gohugoio/hugo · error

both count and seq must be provided

Error message

both count and seq must be provided

What it means

Thrown by the Shuffle template function when its only argument (the list) is nil (line 497). The message text says 'both count and seq must be provided' but Shuffle takes a single list argument; this is a copy-paste message from the After/Last family. It fires before any reflection.

Source

Thrown at tpl/collections/collections.go:498

	}

	seq := make([]int, size)
	val := first
	for i := 0; ; i++ {
		seq[i] = val
		val += inc
		if (inc < 0 && val < last) || (inc > 0 && val > last) {
			break
		}
	}

	return seq, nil
}

// Shuffle returns list l in a randomized order.
func (ns *Namespace) Shuffle(l any) (any, error) {
	if l == nil {
		return nil, errors.New("both count and seq must be provided")
	}

	lv := reflect.ValueOf(l)
	lv, isNil := hreflect.Indirect(lv)
	if isNil {
		return nil, errors.New("can't iterate over a nil value")
	}

	switch lv.Kind() {
	case reflect.Array, reflect.Slice, reflect.String:
		// okay
	default:
		return nil, errors.New("can't iterate over " + reflect.ValueOf(l).Type().String())
	}

	shuffled := reflect.MakeSlice(reflect.TypeOf(l), lv.Len(), lv.Len())

	randomIndices := rand.Perm(lv.Len())

View on GitHub (pinned to 52c9bd7908)

Solutions

1. Coalesce to an empty slice: {{ $pages := .Pages | default slice }} {{ shuffle $pages }}.
2. Guard with {{ with .Pages }}{{ shuffle . }}{{ end }} to skip shuffling an empty set.
3. Ensure upstream providers return empty non-nil slices.

Example fix

// before
{{ shuffle .Pages }}
// after
{{ with .Pages }}{{ shuffle . }}{{ end }}

{{ with .Pages }}{{ shuffle . }}{{ end }}

When it happens

Trigger: Calling {{ shuffle .Pages }} when .Pages is nil (empty section); piping a nil scratch value or failed lookup into shuffle; passing an unset variable.

Common situations: Empty taxonomies/sections; optional partial parameters defaulting to nil; lookups (index, .Param) returning nil fed straight into shuffle.

Related errors

• cannot index slice/array with nil
• both limit and seq must be provided
• nil is not a valid key to group by
• invalid number of arguments to Seq
• invalid arguments to Seq

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/ef40cfbfbb3a8ad1. Report an issue: GitHub.