Use nixpkgs-fmt hook from pre-commit-hooks.nix

.gitignore

@@ -1,2 +1,3 @@
-/result
 /*.qcow2
+/.pre-commit-config.yaml
+/result

default.nix

@@ -0,0 +1,11 @@
+let
+  nix-pre-commit-hooks = import (builtins.fetchTarball "https://github.com/cachix/pre-commit-hooks.nix/tarball/master");
+in
+{
+  pre-commit-check = nix-pre-commit-hooks.run {
+    src = ./.;
+    hooks = {
+      nixpkgs-fmt.enable = true;
+    };
+  };
+}

pre-commit-hook

@@ -1,2 +0,0 @@
-#!/usr/bin/env bash
-nixpkgs-fmt --check .

shell.nix

@@ -1,10 +1,10 @@
-{ pkgs ? import <nixpkgs> { } }:
+{ pkgs ? import <nixpkgs> {} }:
 
 pkgs.mkShell {
   nativeBuildInputs = with pkgs; [
     nixpkgs-fmt
   ];
-  buildPhase = ''
+  shellHook = ''
-    ln -f -s ../../pre-commit-hook .git/hooks/pre-commit
+    ${(import ./default.nix).pre-commit-check.shellHook}
   '';
 }