Currently, flags allow to set both OCaml and Melange flags. But if one wants to set flags for either Melange or OCaml libraries in a shared code setup, it's not possible:

• For OCaml only flags, one can set ocamlc_flags combined with ocamlopt_flags
• For Melange only flags, it is not possible

It would be nice to have a way to define flags conditionally, e.g. (flags (if (<> %{modes} melange) ...)). Or alternatively, leave flags only for OCaml compilation, and add a new field melange_flags.