nixos-config/hosts/aarch64-linux/alastor/apple-silicon-support/modules/mesa/default.nix

{
  config,
  pkgs,
  lib,
  ...
}: {
  config = let
    isMode = mode: (config.hardware.asahi.useExperimentalGPUDriver
      && config.hardware.asahi.experimentalGPUInstallMode == mode);
  in
    lib.mkIf config.hardware.asahi.enable (lib.mkMerge [
      {
        # required for proper DRM setup even without GPU driver
        services.xserver.config = ''
          Section "OutputClass"
              Identifier "appledrm"
              MatchDriver "apple"
              Driver "modesetting"
              Option "PrimaryGPU" "true"
          EndSection
        '';
      }
      (lib.mkIf config.hardware.asahi.useExperimentalGPUDriver {
        # install the drivers
        hardware.opengl.package = config.hardware.asahi.pkgs.mesa-asahi-edge.drivers;

        # required for in-kernel GPU driver
        hardware.asahi.withRust = true;
      })
      (lib.mkIf (isMode "replace") {
        # replace the Mesa linked into system packages with the Asahi version
        # without rebuilding them to avoid rebuilding the world.
        system.replaceRuntimeDependencies = [
          {
            original = pkgs.mesa;
            replacement = config.hardware.asahi.pkgs.mesa-asahi-edge;
          }
        ];
      })
      (lib.mkIf (isMode "overlay") {
        # replace the Mesa used in Nixpkgs with the Asahi version using an overlay,
        # which requires rebuilding the world but ensures it is done faithfully
        # (and in a way compatible with pure evaluation)
        nixpkgs.overlays = [
          (final: prev: {
            mesa = final.mesa-asahi-edge;
          })
        ];
      })
    ]);

  options.hardware.asahi.useExperimentalGPUDriver = lib.mkOption {
    type = lib.types.bool;
    default = false;
    description = ''
      Use the experimental Asahi Mesa GPU driver.

      Do not report issues using this driver under NixOS to the Asahi project.
    '';
  };

  options.hardware.asahi.experimentalGPUInstallMode = lib.mkOption {
    type = lib.types.enum ["driver" "replace" "overlay"];
    default = "replace";
    description = ''
      Mode to use to install the experimental GPU driver into the system.

      driver: install only as a driver, do not replace system Mesa.
        Causes issues with certain programs like Plasma Wayland.

      replace (default): use replaceRuntimeDependencies to replace system Mesa with Asahi Mesa.
        Does not work in pure evaluation context (i.e. in flakes by default).

      overlay: overlay system Mesa with Asahi Mesa
        Requires rebuilding the world.
    '';
  };
}