Guard against unexpected delta types in batch processing

staging/src/k8s.io/client-go/tools/cache/controller.go

@@ -679,6 +679,8 @@ func processDeltasInBatch(
 			callbacks = append(callbacks, func() {
 				handler.OnDelete(obj)
 			})
+		default:
+			return fmt.Errorf("Delta type %s is not supported in batch processing", d.Type)
 		}
 	}
 

staging/src/k8s.io/client-go/tools/cache/the_real_fifo.go

@@ -264,6 +264,15 @@ func (f *RealFIFO) Pop(process PopProcessFunc) (interface{}, error) {
 	return Deltas{item}, err
 }
 
+// batchable stores the delta types that can be batched
+var batchable = map[DeltaType]bool{
+	Sync:     true,
+	Replaced: true,
+	Added:    true,
+	Updated:  true,
+	Deleted:  true,
+}
+
 // PopBatch pops as many items as possible to be processed as a batch using processBatch,
 // or pop a single item using processSingle if multiple items cannot be batched.
 func (f *RealFIFO) PopBatch(processBatch ProcessBatchFunc, processSingle PopProcessFunc) error {
@@ -295,6 +304,14 @@ func (f *RealFIFO) PopBatch(processBatch ProcessBatchFunc, processSingle PopProc
 			break
 		}
 		item := f.items[i]
+		if !batchable[item.Type] {
+			if len(deltas) == 0 {
+				// if an unbatchable delta is first in the list, process just that one by itself
+				moveDeltaToProcessList(i)
+			}
+			// close the batch when an unbatchable delta is encountered
+			break
+		}
 		id, err := f.keyOf(item)
 		if err != nil {
 			// close the batch here if error happens