derailed/k9s · error

expected Unstructured, but got %T

Error message

expected Unstructured, but got %T

What it means

ReplicaSet.Render implements the k9s renderer contract for replicaset rows: the object must be *unstructured.Unstructured so defaultRow can fill base columns and the custom-column engine (r.specs.realize against defaultRSHeader, including READY/CONTAINERS/IMAGES/SELECTOR) 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/rs.go:52

var defaultRSHeader = model1.Header{
	model1.HeaderColumn{Name: "NAMESPACE"},
	model1.HeaderColumn{Name: "NAME"},
	model1.HeaderColumn{Name: "VS", Attrs: model1.Attrs{VS: true}},
	model1.HeaderColumn{Name: "DESIRED", Attrs: model1.Attrs{Align: tview.AlignRight}},
	model1.HeaderColumn{Name: "CURRENT", Attrs: model1.Attrs{Align: tview.AlignRight}},
	model1.HeaderColumn{Name: "READY", Attrs: model1.Attrs{Align: tview.AlignRight}},
	model1.HeaderColumn{Name: "CONTAINERS", Attrs: model1.Attrs{Wide: true}},
	model1.HeaderColumn{Name: "IMAGES", Attrs: model1.Attrs{Wide: true}},
	model1.HeaderColumn{Name: "SELECTOR", Attrs: model1.Attrs{Wide: true}},
	model1.HeaderColumn{Name: "VALID", Attrs: model1.Attrs{Wide: true}},
	model1.HeaderColumn{Name: "AGE", Attrs: model1.Attrs{Time: true}},
}

// Render renders a K8s resource to screen.
func (r ReplicaSet) 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 := r.defaultRow(raw, row); err != nil {
		return err
	}
	if r.specs.isEmpty() {
		return nil
	}
	cols, err := r.specs.realize(raw, defaultRSHeader, row)
	cols.hydrateRow(row)

	return err
}

func (r ReplicaSet) defaultRow(raw *unstructured.Unstructured, row *model1.Row) error {
	var rs appsv1.ReplicaSet
	err := runtime.DefaultUnstructuredConverter.FromUnstructured(raw.Object, &rs)
	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 ReplicaSet only to the RS GVR
4. Guard custom call sites with a comma-ok check and skip the row on mismatch

Example fix

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

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

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

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

When it happens

Trigger: Calling ReplicaSet{}.Render with a typed *appsv1.ReplicaSet, a map[string]any, a value unstructured.Unstructured, or a synthetic row type; binding the rs 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/a3cd7f9000f07234. Report an issue: GitHub.