dune 2.8 no longer generate .merlin files. Files with unusual names are now not longer treated in the usual way, e.g:

ocamlmerlin single dump-configuration -filename msource.foo.ml < /dev/null | jq:

    "merlin": {
      "build_path": [],
      "source_path": [],
      "cmi_path": [],
      "cmt_path": [],
      "flags_applied": [], ...

With .merlin files however, msource.foo.ml was processed like msource.ml (build_path, source_path, etc. are filled as expected and type hints, etc. are provided in the usual way.)

How do I get the old behavior back under the new setup?