In reply to @rikudou:lemmings.world

Here's a fully working shell.nix with what you want, it can easily be adapted to configuration.nix:

{ pkgs ? import <nixpkgs> {} }:
pkgs.mkShell {
    nativeBuildInputs = with pkgs.buildPackages;
    let
      custom = import (builtins.fetchTarball https://github.com/nixos/nixpkgs/tarball/1d8b8365a02efbf668311dc9db06cb98d49e7302) {};
      php74 = custom.php74.buildEnv {
        extensions = ({ enabled, all }: enabled ++ (with all; [
          redis
          xdebug
        ]));
        extraConfig = ''
          xdebug.mode=debug
          date.timezone=Australia/Brisbane
        '';
      };
    in
    [
      php74
      custom.php74Packages.composer
      custom.php74Extensions.pdo
      custom.php74Extensions.redis
      custom.php74Extensions.xdebug
    ];
}

In reply to @rikudou:lemmings.world
Where does this come from on line 5? nixpkgs_php7429

In reply to @rikudou:lemmings.world
Hm, but the same file works in a different dir. How's that possible?