Customize the layering strategy about rails-nix HOT 1 CLOSED

Noting here that while NixOS/nixpkgs#157670 seems relevant, and might help in many situations, it won't provide the desired control over layers. It only allows ensuring specific layers are made, dependencies of these layers may still be pushed in the "upper-most" (last) layer.

So e.g. having app.wrappedRuby in an explicit layer does not ensure all of its dependencies are present in previous layers, or at the layer itself.

What this means is that the "catch-all" layer with leftovers may still change in uncontrollable undesirable ways, and it may still be the biggest layer depending on layering elsewhere.

from rails-nix.