What causes "unmarshal takes 1 or 2 arguments" in gohugoio/hugo?

Call it as `transform.Unmarshal DATA` or `transform.Unmarshal OPTIONS_MAP DATA`.

unmarshal takes 1 or 2 arguments

Error message

unmarshal takes 1 or 2 arguments

What it means

`transform.Unmarshal` requires either one argument (the data: a string, json.RawMessage, or Resource) or two (an options map first, then the data). Zero arguments or three-plus fail this arity check immediately, before any decoding is attempted.

Source

Thrown at tpl/transform/unmarshal.go:40

	"github.com/gohugoio/hugo/resources"
	"github.com/gohugoio/hugo/resources/resource"

	"github.com/gohugoio/hugo/common/hashing"
	"github.com/gohugoio/hugo/common/types"

	"github.com/mitchellh/mapstructure"

	"github.com/gohugoio/hugo/parser/metadecoders"

	"github.com/spf13/cast"
)

// Unmarshal unmarshals the data given, which can be either a string, json.RawMessage
// or a Resource. Supported formats are JSON, TOML, YAML, and CSV.
// You can optionally provide an options map as the first argument.
func (ns *Namespace) Unmarshal(args ...any) (any, error) {
	if len(args) < 1 || len(args) > 2 {
		return nil, errors.New("unmarshal takes 1 or 2 arguments")
	}

	var data any
	decoder := metadecoders.Default

	if len(args) == 1 {
		data = args[0]
	} else {
		m, ok := args[0].(map[string]any)
		if !ok {
			return nil, errors.New("first argument must be a map")
		}

		var err error

		data = args[1]
		decoder, err = decodeDecoder(m)
		if err != nil {

View on GitHub ↗ (pinned to 8a468df065)

Solutions

Call it as `transform.Unmarshal DATA` or `transform.Unmarshal OPTIONS_MAP DATA`.
Bundle all options into a single dict: `{{ transform.Unmarshal (dict "delimiter" ";") $csv }}`.
When piping, remember the piped value is appended as the final argument — only the options map should precede it.

Example fix

<!-- before -->
{{ transform.Unmarshal "delimiter" ";" $csv }}
<!-- after -->
{{ transform.Unmarshal (dict "delimiter" ";") $csv }}

Defensive patterns

Strategy: validation

Validate before calling

{{/* unmarshal (options?, data): */}}
{{ $d := unmarshal $yaml }} or {{ $d := unmarshal (dict "delimiter" ";") $csv }}

Prevention

Call transform.Unmarshal with 1 or 2 args: optional options map, then the data
When piping, the piped resource/string is the last argument — pass only the options map explicitly
Don't pass multiple documents; unmarshal one at a time

When it happens

Trigger: `{{ transform.Unmarshal }}` with nothing; `{{ transform.Unmarshal $opts $data $extra }}`; pipeline mistakes like `{{ $a $b | transform.Unmarshal $c }}` where the pipe adds a final argument beyond two.

Common situations: Forgetting that piped values count as the last argument (`$data | transform.Unmarshal $opts` is fine — two args — but adding more breaks it); passing CSV options as separate arguments instead of one dict; splitting an unquoted string into multiple arguments.

Related errors

AI-assisted analysis of gohugoio/hugo@8a468df065 (2026-07-31). Data as JSON: /data/errors/3dfd87e8dac1bd4b.json. Report an issue: GitHub ↗.