Unbound module Fields

Learning
1

This is another case where I’m sure I’m doing something stupid, but it is not obvious to me where the stupidity is:

problem

I am trying to replace this example here: bonsai/user_info.ml at v0.15 · janestreet/bonsai · GitHub

My code looks like:

open Core

module User_info = struct
  type t = { name : string; int_id : int } [@@deriving compare, equal, fields, sexp]
end

let sample_data =
  lazy
    (List.mapi [ "prod"; "dev"; "test" ] ~f:(fun i suffix ->
         List.mapi [ "bonsai"; "incremental"; "app" ] ~f:(fun j name ->
             let name = String.concat ~sep:"-" [ name; suffix ] in
             let int_id = (10 * i) + j in
             (name, Fields.create ~name ~int_id)))
    |> List.concat |> String.Map.of_alist_exn)

module Input = struct
  type t = { all_users : User_info.t String.Map.t } [@@deriving fields]

  let default () = Fields.create ~all_users:(Laxy.force User_info.sample_data)
end

I am getting an error of:

13 |              (name, Fields.create ~name ~int_id)))
                         ^^^^^^^^^^^^^
Error: Unbound module Fields
Hint: Did you mean Field?

debug 1

The only open statement in bonsai/user_info.ml at v0.15 · janestreet/bonsai · GitHub is an open Core, which my code also has.

So maybe the problem is this Fields is coming in from dune file.

debug 2

Here is my dune file:

(library
 (name v0_cmd)
 (preprocess
  (pps ppx_jane ppx_pattern_bind js_of_ocaml-ppx))
 (libraries
  async_kernel
  bonsai
  bonsai_web
  bonsai_experimental_animation
  bonsai_web_ui_form
  bonsai_web_ui_search_bar
  core
  js_of_ocaml
  virtual_dom.keyboard
  incr_dom
  incr_dom_partial_render))

As far as I can tell, for both libraries & pps, mine is a superset of: bonsai/dune at v0.15 · janestreet/bonsai · GitHub

I’ve tried grepping for “module Fields” in the bonsai github tree; no response. Grepping for “Fields” in the bonsai github tree shows usages, but as far as I an tell, no definitions.

question

Where is this Fields coming in from? And how is the bonsai example pulling it in?

Thanks!

2

Looking at the docs for ppx_field_conv it looks like it generates a module called Fields for you from the type. This will be placed in the module that encloses your type presumably and so yours would be User_info.Fields in this case (the bonsai example doesn’t have this problem because everything is in the top level). The usage in Inputs should be fine.

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