Report exits from the toplevel correctly

Previously, you just got:

    ocaml-mdx-test: internal error, uncaught exception:
                    Compenv.Exit_with_status(125)

Author: talex5

lib/top/mdx_top.ml

@@ -337,7 +337,7 @@ type t = {
 let toplevel_exec_phrase t ppf p =
   match Phrase.result p with
   | Error exn -> raise exn
-  | Ok phrase ->
+  | Ok phrase -> (
       Warnings.reset_fatal ();
       let mapper = Lexbuf.position_mapper (Phrase.start p) in
       let phrase =
@@ -356,7 +356,10 @@ 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 ();
-      Toploop.execute_phrase t.verbose ppf phrase
+      try Toploop.execute_phrase t.verbose ppf phrase
+      with Compenv.Exit_with_status code ->
+        Format.fprintf ppf "[%d]@." code;
+        false)
 
 type var_and_value = V : 'a ref * 'a -> var_and_value
 

test/bin/mdx-test/expect/compenv-exit/test-case.md

@@ -0,0 +1,5 @@
+Exits from the toplevel are reported correctly:
+
+```ocaml
+# #use "idontexist.ml";;
+```

test/bin/mdx-test/expect/compenv-exit/test-case.md.expected

@@ -0,0 +1,7 @@
+Exits from the toplevel are reported correctly:
+
+```ocaml
+# #use "idontexist.ml";;
+Cannot find file idontexist.ml.
+[125]
+```

test/bin/mdx-test/expect/dune.inc

@@ -35,6 +35,18 @@
  (alias runtest)
  (action (diff code/test-case.md code.actual)))
 
+(rule
+ (target compenv-exit.actual)
+ (deps (package mdx) (source_tree compenv-exit))
+ (action
+  (with-stdout-to %{target}
+   (chdir compenv-exit
+    (run ocaml-mdx test --output - test-case.md)))))
+
+(rule
+ (alias runtest)
+ (action (diff compenv-exit/test-case.md.expected compenv-exit.actual)))
+
 (rule
  (target cram.actual)
  (deps (package mdx) (source_tree cram))