The *correct* way to override the latest kernel config

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Ah, so now I’m getting what @layus was referring to :bulb: (hopefully).

So let’s say you want to override the kernel in linuxPackages_latest, independent of NixOS.

Let’s look at how linuxPackages_latest is defined:

{
  # ...
  # Here is the composition of all the kernel packages for the given kernel:
  linuxPackagesFor = kernel: lib.makeExtensible ...;
  # linuxPackages_latest is just an alias for the latest kernel version.
  linuxPackages_latest = linuxPackages_4_17;
  # This composes the kernel packages for linux_4_17, not it is NOT linux_latest:
  linuxPackages_4_17 = recurseIntoAttrs (linuxPackagesFor pkgs.linux_4_17);
  # ... and linux_latest just refers to the kernel within previously
  # defined kernelPackages_latest
  linux_latest = linuxPackages_latest.kernel;
  # ...
}

So what this means is that we can’t simply override linux_latest and get a new linuxPackages_latest with the overrides. We would have to override linux_4_17 instead, which isn’t very practical if you want to stay on the latest kernel.

Instead, we need to override linuxPackages_latest, by using .extend (note the makeExtensible above):

{ lib, ... }:

{
  nixpkgs.overlays = lib.singleton (lib.const (super: {
    linuxPackages_latest = super.linuxPackages_latest.extend (lib.const (ksuper: {
      kernel = ksuper.kernel.override {
        extraConfig = ''
          LIRC y
        '';
      };
    }));
  }));
}
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