flake.nix: add treefmt-nix

flake.lock

@@ -1136,7 +1136,8 @@
         "nixvim": "nixvim",
         "pre-commit-hooks": "pre-commit-hooks_2",
         "secrets": "secrets",
-        "thunderbird-gnome-theme": "thunderbird-gnome-theme"
+        "thunderbird-gnome-theme": "thunderbird-gnome-theme",
+        "treefmt-nix": "treefmt-nix_2"
       }
     },
     "secrets": {
@@ -1282,6 +1283,26 @@
         "type": "github"
       }
     },
+    "treefmt-nix_2": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1754847726,
+        "narHash": "sha256-2vX8QjO5lRsDbNYvN9hVHXLU6oMl+V/PsmIiJREG4rE=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "7d81f6fb2e19bf84f1c65135d1060d829fae2408",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
+    },
     "utils": {
       "inputs": {
         "systems": "systems_2"

flake.nix

@@ -14,7 +14,10 @@
       inputs.pre-commit-hooks.follows = "pre-commit-hooks";
     };
 
-    deploy-rs.url = "github:serokell/deploy-rs";
+    deploy-rs = {
+      url = "github:serokell/deploy-rs";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
 
     devshell = {
       url = "github:numtide/devshell";
@@ -95,6 +98,11 @@
       url = "github:rafaelmardojai/thunderbird-gnome-theme";
       flake = false;
     };
+
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs =
@@ -108,6 +116,7 @@
         inputs.agenix-rekey.flakeModule
         inputs.pre-commit-hooks.flakeModule
         inputs.nix-topology.flakeModule
+        inputs.treefmt-nix.flakeModule
         ./nix/devshell.nix
         ./nix/hosts.nix
       ];
@@ -141,21 +150,28 @@
                 check-case-conflicts.enable = true;
                 check-executables-have-shebangs.enable = true;
                 check-merge-conflicts.enable = true;
-                deadnix = {
-                  enable = true;
-                  settings = {
-                    noLambdaArg = true;
-                  };
-                };
                 detect-private-keys.enable = true;
                 end-of-file-fixer.enable = true;
                 fix-byte-order-marker.enable = true;
                 mixed-line-endings.enable = true;
-                nixfmt-rfc-style.enable = true;
+                treefmt.enable = true;
                 trim-trailing-whitespace.enable = true;
               };
             };
           };
+
+          treefmt = {
+            projectRootFile = "flake.nix";
+            programs = {
+              deadnix = {
+                enable = true;
+                no-lambda-arg = true;
+              };
+              mdformat.enable = true;
+              nixfmt-rfc-style.enable = true;
+              shellcheck.enable = true;
+            };
+          };
         };
     };
 }

nix/devshell.nix

@@ -5,10 +5,14 @@
   ];
 
   perSystem =
-    { pkgs, ... }:
+    { config, pkgs, ... }:
     {
       devshells.default = {
         commands = [
+          {
+            package = config.treefmt.build.wrapper;
+            help = "Format all files";
+          }
           {
             package = pkgs.deploy-rs;
             name = "deploy";