In reply to @edrex:matrix.org
I should ask, "how can I update the system nix to a different branch of nixpkgs"?

In reply to @jez:petrichor.me
nix shell might be a better option for that?

In reply to @roosemberth:orbstheorem.ch
If using flakes, you can add --override-input nixpkgs github:NixOS/nixpkgs/foo, where foo is the target branch (or commit). If not using flakes, you can probably just export NIX_PATH="nixpkgs=/nix/var/nix/profiles/per-user/myuser/channels/mychannel:$NIX_PATH" before running your nix command.

In reply to @edrex:matrix.org
nix shell nixpkgs/nixpkgs-unstable#nixUnstable gives
which nix => /home/eric/.nix-profile/bin/nix, which isn't what I expect (the version in my profile isn't from nixpkgs-unstable)

In reply to @roosemberth:orbstheorem.ch
Unless nixpkgs/foo is some syntax I do not know.

In reply to @roosemberth:orbstheorem.ch
If using flakes, you can add --override-input nixpkgs github:NixOS/nixpkgs/foo, where foo is the target branch (or commit). If not using flakes, you can probably just export NIX_PATH="nixpkgs=/nix/var/nix/profiles/per-user/myuser/channels/mychannel:$NIX_PATH" before running your nix command.

Roos: i'm not using a flake for this rn. i have home-manager set up with my nixos hosts but not on laptop yet. To override NIX_PATH in that way, i guess I would have to create another channel with the branch set to nixpkgs-unstable?

note: first sent a few minutes ago, matrix troubles

In reply to @edrex:matrix.org
nix shell nixpkgs/nixpkgs-unstable#nixUnstable gives
which nix => /home/eric/.nix-profile/bin/nix, which isn't what I expect (the version in my profile isn't from nixpkgs-unstable)

In reply to @Las:matrix.org
The issue with that is that GC might remove the Nix in that small timeframe.

I've found a weird issue with Nix not adding a flake source as a runtime dependency. In particular:

  environment.etc."nixpkgs".source = pkgs.path;

When pkgs comes from a nixpkgs flake produces a "broken" etc: it has nixpkgs symlink pointing to -source nix store path containing the nixpkgs flake, but this path is not a runtime dependency of etc derivation, e.g. doesn't show up nix-store -qR or nix why-depends. toString-ing the pkgs.path beforehand doesn't fix the issue (as expected, since it gets toString-ed down the line anyways). Doing

  environment.etc."nixpkgs".source = pkgs.copyPathToStore pkgs.path;

Fixes the problem, but it's just weird.

In reply to @tomberek:matrix.org
Does it help to do string interpolation with pkgs.path as you use it? “${pkgs.path}” ?

But yeah,

nix-repl> :t toString pkgs.path
a string

nix-repl> :t "${pkgs.path}"
a string with context