Postgresql commands no longer working inside dockerTools

[ailocam]

Describe the bug

The command line tools such as psql are not being symlinked into /bin inside Docker images created with pkgs.dockerTools.buildLayeredImage

The issue was introduced here 5547322#diff-3a40021ad7a436b9b71a4552b7b0ad4191dc190654bcfd383bf5fac2248e2ca9L292 #294504

Steps To Reproduce

Create a flake like so, note the commit hash is from before the change and works fine.

{
  description = "A very basic flake";
  inputs = {
    nixpkgs.url =
      "github:nixos/nixpkgs?ref=a3836576dd7d7e606f393434d39661ff096859f9";
  };
  outputs = { self, nixpkgs }:
    let
      pkgs = nixpkgs.legacyPackages.x86_64-linux;
      customPostgresql = pkgs.postgresql.withPackages (nixPgExtensions:
        [
          # I have some extensions here. 
        ]);
      dockerOptions = {
        name = "test-docker";
        tag = "latest";
        contents = [ pkgs.bash pkgs.coreutils customPostgresql ];
        config = {
          Entrypoint = [ "/bin/bash" ];
          WorkingDir = "/";
        };
      };
      dockerImageGzip = pkgs.dockerTools.buildLayeredImage dockerOptions;
    in {
      packages.x86_64-linux.docker = dockerImageGzip;
      packages.x86_64-linux.postgres = customPostgresql;
    };
}

It can be used like so and works fine.

nix build .#docker
docker load < result
docker run -it test-docker:latest
psql --version

Changing the nixpkgs url to github:nixos/nixpkgs?ref=5547322a0c01dd30a7e0111adc1f02bafbbd6ebc and running the same commands as above results in bash: psql: command not found

Expected behavior

That the contents of postgresql derivation's bin directory be symlinked into /bin like it is for other packages.

Additional context

Looks like dockerTools does not support derivations where the bin directory is a symlink.
This only happens when using pkgs.postgresql.withPackages using just pkgs.postgresql works fine.

Notify maintainers

@wolfgangwalther
I'm not sure who maintains dockerTools.

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

> nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.6.52, NixOS, 24.05 (Uakari), 24.05.5366.fbca5e745367`
 - multi-user?: `yes`
 - sandbox: `relaxed`
 - version: `nix-env (Nix) 2.18.8`
 - channels(root): `"nixos-24.05, nixos-hardware"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[wolfgangwalther]

Is this a duplicate of #102962? There's some discussion about contents not being the right tool for the job in there. I didn't go through that in detail, but maybe you want to see whether there are alternative ways to write your flake?