symfony/routing · error · LogicException

Collection " " is missing prefixes for locale(s) " ".

Error message

Collection "%s" is missing prefixes for locale(s) "%s".

What it means

CollectionConfigurator::prefix() supports locale-keyed prefixes. When a parent collection already has locale prefixes, a child prefix array must cover every parent locale. Missing locales are detected via array_diff_key and throw LogicException naming the collection and locales.

Solutions

  1. Add the missing locale keys to the child ->prefix([...]) call
  2. Remove the extra locale from the parent collection's prefix
  3. Make both parent and child prefix arrays use identical locale keys

Example fix

// before
$collection->collection('blog')->prefix(['en' => '/en']); // parent has en+nl
// after
$collection->collection('blog')->prefix(['en' => '/en', 'nl' => '/nl']);
Defensive patterns

Strategy: validation

Validate before calling

$missing = array_diff_key($parentPrefixes, $childPrefix); if ($missing) { /* extend child prefix before calling ->prefix() */ }

Type guard

function coversParentLocales(array $parent, array $child): bool { return !array_diff_key($parent, $child); }

Try / catch

try { $routes = $loader->load($file); } catch (\LogicException $e) { if (str_contains($e->getMessage(), 'missing prefixes')) { /* sync collection prefixes */ } throw $e; }

Prevention

When it happens

Trigger: $collection->prefix(['en' => '/en']) (or ->prefix(...)) on a nested collection whose parent was prefixed with locales ['en','nl'], but the child prefix omits 'nl'.

Common situations: Localized route groups where a sub-collection adds a new parent locale without updating all children; partially translated route trees; copying a ->prefix() call between collections.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

AI-assisted analysis of symfony/routing@83fa223250 (2026-09-14). Data as JSON: /api/errors/3820ed48681e0a59. Report an issue: GitHub.

Appendix: source

Thrown at Loader/Configurator/CollectionConfigurator.php:86

        return new self($this->collection, $this->name.$name, $this, $this->prefixes);
    }

    /**
     * Sets the prefix to add to the path of all child routes.
     *
     * @param string|array $prefix the prefix, or the localized prefixes
     *
     * @return $this
     */
    final public function prefix(string|array $prefix, bool $trailingSlashOnRoot = true): static
    {
        $this->trailingSlashOnRoot = $trailingSlashOnRoot;

        if (\is_array($prefix)) {
            if (null === $this->parentPrefixes) {
                // no-op
            } elseif ($missing = array_diff_key($this->parentPrefixes, $prefix)) {
                throw new \LogicException(\sprintf('Collection "%s" is missing prefixes for locale(s) "%s".', $this->name, implode('", "', array_keys($missing))));
            } else {
                foreach ($prefix as $locale => $localePrefix) {
                    if (!isset($this->parentPrefixes[$locale])) {
                        throw new \LogicException(\sprintf('Collection "%s" with locale "%s" is missing a corresponding prefix in its parent collection.', $this->name, $locale));
                    }

                    $prefix[$locale] = $this->parentPrefixes[$locale].$localePrefix;
                }
            }
            $this->prefixes = $prefix;
            $this->route->setPath('/');
        } else {
            $this->prefixes = null;
            $this->route->setPath($prefix);
        }

        return $this;
    }

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