[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.

1 files changed, 27 insertions, 0 deletions

diff --git a/clib/cPath.ml b/clib/cPath.ml
new file mode 100644
index 0000000000..66d03078dc
--- /dev/null
+++ b/clib/cPath.ml
@@ -0,0 +1,27 @@
+(************************************************************************)
+(*         *   The Coq Proof Assistant / The Coq Development Team       *)
+(*  v      *         Copyright INRIA, CNRS and contributors             *)
+(* <O___,, * (see version control and CREDITS file for authors & dates) *)
+(*   \VV/  **************************************************************)
+(*    //   *    This file is distributed under the terms of the         *)
+(*         *     GNU Lesser General Public License Version 2.1          *)
+(*         *     (see LICENSE file for the text of the license)         *)
+(************************************************************************)
+
+(* This API is loosely inspired by [Stdune.Path], for now we keep it
+   minimal, but at some point we may extend it, see developer notes in
+   the implementation file. *)
+
+type t = string
+
+(* Note that in general, make is not safe, due to its type, however
+   relative is as you can enforce a particular root. So we eventually
+   should remove [make] *)
+let make = List.fold_left Filename.concat ""
+
+let relative = Filename.concat
+
+let rec choose_existing = function
+  | [] -> None
+  | f :: fs ->
+    if Sys.file_exists f then Some f else choose_existing fs