twigphp/Twig · error · SyntaxError

The last parameter of

Error message

The last parameter of "%s" for %s "%s" must be an array with default value, eg. "array $arg = []".

What it means

Twig's callable arguments extractor inspects the signature of a PHP function/method registered as a Twig function or filter via Reflection. When the Twig callable is declared as variadic, Twig expects the LAST reflected parameter to either be an array with an empty-array default ("array $arg = []") or a native PHP variadic (...$args). If neither holds, it throws this SyntaxError because Twig cannot map arbitrary extra template arguments onto the signature at compile time.

Solutions

1. Change the last parameter of the callable to an array with an empty default: "array $arg = []".
2. Alternatively use a native PHP variadic: "...$args" so the isVariadic() branch pops it.
3. If the callable is not meant to accept extra arguments, remove the 'is_variadic' => true option from the TwigFunction/TwigFilter options.

Example fix

// before
TwigFunction('sum', function (int $a, array $rest = null) { ... }, ['is_variadic' => true]);
// after
TwigFunction('sum', function (int $a, array $rest = []) { ... }, ['is_variadic' => true]);

$r = new ReflectionFunction($callable);
$last = $r->getNumberOfParameters() ? $r->getParameters()[count($r->getParameters()) - 1] : null;
$ok = $last && ($last->isVariadic() || ($last->getType()?->getName() === 'array' && $last->isDefaultValueAvailable() && $last->getDefaultValue() === []));
if (!$ok) throw new LogicException('Callable is not a valid Twig variadic callable.');

When it happens

Trigger: Registering a Twig function/filter whose callable has a trailing parameter that is neither "array $x = []" nor a native variadic, while the Twig callable is registered with is_variadic=true (or Twig infers variadic support), e.g. new TwigFunction('foo', 'foo', ['is_variadic' => true]) pointing at fn($a, string $b).

Common situations: Wrapping legacy PHP helpers as Twig filters with is_variadic enabled; typos like "array $arg = null" or a non-array typed last parameter; upgrading Twig after refactoring a callable signature and forgetting the variadic convention; passing a closure whose last param has a non-empty default like "array $opts = ['x' => 1]".

Related errors

• The variadic argument
• Callback for " " is not callable in the current scope.
• Unknown " " configuration.
• The "format_list" filter requires the "IntlListFormatter"…
• SpanishInflector is not available.

AI-assisted analysis of twigphp/Twig@a414c3a491 (2026-09-13). Data as JSON: /api/errors/45a4afc1c3f4dd03. Report an issue: GitHub.

Appendix: source

Thrown at src/Util/CallableArgumentsExtractor.php:198

    {
        return strtolower(preg_replace(['/([A-Z]+)([A-Z][a-z])/', '/([a-z0-9])([A-Z])/'], '\1_\2', $name));
    }

    private function getCallableParameters(): array
    {
        $parameters = $this->rc->getTwigParameters($this->node->hasNode('node'));

        $isPhpVariadic = false;
        if ($this->twigCallable->isVariadic()) {
            $argument = end($parameters);
            $isArray = $argument && $argument->hasType() && $argument->getType() instanceof \ReflectionNamedType && 'array' === $argument->getType()->getName();
            if ($isArray && $argument->isDefaultValueAvailable() && [] === $argument->getDefaultValue()) {
                array_pop($parameters);
            } elseif ($argument && $argument->isVariadic()) {
                array_pop($parameters);
                $isPhpVariadic = true;
            } else {
                throw new SyntaxError(\sprintf('The last parameter of "%s" for %s "%s" must be an array with default value, eg. "array $arg = []".', $this->rc->getName(), $this->twigCallable->getType(), $this->twigCallable->getName()));
            }
        }

        return [$parameters, $isPhpVariadic];
    }
}

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