flake: add treefmt-nix

Signed-off-by: Christoph Heiss <christoph@c8h4.io>

flake.lock

@@ -58,7 +58,8 @@
         "crane": "crane",
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
-        "rust-overlay": "rust-overlay"
+        "rust-overlay": "rust-overlay",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "rust-overlay": {
@@ -95,6 +96,26 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1723808491,
+        "narHash": "sha256-rhis3qNuGmJmYC/okT7Dkc4M8CeUuRCSvW6kC2f3hBc=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "1d07739554fdc4f8481068f1b11d6ab4c1a4167a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -4,6 +4,10 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs";
     flake-utils.url = "github:numtide/flake-utils";
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     crane = {
       url = "github:ipetkov/crane";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -14,7 +18,8 @@
     };
   };
 
-  outputs = { self, nixpkgs, flake-utils, crane, rust-overlay, ... }:
+  outputs =
+    { self, nixpkgs, flake-utils, treefmt-nix, crane, rust-overlay, ... }:
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = import nixpkgs {
@@ -23,6 +28,20 @@
         };
         inherit (pkgs) lib;
 
+        treefmt = treefmt-nix.lib.evalModule pkgs {
+          projectRootFile = "flake.nix";
+          programs = {
+            deadnix.enable = true;
+            nixfmt = {
+              enable = true;
+              package = pkgs.nixfmt-classic;
+            };
+            prettier.enable = true;
+            statix.enable = true;
+            taplo.enable = true;
+          };
+        };
+
         rustToolchain = pkgs.rust-bin.stable.latest.default.override {
           extensions = [ "rust-analyzer" ];
         };
@@ -63,6 +82,7 @@
         checks = {
           inherit bwtui;
           default = bwtui;
+          formatting = treefmt.config.build.check self;
           bwtui-clippy = craneLib.cargoClippy commonArgsWithArtifacts // {
             cargoClippyExtraArgs = "--all-targets -- --deny warnings";
           };
@@ -73,6 +93,8 @@
           bwtui-coverage = craneLib.cargoTarpaulin commonArgsWithArtifacts;
         };
 
+        formatter = treefmt.config.build.wrapper;
+
         packages = rec {
           inherit bwtui;
           default = bwtui;