Shopware 6 Admin Backend Broken After Update: Twig Compatibility Error Explained

Shopware 6 Admin Backend Broken After Update: Understanding the Twig Compatibility Error

Many Shopware 6 users, particularly those updating from version 6.7.8.2 to 6.7.9.0 and higher, have reported a critical issue where the administration backend becomes inaccessible, presenting a '500 Internal Server Error'. This problem affects both web updater and Composer-based updates, even when all non-default extensions are deactivated and the default theme is selected. This insight delves into the root cause of this frustrating error and the temporary solutions available.

The Problem: A 500 Internal Server Error in the Admin Backend

Users attempting to access their Shopware 6 admin panel after an update are met with an error message similar to this:

errors
0
code    "0"
status  "500"
title   "Internal Server Error"
detail  'An exception has been thrown during the rendering of a template ("Shopware\Core\Framework\Adapter\Twig\Extension\TwigFeaturesWithInheritanceExtension::include(): Return value must be of type string, Twig\Markup returned") in "@Administration/administration/index.html.twig" at line 11.'

This error specifically points to a type mismatch within Shopware's core framework, indicating that a function expected a string but received a Twig\Markup object instead. One user also noted experiencing this issue when setting up a new Shopware instance using Docker, suggesting it's not limited to existing update scenarios.

The Root Cause: Twig Version Incompatibility

The core of this issue lies in a compatibility break introduced by recent updates to the twig/twig library. As detailed in a GitHub issue (#18028), Twig versions 3.26.0 and later (e.g., v3.28.0) changed the return type of its internal include() function. Previously, this function returned a plain string, but now it returns a Twig\Markup object.

Shopware's own TwigFeaturesWithInheritanceExtension::include() method, however, still strictly declares its return type as : string. When Shopware's method internally calls Twig's updated include(), and a Twig\Markup object is returned instead of a string, PHP throws a TypeError. This critical error occurs during the rendering of Shopware's core administration bootstrap template, making the entire admin backend inaccessible.

This is not an issue caused by specific plugins but a fundamental compatibility problem within Shopware's core platform when combined with newer Twig versions. The GitHub issue, currently marked as 'offen' (open) and 'needs-triage', also highlights that Twig versions 3.26.0+ contain important security fixes, making a simple downgrade undesirable in the long term.

Temporary Solutions and Workarounds

While Shopware works on an official fix, two main approaches have emerged:

1. Downgrading Twig: The most immediate and confirmed solution by forum users is to downgrade the twig/twig dependency to a version prior to 3.26.0. This can typically be done by adjusting your composer.json or running a specific Composer command to install an older version. For example, explicitly setting "twig/twig": "~3.25.0" might resolve the issue temporarily.
2. Manual Code Patch (Not Recommended for Production): The GitHub issue suggests a workaround by manually casting the return value in TwigFeaturesWithInheritanceExtension::include() to (string) before returning. While this fixes the immediate error, it involves directly modifying a vendor file, which will be overwritten and reverted by any subsequent composer install or composer update command. This is not a sustainable solution for production environments.

Next Steps for Shopware Users

If you're encountering this issue, the recommended approach is to temporarily downgrade your Twig version. Keep a close eye on the official Shopware GitHub repository, specifically issue #18028, for updates on the official fix. An official patch from Shopware will be necessary to fully resolve this compatibility problem, allowing users to leverage the latest Twig versions with their security enhancements without breaking the admin backend.

Migrate My Store advises all merchants and developers to ensure their development and staging environments are updated first, and to always back up their stores before performing any major updates or dependency changes.