I have a flake dev-env that itself references a sub-flake myNixpkgs from the same local git repo by relative path.
As the sub-flake input is also locked in the main flake.lock file, its path is recorded in there.
Unfortunately I’ve discovered that each evaluation of the flake now changes the flake.lock file again.
$ nix develop
warning: Git tree '[…]' is dirty
warning: updating lock file '[…]/flake.lock':
• Updated input 'myNixpkgs':
'path:/nix/store/whdbxck4f86n3244v9pqmvl81p1qsg65-source/flakeSupport/myNixpkgs?lastModified=1&narHash=sha256-6+DqW6+6Bf1Ea3t8SaGhB9zfx2fkl3ZtolWM8LC7Oto=' (1970-01-01)
→ 'path:/nix/store/3y3cfmdy6vnv4pgl30r883j37p98nikv-source/flakeSupport/myNixpkgs?lastModified=1&narHash=sha256-6+DqW6+6Bf1Ea3t8SaGhB9zfx2fkl3ZtolWM8LC7Oto=' (1970-01-01)
warning: Git tree '[…]' is dirty
$ nix develop
warning: Git tree '[…]' is dirty
warning: updating lock file '[…]/flake.lock':
• Updated input 'myNixpkgs':
'path:/nix/store/3y3cfmdy6vnv4pgl30r883j37p98nikv-source/flakeSupport/myNixpkgs?lastModified=1&narHash=sha256-6+DqW6+6Bf1Ea3t8SaGhB9zfx2fkl3ZtolWM8LC7Oto=' (1970-01-01)
→ 'path:/nix/store/69skdc3dhdmf5g0iq7gh6r7pr2jic1r7-source/flakeSupport/myNixpkgs?lastModified=1&narHash=sha256-6+DqW6+6Bf1Ea3t8SaGhB9zfx2fkl3ZtolWM8LC7Oto=' (1970-01-01)
warning: Git tree '[…]' is dirty
Especially with direnv this is a no-go behaviour, as the flake is re-evaluated after each command run in the shell.
The reason for this is quite clear: For pure evaluation, the whole git repo of the flake is copied to the nix store. Its out path there depends on the repo’s content. So the following happens:
- nix copies the whole repo to store
- nix detects a path mismatch of the relatively referenced flake file
- nix updates the path in the lock file
- this causes the repo contents to change…
- …causing the out path of the repo to change when it is copied to the store at the next evaluation. GOTO 1.
I mainly wonder whether I am holding this wrong and there is a better solution to this? Or is this still one of the cases why flakes are experimental and the issue about relative flake path references is still open? Allow flakes to refer to other flakes by relative path · Issue #3978 · NixOS/nix · GitHub
I’d be so bold to say that my approach is a rather obvious one, so even if there is a better approach, it is easy to do things the wrong way.
the flake.nix at the repo top-level:
{
inputs = {
myNixpkgs = {
url = "./flakeSupport/myNixpkgs";
inputs.nixpkgs.follows = "nixpkgs";
};
nixpkgs = {
#url = "github:NixOS/nixpkgs/nixos-23.05";
url = "nixpkgs";
};
nixpkgsOld.url = "github:NixOS/nixpkgs/nixos-21.05";
poetry2nix = {
url = "github:nix-community/poetry2nix";
inputs.nixpkgs.follows = "myNixpkgs";
};
};
outputs = { self, myNixpkgs, poetry2nix, ... }:
let
inherit (myNixpkgs) lib;
supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
forAllSystems = lib.genAttrs supportedSystems;
pkgs = forAllSystems (system: myNixpkgs.legacyPackages.${system});
p2n = forAllSystems (system: poetry2nix.legacyPackages.${system});
in
{
devShells = forAllSystems (system: {
default = pkgs.${system}.mkShellNoCC {
packages = with pkgs.${system}; [
(p2n.${system}.mkPoetryEnv poetryCommonOpts.${system})
pkgs.${system}.python38
poetry
openssl_1_1
];
};
});
};
}
The sub-flake flakeSupport/myNixpkgs/flake.nix:
# vaguely inspired by https://github.com/numtide/nixpkgs-unfree/blob/9545d844027c1b91b14b19d225856efc931b22b2/flake.nix
{
description = "nixpkgs reexported with some required configuration, e.g. permitted insecure packages";
outputs = inputs@{self, nixpkgs}:
let
inherit (nixpkgs) lib;
# re-use same supported systems as in the upstream nixpkgs
systems = lib.systems.flakeExposed;
forEachSystem = lib.genAttrs systems;
nixpkgsConfig = {
permittedInsecurePackages = [
"openssl-1.1.1w"
];
};
in
nixpkgs // { legacyPackages = forEachSystem (system:
import nixpkgs {
inherit system;
config = nixpkgsConfig;
});};
}