Error when trying to use decco for variants

[mrmurphy]

Very strange, but when I drop this into any file in my project:

[@decco]
type bobby =
  | A
  | B
  | C;

I get the following error message:

  We've found a bug for you!
  (No file name)

  The constructor Js.Json.JSONString belongs to the variant type
    Js.Json.tagged_t = Js_json.tagged_t
  but a constructor was expected belonging to the variant type option

Decco version 0.1.0, bs-platform version 5.2.1.

Thank you!

[baransu]

Experiencing the same issue 🙁

[ryb73]

I'm not able to reproduce this. Can you provide your bsconfig?

[baransu]

Repro: https://github.com/baransu/ppx_decco-variant-error-repo Code:

[@decco]
type status =
  | Active
  | Inactive(float);

[@decco]
type user = {
  name: string,
  status,
};

[ryb73]

Thanks for the repo. It looks like it's caused by opening Belt. I'll take a closer look later

[ryb73]

TIL OCaml's array indexing syntax is just syntactic sugar for Array.get. In other words, var[0] is equivalent to Array.get(var, 0)

This is the source of your error: OCaml's native Array.get returns the actual value directly (throwing an error if the index is out of bounds), while Belt.Array.get returns an option. When you open Belt, it changes the behavior of var[0].

See: https://stackoverflow.com/a/46394530/1953740

I guess I can fix it by avoiding that array syntax and just using Belt.Array directly.

[ryb73]

Deployed a fix in version v0.2.2 for BS 6 and v0.1.1 for BS 5.

[baransu]

Thank you a lot!