chore: add treefmt

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1756128520,
+        "narHash": "sha256-R94HxJBi+RK1iCm8Y4Q9pdrHZl0GZoDPIaYwjxRNPh4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c53baa6685261e5253a1c355a1b322f82674a824",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,32 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs =
+    { nixpkgs, ... }:
+
+    let
+      inherit (nixpkgs) lib;
+
+      eachSystem = f: lib.genAttrs systems (s: f nixpkgs.legacyPackages.${s});
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+    in
+
+    {
+      formatter = eachSystem (
+        pkgs:
+        pkgs.treefmt.withConfig {
+          settings = lib.mkMerge [
+            ./treefmt.nix
+            { _module.args = { inherit pkgs; }; }
+          ];
+        }
+      );
+    };
+}

treefmt.nix

@@ -0,0 +1,32 @@
+{ lib, pkgs, ... }:
+
+{
+  tree-root-file = "treefmt.nix";
+  on-unmatched = "fatal";
+
+  excludes = [
+    "*.lock"
+    "*.md"
+    ".gitignore"
+    "LICENSE"
+  ];
+
+  formatter.nixfmt = {
+    command = lib.getExe pkgs.nixfmt;
+    includes = [ "*.nix" ];
+    options = [ "--strict" ];
+  };
+
+  formatter.prettier = {
+    command = lib.getExe pkgs.nodePackages.prettier;
+    includes = [
+      "*.js"
+      "*.yml"
+    ];
+    options = [
+      "--write"
+      "--print-width=120"
+      "--arrow-parens=avoid"
+    ];
+  };
+}