flake.nix: add treefmt-nix

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;
+            };
+          };
         };
     };
 }