argoproj/argo-workflows · error

failed to marshal evaluated expression: %w

Error message

failed to marshal evaluated expression: %w

What it means

After successful evaluation, json.Marshal of the expression's result failed — the evaluated value cannot be serialized to JSON for insertion into the template. Rare; indicates an unserializable value (e.g. chan, func, or cyclic structure) coming out of the expression.

Source

Thrown at util/template/expression_template.go:266

	result, err := expr.Run(program, env)
	if (err != nil || result == nil) && (allowUnresolved || shouldAllowFailure) {
		//  <nil> result is also un-resolved, and any error can be unresolved
		log.WithError(err).Debug(ctx, "Result and error are unresolved")
		return fmt.Fprintf(w, "{{%s%s}}", kindExpression, expression)
	}
	if err != nil {
		return 0, fmt.Errorf("failed to evaluate expression: %w", err)
	}
	if result == nil {
		return 0, fmt.Errorf("failed to evaluate expression %q", expression)
	}
	resultMarshaled, err := json.Marshal(result)
	if (err != nil || resultMarshaled == nil) && allowUnresolved {
		log.WithError(err).Debug(ctx, "resultMarshaled is nil and unresolved is allowed ")
		return fmt.Fprintf(w, "{{%s%s}}", kindExpression, expression)
	}
	if err != nil {
		return 0, fmt.Errorf("failed to marshal evaluated expression: %w", err)
	}
	if resultMarshaled == nil {
		return 0, fmt.Errorf("failed to marshal evaluated marshaled expression %q", expression)
	}
	marshaledLength := len(resultMarshaled)

	// Trim leading and trailing quotes. The value is being inserted into something that's already a string.
	if len(resultMarshaled) > 1 && resultMarshaled[0] == '"' && resultMarshaled[marshaledLength-1] == '"' {
		return w.Write(resultMarshaled[1 : marshaledLength-1])
	}

	resultQuoted := []byte(strconv.Quote(string(resultMarshaled)))
	return w.Write(resultQuoted[1 : len(resultQuoted)-1])
}

func EnvMap(replaceMap map[string]string) map[string]any {
	envMap := make(map[string]any)
	for k, v := range replaceMap {

View on GitHub (pinned to 35bff19146)

Solutions

1. Change the expression to return a JSON-serializable type
2. Avoid returning raw complex objects from custom contexts

When it happens

Trigger: Thrown at util/template/expression_template.go:266 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of argoproj/argo-workflows@35bff19146 (2026-09-03). Data as JSON: /api/errors/073d831851c7fd8e. Report an issue: GitHub.