{  inputs = {    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";    flake-utils.url = "github:numtide/flake-utils";  };  outputs =    {      nixpkgs,      flake-utils,      ...    }:    flake-utils.lib.eachDefaultSystem (      system:      let        pkgs = nixpkgs.legacyPackages.${system};      in      {        devShells.default = import ./shell.nix { inherit pkgs; };        formatter = pkgs.nixfmt-rfc-style;      }    );}