mingw: allow mingw_chdir() to change to symlink-resolved directories

If symlinks are enabled, resolve all symlinks when changing directories,
as required by POSIX.

Note: Git's `real_path()` function bases its link resolution algorithm
on this property of `chdir()`. Unfortunately, the current directory on
Windows is limited to only MAX_PATH (260) characters. Therefore using
symlinks and long paths in combination may be problematic.

Signed-off-by: Karsten Blees <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: kblees

compat/mingw.c

@@ -866,9 +866,27 @@ int mingw_access(const char *filename, int mode)
 int mingw_chdir(const char *dirname)
 {
 	wchar_t wdirname[MAX_PATH];
+
 	if (xutftowcs_path(wdirname, dirname) < 0)
 		return -1;
-	return _wchdir(wdirname);
+
+	if (has_symlinks) {
+		HANDLE hnd = CreateFileW(wdirname, 0,
+				FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+				OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+		if (hnd == INVALID_HANDLE_VALUE) {
+			errno = err_win_to_posix(GetLastError());
+			return -1;
+		}
+		if (!GetFinalPathNameByHandleW(hnd, wdirname, ARRAY_SIZE(wdirname), 0)) {
+			errno = err_win_to_posix(GetLastError());
+			CloseHandle(hnd);
+			return -1;
+		}
+		CloseHandle(hnd);
+	}
+
+	return _wchdir(normalize_ntpath(wdirname));
 }
 
 int mingw_chmod(const char *filename, int mode)