The current DB Layer needs to be rewritten, at least to use PDO.
There are different options: we could use a layer similar to Panther's one: https://gitlab.com/vank1ta/Panther/blob/master/include/database.php
We could use Idiorm, which seems to be rather popular and well-maintained: https://github.com/j4mie/idiorm
Or simply use the layer written by Reines for late-FluxBB 2.0: https://github.com/fluxbb/database
If you have another idea, don't hesitate to share it.
As I'm not a developper, my answer shouldn't help much, but if Reines' layer is cleanly extensible, why wouldn't you use it ?
Idiorm would allow using a single file for DB config, as it supports multiple query languages. Plus it has nice features (chained queries, simple CRUD...) rather developer-friendly for those who want to extend Feather's core. That would be my choice
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