How to create flake.nix for nix shell loading a few packages?

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Thank you for the hints, @waffle8946!

This works:

{
  description = "A flake that loads some packages";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in
      rec {
        devShells.default = pkgs.mkShellNoCC {
          packages = with pkgs; [
            python312
            sqlite
            ffmpeg
            nodejs
          ];
        };
      }
    );
}

But nix develop gives me a bash shell just like nix-shell does.

From nix develop --help:

nix develop - run a bash shell that provides the build environment of a derivation

For me, a zsh user, the benefit of nix shell over nix-shell is exactly that it respects my user’s shell shell configuration and creates a zsh shell for zsh users. But getting zsh is apparently not possible without workarounds: