[Caml-list] pre-process myocamlbuild.ml with ocamlbuild ...

[Pietro Abate <Pietro.Abate@pps.univ-paris-diderot.fr>]

Hi all,

maybe, not the best subject of the week, I know . I'd like to
pre-process the file myocamlbuild.ml with cppo before building it. The
reason is that I have a few unused ocamlbuild tags in my _tags file
(that is auto generated by a script ...), and I'd like to remove all
warnings using 

#ifdef OCAML4022
Ocamlbuild_pack.Flags.mark_tag_used "use_" ;;
Ocamlbuild_pack.Flags.mark_tag_used "pkg_" ;;
Ocamlbuild_pack.Flags.mark_tag_used "link_" ;;
#endif

The problem is that Ocamlbuild_pack.Flags.mark_tag_used exists only 
with ocamlbuild < 4.02 .

my naive idea is to pass ocamlbuild a preprocessing tag of the form
-plugin-tag "pp(cppo)" and then let it handle the rest.

But apparently this does not work. How can I convince ocamlbuild to 
build my plugin using a preprocessing step ?

Instead of this :
e$ocamlbuild
+ /usr/bin/ocamlopt.opt unix.cmxa -I /usr/lib/ocaml/ocamlbuild /usr/lib/ocaml/ocamlbuild/ocamlbuildlib.cmxa myocamlbuild.ml /usr/lib/ocaml/ocamlbuild/ocamlbuild.cmx -o myocamlbuild
File "myocamlbuild.ml", line 5, characters 0-1:
Error: Syntax error

I'd like to build it as : 
$/usr/bin/ocamlopt.opt unix.cmxa -I /usr/lib/ocaml/ocamlbuild /usr/lib/ocaml/ocamlbuild/ocamlbuildlib.cmxa -pp "cppo" myocamlbuild.ml /usr/lib/ocaml/ocamlbuild/ocamlbuild.cmx -o myocamlbuild

what is the magic ocamlbuild incantation ? Or alternatively, Do you
see another solution to my small problem ?

thanks,
p