mingw: let lstat() fail with errno == ENOTDIR when appropriate

POSIX semantics requires lstat() to fail with ENOTDIR when "[a]
component of the path prefix names an existing file that is neither a
directory nor a symbolic link to a directory".

See http://pubs.opengroup.org/onlinepubs/9699919799/functions/lstat.html

This behavior is expected by t1404-update-ref-df-conflicts now.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -454,6 +454,39 @@ static inline time_t filetime_to_time_t(const FILETIME *ft)
 	return (time_t)(filetime_to_hnsec(ft) / 10000000);
 }
 
+/**
+ * Verifies that safe_create_leading_directories() would succeed.
+ */
+static int has_valid_directory_prefix(wchar_t *wfilename)
+{
+	int n = wcslen(wfilename);
+
+	while (n > 0) {
+		wchar_t c = wfilename[--n];
+		DWORD attributes;
+
+		if (!is_dir_sep(c))
+			continue;
+
+		wfilename[n] = L'\0';
+		attributes = GetFileAttributesW(wfilename);
+		wfilename[n] = c;
+		if (attributes == FILE_ATTRIBUTE_DIRECTORY ||
+				attributes == FILE_ATTRIBUTE_DEVICE)
+			return 1;
+		if (attributes == INVALID_FILE_ATTRIBUTES)
+			switch (GetLastError()) {
+			case ERROR_PATH_NOT_FOUND:
+				continue;
+			case ERROR_FILE_NOT_FOUND:
+				/* This implies parent directory exists. */
+				return 1;
+			}
+		return 0;
+	}
+	return 1;
+}
+
 /* We keep the do_lstat code in a separate function to avoid recursion.
  * When a path ends with a slash, the stat will fail with ENOENT. In
  * this case, we strip the trailing slashes and stat again.
@@ -514,6 +547,12 @@ static int do_lstat(int follow, const char *file_name, struct stat *buf)
 	case ERROR_NOT_ENOUGH_MEMORY:
 		errno = ENOMEM;
 		break;
+	case ERROR_PATH_NOT_FOUND:
+		if (!has_valid_directory_prefix(wfilename)) {
+			errno = ENOTDIR;
+			break;
+		}
+		/* fallthru */
 	default:
 		errno = ENOENT;
 		break;