Reimplement Sys.rename under Win32 to be more POSIX (#1306)

* Reimplement Sys.rename under Win32 to be more POSIX

Specifically: "Sys.rename src dst" no longer fails if file "dst" exists,
but replaces it with file "src", as in POSIX.

Test added.

* Sys.rename: document the "replace if existing" behavior

Now that we have this behavior under Win32, let's guarantee it.

* byterun/win32.c: typos in names of error codes

* Tests for Unix.rename similar to those for Sys.rename

* win32unix/rename.c: simplify the implementation

All versions of Windows we support provide MoveFileEx.

* Sys.remove: for backward compatibility, copy if cannot move

This is what the old implementation (based on MoveFile() and on rename() from the CRT) did.

* Improve documentation of Sys.remove

* Improve documentation of Unix.rename

Bring it in line with that of Sys.rename.

2 files changed, 9 insertions, 18 deletions

diff --git a/otherlibs/unix/unix.mli b/otherlibs/unix/unix.mli
index d134157061..32ea7f13a6 100644
--- a/otherlibs/unix/unix.mli
+++ b/otherlibs/unix/unix.mli
@@ -557,7 +557,12 @@ val unlink : string -> unit
 *)
 
 val rename : string -> string -> unit
-(** [rename old new] changes the name of a file from [old] to [new]. *)
+(** [rename old new] changes the name of a file from [old] to [new],
+    moving it between directories if needed.  If [new] already
+    exists, its contents will be replaced with those of [old].
+    Depending on the operating system, the metadata (permissions,
+    owner, etc) of [new] can either be preserved or be replaced by
+    those of [old].  *)
 
 val link : string -> string -> unit
 (** [link source dest] creates a hard link named [dest] to the file
diff --git a/otherlibs/win32unix/rename.c b/otherlibs/win32unix/rename.c
index 155a73fb94..dee4cd5eeb 100644
--- a/otherlibs/win32unix/rename.c
+++ b/otherlibs/win32unix/rename.c
@@ -19,25 +19,11 @@
 
 CAMLprim value unix_rename(value path1, value path2)
 {
-  static int supports_MoveFileEx = -1; /* don't know yet */
-  BOOL ok;
-
   caml_unix_check_path(path1, "rename");
   caml_unix_check_path(path2, "rename");
-  if (supports_MoveFileEx < 0) {
-    OSVERSIONINFO VersionInfo;
-    VersionInfo.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
-    supports_MoveFileEx =
-      (GetVersionEx(&VersionInfo) != 0)
-      && (VersionInfo.dwPlatformId == VER_PLATFORM_WIN32_NT);
-  }
-  if (supports_MoveFileEx > 0)
-    ok = MoveFileEx(String_val(path1), String_val(path2),
-                    MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH |
-                    MOVEFILE_COPY_ALLOWED);
-  else
-    ok = MoveFile(String_val(path1), String_val(path2));
-  if (! ok) {
+  if (! MoveFileEx(String_val(path1), String_val(path2),
+                   MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH |
+                   MOVEFILE_COPY_ALLOWED)) {
     win32_maperr(GetLastError());
     uerror("rename", path1);
   }