[BUG] failed to load zls activated in nix-shell

[pseudocc]

Field	Description
Plugin	lsp
Nixpkgs	24.11
Home Manager	24.11
Project Flake	master

• I have read the FAQ and my bug is not listed there.

Description

I use zig and zls (0.13.0) on my system, but for some reason I have projects developed in zig (0.14.0) which is managed in flake.nix, but zls (0.13.0) is always loaded instead of zls (0.14.0).

Minimal, Reproducible Example (MRE)

programs.nixvim = {
  enable = true;
  plugins.lsp = {
    enable = true;
    servers.zls.enable = true;
  };
}

project flake.nix

{
  description = "MRE";

  # zig 0.14.0
  inputs.nixpkgs.url = "github:nixos/nixpkgs";

  outputs = { self, nixpkgs, ... } @ inputs: let
    inherit (nixpkgs) lib;
    eachSystem = fn:
      lib.foldl' (
        acc: system:
          lib.recursiveUpdate
          acc
          (lib.mapAttrs (_: value: {${system} = value;}) (fn system))
      ) {}
      lib.platforms.unix;
  in
    eachSystem (
      system: let
        pkgs = import nixpkgs {inherit system;};
        zig = pkgs.zig_0_14;
      in {
        devShells.default = pkgs.mkShell {
          buildInputs = [ zig pkgs.zls ];
        };
      }
    );
}

project flake.lock

{
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1741673466,
        "narHash": "sha256-VVXaC6uiwDMabeJE0iz3PmPj6UPrUa2naPT3Yi6ucpA=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "8bf6db44e9869a9bc97fb1a7ffb861a15882eae4",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs"
      }
    }
  },
  "root": "root",
  "version": 7
}

Additional Informations

zls-0.13.0 comes first, echo $PATH in neovim:

/nix/store/4zl0m2kisdpy5padk4i8wn6wf041dj5m-zls-0.13.0/bin
...
/nix/store/dh51hvagkd76nlixh4y79k8hl273847w-zig-0.14.0/bin
/nix/store/nn1v1aqacd09i9fzbirqzsy4sh0vnyqv-zls-0.14.0/bin
...

[pseudocc]

Probly related to this "--prefix" line

      extraWrapperArgs = builtins.concatStringsSep " " (
        (optional (
          config.extraPackages != [ ]
        ) ''--prefix PATH : "${lib.makeBinPath config.extraPackages}"'')
        ++ (optional config.wrapRc ''--add-flags -u --add-flags "${initFile}"'')
      );

[MattSturgeon]

I think this is effectively a duplicate of #2893.

Note that neither --suffix or --prefix are “better” for adding to the PATH, rather it is situational and/or subjective which to use.

Nixvim abruptly switching from prefix to suffix would be a potentially disruptive breaking change, as many users will be expecting the executables installed by nixvim to take priority in vim's PATH.

In general, allowing the impure environment to take priority on the PATH sounds like a bad idea, although for LSPs it is often what is desired.

Up until now, we have advised setting the relevant package option to null when you want to use the impure executable from the environment's PATH. However I can see a use case for specific packages to be installed as fallbacks.

I think we need to do a bit of head scratching, and come up with a way to define both overrides (prefix) and fallbacks (suffix).