Fix compilation with older versions of OCaml

Author: Leonidas-from-XIV

lib/top/compat_top.ml

@@ -167,3 +167,15 @@ let ctype_get_desc ty =
 #else
   (Ctype.repr ty).Types.desc
 #endif
+
+exception Exit_with_status of int
+
+let execute_phrase print_outcome ppf phr =
+#if OCAML_VERSION >= (4, 12, 0)
+  match Toploop.execute_phrase print_outcome ppf phr with
+  | v -> v
+  | exception Compenv.Exit_with_status status ->
+      raise (Exit_with_status status)
+#else
+  Toploop.execute_phrase print_outcome ppf phr
+#endif

lib/top/compat_top.mli

@@ -59,3 +59,8 @@ val ctype_is_equal :
 
 val ctype_expand_head_and_get_desc : Env.t -> Types.type_expr -> Types.type_desc
 val ctype_get_desc : Types.type_expr -> Types.type_desc
+
+exception Exit_with_status of int
+
+val execute_phrase :
+  bool -> Format.formatter -> Parsetree.toplevel_phrase -> bool

lib/top/mdx_top.ml

@@ -305,7 +305,7 @@ module Rewrite = struct
   let preload verbose ppf =
     let require pkg =
       let p = top_directive_require pkg in
-      let _ = Toploop.execute_phrase verbose ppf p in
+      let _ = execute_phrase verbose ppf p in
       ()
     in
     match active_rewriters () with
@@ -356,8 +356,8 @@ let toplevel_exec_phrase t ppf p =
       if !Clflags.dump_parsetree then Printast.top_phrase ppf phrase;
       if !Clflags.dump_source then Pprintast.top_phrase ppf phrase;
       Env.reset_cache_toplevel ();
-      try Toploop.execute_phrase t.verbose ppf phrase
-      with Compenv.Exit_with_status code ->
+      try execute_phrase t.verbose ppf phrase
+      with Exit_with_status code ->
         Format.fprintf ppf "[%d]@." code;
         false)