Keep users from running packages that are only supposed to be run in a module

[erictapen]

As a user of NGIpks, I want to run packaged software on my computer. In some cases the most direct path is not the right one. Projects that only are supposed to provide a service necessarily also contain a package with an executable, that is run by the service. That executable is often not really meant to be run on its own.

Example: In NixOS/nixpkgs#377713 (comment) a user tried to run canaille in their local shell instead of deploying the service.

Implementation

Introduce a flag that marks a package as something that is not supposed to be run directly by users. Project documentation won't show information on how to run that package locally then (e.g. by not showing a nix-shell -p command.

[fricklerhandwerk]

How about turning that around and only exposing executables via e.g. programs?

[erictapen]

So we would ditch environment.systemPackages entirely? It's kind of a well known interface to "install" software.
Only exposing modules for NixOS users would certainly solve the descriped problem, yes.