From fb530e878f701795fe608f499796860ca303a624 Mon Sep 17 00:00:00 2001
From: Archit Gupta <archit@accelbread.com>
Date: Sat, 6 Apr 2024 17:53:50 -0700
Subject: [PATCH] Propagate nixpkgs.config to NixOS and HM

---
 API_GUIDE.md                         |  3 ++-
 builtinModules/propagationModule.nix | 14 ++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/API_GUIDE.md b/API_GUIDE.md
index 3d58fd2..a92fb98 100644
--- a/API_GUIDE.md
+++ b/API_GUIDE.md
@@ -954,7 +954,8 @@ or a function that takes `moduleArgs` and returns one of the prior.
 When using a set of `nixpkgs.lib.nixosSystem` args, NixOS modules will have
 access to a `flake` module arg equivalent to `moduleArgs` plus `inputs'` and
 `outputs'`. Flakelight's pkgs attributes, `withOverlays`, and `packages` will
-also be available in the NixOS instance's pkgs.
+also be available in the NixOS instance's pkgs, and Flakelight's
+`nixpkgs.config` will apply to it as well.
 
 When using the result of calling `nixpkgs.lib.nixosSystem`, the
 `config.propagationModule` value can be used as a NixOS module to gain the above
diff --git a/builtinModules/propagationModule.nix b/builtinModules/propagationModule.nix
index 6f49a4c..08ba59c 100644
--- a/builtinModules/propagationModule.nix
+++ b/builtinModules/propagationModule.nix
@@ -18,10 +18,16 @@ in
   config.propagationModule =
     { lib, pkgs, options, config, ... }:
     let inherit (pkgs.stdenv.hostPlatform) system; in {
-      config = (optionalAttrs (options ? nixpkgs.overlays) {
-        # Apply flakelight overlays to NixOS/home-manager configurations
-        nixpkgs.overlays = lib.mkOrder 10
-          (flakeConfig.withOverlays ++ [ flakeConfig.packageOverlay ]);
+      config = (optionalAttrs (options ? nixpkgs) {
+        nixpkgs = (optionalAttrs (options ? nixpkgs.overlays) {
+          # Forward overlays to NixOS/home-manager configurations
+          overlays = lib.mkOrder 10
+            (flakeConfig.withOverlays ++ [ flakeConfig.packageOverlay ]);
+        })
+        // (optionalAttrs (options ? nixpkgs.config) {
+          # Forward nixpkgs.config to NixOS/home-manager configurations
+          inherit (flakeConfig.nixpkgs) config;
+        });
       })
       // (optionalAttrs (options ? home-manager.sharedModules) {
         # Propagate module to home-manager when using its nixos module