atdgen -v generates calls to unknown function

[kit-ty-kate]

Using the following test.atd file:

type t <ocaml module="Yojson.Safe"> = abstract
type hook_config = [
  | A of t nullable
] 

leads to the following failure when compiling the generated module:

atdgen -t test.atd
atdgen -v test.atd
ocamlfind ocamlopt -package atdgen-runtime,yojson test_t.mli
ocamlfind ocamlopt -package atdgen-runtime,yojson test_v.mli
ocamlfind ocamlopt -package atdgen-runtime,yojson test_v.ml
File "test_v.ml", line 9, characters 2-24:
9 |   Yojson.Safe.validate_t
      ^^^^^^^^^^^^^^^^^^^^^^
Error: Unbound value Yojson.Safe.validate_t

[mjambon]

Solution 1

The module specified with <ocaml module="Yojson.Safe"> is expected to provide a validation function. A conservative solution here is to create a wrapper called JSON around Yojson.Safe that provides the expected signature. Something like this would work:

(* JSON.ml: custom wrapper that has the signature expected by code generated by atdgen *)
include Yojson.Safe
let validate_t _path _data = None

Ideally, this should be provided by the atdgen-runtime library.

Solution 2

Now, if you don't use the validation feature (which doesn't have anything to do with JSON and I think is best left for a ppx extension) and you're in a position of switching to atdml, you should do this:

type t = abstract
type hook_config = [
  | A of t nullable
]

atdml will generate the create_ functions like atdgen -v but no validate_ functions.