Excerpts from romain.bardou's message of Thu Oct 16 10:30:49 +0200 2008:
> > I observe that ocamlbuild does not build cmx cmi and o files from a ml 
> > file (which has no associated mli) directly.  Do others see different 
> > behavior?  Instead it builds cmo and cmi from the ml using ocamlc, and 
> > then builds the cmx and o files from there using ocamlopt.  Is there a 
> > reason I’m missing that ocamlbuild does not have a default rule for this 
> > case, using only one call to ocamlopt?  If so, is there an easy way to 
> > do this with a plugin?

There is a deep reason for this, the short answer is:

  "if you want native-compilation only, then all your .ml files must have a
  .mli"

Indeed ocamlbuild only generates .cmi from .ml using ocamlc, this is to avoid
conflicting defaulting rules in the engine.

> I observe the same behavior. I think it's just a matter of reordering 
> the rules in ocaml_specific.ml, as the following plug-in solves the 
> problem thanks to "~insert: `top":
> 
> open Ocamlbuild_plugin
> 
> let () = dispatch begin function
>    | After_rules ->
>        rule "ml -> cmx"
>          ~dep: "%.ml"
>          ~prods: ["%.cmx"; "%.o"; "%.cmi"]
>          ~insert: `top
>          begin fun env _ ->
>            let ml = env "%.ml" in
>            Cmd(S[!Options.ocamlopt; A "-c"; P ml])
>          end
>    | _ -> ()
> end

I won't recommend that.

-- 
Nicolas Pouillard aka Ertai