Arch Linux

Description:

I believe the packaged `user.environment.conf`: https://gitlab.archlinux.org/archlinux/packaging/packages/nix/-/blob/main/user.environment.conf is originally included to ease the user setup process. However, since then the upstream installation has improved and `user.environment.conf` is now outdated.

Additional info:
* package version(s): `nix: 2.17.0-1`

- incorrect `NIX_PATH`: the default user channel is changed to be `~/.nix-defexpr/channels -> ～/.local/state/nix/profiles/channels`. This works _without_ setting `NIX_PATH`. Our `user.environment.conf` sets `nixpkgs=/nix/var/nix/profiles/per-user/$USER/channels/nixpkgs` instead, which is deprecated some time ago.

The new standard is documented here: https://nixos.org/manual/nix/stable/command-ref/nix-env#user-channel-link
`NIX_PATH` fallback is documented here: https://nixos.org/manual/nix/stable/command-ref/env-common.html#env-NIX_PATH

The wrong `NIX_PATH` will cause the new standard `～/.local/state/nix/profiles/channels` to be ignored and trigger warnings.

- unnecessary `PATH`: this is now automatically set via `/etc/profile.d/nix-daemon.sh`: https://github.com/NixOS/nix/blob/master/scripts/nix-profile-daemon.sh.in. Setting `PATH` again results in duplicated entries.


Resolution:

In our `user.environment.conf`: https://gitlab.archlinux.org/archlinux/packaging/packages/nix/-/blob/main/user.environment.conf,

- remove `PATH`. This should just work.
- remove `NIX_PATH`. This is a bit subtle; I am not sure if removing this will break old installs that have not yet migrated to the current standard. If this is the case, then one can keep `NIX_PATH` but include `$HOME/.local/state/nix/profiles/channels`.

I think it's best to leave everything to the upstream `/etc/profile.d/nix-daemon.sh`. I have removed `user.environment.conf` entirely with `~/.config/environment.d/nix-daemon.conf -> /dev/null` and things have been working smoothly for me.