Flake's overlay should use prev instead of inputs.nixpkgs... ?

[PaulGrandperrin]

The flake's overlay should use prev instead of inputs.nixpkgs... ?

Maybe I'm mistaken about what is expected from overlays, but I thought overlays should work this way and not pull pkgs from the outside.

Anyway, it makes integration with my system a bit harder, the only solution I found so far is to directly use pkgs.callPackage on nix-alien.nix to force the use of my system's pkgs.

Maybe my needs are weirds also, I can explain more if needed :)

[thiagokokada]

Maybe my needs are weirds also, I can explain more if needed :)

I think a PR could explain better what you actually want 😅 ?

[PaulGrandperrin]

ok ok :) I'll do that tomorrow (it's too late in france rn)

[thiagokokada]

But after re-reading your comment. Yeah, you're completely right 😅 .

I am not sure why I got to this code. I do remember that it was kinda difficult to get poetry2nix to be injected correctly without actually exposing it to the Flakes (that I didn't want).

Anyway, PRs are welcome.

[thiagokokada]

Fixed with commit f313de0.

The overlay now uses prev for poetry2nix and final for pkgs. The reason for this is because thanks to some issue that I am not sure what is happening, if I used pkgs = prev; this would result in a glibc rebuild at every dependency update. So while the solution is not ideal (the overlay now depends on both prev and final), it works. Also it is not that bad I think since final is only used by non-Python dependencies in this context.

Also, I had misunderstood before what nixpkgs.lib.composeManyExtensions function does. It doesn't seem to actually expose poetry2nix in the final overlay, so it seems to be fine for me.

[PaulGrandperrin]

Thanks @thiagokokada !
I haven't had time to really put together my PR but I was playing with this code and it didn't raise your glibc issues during my tests:

      overlay =
        final: prev:
          import ./default.nix {
            poetry2nix = (poetry2nix.overlay prev final).poetry2nix;
            pkgs = prev;
            inherit (prev.stdenv.hostPlatform) system;
            rev = if (self ? rev) then self.rev else "dirty";
          };

I didn't know about nixpkgs.lib.composeManyExtensions and maybe what I'm doing is wrong but I liked the fact that it's not dependent on nixpkgs.

It means that, when only using the overlay, one can use as inputs:

    nix-alien = {
      url = "path:/home/paulg/git/nix-alien";
      inputs.nixpkgs.follows = ""; # good enough for type-check but ensure that it is not used
    };

Why I want that?
Because I then use nix-alien on many different channels for my different machines, like 21.11, 21.11-small, unstable, unstable-small... so there isn't really an obvious channel that I can put in inputs.nix-alien.inputs.nixpkgs.follows.
And if I need to set one, it means that my systems are going to pull an entire channel (thousands of files and hundreds of bytes of wear leveling at each upgrades ) just to get access to nixpkgs.lib.composeManyExtensions.

[thiagokokada]

I didn't know about nixpkgs.lib.composeManyExtensions and maybe what I'm doing is wrong but I liked the fact that it's not dependent on nixpkgs.

Well, PRs are welcome them.

[thiagokokada]

Because I then use nix-alien on many different channels for my different machines, like 21.11, 21.11-small, unstable, unstable-small

Not sure if this is really a problem. You can pin any one of them and it should work anyway.

And if I need to set one, it means that my systems are going to pull an entire channel (thousands of files and hundreds of bytes of wear leveling at each upgrades ) just to get access to nixpkgs.lib.composeManyExtensions.

It will only pull another one if you don't set inputs.nix-alien.inputs.nixpkgs.follows at all, otherwise as long you use at least one nixpkgs it can be any one of them.

[PaulGrandperrin]

It will only pull another one if you don't set inputs.nix-alien.inputs.nixpkgs.follows at all, otherwise as long you use at least one nixpkgs it can be any one of them.

I'm not sure I get that. What I mean is that if I want my machines to only depend on one channel at a time, I need to do something like this:

inputs = {
    nixos-21.11.url= "...";
    nixos-21.11-small.url= "...";
    nixos-unstable.url= "...";
    nixos-unstable-small.url= "...";

    nix-alien-21.11 = {
      url = "path:/home/paulg/git/nix-alien";
      inputs.nixpkgs.follows = "nixos-21.11";
    };
    nix-alien-21.11-small = {
      url = "path:/home/paulg/git/nix-alien";
      inputs.nixpkgs.follows = "nixos-21.11-small";
    };
    nix-alien-unstable = {
      url = "path:/home/paulg/git/nix-alien";
      inputs.nixpkgs.follows = "nixos-unstable";
    };
    nix-alien-unstable-small = {
      url = "path:/home/paulg/git/nix-alien";
      inputs.nixpkgs.follows = "unstable-small";
    };
};
outputs = inputs: {
  nixosConfigurations = {
     a = { ... ; overlays = inputs.nix-alien-21.11; ...}
     b = { ... ; overlays = inputs.nix-alien-21.11-small; ...}
     c = { ... ; overlays = inputs.nix-alien-unstable; ...}
     d = { ... ; overlays = inputs.nix-alien-unstable-small; ...}
  };
}