mingw_rename: do support directory renames

From: Johannes Schindelin <[email protected]>

In 391bceae435 (compat/mingw: support POSIX semantics for atomic renames, 2024-10-27), we taught the mingw_rename() function to respect POSIX semantics, but we did so only as a fallback after _wrename() fails.

This hid a bug in the implementation that was not caught by Git's test
suite: The CreateFileW() function _can_ open handles to directories, but not when asked to use the FILE_ATTRIBUTE_NORMAL flag, as that flag only is allowed for files.

Let's fix this by using the common FILE_FLAG_BACKUP_SEMANTICS flag that can be used for opening handles to directories, too.

---
mingw_rename: do support directory renames

This is not quite a critical bug fix for Git because (unlike Git for Windows) it attempts _wrename() first. If that succeeds, we'll not bother with the POSIX semantics.

However, Git for Windows knows how to deal with symbolic links, and _wrename() does not work for them. Therefore, that _wrename() call was patched out there and we rely on the native Win32 API call to SetFileInformationByHandle() to rename files and directories.

It is that latter part that is at heart of this here bug fix: To be able to call SetFileInformationByHandle(), we need a handle, and CreateFileW() is what we use, for files, and crucially, also for directories.

So while it is not critical for Git to take this patch, it still is important because that _wrename() call can fail, even when renaming directories, and then we want the fallback to fail not because we tried to obtain a handle using incorrect flags, but only because the actual rename operation failed.

This patch is based on ps/mingw-rename.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1839%2Fdscho%2Fps%2Fmingw-rename-followup-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1839/dscho/ps/mingw-rename-followup-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1839

 compat/mingw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index c4320769db6..e8f491d03a7 100644
@@ -2273,7 +2273,7 @@ repeat:
 
 		old_handle = CreateFileW(wpold, DELETE,
 					 FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_SHARE_DELETE,
-					 NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+					 NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
 		if (old_handle == INVALID_HANDLE_VALUE) {
 			errno = err_win_to_posix(GetLastError());
 			return -1;

base-commit: 391bceae4350136a05d977573caeaa07059f2136

gitgitgadget

"Johannes Schindelin via GitGitGadget" <[email protected]>

Thanks.

As this will be part of GfW 2.48 anyway (I presume), let me take it and include it in my tree to keep the divergence between our trees small.