Thanks for the report and the patch! I also agree that the behavior you
described seems like a bug.

However, though I'm new to git community, I still have concerns about
the fix in 'dir.c':

quoted

- if (!pathspec || !pathspec->nr)
+ if (!pathspec || !pathspec->nr || pathspec->magic & PATHSPEC_EXCLUDE)
return 0;

I tried to analyze the logic and I believe this patch breaks the basic
functionality of the negative pathspec (:!):

(I didn't check the caller of exclude_matches_pathspec and I only focus
on the function itself. Tell me if I'm wrong :)

By returning 0 whenever PATHSPEC_EXCLUDE is set globally,
exclude_matches_pathspec will report "no match" for all files,
effectively disabling the exclusion mechanism entirely.

Instead of fixing the issue with ignored files, this patch causes valid
exclusions to be ignored.

We must check if the specific path matches the exclude pattern, not
short-circuit based on the global flag.

Oops. Somehow I was convinced struct pathspec represents only a single path.
This way something like this would silently succeed, without actually indexing x:

  touch x
  echo x >.gitignore
  git add -n ":(exclude)smth/else" x

Thank you for pointing out.

It will be great if we set a test script for this. I will be working on
it in the next few days.

---
 dir.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/dir.c b/dir.c
index b00821f2..ed6b99e3 100644
--- a/dir.c
+++ b/dir.c

@@ -2280,6 +2280,9 @@ static int exclude_matches_pathspec(const char *path, int pathlen,
 		const struct pathspec_item *item = &pathspec->items[i];
 		int len = item->nowildcard_len;
 
+		if (item->magic & PATHSPEC_EXCLUDE)
+			continue;
+
 		if (len == pathlen &&
 		    !ps_strncmp(item, item->match, path, pathlen))
 			return 1;

-- 
2.51.2