mingw: refuse paths containing reserved names

There are a couple of reserved names that cannot be file names on
Windows, such as `AUX`, `NUL`, etc. For an almost complete list, see
https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file

If one would try to create a directory named `NUL`, it would actually
"succeed", i.e. the call would return success, but nothing would be
created.

Worse, even adding a file extension to the reserved name does not make
it a valid file name. To understand the rationale behind that behavior,
see https://devblogs.microsoft.com/oldnewthing/20031022-00/?p=42073

Let's just disallow them all.

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

1 files changed, 9 insertions, 2 deletions

diff --git a/compat/mingw.h b/compat/mingw.h
index 04ca731a6b..ebc1e6a773 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -461,10 +461,17 @@ char *mingw_query_user_email(void);
  *
  * - contain any of the reserved characters, e.g. `:`, `;`, `*`, etc
  *
+ * - correspond to reserved names (such as `AUX`, `PRN`, etc)
+ *
+ * The `allow_literal_nul` parameter controls whether the path `NUL` should
+ * be considered valid (this makes sense e.g. before opening files, as it is
+ * perfectly legitimate to open `NUL` on Windows, just as it is to open
+ * `/dev/null` on Unix/Linux).
+ *
  * Returns 1 upon success, otherwise 0.
  */
-int is_valid_win32_path(const char *path);
-#define is_valid_path(path) is_valid_win32_path(path)
+int is_valid_win32_path(const char *path, int allow_literal_nul);
+#define is_valid_path(path) is_valid_win32_path(path, 0)
 
 /**
  * Converts UTF-8 encoded string to UTF-16LE.