twigphp/Twig · error · SyntaxError

Empty array elements are only allowed in destructuring…

Error message

Empty array elements are only allowed in destructuring assignments.

What it means

While compiling an array/tuple expression, ArrayExpression checks that no element is an EmptyExpression (the parser's placeholder for holes, like the middle slot of [1, , 3]). Empty slots are only meaningful in destructuring assignment, so an empty element in a plain array expression throws this SyntaxError at compile time.

Solutions

Remove the empty slot: write [1, 3], or use null explicitly: [1, null, 3].
Check for accidental double commas or a dangling comma inside the array literal.
Use destructuring assignment syntax ({% set [a, , c] = foo %}) if a skipped slot is intended.
Run twig's lint command (bin/console lint:twig) in CI to catch this before deployment.

Example fix

// before (Twig template)
{% set arr = [1, , 3] %}
// after
{% set arr = [1, null, 3] %}

Defensive patterns

Strategy: type-guard

Validate before calling

// pre-parse check of template source for holes in array literals
if (preg_match('/\[[^\]]*\b,\s*(,|\])/s', $templateSource)) {
    throw new InvalidArgumentException('Array literal contains empty element(s).');
}

Type guard

function hasNoEmptyArrayElements(array $pairs): bool {
    return !in_array(null, $pairs, true); // null slots only legal in destructuring
}

Try / catch

try {
    $twig->parse($twig->tokenize(new \Twig\Source($code, 'tpl')));
} catch (\Twig\Error\SyntaxError $e) {
    if (str_contains($e->getMessage(), 'Empty array elements')) {
        // report template line and fix the literal
    }
    throw $e;
}

Prevention

Lint templates in CI (twig lint command) to catch array holes before deploy.
Avoid double commas in array literals; use null explicitly for empty values.
Reserve empty slots for destructuring ({% set [a, , c] = ... %}) only.
When generating templates, never emit placeholder nodes into plain array literals.

When it happens

Trigger: Writing an array literal with a missing element in a template ({{ [1, , 3] }}), leaving a hole when editing arrays, or generating array-literal nodes containing EmptyExpression outside destructuring context.

Common situations: Typos with double commas in templates; dangling commas inside brackets after edits; template-generation code emitting placeholders that are only valid in destructuring ({% set [a, , c] = foo %} is fine, {{ [a, , c] }} is not).

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of twigphp/Twig@a414c3a491 (2026-09-13). Data as JSON: /api/errors/5ae7ca1f370c93af. Report an issue: GitHub.

Appendix: source

Thrown at src/Node/Expression/ArrayExpression.php:127

            $names[] = (string) ($i * 2);
        }

        return $names;
    }

    public function compile(Compiler $compiler): void
    {
        if ($this->definedTest) {
            $compiler->repr(true);

            return;
        }

        // Check for empty expressions which are only allowed in destructuring
        foreach ($this->getKeyValuePairs() as $pair) {
            if ($pair['value'] instanceof EmptyExpression) {
                throw new SyntaxError('Empty array elements are only allowed in destructuring assignments.', $pair['value']->getTemplateLine(), $this->getSourceContext());
            }
        }

        $compiler->raw('[');
        $isSequence = true;
        foreach ($this->getKeyValuePairs() as $i => $pair) {
            if (0 !== $i) {
                $compiler->raw(', ');
            }

            $key = null;
            if ($pair['key'] instanceof TempNameExpression) {
                $key = $pair['key']->getAttribute('name');
                $pair['key'] = new ConstantExpression($key, $pair['key']->getTemplateLine());
            } elseif ($pair['key'] instanceof ConstantExpression) {
                $key = $pair['key']->getAttribute('value');
            } else {
                // dynamic key: cast to string so PHP accepts it as an array offset

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