working devShell!

parts/fmt.nix

@@ -0,0 +1,34 @@
+{
+  perSystem = {
+    config,
+    pkgs,
+    ...
+  }: {
+    # https://github.com/numtide/treefmt-nix?tab=readme-ov-file#flake-parts
+    formatter = config.treefmt.build.wrapper;
+    treefmt = {
+      projectRootFile = "flake.nix";
+      enableDefaultExcludes = true;
+      programs = {
+        alejandra.enable = true;
+
+        shellcheck.enable = true; # cannot be configured, errors on basic bash convention
+
+        prettier = {
+          enable = true;
+          package = pkgs.prettierd;
+          excludes = ["*.age"];
+          settings = {
+            editorconfig = true;
+          };
+        };
+
+        shfmt = {
+          enable = true;
+          # https://flake.parts/options/treefmt-nix.html#opt-perSystem.treefmt.programs.shfmt.indent_size
+          indent_size = 2; # set to 0 to use tabs
+        };
+      };
+    };
+  };
+}