How to deal with conflicting packages?

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1

I’ve been trying to set up my environment to work with rust. I followed a similar path to here: installed rustup with nix-env, and ended up with cargo run answering with:

error: linker ` cc ` not found

I figured things would get better if I installed gcc in my user profile, just to try (i know, use nix-shell instead). So I tried nix-env -iA nixos.gcc which replied:

installing 'gcc-wrapper-9.3.0'
building '/nix/store/4v0073lgw6yql2j3bcza5glqfcl5cf0x-user-environment.drv'...
error: packages '/nix/store/8pbwywcj6vbswz7xmy2dh716x8blgh8w-gcc-wrapper-9.3.0/bin/ld.gold' and '/nix/store/5sj06x18pd8an12ndl65hlwmp8afnrwa-binutils-wrapper-2.31.1/bin/ld.gold' have the same priority 10; use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' to change the priority of one of the conflicting packages (0 being the highest priority)

To continue my quick and dirty attempt to try and make things work, I tried setting the priority of something to some number… but I’m unable to find a valid package name to set the flag:

> nix-env --set-flag priority 5 nixos.gcc-wrapper
error: selector 'nixos.gcc-wrapper' matches no derivations

(I tried all sorts of variants of derivation “names”: gcc, nixos.gcc, gcc-wrapper, gcc-wrapper-9.3.0, I admit that I don’t really know what I’m doing anymore)

I have two question:

  1. How do you set a priority?
  2. How do you properly handle conflicting packages? Is the conflict a mere result of trying to put stuff in my user profile with nix-env inappropriately, and would it never happen if I were to do things in a nix-er way?

The end of the story is that I created a shell.nix with buildInput = [pkgs.rustup pkgs.gcc] and everything works. I don’t know if that’s the best way to go, but I want to use rustup rather than a pure nix way because I feel like it’ll ease interactions with other rust developers not using nix.

1 Like
2

Maybe this would work?

$ nix-env -iE 'with import <nixpkgs> {}; hiPrio gcc'
3

This is what it gives:

> nix-env -iE 'with import <nixpkgs> {}; hiPrio gcc'
error: attempt to call something which is not a function but a set, at undefined position
4

That was probably a dumb idea from my side. Would you be willing to switch to a declarative package management for your user environment? That allows some more fine-grained control over priorities.

For starters I recommend option 2) buildEnv.

5

Thanks, I’ll have a look at the buildEnv option. For the moment, I put all the packages I need in ~/default.nix and install them with nix-env -f ~ -ir. It somewhat looks like the approach 1), but I’m not sure. Will buildEnv help with conflicting packages?

I couldn’t find much documentation on buildEnv. What does it do?

6

buildEnv is what is used to build e.g. the system path in NixOS (the stuff you put in environment.systemPackages). To deal with conflicting packages you can assign priorities as I attempted to for nix-env with

{ pkgs ? import <nixpkgs> {} }:
with pkgs;
buildEnv {
  name = "user-env";
  paths = [
    nix # needed on non-NixOS
    rustup
    (hiPrio gcc)
  ];
}
7

I’m taking some time to look at that again. Can you elaborate on why you recommend buildEnv, especially over the attrset one? I’m trying to understand the differences