flake: use treefmt-nix

flake.lock

@@ -2,7 +2,9 @@
   "nodes": {
     "flake-utils": {
       "inputs": {
-        "systems": "systems"
+        "systems": [
+          "systems"
+        ]
       },
       "locked": {
         "lastModified": 1705309234,
@@ -37,7 +39,9 @@
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "systems": "systems",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "systems": {
@@ -54,6 +58,26 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1709911575,
+        "narHash": "sha256-yC2iOKe0BSZAeXLNPXPrsGn5BwUTYYZESKb+OblLnXY=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "9c57261c71871d2208a6dd4394774cca226c6dbc",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -3,13 +3,25 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
+
+    flake-utils = {
+      url = "github:numtide/flake-utils";
+      inputs.systems.follows = "systems";
+    };
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    ### De-dupe flake dependencies
+    systems.url = "github:nix-systems/default";
   };
 
   outputs = inputs:
     inputs.flake-utils.lib.eachDefaultSystem (system: let
       inherit (inputs.nixpkgs) lib;
       pkgs = inputs.nixpkgs.legacyPackages.${system};
+      treefmtEval = inputs.treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
       runtimeDeps = with pkgs; [
         # mason / tree-sitter
         gcc
@@ -33,7 +45,10 @@
           // {wrapperArgs = ["--prefix" "PATH" ":" "${lib.makeBinPath runtimeDeps}"];});
 
       ### nix fmt
-      formatter = pkgs.alejandra;
+      formatter = treefmtEval.config.build.wrapper;
+
+      ### nix flake check
+      checks = {formatting = treefmtEval.config.build.check inputs.self;};
 
       ### nix develop
       devShells.default = pkgs.mkShell {

treefmt.nix

@@ -0,0 +1,17 @@
+{
+  projectRootFile = "flake.nix";
+
+  ### nix
+  programs.deadnix.enable = true;
+  programs.statix.enable = true;
+  programs.alejandra.enable = true;
+
+  ### lua
+  programs.stylua.enable = true;
+
+  ### toml
+  programs.taplo.enable = true;
+
+  ### misc
+  programs.prettier.enable = true;
+}