Overlays

Advanced overlay composition patterns.

Composing Multiple Overlays

{ lib, ... }:
{
  flake.overlays.default = lib.composeManyExtensions [
    (import ./cuda.nix)
    (import ./stdenvs.nix)
    (import ./internal-tools.nix)
  ];
}

Overlay Order

Overlays are applied in order. Later overlays see the changes from earlier ones in prev.

Referencing final

Use final to reference the fixed-point—packages as they will be after all overlays:

final: prev: {
  my-tool = final.callPackage ./my-tool.nix { };
  # my-tool can depend on packages defined in later overlays
}

Per-System Overlays

For overlays that need system-specific logic:

final: prev:
let
  inherit (final.stdenv.hostPlatform) system isAarch64;
in {
  my-tool = final.callPackage ./my-tool.nix {
    cuda-arch = if isAarch64 then "sm_90a" else "sm_120";
  };
}

See The Overlay for the philosophy.