Nix: basic configuration for a newly created Rails 7 application

.envrc

if ! has nix_direnv_version || ! nix_direnv_version 2.3.0; then
    source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.3.0/direnvrc" "sha256-Dmd+j63L84wuzgyjITIfSxSD57Tx7v51DMxVZOsiUD8="
fi
use flake

PATH_add bin

flake.nix

{
  description = "Rails 7 dev environment";
  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system};
      in with pkgs; {
        devShells.default = pkgs.mkShell {
          packages = [ ruby_3_2 postgresql_14 redis ];
          shellHook = ''
            export PGDATA=$PWD/.pgdata

            # Initialize MySQL data directory
            if [ ! -d "$PGDATA" ]; then
              initdb $PGDATA
            fi
          '';
        };
      });
}

Procfile.dev

web: bin/rails server -p 3000
css: bin/rails tailwindcss:watch
db:  postgres