[loadpath] Rework and simplify ML loadpath handling

This PR refactors the handling of ML loadpaths to get it closer to
what (as of 2020) the standard OCaml toolchain (ocamlfind, dune) does.

This is motivated as I am leaning toward letting the standard OCaml
machinery handle OCaml includes; this has several benefits [for
example plugins become regular OCaml libs] It will also help in
improving dependency handling in plugin dynload.

The main change is that "recursive" ML loadpaths are no longer
supported, so Coq's `-I` option becomes closer to OCaml's semantics.

We still allow `-Q` to extend the OCaml path recursively, but this may
become deprecated in the future if we decide to install the ML parts
of plugins in the standard OCaml location.

Due to this `Loadpath` still hooks into `Mltop`, but other than that
`.v` location handling is actually very close to become fully
independent of Coq [thus it can be used in other tools such coqdep,
the build system, etc...]

In terms of vernaculars the changes are:

- The `Add Rec ML Path` command has been removed,
- The `Add Loadpath "foo".` has been removed. We now require that the
  form with the explicit prefix `Add Loadpath "foo" as Prefix.` is used.

We did modify `fake_ide` as not to add a directory with the empty
`Prefix`, which was not used. This exposed some bugs in the
implementation of the document model, which relied on having an
initial sentence; we have workarounded them just by adding a dummy one
in the two relevant cases.

1 files changed, 8 insertions, 7 deletions

diff --git a/toplevel/ccompile.ml b/toplevel/ccompile.ml
index dceb811d66..f75a706041 100644
--- a/toplevel/ccompile.ml
+++ b/toplevel/ccompile.ml
@@ -104,7 +104,7 @@ let compile opts copts ~echo ~f_in ~f_out =
                         |> prlist_with_sep pr_comma Names.Id.print)
                     ++ str ".")
   in
-  let iload_path = build_load_path opts in
+  let ml_load_path, vo_load_path = build_load_path opts in
   let require_libs = require_libs opts in
   let stm_options = opts.config.stm_flags in
   let output_native_objects = match opts.config.native_compiler with
@@ -129,8 +129,8 @@ let compile opts copts ~echo ~f_in ~f_out =
   | BuildVo | BuildVok ->
       let doc, sid = Topfmt.(in_phase ~phase:LoadingPrelude)
           Stm.new_doc
-          Stm.{ doc_type = VoDoc long_f_dot_out;
-                iload_path; require_libs; stm_options;
+          Stm.{ doc_type = VoDoc long_f_dot_out; ml_load_path;
+                vo_load_path; require_libs; stm_options;
               } in
       let state = { doc; sid; proof = None; time = opts.config.time } in
       let state = load_init_vernaculars opts ~state in
@@ -181,8 +181,8 @@ let compile opts copts ~echo ~f_in ~f_out =
 
       let doc, sid = Topfmt.(in_phase ~phase:LoadingPrelude)
           Stm.new_doc
-          Stm.{ doc_type = VioDoc long_f_dot_out;
-                iload_path; require_libs; stm_options;
+          Stm.{ doc_type = VioDoc long_f_dot_out; ml_load_path;
+                vo_load_path; require_libs; stm_options;
               } in
 
       let state = { doc; sid; proof = None; time = opts.config.time } in
@@ -252,8 +252,9 @@ let do_vio opts copts =
   (* We must initialize the loadpath here as the vio scheduling
      process happens outside of the STM *)
   if copts.vio_files <> [] || copts.vio_tasks <> [] then
-    let iload_path = build_load_path opts in
-    List.iter Loadpath.add_coq_path iload_path;
+    let ml_lp, vo_lp = build_load_path opts in
+    List.iter Mltop.add_ml_dir ml_lp;
+    List.iter Loadpath.add_vo_path vo_lp;
 
   (* Vio compile pass *)
   if copts.vio_files <> [] then schedule_vio copts;