fix: apply nixpkgs overlay to system builds

flake.nix

@@ -28,8 +28,6 @@
     deploy-rs,
     flake-utils,
     nixpkgs,
-    nixpkgs-stable,
-    nixpkgs-unstable,
     ...
   }:
     {
@@ -42,25 +40,9 @@
     }
     // flake-utils.lib.eachDefaultSystem (
       system: let
-        pkgsStable = import nixpkgs-stable {
-          inherit system;
-        };
-
-        pkgsUnstable = import nixpkgs-unstable {
-          inherit system;
-        };
-
         pkgs = import nixpkgs {
           inherit system;
           overlays = [
-            (_: _: pkgsStable) # Overlay latest packages from "stable" upstream release channel
-            (_: _: {
-              # Overlay some latest packages from "unstable" upstream release channel
-              inherit
-                (pkgsUnstable)
-                linux-firmware
-                ;
-            })
             self.overlays.default
           ];
         };

nixosModules/common.nix

@@ -23,6 +23,10 @@ with lib; {
   nix.requireSignedBinaryCaches = true;
   nix.settings.auto-optimise-store = true;
 
+  nixpkgs.overlays = [
+    self.overlays.nixpkgs
+  ];
+
   programs.neovim.defaultEditor = mkDefault true;
   programs.neovim.viAlias = mkDefault true;
   programs.neovim.vimAlias = mkDefault true;

nixosModules/service.nix

@@ -55,7 +55,9 @@ in {
         users.root.name
       ];
 
-      nixpkgs.overlays = [self.overlays.service];
+      nixpkgs.overlays = [
+        self.overlays.service
+      ];
 
       profian.users.deploy.enable = true;
       profian.users.haraldh.enable = true;

overlays/default.nix

@@ -1,8 +1,10 @@
 inputs @ {nixlib, ...}: rec {
   service = import ./service.nix inputs;
   tooling = import ./tooling inputs;
+  nixpkgs = import ./nixpkgs.nix inputs;
 
   default = nixlib.lib.composeManyExtensions [
+    nixpkgs
     service
     tooling
   ];

overlays/nixpkgs.nix

@@ -0,0 +1,16 @@
+{
+  nixlib,
+  nixpkgs-stable,
+  nixpkgs-unstable,
+  ...
+}:
+nixlib.lib.composeManyExtensions [
+  (final: _: nixpkgs-stable.legacyPackages.${final.system}) # Overlay latest packages from "stable" upstream release channel
+  (final: _: {
+    # Overlay some latest packages from "unstable" upstream release channel
+    inherit
+      (nixpkgs-unstable.legacyPackages.${final.system})
+      linux-firmware
+      ;
+  })
+]