Add nix dirs to XDG_DATA_DIRS so it can pick up .desktop files for GUI apps

[chewblacka]

The DS Nix installer is close to becoming a first-class citizen for installing nix packages on non-NixOS distributions. One current issue though is that .desktop files for GUI apps are not auto-picked-up by the DE. This is easy to rectify though. Simply add a file to etc/profile.d/ containing the following line:

export XDG_DATA_DIRS="${HOME}/.nix-profile/share:/nix/var/nix/profiles/default/share:${XDG_DATA_DIRS}"

I called my file nix-xdg-data-dirs.sh but /etc/profile.d/ already contains nix.sh which calls /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh so the XDG_DATA_DIRS line could simply be added to this latter file by the installer.

Using the syntax of the existing file nix-daemon.sh, I believe the correct line to add to it would be:

export XDG_DATA_DIRS="$NIX_LINK/share:/nix/var/nix/profiles/default/share:$XDG_DATA_DIRS"

This could go directly after the existing export PATH command.
Many thanks for the great ongoing work!

[chewblacka]

Oops I see that the files I referenced above are part of the base nix install and not part of the DS installer. I guess this means the DS installer could either install a completely new file in /etc/profile.d (e.g. nix-xdg-data-dirs.sh) or this issue needs to be escalated upstream to nix?

[Hoverbear]

I think that's a solid idea! Since this installer doesn't own /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh, I believe it would be best to recommend this upstream?

[chewblacka]

Many thanks for the reply @Hoverbear
I've done some digging, and apparently the decision not to include XDG_DATA_DIRS in the nix installer is by design not omission. There are a few PRs discussing this but the main one is this:

NixOS/nix#2443

where Elco says:

"I feel that Nix on non-NixOS systems should pollute the user's environment as little as necessary, to minimize the probability that installing a Nix package breaks the host system."

I don't think that modifying XDG_DATA_DIRS in the way I have suggested would break the host system, but I don't know that 100% either. Perhaps a more conservative approach would be to append the nix paths at the end, rather than prepend? In any case, I guess it will remain a user-guided manual intervention. Closing as not a DS issue. Many thanks!