gohugoio/hugo · error

sequence length must be non-negative

Error message

sequence length must be non-negative

What it means

First (collections.go:207-209) rejects a negative limit because you cannot take a negative count of items. The guard runs after the cast to int succeeds.

Solutions

1. Clamp to zero: {{ first (math.Max 0 $n) .Pages }}
2. Guard: {{ if ge $n 0 }}{{ first $n .Pages }}{{ end }}

Example fix

// before
{{ first (sub $a $b) .Pages }}
// after
{{ first (math.Max 0 (sub $a $b)) .Pages }}

{{ $n := math.Max 0 $n }}
{{ first $n .Pages }}

When it happens

Trigger: {{ first -1 .Pages }} or a computed negative count (e.g. {{ first (sub $a $b) .Pages }} with b > a).

Common situations: Subtraction going below zero when deriving a count; user-supplied param not clamped; off-by-one in pagination.

Related errors

• sequence bounds out of range
• the maximum requested value
• the number of requested values
• both limit and seq must be provided
• called apply using as type

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/99de922e37331615. Report an issue: GitHub.

Appendix: source

Thrown at tpl/collections/collections.go:208

		dict[key] = values[i+1]
	}

	return root, nil
}

// First returns the first limit items in list l.
func (ns *Namespace) First(limit any, l any) (any, error) {
	if limit == nil || l == nil {
		return nil, errors.New("both limit and seq must be provided")
	}

	limitv, err := cast.ToIntE(limit)
	if err != nil {
		return nil, err
	}

	if limitv < 0 {
		return nil, errors.New("sequence length must be non-negative")
	}

	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())
	}

	if limitv > lv.Len() {
		limitv = lv.Len()
	}

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