[build] Split stdlib to it's own opam package.

We introduce a new package structure for Coq:

- `coq-core`: Coq's OCaml tools code and plugins
- `coq-stdlib`: Coq's stdlib [.vo files]
- `coq`: meta-package that pulls `coq-{core,stdlib}`

This has several advantages, in particular it allows to install Coq
without the stdlib which is useful in several scenarios, it also open
the door towards a versioning of the stdlib at the package level.

The main user-visible change is that Coq's ML development files now
live in `$lib/coq-core`, for compatibility in the regular build we
install a symlink and support both setups for a while.

Note that plugin developers and even `coq_makefile` should actually
rely on `ocamlfind` to locate Coq's OCaml libs as to be more robust.

There is a transient state where we actually look for both
`$coqlib/plugins` and `$coqlib/../coq-core/plugins` as to support
the non-ocamlfind plus custom variables.

This will be much improved once #13617 is merged (which requires this
PR first), then, we will introduce a `coq.boot` library so finally
`coqdep`, `coqchk`, etc... can share the same path setup code.

IMHO the plan should work fine.

2 files changed, 13 insertions, 4 deletions

diff --git a/checker/checker.ml b/checker/checker.ml
index ba5e3c6d1a..f55ed9e8d6 100644
--- a/checker/checker.ml
+++ b/checker/checker.ml
@@ -107,7 +107,15 @@ let init_load_path () =
   let user_contrib = coqlib/"user-contrib" in
   let xdg_dirs = Envars.xdg_dirs in
   let coqpath = Envars.coqpath in
-  let plugins = coqlib/"plugins" in
+  let plugins =
+    CPath.choose_existing
+      [ CPath.make [ coqlib ; "plugins" ]
+      ; CPath.make [ coqlib ; ".."; "coq-core"; "plugins" ]
+      ] |> function
+    | None ->
+      CErrors.user_err (Pp.str "Cannot find plugins directory")
+    | Some f -> (f :> string)
+  in
   (* NOTE: These directories are searched from last to first *)
   (* first standard library *)
   add_rec_path ~unix_path:(coqlib/"theories") ~coq_root:(Names.DirPath.make[coq_root]);
diff --git a/checker/dune b/checker/dune
index af7d4f2923..78b4032141 100644
--- a/checker/dune
+++ b/checker/dune
@@ -7,13 +7,14 @@
  (synopsis "Coq's Standalone Proof Checker")
  (modules :standard \ coqchk votour)
  (wrapped true)
- (libraries coq.kernel))
+ (libraries coq-core.kernel))
 
 (executable
  (name coqchk)
  (public_name coqchk)
  (modes exe byte)
- (package coq)
+ ; Move to coq-checker?
+ (package coq-core)
  (modules coqchk)
  (flags :standard -open Coq_checklib)
  (libraries coq_checklib))
@@ -21,7 +22,7 @@
 (executable
  (name votour)
  (public_name votour)
- (package coq)
+ (package coq-core)
  (modules votour)
  (flags :standard -open Coq_checklib)
  (libraries coq_checklib))