flake: dev-shells: convert to 'flake-parts'

flake/default.nix

@@ -26,8 +26,6 @@ let
       default = self.apps.${system}.diff-flake;
     };
 
-    devShells = import ./dev-shells.nix inputs system;
-
     packages = import ./packages.nix inputs system;
 
     # Work-around for https://github.com/nix-community/home-manager/issues/3075
@@ -73,6 +71,7 @@ flake-parts.lib.mkFlake { inherit inputs; } {
 
   imports = [
     ./checks.nix
+    ./dev-shells.nix
     ./lib.nix
     ./nixos.nix
     ./overlays.nix

flake/dev-shells.nix

@@ -1,17 +1,17 @@
-{ self, nixpkgs, ... }:
-system:
-let
-  pkgs = nixpkgs.legacyPackages.${system};
-in
+{ inputs, ... }:
 {
-  default = pkgs.mkShell {
-    name = "NixOS-config";
+  perSystem = { self', pkgs, ... }: {
+    devShells = {
+      default = pkgs.mkShell {
+        name = "NixOS-config";
 
-    nativeBuildInputs = with pkgs; [
-      gitAndTools.pre-commit
-      nixpkgs-fmt
-    ];
+        nativeBuildInputs = with pkgs; [
+          gitAndTools.pre-commit
+          nixpkgs-fmt
+        ];
 
-    inherit (self.checks.${system}.pre-commit) shellHook;
+        inherit (self'.checks.pre-commit) shellHook;
+      };
+    };
   };
 }