getgrav/grav · error · UnexpectedValueException

{% link in x %}: x is not a string

Error message

{% link in x %}: x is not a string

What it means

The {% link %} tag compiles the `in <expr>` clause (the asset group) into $group = <expr> followed by an is_string($group) check; anything else throws UnexpectedValueException when the compiled template runs. The group names where the link asset is placed (default 'head' when the clause is absent) must be a string.

Source

Thrown at system/src/Grav/Common/Twig/Node/TwigNodeLink.php:79

            $compiler
                ->write('$attributes += ')
                ->subcompile($this->getNode('attributes'))
                ->raw(';' . PHP_EOL)
                ->write('if (!is_array($attributes)) {' . PHP_EOL)
                ->indent()
                ->write("throw new UnexpectedValueException('{% {$this->tagName} with x %}: x is not an array');" . PHP_EOL)
                ->outdent()
                ->write('}' . PHP_EOL);
        }

        if ($this->hasNode('group')) {
            $compiler
                ->write('$group = ')
                ->subcompile($this->getNode('group'))
                ->raw(';' . PHP_EOL)
                ->write('if (!is_string($group)) {' . PHP_EOL)
                ->indent()
                ->write("throw new UnexpectedValueException('{% {$this->tagName} in x %}: x is not a string');" . PHP_EOL)
                ->outdent()
                ->write('}' . PHP_EOL);
        } else {
            $compiler->write('$group = \'head\';' . PHP_EOL);
        }

        if ($this->hasNode('priority')) {
            $compiler
                ->write('$priority = (int)(')
                ->subcompile($this->getNode('priority'))
                ->raw(');' . PHP_EOL);
        } else {
            $compiler->write('$priority = 10;' . PHP_EOL);
        }

        $compiler->write("\$assets = \\Grav\\Common\\Grav::instance()['assets'];" . PHP_EOL);
        $compiler->write("\$block = \$context['block'] ?? null;" . PHP_EOL);

View on GitHub (pinned to 6040efed04)

Solutions

1. Pass a plain string: {% link 'a.css' in 'head' %}
2. Default the variable: {% set group = group ?? 'head' %} before the tag
3. Cast in the expression if the value may be non-string: in group|default('head')

Example fix

{% set group = ['bottom'] %}
{# before: array passed to in #}
{% link 'app.css' in group %}

{# after: string group name #}
{% link 'app.css' in 'bottom' %}

{# in Twig, guard the group variable before the tag #}
{% set group = group is defined and group is string ? group : 'head' %}
{% link 'app.css' in group %}

try { echo $twig->render($template, $data); } catch (UnexpectedValueException $e) { log_template_error($e); }

When it happens

Trigger: {% link 'a.css' in 5 %} (integer literal); {% link 'a.css' in groupVar %} where groupVar is an array or null; a computed expression like in ['head', 'bottom']|first that unexpectedly yields null.

Common situations: Variables used as group names that were never initialized; refactors turning a scalar group into an array; typos where a mapping is passed instead of a bare string.

Related errors

• {% link with x %}: x is not an array
• {% script with x %}: x is not an array
• {% script in x %}: x is not a string
• {% {$this->tagName} with x %}: x is not an array
• {% {$this->tagName} in x %}: x is not a string

AI-assisted analysis of getgrav/grav@6040efed04 (2026-08-17). Data as JSON: /api/errors/218feed9da06282d. Report an issue: GitHub.