Hi,
I’ve been working for a couple of months on a new builder for PHP/Composer based applications. The upstream PR against nixpkgs is at PHP: add new builder for PHP projects by drupol · Pull Request #225401 · NixOS/nixpkgs · GitHub
Today, I’ve created a single flake containing only the builder so you can include it in your existing projects with ease.
Find it at this URL: GitHub - loophp/nix-php-composer-builder: A PHP builder for Composer based projects
The documentation is on the README page of the project.
Feel free to use it and report any single issue you might encounter, I’ll backport the changes upstream on a monthly basis.