client-go/cache: support errors.Unwrap for KeyError

Signed-off-by: Iceber Gu <wei.cai-nat@daocloud.io>

Kubernetes-commit: 85fa121f84ee33bdc8d77e7a35d1f4d2c063c28f

tools/cache/store.go

@@ -85,6 +85,11 @@ func (k KeyError) Error() string {
 	return fmt.Sprintf("couldn't create key for object %+v: %v", k.Obj, k.Err)
 }
 
+// Unwrap implements errors.Unwrap
+func (k KeyError) Unwrap() error {
+	return k.Err
+}
+
 // ExplicitKey can be passed to MetaNamespaceKeyFunc if you have the key for
 // the object but not the object itself.
 type ExplicitKey string

tools/cache/store_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package cache
 
 import (
+	"errors"
 	"testing"
 
 	"k8s.io/apimachinery/pkg/util/sets"
@@ -154,3 +155,18 @@ func TestUndeltaStore(t *testing.T) {
 func TestIndex(t *testing.T) {
 	doTestIndex(t, NewIndexer(testStoreKeyFunc, testStoreIndexers()))
 }
+
+func TestKeyError(t *testing.T) {
+	obj := 100
+	err := errors.New("error")
+	keyErr := KeyError{obj, err}
+
+	if errors.Unwrap(keyErr) != err {
+		t.Errorf("expected unwrap error: %v", err)
+	}
+
+	nestedKeyErr := KeyError{obj, keyErr}
+	if !errors.Is(keyErr, err) || !errors.Is(nestedKeyErr, err) {
+		t.Errorf("not match target error: %v", err)
+	}
+}