nix-shell --add-root 'urecognised flag' - deliberate or a new bug?

[mpilgrem]

Motivation: commercialhaskell/stack#6329

Stack makes use of the (undocumented: #1908) nix-shell --add-root. Recently, it reports error: unrecognised flag '--add-root'. Is that deliberate, or a new bug? If deliberate, is there an alternative to the original nix-shell --add-root functionality? I have not identified any documentation for the deliberate removal of nix-shell use of --add-root.

The stable manual for nix-shell states:

All options not listed here are passed to nix-store --realise, ...

The stable manual for nix-store --add continues to document the existence of a --add-root flag used with --realise.

For context, Stack's use of --add-root is documented as (via Stack's add-gc-roots option):

  # false by default. Whether to add your Nix dependencies as Nix garbage
  # collection roots. This way, calling nix-collect-garbage will not remove
  # those packages from the Nix store, saving you some time when running
  # stack build again with Nix support activated.
  #
  # This creates a `nix-gc-symlinks` directory in the project `.stack-work`.
  # To revert that, just delete this `nix-gc-symlinks` directory.
  add-gc-roots: false