flake: add treefmt input

flake.lock

@@ -1222,6 +1222,22 @@
         "type": "github"
       }
     },
+    "nixpkgs_3": {
+      "locked": {
+        "lastModified": 1735554305,
+        "narHash": "sha256-zExSA1i/b+1NMRhGGLtNfFGXgLtgo+dcuzHzaWA6w3Q=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "0e82ab234249d8eee3e8c91437802b32c74bb3fd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "pre-commit-hooks": {
       "inputs": {
         "flake-compat": "flake-compat_2",
@@ -1295,7 +1311,8 @@
         "nixpkgs-unstable": "nixpkgs-unstable",
         "rust-overlay": "rust-overlay_2",
         "stylix": "stylix",
-        "systems": "systems_7"
+        "systems": "systems_7",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "rust-overlay": {
@@ -1566,6 +1583,24 @@
         "type": "github"
       }
     },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_3"
+      },
+      "locked": {
+        "lastModified": 1739829690,
+        "narHash": "sha256-mL1szCeIsjh6Khn3nH2cYtwO5YXG6gBiTw1A30iGeDU=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "3d0579f5cc93436052d94b73925b48973a104204",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
+    },
     "xdph": {
       "inputs": {
         "hyprland-protocols": [

flake.nix

@@ -15,6 +15,8 @@
 
     flake-parts.url = "github:hercules-ci/flake-parts";
 
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+
     # this is nice so one-off impure scripts can interact with attributes in
     # this flake
     flake-compat = {
@@ -132,6 +134,7 @@
           ./lib/nixfiles/module.nix
           ./pkgs/module.nix
           ./overlays
+          inputs.treefmt-nix.flakeModule
         ];
 
         config = {