client-go: preserve context cancellation in retry OnError

OnError replaced context cancellation errors with a nil lastErr when
the error was non-retriable. Preserve the callback error when no
retriable error was recorded.

Add a regression test covering a context cancellation returned on the
first invocation.

Kubernetes-commit: 23b344cd1581a871984e44be951249af6018242e

util/retry/util.go

@@ -59,7 +59,7 @@ func OnError(backoff wait.Backoff, retriable func(error) bool, fn func() error)
 			return false, err
 		}
 	})
-	if wait.Interrupted(err) {
+	if wait.Interrupted(err) && lastErr != nil {
 		err = lastErr
 	}
 	return err

util/retry/util_test.go

@@ -17,6 +17,8 @@ limitations under the License.
 package retry
 
 import (
+	"context"
+	stderrors "errors"
 	"fmt"
 	"testing"
 
@@ -69,3 +71,12 @@ func TestRetryOnConflict(t *testing.T) {
 		t.Errorf("unexpected error: %v", err)
 	}
 }
+
+func TestRetryOnConflictPreservesContextErrorWithoutLastError(t *testing.T) {
+	err := RetryOnConflict(DefaultBackoff, func() error {
+		return context.Canceled
+	})
+	if !stderrors.Is(err, context.Canceled) {
+		t.Fatalf("expected context.Canceled, got %v", err)
+	}
+}