derailed/k9s · error

expected Unstructured, but got %T

Error message

expected Unstructured, but got %T

What it means

StatefulSet.Render implements the k9s renderer contract for statefulset rows: the object must be *unstructured.Unstructured so defaultRow can fill base columns and the custom-column engine (s.specs.realize against defaultSTSHeader) can walk the raw JSON. The comma-ok assertion fails and returns this error, printing the concrete %T, when any other Go type reaches the renderer — a wiring bug in the caller.

Source

Thrown at internal/render/sts.go:45

	model1.HeaderColumn{Name: "VALID", Attrs: model1.Attrs{Wide: true}},
	model1.HeaderColumn{Name: "AGE", Attrs: model1.Attrs{Time: true}},
}

// StatefulSet renders a K8s StatefulSet to screen.
type StatefulSet struct {
	Base
}

// Header returns a header row.
func (s StatefulSet) Header(_ string) model1.Header {
	return s.doHeader(defaultSTSHeader)
}

// Render renders a K8s resource to screen.
func (s StatefulSet) Render(o any, _ string, row *model1.Row) error {
	raw, ok := o.(*unstructured.Unstructured)
	if !ok {
		return fmt.Errorf("expected Unstructured, but got %T", o)
	}
	if err := s.defaultRow(raw, row); err != nil {
		return err
	}
	if s.specs.isEmpty() {
		return nil
	}
	cols, err := s.specs.realize(raw, defaultSTSHeader, row)
	cols.hydrateRow(row)

	return err
}

func (s StatefulSet) defaultRow(raw *unstructured.Unstructured, r *model1.Row) error {
	var sts appsv1.StatefulSet
	err := runtime.DefaultUnstructuredConverter.FromUnstructured(raw.Object, &sts)
	if err != nil {
		return err

View on GitHub (pinned to 2d3ccc6ba2)

Solutions

1. Pass the informer-cached object untouched as *unstructured.Unstructured
2. Convert typed objects with runtime.DefaultUnstructuredConverter.ToUnstructured and wrap in &unstructured.Unstructured{Object: m}
3. Verify the view factory binds StatefulSet only to the STS GVR
4. Guard custom call sites with a comma-ok check and skip the row on mismatch

Example fix

// before
typed := &appsv1.StatefulSet{}
err := stsRenderer.Render(typed, ns, row)
// after
m, _ := runtime.DefaultUnstructuredConverter.ToUnstructured(typed)
err := stsRenderer.Render(&unstructured.Unstructured{Object: m}, ns, row)

// gate before invoking the StatefulSet renderer
if _, ok := o.(*unstructured.Unstructured); !ok {
	return fmt.Errorf("sts view requires *unstructured.Unstructured, got %T", o)
}
err := stsRenderer.Render(o, ns, row)

func isUnstructured(o any) bool {
	_, ok := o.(*unstructured.Unstructured)
	return ok
}

if err := stsRenderer.Render(o, ns, row); err != nil {
	slog.Warn("sts row skipped", "type", fmt.Sprintf("%T", o), slogs.Error, err)
	return nil // drop the row, keep the view alive
}

When it happens

Trigger: Calling StatefulSet{}.Render with a typed *appsv1.StatefulSet, a map[string]any, a value unstructured.Unstructured, or a synthetic row type; binding the sts renderer to a different GVR in a custom view factory.

Common situations: Writing k9s plugins or custom views that register renderers per GVR; refactoring a workload view to feed typed client-go objects; unit tests with typed fixtures.

Related errors

• expected Unstructured, but got %T
• expecting a ForwardRes but got %T
• expected Unstructured, but got %T
• expected Unstructured, but got %T
• expecting PolicyRes but got %T

AI-assisted analysis of derailed/k9s@2d3ccc6ba2 (2026-08-15). Data as JSON: /api/errors/0b3cdf3ee748ba53. Report an issue: GitHub.