How to Customize Error Pages in Symfony apps has bugged me since day one. In the past we could understand why it worked that way. But now that Twig is a first class citizen, in-app bundles are gone and bundle inheritance is in question we could reconsider this.

The Proposal

Make Symfony/Twig/TwigBundle look for in the templates/error/ directory for custom error pages, and keep using the same logic to pick the template (error500.json.twig, error.xml.twig, etc.)

This change could be made for Symfony 4.0, which introduces the new templates/ directory at project root, but we may need to deprecate or change something in Symfony 3.4 in preparation for that.