Add re_exports field to library

This field allows libraries to re-export the interfaces of other
libraries

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/dune/dune_file.ml

@@ -955,6 +955,7 @@ module Library = struct
     ; stdlib : Stdlib.t option
     ; special_builtin_support : Special_builtin_support.t option
     ; enabled_if : Blang.t
+    ; re_exports : Predicate_lang.t
     }
 
   let decode =
@@ -1013,7 +1014,11 @@ module Library = struct
          field_o "special_builtin_support"
            ( Syntax.since Stanza.syntax (1, 10)
            >>> Special_builtin_support.decode )
-       and+ enabled_if = enabled_if ~since:(Some (1, 10)) in
+       and+ enabled_if = enabled_if ~since:(Some (1, 10))
+       and+ re_exports =
+         field "re_exports" ~default:Predicate_lang.false_
+           (Syntax.since Stanza.syntax (2, 0) >>> Predicate_lang.decode)
+       in
        let wrapped =
          Wrapped.make ~wrapped ~implements ~special_builtin_support
        in
@@ -1138,6 +1143,7 @@ module Library = struct
            ; stdlib
            ; special_builtin_support
            ; enabled_if
+           ; re_exports
            } ))
 
   let has_stubs t =

src/dune/dune_file.mli

@@ -266,6 +266,7 @@ module Library : sig
     ; stdlib : Stdlib.t option
     ; special_builtin_support : Special_builtin_support.t option
     ; enabled_if : Blang.t
+    ; re_exports : Predicate_lang.t
     }
 
   val has_stubs : t -> bool

src/dune/dune_package.ml

@@ -35,13 +35,14 @@ module Lib = struct
     ; modes : Mode.Dict.Set.t
     ; special_builtin_support :
         Dune_file.Library.Special_builtin_support.t option
+    ; re_exports : Lib_name.t list
     }
 
   let make ~loc ~kind ~name ~synopsis ~archives ~plugins ~foreign_objects
       ~foreign_archives ~jsoo_runtime ~main_module_name ~sub_systems ~requires
       ~ppx_runtime_deps ~implements ~default_implementation ~virtual_
       ~known_implementations ~modules ~modes ~version ~orig_src_dir ~obj_dir
-      ~special_builtin_support =
+      ~special_builtin_support ~re_exports =
     let dir = Obj_dir.dir obj_dir in
     let map_path p =
       if Path.is_managed p then
@@ -74,6 +75,7 @@ module Lib = struct
     ; modes
     ; obj_dir
     ; special_builtin_support
+    ; re_exports
     }
 
   let obj_dir t = t.obj_dir
@@ -112,6 +114,7 @@ module Lib = struct
       ; modules
       ; modes
       ; special_builtin_support
+      ; re_exports
       } =
     let open Dune_lang.Encoder in
     let no_loc f (_loc, x) = f x in
@@ -148,6 +151,7 @@ module Lib = struct
        ; field_o "special_builtin_support"
            Dune_file.Library.Special_builtin_support.encode
            special_builtin_support
+       ; field_l "re_exports" Lib_name.encode re_exports
        ]
     @ ( Sub_system_name.Map.to_list sub_systems
       |> List.map ~f:(fun (name, (_ver, sexps)) ->
@@ -203,6 +207,9 @@ module Lib = struct
          field_o "special_builtin_support"
            ( Syntax.since Stanza.syntax (1, 10)
            >>> Dune_file.Library.Special_builtin_support.decode )
+       and+ re_exports =
+         field_l "re_exports"
+           (Syntax.since Stanza.syntax (2, 0) >>> Lib_name.decode)
        in
        let known_implementations =
          Variant.Map.of_list_exn known_implementations
@@ -231,6 +238,7 @@ module Lib = struct
        ; modules
        ; modes
        ; special_builtin_support
+       ; re_exports
        })
 
   let name t = t.name
@@ -278,6 +286,8 @@ module Lib = struct
   let compare_name x y = Lib_name.compare x.name y.name
 
   let wrapped t = Option.map t.modules ~f:Modules.wrapped
+
+  let re_exports t = t.re_exports
 end
 
 type 'sub_system t =

src/dune/dune_package.mli

@@ -58,6 +58,8 @@ module Lib : sig
 
   val wrapped : _ t -> Wrapped.t option
 
+  val re_exports : _ t -> Lib_name.t list
+
   val make :
        loc:Loc.t
     -> kind:Lib_kind.t
@@ -83,6 +85,7 @@ module Lib : sig
     -> obj_dir:Path.t Obj_dir.t
     -> special_builtin_support:
          Dune_file.Library.Special_builtin_support.t option
+    -> re_exports:Lib_name.t list
     -> 'a t
 
   val set_subsystems : 'a t -> 'b Sub_system_name.Map.t -> 'b t

src/dune/findlib/findlib.ml

@@ -239,6 +239,7 @@ module Package = struct
       else
         discovered
     in
+    let re_exports = [] in
     Dune_package.Lib.make ~orig_src_dir:None ~loc ~kind:Normal ~name:(name t)
       ~synopsis:(description t) ~archives ~plugins:(plugins t)
       ~foreign_objects:[] ~foreign_archives:(Mode.Dict.make_both [])
@@ -248,7 +249,7 @@ module Package = struct
       ~virtual_:false ~implements:None ~known_implementations:Variant.Map.empty
       ~default_implementation:None ~modules:None
       ~main_module_name:None (* XXX remove *) ~version:(version t) ~modes
-      ~obj_dir
+      ~obj_dir ~re_exports
       ~special_builtin_support:
         ( (* findlib has been around for much longer than dune, so it is
              acceptable to have a special case in dune for findlib. *)

src/dune/lib.ml

@@ -282,6 +282,7 @@ module T = struct
     { info : Lib_info.external_
     ; name : Lib_name.t
     ; unique_id : Id.t
+    ; re_exports : t list Or_exn.t
     ; requires : t list Or_exn.t
     ; ppx_runtime_deps : t list Or_exn.t
     ; pps : t list Or_exn.t
@@ -1000,6 +1001,19 @@ end = struct
           Dep_path.prepend_exn e (Library (src_dir, name)))
     in
     let requires = map_error requires in
+    let re_exports : t list Or_exn.t =
+      let plang =
+        match Lib_info.re_exports info with
+        | Local plang -> plang
+        | External_ l ->
+          String.Set.of_list_map l ~f:Lib_name.to_string
+          |> Predicate_lang.of_string_set
+      in
+      let+ requires = requires in
+      List.filter requires ~f:(fun lib ->
+          Predicate_lang.exec plang ~standard:Predicate_lang.empty
+            (Lib_name.to_string lib.name))
+    in
     let ppx_runtime_deps = map_error ppx_runtime_deps in
     let t =
       { info
@@ -1015,6 +1029,7 @@ end = struct
       ; default_implementation
       ; resolved_implementations
       ; stdlib_dir = db.stdlib_dir
+      ; re_exports
       }
     in
     t.sub_systems <-
@@ -1813,6 +1828,8 @@ let to_dune_lib ({ name; info; _ } as lib) ~modules ~foreign_objects ~dir =
     use_public_name ~info_field:(Lib_info.implements info)
       ~lib_field:(implements lib)
   in
+  let* re_exports = lib.re_exports in
+  let re_exports = List.map ~f:(fun t -> t.name) re_exports in
   let+ default_implementation =
     use_public_name
       ~info_field:(Lib_info.default_implementation info)
@@ -1827,7 +1844,7 @@ let to_dune_lib ({ name; info; _ } as lib) ~modules ~foreign_objects ~dir =
     ~modules:(Some modules)
     ~main_module_name:(Result.ok_exn (main_module_name lib))
     ~sub_systems:(Sub_system.dump_config lib)
-    ~special_builtin_support
+    ~special_builtin_support ~re_exports
 
 module Local : sig
   type t = private lib

src/dune/lib.mli

@@ -116,7 +116,8 @@ module Compile : sig
   (** Return the list of dependencies needed for linking this library/exe *)
   val requires_link : t -> L.t Or_exn.t Lazy.t
 
-  (** Dependencies listed by the user + runtime dependencies from ppx *)
+  (** Dependencies listed by the user + runtime dependencies from ppx +
+      exported dependencies *)
   val direct_requires : t -> L.t Or_exn.t
 
   module Resolved_select : sig

src/dune/lib_info.ml

@@ -59,6 +59,12 @@ module Source = struct
     | External a -> External (f a)
 end
 
+module Re_exports = struct
+  type t =
+    | Local of Predicate_lang.t
+    | External_ of Lib_name.t list
+end
+
 module Enabled_status = struct
   type t =
     | Normal
@@ -99,6 +105,7 @@ type 'path t =
   ; modes : Mode.Dict.Set.t
   ; special_builtin_support :
       Dune_file.Library.Special_builtin_support.t option
+  ; re_exports : Re_exports.t
   }
 
 let name t = t.name
@@ -161,6 +168,8 @@ let orig_src_dir t = t.orig_src_dir
 
 let best_src_dir t = Option.value ~default:t.src_dir t.orig_src_dir
 
+let re_exports t = t.re_exports
+
 let user_written_deps t =
   List.fold_left (t.virtual_deps @ t.ppx_runtime_deps)
     ~init:(Deps.to_lib_deps t.requires) ~f:(fun acc s ->
@@ -255,6 +264,7 @@ let of_library_stanza ~dir
      |Private _ ->
       None
   in
+  let re_exports = Re_exports.Local conf.re_exports in
   { loc = conf.buildable.loc
   ; name
   ; kind = conf.kind
@@ -286,6 +296,7 @@ let of_library_stanza ~dir
   ; modes
   ; wrapped = Some conf.wrapped
   ; special_builtin_support = conf.special_builtin_support
+  ; re_exports
   }
 
 let of_dune_lib dp =
@@ -303,6 +314,7 @@ let of_dune_lib dp =
     |> Option.map ~f:(fun w -> Dune_file.Library.Inherited.This w)
   in
   let obj_dir = Lib.obj_dir dp in
+  let re_exports = Re_exports.External_ (Lib.re_exports dp) in
   { loc = Lib.loc dp
   ; name = Lib.name dp
   ; kind = Lib.kind dp
@@ -334,6 +346,7 @@ let of_dune_lib dp =
   ; modes = Lib.modes dp
   ; wrapped
   ; special_builtin_support = Lib.special_builtin_support dp
+  ; re_exports
   }
 
 type external_ = Path.t t

src/dune/lib_info.mli

@@ -37,6 +37,12 @@ module Source : sig
     | External of 'a
 end
 
+module Re_exports : sig
+  type t =
+    | Local of Predicate_lang.t
+    | External_ of Lib_name.t list
+end
+
 module Enabled_status : sig
   type t =
     | Normal
@@ -105,6 +111,8 @@ val orig_src_dir : 'path t -> 'path option
 
 val version : _ t -> string option
 
+val re_exports : _ t -> Re_exports.t
+
 (** Directory where the source files for the library are located. Returns the
     original src dir when it exists *)
 val best_src_dir : 'path t -> 'path