Nix commands returning unexpected packages

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1

Hi I’m trying to understand (and perhaps fix) these unexpected results to simple nix commands

Given nix-env -qaP ‘ruby.*’ output includes this…

nixpkgs.ruby                                                    ruby-2.7.5
nixpkgs.ruby_3_0                                                ruby-3.0.3
nixpkgs.ruby_3_1                                                ruby-3.1.0

And I can :

$nix-shell -p "ruby_3_0" --run "which ruby"    
/nix/store/nhy5jkwh4g87msljr9ig3mym6w0fvij6-ruby-3.0.2/bin/ruby

and

 $ nix-shell -p "ruby" --run "which ruby"                                                                                                                                /nix/store/fc9zf2l14j9z213dnj1rz71rc04qzqch-ruby-2.7.4/bin/ruby

Shouldn’t I expect something similar for ruby_3_1:

$nix-shell -p "ruby_3_1" --run "which ruby"                                                                                                         error: undefined variable 'ruby_3_1'
 at «string»:1:107:
 1| {...}@args: with import <nixpkgs> args; (pkgs.runCommandCC or pkgs.runCommand) "shell" { buildInputs = [ (ruby_3_1) ]; } ""

Another scenario; the package ‘rubyPackages_3_0.rails’ should return rails 7 but instead it returns rails 6:

$>nix-env -qaP 'ruby.*'|grep rails|grep 3_0|grep 7
nixpkgs.rubyPackages_3_0.rails                                  ruby3.0.3-rails-7.0.1
$> nix-shell -p "rubyPackages_3_0.rails" --run "rails --version" --pure
Rails 6.1.4.1

Do I fundamentally have a misunderstanding of how these commands should work? or, is there something else going on? And is there a way I can have these commands behave as expected?

Thanks in advance,

2

As meantioned in the discord earlier today, it doesn’t really make sense on the first glance, though on the second it might be related to the different ways how nix-env and the rest of the nix ecosystem treat channels.

Can you please share the output of each of these commands?

sudo nix-channel --list
nix-channel --list
printenv NIX_PATH
3

Hey NoobZ, man you are everywhere… thanks for replying

glenn@quokka> sudo nix-channel --list                                                                                                                                               ~/w/rails-template-01
Password:
darwin https://github.com/LnL7/nix-darwin/archive/master.tar.gz
home-manager https://github.com/nix-community/home-manager/archive/master.tar.gz
nixpkgs https://nixos.org/channels/nixpkgs-unstable
glenn@quokka> nix-channel --list                                                                                                                                                    
darwin https://github.com/LnL7/nix-darwin/archive/master.tar.gz
home-manager https://github.com/nix-community/home-manager/archive/master.tar.gz
nixpkgs https://nixos.org/channels/nixpkgs-unstable
glenn@quokka> printenv NIX_PATH                                                                                                                                                     
darwin-config=/Users/glenn/.nixpkgs/darwin-configuration.nix:/nix/var/nix/profiles/per-user/root/channels:/Users/glenn/.nix-defexpr/channels
4

Is this a single user install or multiuser?

5

multi user (at least as I understand it… it uses a nix daemon)

6

This supports my claim of the different behaviour between nix-env and the rest of the nix-world.

nix-env looks in ~/.nix-defexpr and only there, unless -f is provided.

Though the rest of the world uses NIX_PATH to resolve. They will look up in /nix/var/nix/profiles/per-user/root/channels first, and if they find a folder nixpgs there, they will not search further.

So your roots channels “win” when you do nix-shell, while nix-env doesn’t consider them.

Try nix-shell -I nixpkgs=/Users/glenn/.nix-defexpr/channels/nixpkgs -p "ruby_3_1" --run "which ruby" to enforce usage of the users channel.

Alternatively you should be able to do nix-env -f '<nixpkgs>' -qaP 'ruby.*' to actually search the channels of root, as -f '<nixpkgs>' enforces NIX_PATH resolution.

The rails version mismatch is probably because of the channel mismatches as well, and versions would congruent if usage of same channel locations is enforced.

1 Like
7

Oh my… seems crazy to me… but, you are correct, that invocation of nix-shell does install the correct version of ruby. Thanks again, that was very enlightening.