Use create_process instead of execvp

On Windows, execvp creates a separate process, which can confuse dune
when it is waiting for the mdx process. This causes it to miss that the
output file has been created. This affects mdx's test suite and
possibly users of the mdx stanza. Instead we create a process and
immediately wait for it in the parent.

See realworldocaml#295, ocaml/dune#3849.

CHANGES.md

@@ -18,6 +18,7 @@
 - Report `#require` directive errors (#276, @gpetiot)
 - Handle no such file exception: the input file and the values of options `--root` and `--prelude` are checked (#292, @gpetiot)
 - Keep locations from parsing instead of recomputing the lines, providing better error messages (#241, @gpetiot)
+- Use `create_process` instead of `execvp` to call `mdx-test` from `mdx`. This fixes part of the test suite on Windows (#299, @emillon)
 
 #### Security
 

bin/test.ml

@@ -41,7 +41,12 @@ let run (`Setup ()) _ _ _ _ _ _ _ _ _ _ =
   let argv = Array.sub Sys.argv 1 (Array.length Sys.argv - 1) in
   argv.(0) <- cmd;
   Log.debug (fun l -> l "executing %a" Fmt.(Dump.array string) argv);
-  Unix.execvp cmd argv
+  let pid = Unix.create_process cmd argv Unix.stdin Unix.stdout Unix.stderr in
+  let _pid, status = Unix.waitpid [] pid in
+  let exit_code =
+    match status with WEXITED n -> n | WSIGNALED _ -> 1 | WSTOPPED _ -> 1
+  in
+  exit exit_code
 
 open Cmdliner