Discard references in Nix

discardRefs.nix

let p = import <nixpkgs> {}; in

let
  discardReferences = path:
  let
    # We want to use a different nixpkgs here to make sure that the `noref`
    # version won't accidentally share some build-time references with the
    # original one
    p2 = (builtins.getFlake "github:nixos/nixpkgs/nixos-unstable").legacyPackages.${builtins.currentSystem};
    mangledPath = p2.runCommandNoCC "${path.name}.tar.gz" {} ''
      cd ${path}
      tar -cz . > $out
    '';
    mangledPathNoRef = builtins.seq
      (builtins.pathExists mangledPath)
      (/${builtins.unsafeDiscardStringContext mangledPath});
    pathNoRef = p2.runCommandNoCC "${path.name}-noref" { passthru.original = path; } ''
      mkdir -p $out
      cd $out
      tar -xzf ${mangledPathNoRef}
    '';
  in pathNoRef;
in discardReferences p.hello