Add formatter

flake.lock

@@ -549,6 +549,22 @@
         "type": "github"
       }
     },
+    "nixpkgs_4": {
+      "locked": {
+        "lastModified": 1726871744,
+        "narHash": "sha256-V5LpfdHyQkUF7RfOaDPrZDP+oqz88lTJrMT1+stXNwo=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "a1d92660c6b3b7c26fb883500a80ea9d33321be2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "nur": {
       "locked": {
         "lastModified": 1729855863,
@@ -608,7 +624,8 @@
         "nixpkgs-unstable": "nixpkgs-unstable",
         "nur": "nur",
         "sops-nix": "sops-nix",
-        "stylix": "stylix"
+        "stylix": "stylix",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "rust-overlay": {
@@ -721,6 +738,24 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_4"
+      },
+      "locked": {
+        "lastModified": 1729613947,
+        "narHash": "sha256-XGOvuIPW1XRfPgHtGYXd5MAmJzZtOuwlfKDgxX5KT3s=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "aac86347fb5063960eccb19493e0cadcdb4205ca",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -7,6 +7,7 @@
     nur.url = "github:nix-community/NUR";
     nixos-hardware.url = "github:NixOS/nixos-hardware/master";
     stylix.url = "github:pizzapim/stylix/release-24.05";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
 
     nix-index-database = {
       url = "github:nix-community/nix-index-database";
@@ -52,6 +53,23 @@
     , ...
     }@inputs:
     let
+      supportedSystems = [
+        "x86_64-linux"
+        "i686-linux"
+        "aarch64-linux"
+      ];
+      forAllSystems' = nixpkgs.lib.genAttrs;
+      forAllSystems = forAllSystems' supportedSystems;
+      pkgsForSystem =
+        system:
+        import nixpkgs {
+          inherit system;
+        };
+
+      treefmtEval = forAllSystems (
+        system: inputs.treefmt-nix.lib.evalModule (pkgsForSystem system) ./treefmt.nix
+      );
+
       mkNixosSystem = {extraModule, nixpkgs' ? nixpkgs, useDefaultConfiguration ? true}: nixpkgs'.lib.nixosSystem rec {
         system = "x86_64-linux";
 
@@ -66,6 +84,8 @@
       };
     in
     {
+      formatter = forAllSystems (system: (treefmtEval.${system}.config.build.wrapper));
+
       nixosConfigurations = {
         x260 = mkNixosSystem { extraModule = ({ pkgs, lib, ... }: {
             imports = [ inputs.nixos-hardware.nixosModules.lenovo-thinkpad-x260 ];

treefmt.nix

@@ -0,0 +1,5 @@
+{ ... }:
+{
+  projectRootFile = "flake.nix";
+  programs.alejandra.enable = true;
+}