Support [@json.drop_default] with [@json.default]

[tatchi]

File "backend/api/endpoints_csp_report/csp_report/csp_report.ml", line 10, characters 2-72:
10 |   disposition : string option; [@json.default None] [@json.drop_default]
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: found [@drop_default] attribute without [@option]
Had 1 error, waiting for filesystem changes...

But the doc says

[@json.option]: a shortcut for [@json.default None]

[zazedd]

+1
Also would be useful to use [@json.drop_default] for an arbitrary default value

disposition : string; [@json.default "something"] [@json.drop_default]

Where if disposition is "something" then it is dropped

[andreypopp]

We can make @drop_default support arbitrarily values but need to decide how we do comparison. Using structural comparison is probably not a good idea. See details on the same feature in ppx_yojson_conv.

[zazedd]

Opened a PR, where it is possible to provide a comparison function
Thanks @andreypopp