feat: Include Prelude/Prepare and shadow them

instead of just `open`. This restores the toplevel output on values defined in
Prelude, and forbids access to the interface of Prepare (which were two small
regressions with pre-compilation).

Author: AltGr

src/app/learnocaml_exercise_main.ml

@@ -129,13 +129,17 @@ let () =
     Learnocaml_toplevel.load_cmi_from_string top
       Learnocaml_exercise.(decipher File.prepare_cmi exo) >>= fun _ ->
     Learnocaml_toplevel.load_js ~print_outcome:false top
-      ~message: [%i"loading the prelude..."]
       exercise_js
     >>= fun r ->
     if not r then Lwt.fail_with  [%i"error in prelude"] else
-    Learnocaml_toplevel.load top "open! Prelude ;;" >>= fun r ->
+    Learnocaml_toplevel.load top "include Prelude ;;"
+      ~message: [%i"loading the prelude..."] >>= fun r ->
     if not r then Lwt.fail_with [%i"error in prelude"] else
-    Learnocaml_toplevel.load top "open! Prepare ;;" >>= fun r ->
+    Learnocaml_toplevel.load ~print_outcome:false top "module Prelude = struct end;;" >>= fun r ->
+    if not r then Lwt.fail_with [%i"error in prelude"] else
+    Learnocaml_toplevel.load ~print_outcome:false top "include Prepare ;;" >>= fun r ->
+    if not r then Lwt.fail_with [%i"error in prelude"] else
+    Learnocaml_toplevel.load ~print_outcome:false top "module Prepare = struct end;;" >>= fun r ->
     if not r then Lwt.fail_with [%i"error in prelude"] else
     (* TODO: maybe remove Prelude, Prepare modules from the env ? *)
     Learnocaml_toplevel.set_checking_environment top >>= fun () ->

src/grader/grading.ml

@@ -115,10 +115,16 @@ let get_grade
         };
 
       handle_error (internal_error [%i"while preparing the tests"]) @@
-      Toploop_ext.use_string ~print_outcome:false ~ppf_answer {|open! Prelude|};
+      Toploop_ext.use_string ~print_outcome ~ppf_answer
+        {|include Prelude|};
       handle_error (internal_error [%i"while preparing the tests"]) @@
-      Toploop_ext.use_string ~print_outcome:false ~ppf_answer {|open! Prepare|};
-
+      Toploop_ext.use_string ~print_outcome:false ~ppf_answer
+        {|module Prelude = struct end|};
+      handle_error (internal_error [%i"while preparing the tests"]) @@
+      Toploop_ext.use_string ~print_outcome:false ~ppf_answer
+        {|include Prepare|};
+      Toploop_ext.use_string ~print_outcome:false ~ppf_answer
+        {|module Prepare = struct end|};
 
       set_progress [%i"Loading your code."] ;
       handle_error user_code_error @@