What causes "invalid number of arguments to Seq" in gohugoio/hugo?

Use the correct arity: {{ seq N }} (1..N), {{ seq A B }} (A..B), or {{ seq A I B }} (A, A+I, ... B).

invalid number of arguments to Seq

Error message

invalid number of arguments to Seq

What it means

Thrown by Seq when the variadic argument count is not between 1 and 3 inclusive (line 429). Seq accepts exactly 1 (end), 2 (start end), or 3 (start increment end) integer arguments; zero or 4+ is rejected before any value is inspected.

Solutions

Use the correct arity: {{ seq N }} (1..N), {{ seq A B }} (A..B), or {{ seq A I B }} (A, A+I, ... B).
Count your arguments in the template expression and remove extras or add the missing one.
In Go callers, ensure the slice passed to Seq has 1-3 elements.

Example fix

// before
{{ seq 1 2 3 4 }}
// after
{{ seq 1 2 3 }}

Defensive patterns

Strategy: validation

Validate before calling

// Ensure 1-3 integer args:
{{ seq 5 }}        {{/* 1 arg: 1..5 */}}
{{ seq 2 6 }}      {{/* 2 args: 2..6 */}}
{{ seq 1 2 9 }}    {{/* 3 args: 1,3,5,7,9 */}}

Prevention

Memorize seq's arity: 1 (end), 2 (start end), 3 (start inc end).
Count arguments in the template expression before rendering.
In Go callers, validate the args slice length is 1-3 before calling Seq.

When it happens

Trigger: Calling {{ seq }} with no args; {{ seq 1 2 3 4 }} with four args; passing a slice that expands to the wrong arity in a Go caller (ns.Seq(manyArgs...)).

Common situations: Template authoring mistake omitting or adding an argument; copy-paste from a 3-arg example into a context needing 1; dynamic arg construction producing the wrong count.

Related errors

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/fe83b5aded1ff4c7. Report an issue: GitHub.

Appendix: source

Thrown at tpl/collections/collections.go:430

}

// Sanity check for slices created by Seq and D.
const maxSeqSize = 1000000

var errSeqSizeExceedsLimit = errors.New("size of result exceeds limit")

// Seq creates a sequence of integers from args. It's named and used as GNU's seq.
//
// Examples:
//
//	3 => 1, 2, 3
//	1 2 4 => 1, 3
//	-3 => -1, -2, -3
//	1 4 => 1, 2, 3, 4
//	1 -2 => 1, 0, -1, -2
func (ns *Namespace) Seq(args ...any) ([]int, error) {
	if len(args) < 1 || len(args) > 3 {
		return nil, errors.New("invalid number of arguments to Seq")
	}

	intArgs := cast.ToIntSlice(args)
	if len(intArgs) < 1 || len(intArgs) > 3 {
		return nil, errors.New("invalid arguments to Seq")
	}

	inc := 1
	var last int
	first := intArgs[0]

	if len(intArgs) == 1 {
		last = first
		if last == 0 {
			return []int{}, nil
		} else if last > 0 {
			first = 1
		} else {

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