gohugoio/hugo · error

invalid argument type %T

Error message

invalid argument type %T

What it means

Pages.Related accepts either a related.Document (typically a Page) or a map of search options that is weak-decoded into related.SearchOpts. Any other argument type falls through the switch and is rejected with this error, because Hugo cannot infer what to search for.

Source

Thrown at resources/page/pages_related.go:69

}

// Related searches all the configured indices with the search keywords from the
// supplied document.
func (p Pages) Related(ctx context.Context, optsv any) (Pages, error) {
	if len(p) == 0 {
		return nil, nil
	}

	var opts related.SearchOpts
	switch v := optsv.(type) {
	case related.Document:
		opts.Document = v
	case map[string]any:
		if err := mapstructure.WeakDecode(v, &opts); err != nil {
			return nil, err
		}
	default:
		return nil, fmt.Errorf("invalid argument type %T", optsv)
	}

	result, err := p.search(ctx, opts)
	if err != nil {
		return nil, err
	}

	return result, nil
}

// RelatedIndices searches the given indices with the search keywords from the
// supplied document.
// Deprecated: Use Related instead.
func (p Pages) RelatedIndices(ctx context.Context, doc related.Document, indices ...any) (Pages, error) {
	indicesStr, err := cast.ToStringSliceE(indices)
	if err != nil {
		return nil, err
	}

View on GitHub ↗ (pinned to 8a468df065)

Solutions

1. Pass the current page: `{{ $related := site.RegularPages.Related . }}`.
2. For options, pass a dict: `{{ site.RegularPages.Related (dict "document" . "indices" (slice "tags")) }}`.
3. If you were using `.RelatedIndices . "tags"` or `.RelatedTo (keyVals ...)`, either keep those deprecated methods or convert the arguments into the options dict form.

Example fix

<!-- before -->
{{ $related := site.RegularPages.Related "tags" }}
<!-- after -->
{{ $related := site.RegularPages.Related (dict "document" . "indices" (slice "tags")) }}

func relatedArg(v any) (any, bool) {
    switch v.(type) {
    case page.Page, []page.Page, page.Pages:
        return v, true
    default:
        return nil, false
    }
}

{{ with .Site.RegularPages.Related . }}{{ range . }}...{{ end }}{{ end }}

When it happens

Trigger: Calling `.Related` in a template with an argument that is neither a page nor an options map/dict — e.g. `{{ site.RegularPages.Related "tags" }}` (a string), a slice, a nil-ish value from a failed lookup, or a taxonomy term object. The %T in the message names the offending Go type.

Common situations: Migrating from the deprecated `.RelatedIndices`/`.RelatedTo` calling conventions and passing the old string/keyVals arguments to `.Related`; passing `.Params.something` that isn't a map; forgetting `(dict ...)` around options.

Related errors

• arguments to symdiff must be slices or arrays
• can't iterate over %T
• text must be a string
• first argument must be a map
• type %T not supported

AI-assisted analysis of gohugoio/hugo@8a468df065 (2026-07-31). Data as JSON: /data/errors/71cc09c466dd8743.json. Report an issue: GitHub ↗.