nixos/os-release: generate from attrset

[peterhoeg]

Motivation for this change

I've had this sitting around for ages - instead of interpolating a large string
in order to generate =/etc/os-release=, build it from an attribute set instead
which is less likely to be broken in case of changes.

Additionally, generate =/etc/lsb-release= for compatibility with older software.
The cost of doing this is a few hundred bytes, so it should be fairly
non-controversial.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[peterhoeg]

Kinda, sorta related to RFC42.

[aanderse]

I like it 👍

[andrevmatos]

I have /etc/NIXOS as a symlink (currently to /dev/null, tmpfs root, since this may be just be an empty file), and it seems that the check for "This is not a NixOS installation!" in switch-to-configuration checks that either /etc/NIXOS is an actual file (couldn't it just check that the path exists?) or that os-release has exactly the string ID=nixos, which broke with this PR, since this now renders to ID="nixos"

[peterhoeg]

Couple of things here. 1. are you by chance creating /etc/NIXOS using tmpfiles? If so, instead of creating a link to /dev/null, you can use the "f" command to create an empty file instead. 2. there is no reason that I can think of that /etc/NIXOS couldn't be a symlink though 3. the check for ID=nixos is definitely broken as there is nothing wrong with it being quoted Can you confirm 1?

[andrevmatos]

I was actually using environment.etc."NIXOS".source = "/dev/null";, but tmpfiles is a good approach as well, thanks!

[peterhoeg]

You could also use: environment.etc."NIXOS".text = "";

[andrevmatos]

Yes, that should also work. It'll still create it as a symlink, but being symlinked to an actual file would allow the -f test to pass. Either way, the os-release check may still require fixing. Thanks

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/veloren-airshipper-libegl-so-not-found/18225/8