move treefmt to tests flake

this way we don't polute our consumers flake.lock with treefmt

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v31
-    - run: nix fmt .
+    - run: cd tests && nix fmt .. -- --fail-on-change
   tests:
     needs: nixfmt
     runs-on: ubuntu-latest

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1748995760,
-        "narHash": "sha256-f6UIyqm6JZs45pG667YdHOFYgDt+gvxQvt32ZLBp1h4=",
+        "lastModified": 1751290770,
+        "narHash": "sha256-u4s8yKAqTzPGY3vTcDyAIet11uXaNCM//93/0O0NlbA=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "26a54a5886c238b5df6f1e9ba0aa713434d73f06",
+        "rev": "0620a50e9a847851bf802c59a4202552ed79b821",
         "type": "github"
       },
       "original": {
@@ -16,44 +16,9 @@
         "type": "github"
       }
     },
-    "nixpkgs_2": {
-      "locked": {
-        "lastModified": 1747958103,
-        "narHash": "sha256-qmmFCrfBwSHoWw7cVK4Aj+fns+c54EBP8cGqp/yK410=",
-        "owner": "nixos",
-        "repo": "nixpkgs",
-        "rev": "fe51d34885f7b5e3e7b59572796e1bcb427eccb1",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nixos",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "root": {
       "inputs": {
-        "nixpkgs": "nixpkgs",
-        "treefmt-nix": "treefmt-nix"
-      }
-    },
-    "treefmt-nix": {
-      "inputs": {
-        "nixpkgs": "nixpkgs_2"
-      },
-      "locked": {
-        "lastModified": 1748243702,
-        "narHash": "sha256-9YzfeN8CB6SzNPyPm2XjRRqSixDopTapaRsnTpXUEY8=",
-        "owner": "numtide",
-        "repo": "treefmt-nix",
-        "rev": "1f3f7b784643d488ba4bf315638b2b0a4c5fb007",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "treefmt-nix",
-        "type": "github"
+        "nixpkgs": "nixpkgs"
       }
     }
   },

flake.nix

@@ -1,34 +1,9 @@
 {
   description = "nixos-hardware";
 
-  inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05-small";
-    treefmt-nix.url = "github:numtide/treefmt-nix";
-  };
-
   outputs =
+    { ... }:
     {
-      nixpkgs,
-      self,
-      treefmt-nix,
-    }:
-    let
-      systems = [
-        "aarch64-darwin"
-        "aarch64-linux"
-        "x86_64-darwin"
-        "x86_64-linux"
-      ];
-      forEachSystem =
-        function: nixpkgs.lib.genAttrs (systems) (system: function nixpkgs.legacyPackages.${system});
-
-      treefmtEval = forEachSystem (pkgs: treefmt-nix.lib.evalModule pkgs ./treefmt.nix);
-    in
-    {
-      checks = forEachSystem (pkgs: {
-        formatting = treefmtEval.${pkgs.system}.config.build.check self;
-      });
-      formatter = forEachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);
 
       nixosModules =
         let

tests/flake.lock

@@ -74,7 +74,28 @@
         "flake-parts": "flake-parts",
         "nixos-hardware": "nixos-hardware",
         "nixos-stable": "nixos-stable",
-        "nixos-unstable-small": "nixos-unstable-small"
+        "nixos-unstable-small": "nixos-unstable-small",
+        "treefmt-nix": "treefmt-nix"
+      }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixos-unstable-small"
+        ]
+      },
+      "locked": {
+        "lastModified": 1750931469,
+        "narHash": "sha256-0IEdQB1nS+uViQw4k3VGUXntjkDp7aAlqcxdewb/hAc=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "ac8e6f32e11e9c7f153823abc3ab007f2a65d3e1",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
       }
     }
   },

tests/flake.nix

@@ -8,11 +8,16 @@
     nixos-hardware.url = "github:NixOS/nixos-hardware";
     flake-parts.url = "github:hercules-ci/flake-parts";
     flake-parts.inputs.nixpkgs-lib.follows = "nixos-unstable-small";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixos-unstable-small";
   };
 
   outputs =
     inputs@{ flake-parts, ... }:
     flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [
+        inputs.treefmt-nix.flakeModule
+      ];
       systems = [
         "aarch64-linux"
         "x86_64-linux"
@@ -85,6 +90,24 @@
         in
         {
           _module.args.pkgs = nixpkgsUnstable;
+
+          treefmt = {
+            projectRootFile = "COPYING";
+            programs = {
+              deadnix = {
+                enable = true;
+                no-lambda-pattern-names = true;
+              };
+              nixfmt = {
+                enable = true;
+                package = pkgs.nixfmt-rfc-style;
+              };
+            };
+            settings = {
+              on-unmatched = "info";
+            };
+          };
+
           checks =
             checksForNixpkgs "nixos-unstable" nixpkgsUnstable
             // checksForNixpkgs "nixos-stable" nixpkgsStable;

treefmt.nix

@@ -1,19 +0,0 @@
-{ pkgs, ... }:
-{
-  projectRootFile = "flake.nix";
-
-  programs = {
-    deadnix = {
-      enable = true;
-      no-lambda-pattern-names = true;
-    };
-    nixfmt = {
-      enable = true;
-      package = pkgs.nixfmt-rfc-style;
-    };
-  };
-
-  settings = {
-    on-unmatched = "info";
-  };
-}