Add and clean-up existing workarounds for MSVC/MinGW Sys issues

Author: jmid

src/sys/stm_tests.ml

@@ -213,6 +213,8 @@ struct
     | _::_, [] -> false
     | n1::p1, n2::p2 -> n1=n2 && is_true_prefix p1 p2
 
+  let ocaml_version = Sys.(ocaml_release.major,ocaml_release.minor)
+
   let next_state c fs =
     match c with
     | File_exists _path -> fs
@@ -226,17 +228,24 @@ struct
       else fs
     | Rename (old_path, new_path) ->
       if is_true_prefix old_path new_path
-      then fs
+      then (* workaround for parent-to-empty-child-dir *)
+        (if Sys.win32 && ocaml_version >= (5,1) && path_is_an_empty_dir fs new_path
+         then
+           (match Model.separate_path new_path with
+             | None -> fs
+             | Some (new_path_pref, new_name) ->
+               remove fs new_path_pref new_name)
+         else fs)
       else
         (match Model.find_opt fs old_path with
          | None -> fs
          | Some File ->
            if (not (Model.mem fs new_path) || path_is_a_file fs new_path) then Model.rename fs old_path new_path else fs
          | Some (Directory _) ->
-           (* temporary workaround for dir-to-empty-target-dir https://github.com/ocaml/ocaml/issues/12073 *)
-           if Sys.win32 && path_is_an_empty_dir fs new_path then fs else
-           (* temporary workaround for dir-to-file https://github.com/ocaml/ocaml/issues/12073 *)
-           if (Sys.win32 && path_is_a_file fs new_path) then
+           (* workaround for dir-to-empty-target-dir https://github.com/ocaml/ocaml/issues/12073 *)
+           if Sys.win32 && ocaml_version <= (5,0) && path_is_an_empty_dir fs new_path then fs else
+           (* workaround for dir-to-file https://github.com/ocaml/ocaml/issues/12073 *)
+           if (Sys.win32 && ocaml_version <= (5,0) && path_is_a_file fs new_path) then
              (match Model.separate_path new_path with
               | None -> fs
               | Some (new_path_pref, new_name) ->
@@ -315,10 +324,10 @@ struct
       (match res with
        | Ok () -> Model.mem fs old_path (* permits dir-to-file MingW success https://github.com/ocaml/ocaml/issues/12073 *)
        | Error (Sys_error _) ->
-         (* temporary workaround for dir-to-empty-target-dir https://github.com/ocaml/ocaml/issues/12073 *)
-         (Sys.win32 && path_is_a_dir fs old_path && path_is_an_empty_dir fs new_path) ||
-         (* temporary workaround for identity regression renaming under MingW *)
-         (Sys.win32 && old_path = new_path && path_is_an_empty_dir fs new_path) ||
+         (* workaround for dir-to-empty-target-dir https://github.com/ocaml/ocaml/issues/12073 *)
+         (Sys.win32 && ocaml_version <= (5,0) && path_is_a_dir fs old_path && path_is_an_empty_dir fs new_path) ||
+         (* workaround for identity regression renaming under MingW *)
+         (Sys.win32 && ocaml_version <= (5,0) && old_path = new_path && path_is_an_empty_dir fs new_path) ||
          (* general conditions *)
          (not (Model.mem fs old_path)) ||
          is_true_prefix old_path new_path || (* parent-to-child *)
@@ -348,8 +357,8 @@ struct
     | Readdir path, Res ((Result (Array String,Exn),_), res) ->
       (match res with
        | Ok array_of_subdir ->
-         (* Temporary work around for mingW, see https://github.com/ocaml/ocaml/issues/11829 *)
-         if Sys.win32 && not (Model.mem fs path)
+         (* workaround for non-existing readdir on MinGW https://github.com/ocaml/ocaml/issues/11829 *)
+         if Sys.win32 && ocaml_version <= (5,0) && not (Model.mem fs path)
          then array_of_subdir = [||]
          else
            (Model.mem fs path && path_is_a_dir fs path &&