{T,Optt}opdirs: add load_lib function to API.

This will be used by {T,Opt}opmain. The signature of this function is
largely suboptimal. But we take care not to introduce any new type
dependency like Lib.Name.t because this module is used and visible by
downstream packages while those may not have have access to
`compiler-libs`'s module because of the expunge process. Maybe once
all this will be improved see ocaml#7589.

toplevel/opttopdirs.ml

@@ -136,6 +136,13 @@ let dir_require ppf name = match Lib.Name.of_string name with
 let () =
   Hashtbl.add directive_table "require" (Directive_string (dir_require std_out))
 
+let load_lib ppf name = match Lib.Name.of_string name with
+  | Error e -> fprintf ppf "@[%s@]@." e; false
+  | Ok _n ->
+      (* We need to implement the Dynlink lib loading API support *)
+      fprintf ppf "load_lib is not implemented yet (TODO)";
+      false
+
 (* Load commands from a file *)
 
 let dir_use ppf name = ignore(Opttoploop.use_file ppf name)

toplevel/opttopdirs.mli

@@ -44,3 +44,8 @@ val assume_lib_loaded : string -> (unit, string) result
 (** [assume_lib_loaded n] assumes library name [n] is loaded. This
     will prevent [n] from being looked up. An error is returned if
     [n] is not a valid library name. *)
+
+val load_lib : formatter -> string -> bool
+(** [load_lib ppf n] loads library named [n] printing errors on [ppf]
+    and returns [true] if there was no error (including if [n] as
+    already loaded) and [false] otherwise. *)

toplevel/topdirs.ml

@@ -299,6 +299,12 @@ let assume_lib_loaded n = match Lib.Name.of_string n with
 | Ok n -> loaded_libs := Lib.Name.Set.add n !loaded_libs; Ok ()
 
 let loaded_libs () = Lib.Name.Set.to_string_set !loaded_libs
+let load_lib ppf name = match Lib.Name.of_string name with
+  | Error e -> fprintf ppf "@[%s@]@." e; false
+  | Ok n ->
+      match load_lib ppf ~from_file:None n with
+      | exception Load_failed -> false
+      | _ -> true
 
 (* Load commands from a file *)
 

toplevel/topdirs.mli

@@ -48,3 +48,8 @@ val assume_lib_loaded : string -> (unit, string) result
 (** [assume_lib_loaded n] assumes library name [n] is loaded. This
     will prevent [n] from being looked up. An error is returned if
     [n] is not a valid library name. *)
+
+val load_lib : formatter -> string -> bool
+(** [load_lib ppf n] loads library named [n] printing errors on [ppf]
+    and returns [true] if there was no error (including if [n] as
+    already loaded) and [false] otherwise. *)