Before Twig 2.7, the Twig base classes strove to be compatible with PHP 5.2, and therefore were not namespaced. (They used PEAR-style pseudo-namespaces instead.) Starting with Drupal 9.0, Twig was updated to 2.7 (and now well beyond), which uses classes in the Twig namespace.
Using the old non-namespaced classes will still work (for now), but doing so generates deprecation warnings in dblog. (See vendor/twig/twig/lib/Twig/Extension.php for an example.)
Because Drupal 8 is entirely out-of-support, and the migration path from D8 to D9 is so trivial, there is no reason to support the old class names anymore. The new namespaced classes should be used instead. This will also require an update of emulsify_twig.info.yml to remove D8 support.
Fixed
2.1
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
codechefmarc → credited ccjjmartin → .
Hi all, I've pulled code from this issue as well as from an issue on the Emulsify Twig GitHub repo. This is now fixed and released in version 4.0.0. Thank you all!
Automatically closed - issue fixed for 2 weeks with no activity.