From cab0e3e023c85dd85d6944ca068c4e4d373a781c Mon Sep 17 00:00:00 2001
From: NullBite <me@nullbite.com>
Date: Mon, 17 Feb 2025 08:25:40 +0000
Subject: [PATCH] flake(system): use system nixpkgs config in home-manager

This allows for setting overlays at the home level while also inheriting
the global nixpkgs configuration. This should theoretically work exactly
like useGlobalPkgs while still allowing for flexibility at the home
level. See nix-community/home-manager#6172
---
 flake/system.nix              | 26 ++++++++++++++++++--------
 lib/nixfiles/flake-legacy.nix |  4 ++--
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/flake/system.nix b/flake/system.nix
index 5507855..d14ecb6 100644
--- a/flake/system.nix
+++ b/flake/system.nix
@@ -186,9 +186,25 @@ in {
                 lib,
                 ...
               }: let
-                inheritStateVersionModule = {lib, ...}: {
+                perUserDefaultsModule = {lib, ...}: {
                   config = {
+                    # previously, home-manager inherited stateVersion from
+                    # nixos in a really hacky way that depended on the wrapper
+                    # function. this should preserve that behavior in a much
+                    # safer way by directly setting it in a module. ideally, it
+                    # should probably be set manually, but I want to maintain
+                    # backwards compatibility for now.
                     home.stateVersion = lib.mkDefault config.system.stateVersion;
+
+                    # pass the system nixpkgs config as defaults for the
+                    # home-manager nixpkgs config. useGlobalPkgs prevents
+                    # setting overlays at the home level; this allows for doing
+                    # that while inheriting the system overlays.
+                    nixpkgs = {
+                      config = mapAttrs (n: v: lib.mkDefault v) config.nixpkgs.config;
+                      # mkOrder 900 is after mkBefore but before default order
+                      overlays = lib.mkOrder 900 config.nixpkgs.overlays;
+                    };
                   };
                 };
               in {
@@ -197,14 +213,8 @@ in {
                   homeManagerModuleInner
                 ];
 
-                # previously, home-manager inherited stateVersion from nixos in
-                # a really hacky way that depended on the wrapper function.
-                # this should preserve that behavior in a much safer way by
-                # directly setting it in a module. ideally, it should probably
-                # be set manually, but I want to maintain backwards
-                # compatibility for now
                 options.home-manager.users = lib.mkOption {
-                  type = with lib.types; attrsOf (submodule inheritStateVersionModule);
+                  type = with lib.types; attrsOf (submodule perUserDefaultsModule);
                 };
               };
           in
diff --git a/lib/nixfiles/flake-legacy.nix b/lib/nixfiles/flake-legacy.nix
index 3d2a3e2..dc622f5 100644
--- a/lib/nixfiles/flake-legacy.nix
+++ b/lib/nixfiles/flake-legacy.nix
@@ -68,8 +68,8 @@ in rec {
       ];
 
       home-manager = {
-        useGlobalPkgs = true;
-        useUserPackages = true;
+        useGlobalPkgs = lib.mkDefault false;
+        useUserPackages = lib.mkDefault true;
         backupFileExtension = "hm.bak";
         inherit users;
         extraSpecialArgs = {