Capture equality operator in the runtime

[martinslota]

I recently hit a problem with the equality operator being captured from the environment. For example, recent versions of base redefine the operator so it only accepts ints, so this code

open Base

type t = {f : int option [@default None]} [@@deriving to_yojson]

fails with something like this

File "tmp.ml", line 3, characters 0-64:
3 | type t = {f : int option [@default None]} [@@deriving to_yojson]
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This expression has type Base.int option
       but an expression was expected of type int

It seems that the default value is needed for the failure to occur.

[kit-ty-kate]

Thanks a lot for bringing this issue to us. Ppx_deriving_runtime already brings with it all the standard library so re-exporting the equality function was unnecessary. I've rebased your PR by instead changing the case where the equality was used and use the proper function name re-exported by ppx_deriving.

I'm just waiting for the CI to go green and I'll merge this. Thanks a lot for your work!