Why not add the feature to ppx derivers directly?

[gasche]

Naive question: instead of creating a dedicated ppx for this, have you considered improving ppx_deriving and ppx_type_conv/ppxlib to fetch the correct definition in this case?

[giltho]

Hi ! I'm looking into this because of #5.
Right now Ppxlib.Deriving as well as ppx_deriving only allows one to derive structures from types (or module types).
In this case, since we need the case of flow parser to work :

module rec A : sig
   type t = string
   type tt = B.t
end = A and
B : sig
    type t = int
    type tt = A.t
end = B

But there are no way of doing this only with module types.

I think that's what you meant by "improving ppx_deriving to fetch the correct definition" ?
I think that deriving structure items from other structure items is quite tricky thing to do, as opposed to deriving structure items from types...