users-groups module: add per-user packages

[4z3]

Motivation for this change

Currently it's only possible to define a system-wide set of packages that should be added to PATH. This PR allows to define a package set per user.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[mention-bot]

@4z3, thanks for your PR! By analyzing the history of the files in this pull request, we identified @edolstra, @rickynils and @nbp to be potential reviewers.

[edolstra]

This will create a symlink tree + /etc/per-user-pkgs symlink for every user, even if packages is empty, right? Might be nice to filter out users with empty packages. And maybe also filter out system users.

[4z3]

Right. I've added a filter to only create symlinks where packages are defined. Though, I'm not sure about (silently) filtering out system users because it would be counterintuitive in case someone actually tries to define packages for them for some reason. We could add an assertion, but then I wouldn't want to patronize users.

[Mic92]

@nbp what is your opinion on that?

[Mic92]

this probably could be probably also added to environment.profiles in nixos/modules/programs/environment.nix. Just extending PATH will not be sufficient for all kind of applications, for instances a theme also needs to be in XDG_DATA_DIRS (see environment.profileRelativeEnvVars)

[garbas]

👍 from my side. I just used this patch for managing my family machines since my parents use the same laptop but different accounts.

@4z3 thank you

[nbp]

Why are binaries symlink stored in /etc instead of /var/run ?

[Mic92]

is there an easy way to write to /var/run?

[edef1c]

As a fish user, I now get this at every shell startup:

set: Warning: $PATH entry "/etc/per-user-pkgs/edef/bin" is not valid (No such file or directory)
set: Tried to change the read-only variable “_”
edef@cheetah ~>