Use of environment.sessionVariables.PATH interferes with system rebuild

[alrunner4]

Bug description

Use of environment.sessionVariables to set PATH causes system reconfiguration to fail.

Maybe this isn't the right way to configure PATH any more and this isn't really a bug, but it's not listed in the configuration documentation.

To Reproduce

$ cat /etc/nixos/configuration.nix
{ lib, pkgs, config, modulesPath, ... }:

with lib;
{
  imports = [
    "${modulesPath}/profiles/minimal.nix"
    <nixos-wsl/modules>
  ];

  wsl = {
    enable = true;
    wslConf.automount.root = "/mnt";
    defaultUser = "nixos";
    startMenuLaunchers = true;
  };

  # Enable nix flakes
  nix.package = pkgs.nixFlakes;
  nix.extraOptions = ''
    experimental-features = nix-command flakes
  '';

  system.stateVersion = "22.05";

  environment.sessionVariables = rec {
    HOME = "/mnt/c/users/alexca14";
    PATH = ["${HOME}/bin"];
  };
}

sudo nixos-rebuild switch

Logs

$ sudo nixos-rebuild switch
building Nix...
building the system configuration...
error: The option `environment.variables.PATH' is defined multiple times while it's expected to be unique.

       Definition values:
       - In `/nix/var/nix/profiles/per-user/root/channels/nixos-wsl/modules/systemd/native':
           [
             "$PATH"
           ]
       - In `/nix/var/nix/profiles/per-user/root/channels/nixos/nixos/modules/config/shells-environment.nix': "/mnt/c/users/alexca14/bin"
       Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.
(use '--show-trace' to show detailed location information)

WSL version

WSL version: 2.1.5.0
Kernel version: 5.15.146.1-2
WSLg version: 1.0.60
MSRDC version: 1.2.5105
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.25131.1002-220531-1700.rs-onecore-base2-hyp
Windows version: 10.0.19045.4291

shasum -a 256 nixos-wsl.tar.gz
3893395087de58cc68ed1181ecf8cdaa06aac677c9665c2ff696901ab2096898

[Bios-Marcel]

Is this acknowledged as an actual bug? Is there a workaround?

[nzbr]

We do set PATH in modules/systemd/native/default.nix in order to preserve the PATH entries that are passed down from WSL. I'm not really sure why the two definitions aren't merged though.
A workaround would be to just set the variable with lib.mkForce. Make sure to include [ "$PATH" ] as one of the entries though, because otherwise you'll loose that functionality

[reasonableperson]

I think the definitions aren't being merged because this config uses environment.sessionVariables rather than environment.variables. See NixOS/nixpkgs#265890.