flake-modules: add treefmt to fix the 'nix fmt' command

flake-modules/default.nix

@@ -11,6 +11,7 @@
     ./templates.nix
     ./tests.nix
     ./wrappers.nix
+    inputs.flake-root.flakeModule
   ];
 
   perSystem =

flake-modules/dev/default.nix

@@ -2,13 +2,24 @@
 {
   imports = [
     inputs.pre-commit-hooks.flakeModule
+    inputs.treefmt-nix.flakeModule
     ./devshell.nix
   ];
 
   perSystem =
-    { pkgs, ... }:
+    { pkgs, config, ... }:
     {
-      formatter = pkgs.nixfmt-rfc-style;
+      formatter = config.treefmt.build.wrapper;
+
+      treefmt.config = {
+        inherit (config.flake-root) projectRootFile;
+        package = pkgs.treefmt;
+
+        programs = {
+          nixfmt-rfc-style.enable = true;
+          statix.enable = true;
+        };
+      };
 
       pre-commit = {
         settings.hooks = {

flake.lock

@@ -71,6 +71,21 @@
         "type": "github"
       }
     },
+    "flake-root": {
+      "locked": {
+        "lastModified": 1713493429,
+        "narHash": "sha256-ztz8JQkI08tjKnsTpfLqzWoKFQF4JGu2LRz8bkdnYUk=",
+        "owner": "srid",
+        "repo": "flake-root",
+        "rev": "bc748b93b86ee76e2032eecda33440ceb2532fcd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "srid",
+        "repo": "flake-root",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -215,10 +230,12 @@
         "devshell": "devshell",
         "flake-compat": "flake-compat",
         "flake-parts": "flake-parts",
+        "flake-root": "flake-root",
         "home-manager": "home-manager",
         "nix-darwin": "nix-darwin",
         "nixpkgs": "nixpkgs",
-        "pre-commit-hooks": "pre-commit-hooks"
+        "pre-commit-hooks": "pre-commit-hooks",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "systems": {
@@ -250,6 +267,26 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1714058656,
+        "narHash": "sha256-Qv4RBm4LKuO4fNOfx9wl40W2rBbv5u5m+whxRYUMiaA=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "c6aaf729f34a36c445618580a9f95a48f5e4e03f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -16,10 +16,16 @@
       url = "github:hercules-ci/flake-parts";
       inputs.nixpkgs-lib.follows = "nixpkgs";
     };
+    # A flake-parts module for finding the project root directory
+    flake-root.url = "github:srid/flake-root";
     devshell = {
       url = "github:numtide/devshell";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
 
     flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";