Add treemfmt for code formatting

flake.lock

@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1726969270,
-        "narHash": "sha256-8fnFlXBgM/uSvBlLWjZ0Z0sOdRBesyNdH0+esxqizGc=",
+        "lastModified": 1729307008,
+        "narHash": "sha256-QUvb6epgKi9pCu9CttRQW4y5NqJ+snKr1FZpG/x3Wtc=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "23cbb250f3bf4f516a2d0bf03c51a30900848075",
+        "rev": "a9b86fc2290b69375c5542b622088eb6eca2a7c3",
         "type": "github"
       },
       "original": {
@@ -34,10 +34,27 @@
         "type": "github"
       }
     },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1726871744,
+        "narHash": "sha256-V5LpfdHyQkUF7RfOaDPrZDP+oqz88lTJrMT1+stXNwo=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "a1d92660c6b3b7c26fb883500a80ea9d33321be2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "systems": {
@@ -54,6 +71,24 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1729242555,
+        "narHash": "sha256-6jWSWxv2crIXmYSEb3LEVsFkCkyVHNllk61X4uhqfCs=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "d986489c1c757f6921a48c1439f19bfb9b8ecab5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -4,6 +4,7 @@
   inputs = {
     flake-utils.url = "github:numtide/flake-utils";
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
   };
 
   outputs =
@@ -11,16 +12,25 @@
       self,
       flake-utils,
       nixpkgs,
-      ...
+      treefmt-nix,
     }:
     flake-utils.lib.eachDefaultSystem (
       system:
       let
         pkgs = import nixpkgs { inherit system; };
+
+        treefmtEval = treefmt-nix.lib.evalModule pkgs {
+          projectRootFile = "flake.nix";
+          programs = {
+            nixfmt.enable = true;
+            nixfmt.package = pkgs.nixfmt-rfc-style;
+            shfmt.enable = true;
+          };
+        };
       in
       {
-        # Formatter for the Nix code
-        formatter = pkgs.nixpkgs-fmt;
+        # For `nix fmt`
+        formatter = treefmtEval.config.build.wrapper;
 
         # Checks/tests for the project
         checks = {

justfile

@@ -14,7 +14,7 @@ lint:
 
 # Format all source code
 fmt:
- echo FIXME: Add formatter here
+ nix fmt
 
 # Update all dependencies
 update: update-nix-pkgs