builtin-add: simplify (and increase accuracy of) exclude handling

Previously, the code would always set up the excludes, and then manually
pick through the pathspec we were given, assuming that non-added but
existing paths were just ignored. This was mostly correct, but would
erroneously mark a totally empty directory as 'ignored'.

Instead, we now use the collect_ignored option of dir_struct, which
unambiguously tells us whether a path was ignored. This simplifies the
code, and means empty directories are now just not mentioned at all.

Furthermore, we now conditionally ask dir_struct to respect excludes,
depending on whether the '-f' flag has been set. This means we don't have
to pick through the result, checking for an 'ignored' flag; ignored entries
were either added or not in the first place.

We can safely get rid of the special 'ignored' flags to dir_entry, which
were not used anywhere else.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/dir.c b/dir.c
index 6ed9eda..98e24ad 100644
--- a/dir.c
+++ b/dir.c
@@ -275,7 +275,6 @@
 	struct dir_entry *ent;
 
 	ent = xmalloc(sizeof(*ent) + len + 1);
-	ent->ignored = ent->ignored_dir = 0;
 	ent->len = len;
 	memcpy(ent->name, pathname, len);
 	ent->name[len] = 0;
@@ -432,6 +431,18 @@
 	return 0;
 }
 
+static int in_pathspec(const char *path, int len, const struct path_simplify *simplify)
+{
+	if (simplify) {
+		for (; simplify->path; simplify++) {
+			if (len == simplify->len
+			    && !memcmp(path, simplify->path, len))
+				return 1;
+		}
+	}
+	return 0;
+}
+
 /*
  * Read a directory tree. We currently ignore anything but
  * directories, regular files and symlinks. That's because git
@@ -472,7 +483,8 @@
 				continue;
 
 			exclude = excluded(dir, fullname);
-			if (exclude && dir->collect_ignored)
+			if (exclude && dir->collect_ignored
+			    && in_pathspec(fullname, baselen + len, simplify))
 				dir_add_ignored(dir, fullname, baselen + len);
 			if (exclude != dir->show_ignored) {
 				if (!dir->show_ignored || DTYPE(de) != DT_DIR) {