Using fenix.overlay can prevent nix from downloading packages from cachix

[MaeIsBad]

I ran into an issue where my laptop wasn't using the nix-community cache for fenix packages when building my system, despite using the fenix flake and not modifying the fenix nixpkgs input. This is because fenix will use super.callPackage in the overlay, which causes it to use the system nixpkgs and not the ones from the fenix.inputs.nixpkgs.

One solution is to replace the fenix overlay from the repo with a simple:

nixpkgs.overlays = [ (prev: _: { fenix = import fenix { system = prev.system; }) }

This isn't necessarily a bug, but I thought it might be worth it to document this behavior with an issue. Feel free to close or maybe consider mentioning this in the readme.

[figsoda]

Seems intended but I could be more clear about it in the readme. May I ask you what branch of nixpkgs are you using?

[MaeIsBad]

I'm using stable nixos-22.05 although I overlay some packages with their nixos-unstable counterparts

[figsoda]

does this work for you?

{
  nixpkgs.overlays = [ (self: _: fenix.overlay self self) ];
}

[MaeIsBad]

no, that still causes some of the fenix related packages to be built from source instead of getting pulled from cachix

[figsoda]

what about this

{
  nixpkgs.overlays = [ (_: super: (fenix.overlay { } { callPackage = x: _: import x { inherit (super) system; }; })) ];
}

or

{
  nixpkgs.overlays = [ (_: super: let pkgs = fenix.inputs.nixpkgs.legacyPackages.${super.system}; in fenix.overlay pkgs pkgs) ];
}

[MaeIsBad]

Both of those work for me, although the second one seems way cleaner

[figsoda]

I added a note to the readme

[mplanchard]

This may be obvious, but is there a way to do this if using an overlay but not using flakes?