Unable to only load ppx_fields_conv in top-level (utop)

[RogerTarani]

Context: RWO 2nd Edition. I raise this issue as suggested by Yaron Minsky (see https://github.com/realworldocaml/book/issues/2982).

I'm using OCaml 4.06.1 and the required packages are installed:

$ opam list
fieldslib                   v0.11.0  Syntax extension to define first class valu
...
ppx_fields_conv          v0.11.0  Generation of accessor and iteration functi
ppxlib                        0.2.1  A comprehensive toolbox for ppx development

As well as "base" v0.11.0, "jbuilder" 1.0+beta20 (req. build & >= "1.0+beta18.1"} and "ocaml-migrate-parsetree" 1.0.11 (req. >= "1.0") required by these three packages (fieldslib, ppx_fields_conv, ppxlib).

The following directive allowed me immediately to use ppx_fields_conv:

#require "ppx_jane"

But only loading ppx_fields_conv was not enough to be able to use ppx_fields_conv:

#require "ppx_fields_conv"

How can we fix that?

FYI, my ~/.ocamlinit is compliant to RWO 2nd Edition recommendations (see https://dev.realworldocaml.org/install.html):

$ cat ~/.ocamlinit
(* ## added by OPAM user-setup for ocamltop / base ## 3ec62baf6f9c219ae06d98140$
#use "topfind";;
(* ## end of OPAM user-setup addition for ocamltop / base ## keep this line *)
#thread;;
#require "core.top";;
#require "core.syntax";;
open Core

[XVilka]

Can you reproduce this with latest versions of the libraries?

[v-gb]

Please include the actual errors when you report bugs. I'm seeing this, which may be what's being reported, but I can't be sure:

$ utop
...
utop # #require "ppx_fields_conv";;
No such package: ppx_deriving - required by `ppx_fields_conv'

We don't use ppx_deriving. It seems to come because the dune file says (kind ppx_deriver). I'll leave it to @xclerc or @jeremiedimino to look at this one, because it seems to be a problem with the exporting of code to opam or dune or this kind of operation being unsupported.

[ghost]

It's a known issue that is complicated to fix without breaking the build of packages not using Dune. Once the ppx world is unified behind ppxlib, we should be in a better position to make things better. In the meantime, manually installing ppx_deriving via opam should help.