untracked cache: avoid racy timestamps

When a directory is updated within the same second that its timestamp
is last saved, we cannot realize the directory has been updated by
checking timestamps. Assume the worst (something is update). See
29e4d36 (Racy GIT - 2005-12-20) for more information.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -555,6 +555,8 @@ extern void fill_stat_data(struct stat_data *sd, struct stat *st);
  * INODE_CHANGED, and DATA_CHANGED.
  */
 extern int match_stat_data(const struct stat_data *sd, struct stat *st);
+extern int match_stat_data_racy(const struct index_state *istate,
+				const struct stat_data *sd, struct stat *st);
 
 extern void fill_stat_cache_info(struct cache_entry *ce, struct stat *st);
 

dir.c

@@ -682,7 +682,7 @@ static int add_excludes(const char *fname, const char *base, int baselen,
 		if (sha1_stat) {
 			int pos;
 			if (sha1_stat->valid &&
-			    !match_stat_data(&sha1_stat->stat, &st))
+			    !match_stat_data_racy(&the_index, &sha1_stat->stat, &st))
 				; /* no content change, ss->sha1 still good */
 			else if (check_index &&
 				 (pos = cache_name_pos(fname, strlen(fname))) >= 0 &&
@@ -1539,7 +1539,7 @@ static int valid_cached_dir(struct dir_struct *dir,
 		return 0;
 	}
 	if (!untracked->valid ||
-	    match_stat_data(&untracked->stat_data, &st)) {
+	    match_stat_data_racy(&the_index, &untracked->stat_data, &st)) {
 		if (untracked->valid)
 			invalidate_directory(dir->untracked, untracked);
 		fill_stat_data(&untracked->stat_data, &st);

read-cache.c

@@ -294,6 +294,14 @@ static int is_racy_timestamp(const struct index_state *istate,
 		is_racy_stat(istate, &ce->ce_stat_data));
 }
 
+int match_stat_data_racy(const struct index_state *istate,
+			 const struct stat_data *sd, struct stat *st)
+{
+	if (is_racy_stat(istate, sd))
+		return MTIME_CHANGED;
+	return match_stat_data(sd, st);
+}
+
 int ie_match_stat(const struct index_state *istate,
 		  const struct cache_entry *ce, struct stat *st,
 		  unsigned int options)