ParentRef, mergedP.ParentRef, ns) {
+				found = true
+				break
+			}
+		}
+
+		if !found {
+			merged = append(merged, newP)
 		}
 	}
 	return merged