Miscellaneous cleanup

flake.nix

@@ -3,22 +3,49 @@
 
   inputs = {
     flake-utils.url = "github:numtide/flake-utils";
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable-small";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   };
 
-  outputs = { self, flake-utils, nixpkgs, ... }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    {
+      self,
+      flake-utils,
+      nixpkgs,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
-
-      in {
-        builders.default = pkgs.callPackage ./gradle.nix {};
-
-        packages.default = pkgs.callPackage ./default.nix {};
-
-        apps.default = {
-          type = "app";
-          program = "${self.packages.${system}.default}/bin/gradle2nix";
+        inherit (nixpkgs) lib;
+      in
+      {
+        builders = rec {
+          buildGradlePackage = pkgs.callPackage ./gradle.nix { };
+          default = buildGradlePackage;
         };
-      });
+
+        packages = rec {
+          gradle2nix = pkgs.callPackage ./default.nix { };
+          default = gradle2nix;
+        };
+
+        apps = rec {
+          gradle2nix = {
+            type = "app";
+            program = lib.getExe self.packages.${system}.default;
+          };
+
+          default = gradle2nix;
+        };
+
+        formatter = pkgs.writeShellScriptBin "gradle2nix-fmt" ''
+          fail=0
+          ${lib.getExe pkgs.nixfmt-rfc-style} $@ || fail=1
+          ${lib.getExe pkgs.ktlint} --relative -l warn -F || fail=1
+          [ $fail -eq 0 ] || echo "Formatting failed." >&2
+          exit $fail
+        '';
+      }
+    );
 }