Motivation for this change

In a derivation using buildFHSUserEnv, I'd like to support multiple executables in $out/bin using a script such as:

  runScript = writeScript "${name}-wrapper" ''
    arg0="$(basename "$0")"
    for executable in ${lib.concatStringsSep " " (listOfExecutables)}; do
        if [[ "$arg0" == "$executable" ]]; then
            exec -a "$0" ${drvBeingWrapped}/bin/$executable "$@"
        fi
    done
  '';

While in the derivation coming out of buildFHSUserEnv, I'm putting in extraInstallCommands:

  extraInstallCommands = ''
    for executable in ${lib.concatStringsSep " " (listOfExecutables)}; do
        ln -s $out/bin/${name} $out/bin/$executable
    done
  '';

Where listOfExecutables is some list I'm controlling via:

let
  listOfExecutables = [ ..  ];
in
  buildFHSUserEnv rec {
  ...
};

The idea is that every executable's name in listOfExecutables is linked to the main executable - $out/bin/${name} and that executable is calling in turn runScript. I'd like runScript to know the original $0 in order to know what real executable inside the FHS environment to call.

Right now, it's impossible to implement this because the FHS' environment is calling runScript without -a "$0". This change should fix this (untested).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.