What happened?
kubectl get --sort-by uses RuntimeSort.Less and TableSorter.Less to order objects. When both compared objects are missing the selected JSONPath field, both comparators return true in both directions:
Less(i, j) == true
Less(j, i) == true
This violates the sort.Interface contract, which requires Less(i, j) and Less(j, i) to both be false when elements compare equal. The inconsistent comparator can produce unpredictable ordering when multiple resources omit the selected field.
The problem is present in both missing-value branches in staging/src/k8s.io/kubectl/pkg/cmd/get/sorter.go.
What did you expect to happen?
Two objects that both lack the selected sort field should compare equal. Objects with missing fields should still sort before objects with present fields, preserving the existing behavior.
How can we reproduce it?
Construct two runtime objects without the selected field and compare them through RuntimeSort:
objects := []runtime.Object{
&corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: first}},
&corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: second}},
}
sorter := NewRuntimeSort({.metadata.labels.missing}, objects)
// Both currently return true.
sorter.Less(0, 1)
sorter.Less(1, 0)The same behavior is reachable through TableSorter when two rows are missing the selected JSONPath value.
Proposed fix
Compute whether each side is missing first, return false when both are missing, otherwise keep missing values ordered before present values. Add focused unit coverage for both RuntimeSort and TableSorter.
Kubernetes version
Current master (35d4fd6c8148587b5186f50a7e376f1a6c70ce3a).
What happened?
kubectl get --sort-byusesRuntimeSort.LessandTableSorter.Lessto order objects. When both compared objects are missing the selected JSONPath field, both comparators returntruein both directions:This violates the
sort.Interfacecontract, which requiresLess(i, j)andLess(j, i)to both be false when elements compare equal. The inconsistent comparator can produce unpredictable ordering when multiple resources omit the selected field.The problem is present in both missing-value branches in
staging/src/k8s.io/kubectl/pkg/cmd/get/sorter.go.What did you expect to happen?
Two objects that both lack the selected sort field should compare equal. Objects with missing fields should still sort before objects with present fields, preserving the existing behavior.
How can we reproduce it?
Construct two runtime objects without the selected field and compare them through
RuntimeSort:The same behavior is reachable through
TableSorterwhen two rows are missing the selected JSONPath value.Proposed fix
Compute whether each side is missing first, return
falsewhen both are missing, otherwise keep missing values ordered before present values. Add focused unit coverage for bothRuntimeSortandTableSorter.Kubernetes version
Current master (
35d4fd6c8148587b5186f50a7e376f1a6c70ce3a).