OK. I've attached an attempt of patch to ocamlfind that implements what you describe (a META file with just the directory field).
I think it does the right things, but I did not test it extensively.

Le 18/12/2015 22:43, Gabriel Scherer a écrit :
There is no ocamldoc.cm{,x}a in  ocamldoc libraries today. We could probably change ocamldoc's build system to build one, but for now an ocamldoc package would have no archive(...) field, just the directory. It is not clear we need an ocamldoc.cm{,x}a archive if all plugins are to be passed to ocamldoc{,.opt} which is already linked with ocamldoc modules.

On Fri, Dec 18, 2015 at 8:14 PM, Armaël Guéneau <armael.gueneau@ens-lyon.fr> wrote:
Ok, thanks for the explanations.

As for the ocamldoc package, would a META file along these lines do the trick?

# Specification for the "ocamldoc" library
requires = "compiler-libs"
version = "[distributed with Ocaml]"
description = "ocamldoc support library"
directory= "^ocamldoc"
archive(byte) = "ocamldoc.cma"
archive(native) = "ocamldoc.cmxa"

Le 18/12/2015 18:06, Gabriel Scherer a écrit :
> So I just tried¹, and the failure is as follows: > > $ ocamlbuild -tag use_ocamldoc test.cmxs > + /home/gasche/.opam/4.02.3/bin/ocamlopt.opt -shared -I +ocamldoc ocamldoc.cmxa test.cmx -o test.cmxs > File "_none_", line 1: > Error: Cannot find file ocamldoc.cmxa > > It looks like the tag use_ocamldoc expects a file ocamldoc.cmxa to exist, providing library support for ocamldoc plugins, and it does not seem to exist -- it seems that the preferred way to use ocamldoc plugins is to use "ocamldoc.opt -g foo.cmxs", with ocamldoc libraries already linked inside ocamldoc.opt. So just using > >   ocamlbuild -cflags -I,+ocamldoc test.cmxs > > works and seems to do what you expect. > > It goes without saying that this is not a perfect long-term solution, as it assumes that ocamldoc libraries are distributed with the stdlib. It would be cleaner to have an ocamldoc package for them (just like ocamlbuild has a dummy ocamlfind package indicating the location of its library files), but it seems that this is not currently the case. It would be nice (but not super-high priority) to have such a dummy package in ocamlfind in the future, so that you can just do > >   ocamlbuild -use-ocamlfind -package ocamldoc test.cmxs > > ¹: The most time-consuming part was finding the code of a ocamldoc plugin to compile, as the documentation examples are incomplete. Next time, feel free to provide a tarball with a minimal example to reproduce. > > On Fri, Dec 18, 2015 at 5:14 PM, Armaël Guéneau <armael.gueneau@ens-lyon.fr> wrote: > >     Hi list, > >     I'm wondering how one should compile ocamldoc custom generators using >     ocamlbuild. > >     First, the ocamlbuild manual >     (https://github.com/gasche/manual-ocamlbuild/blob/master/manual.md#basic-tags-) >     says that the [use_ocamldoc] tag is deprecated; and that a corresponding >     ocamlfind package should be used instead. Is there such a package for ocamldoc? >     I did not found one. > >     Then, I did not manage to build the plugin into .cma/.cmxs files directly using >     ocamlbuild. My command line was something along these lines: > >        ocamlbuild -use-ocamlfind -tag use_ocamldoc -package compiler-libs plugin.cmxs > >     When trying to build plugin.cma/plugin.cmxs, ocamlbuild complained that "Cannot >     find file ocamldoc.cma/ocamldoc.cmxa" (respectively). However, I can build >     plugin.cmo/plugin.cmx using the same command line, then create the .cma/.cmxs >     manually using ocamlc/ocamlopt - which I ended up doing. > >     Is there a better way to do so? If the whole process can be improved (how?), I >     would be happy to write the required patches/documentation. > >     — Armaël > >