use treemft and also enable stylua

works well with CI

.github/workflows/flake-check.yml

@@ -1,4 +1,4 @@
-name: "nix build and flake check"
+name: "nix flake and fmt check"
 on:
   pull_request:
   push:
@@ -6,20 +6,8 @@ jobs:
   flake-check:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
-    - uses: cachix/install-nix-action@v30
-      with:
-        github_access_token: ${{ secrets.github_token }}
-    - run: nix flake check
-
-  nixfmt:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v4
-    - uses: cachix/install-nix-action@v30
-      with:
-        github_access_token: ${{ secrets.github_token }}
-    - name: install nixfmt
-      run: nix-env -f <nixpkgs> -iAP nixfmt-rfc-style
-    - name: check that nix files are formatted correctly
-      run : nixfmt --check
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+        with:
+          github_access_token: ${{ secrets.github_token }}
+      - run: nix flake check

flake.lock

@@ -84,6 +84,22 @@
         "type": "github"
       }
     },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1733097829,
+        "narHash": "sha256-9hbb1rqGelllb4kVUCZ307G2k3/UhmA8PPGBoyuWaSw=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "2c15aa59df0017ca140d9ba302412298ab4bf22a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "home-manager": "home-manager",
@@ -91,7 +107,8 @@
         "nixpkgs-borg": "nixpkgs-borg",
         "nixpkgs-evolution": "nixpkgs-evolution",
         "nixpkgs-master": "nixpkgs-master",
-        "sops-nix": "sops-nix"
+        "sops-nix": "sops-nix",
+        "treefmt": "treefmt"
       }
     },
     "sops-nix": {
@@ -113,6 +130,24 @@
         "repo": "sops-nix",
         "type": "github"
       }
+    },
+    "treefmt": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1735135567,
+        "narHash": "sha256-8T3K5amndEavxnludPyfj3Z1IkcFdRpR23q+T0BVeZE=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "9e09d30a644c57257715902efbb3adc56c79cf28",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -11,6 +11,7 @@
       url = "github:nix-community/home-manager";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    treefmt.url = "github:numtide/treefmt-nix";
     nixpkgs-borg.url = "github:cything/nixpkgs/borg";
     nixpkgs-master.url = "github:nixos/nixpkgs/master";
     nixpkgs-evolution.url = "github:nixos/nixpkgs/a49023bcb550bcd84e1fa8afcbe7aa8bc0850bf4";
@@ -21,6 +22,7 @@
       self,
       nixpkgs,
       home-manager,
+      treefmt,
       ...
     }@inputs:
     let
@@ -65,10 +67,22 @@
           };
         }
       );
+
+      treefmtEval = forEachSystem (
+        pkgs:
+        treefmt.lib.evalModule pkgs {
+          projectRootFile = "flake.nix";
+          programs.nixfmt.enable = true;
+          programs.stylua.enable = true;
+        }
+      );
     in
     {
       packages = forEachSystem (pkgs: import ./pkgs { inherit pkgs; });
-      formatter = forEachSystem (pkgs: pkgs.nixfmt-rfc-style);
+      formatter = forEachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);
+      checks = forEachSystem (pkgs: {
+        formatting = treefmtEval.${pkgs.system}.config.build.check self;
+      });
 
       nixosConfigurations =
         let