gohugoio/hugo · error

invalid slice type %T

Error message

invalid slice type %T

What it means

Returned by `commonResource.Slice` when the argument is neither `resource.Resources` nor `[]any`. This is the `default` arm of the type switch at resource.go:299-301, hit when the caller passes a typed slice other than `Resources`, a single resource, a map, or a scalar.

Source

Thrown at resources/resource.go:300

// for the template functions. See collections.Slice.
func (commonResource) Slice(in any) (any, error) {
	switch items := in.(type) {
	case resource.Resources:
		return items, nil
	case []any:
		groups := make(resource.Resources, len(items))
		for i, v := range items {
			g, ok := v.(resource.Resource)
			if !ok {
				return nil, fmt.Errorf("type %T is not a Resource", v)
			}
			groups[i] = g
			{
			}
		}
		return groups, nil
	default:
		return nil, fmt.Errorf("invalid slice type %T", items)
	}
}

type fileInfo interface {
	setOpenSource(hugio.OpenReadSeekCloser)
	setSourceFilenameIsHash(bool)
	setTargetPath(internal.ResourcePaths)
	size() int64
	hashProvider
}

type hashProvider interface {
	hash() uint64
}

var _ resource.StaleInfo = (*StaleValue[any])(nil)

type StaleValue[V any] struct {

View on GitHub (pinned to 52c9bd7908)

Solutions

1. Coerce the input to `[]any` of Resources, or pass a `resource.Resources` value directly.
2. Use `collections.Slice` to normalize before calling resource helpers.
3. Verify the template variable holds a list of resources, not a single resource or a Page resource collection.

Example fix

// template -- before
{{ apply .Resources.ByType "image/*" "resourceSlice" }}

// after
{{ $imgs := .Resources.Match "images/*" }}

func isResourceSlice(v any) bool {
	switch v.(type) {
	case resource.Resources, []any:
		return true
	}
	return false
}

When it happens

Trigger: Calling the resource slice adapter with a `[]string`, `[]Page`, single `Resource` value, or any non-slice. The type switch only accepts `resource.Resources` and `[]any`.

Common situations: Template passes `.Page.Resources` typed as `page.Resources` (not `resource.Resources`) into a resource-collection helper; passing a single Resource where a list is expected; passing a typed Go slice through reflection.

Related errors

• type %T is not a Resource
• type %T is not a WeightedPage
• invalid slice type %T
• %T cannot be merged by language
• called apply using {xt} as type {targ}

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/8352e4c3b934c81c. Report an issue: GitHub.